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The ultrafast relaxation dynamics of tetracene following UV excitation to the bright singlet state S6 has been studied with time-resolved photoelectron spectroscopy. With the help of high-level ab initio multireference perturbation theory calculations, we assign photoelectron signals to intermediate dark electronic states S3, S4, and S5 as well as to a low-lying electronic state S2. The energetic structure of these dark states has not been determined experimentally previously. The time-dependent photoelectron yields assigned to the states S6, S5, and S4 have been analyzed and reveal the depopulation of S6 within 60 fs, while S5 and S4 are populated with delays of about 50 and 80 fs. The dynamics of the lower-lying states S3 and S2 seem to agree with a delayed population coinciding with the depopulation of the higher-lying states S4–S6 but could not be elucidated in full detail due to the low signal levels of the corresponding two-photon ionization probe processes. [ABSTRACT FROM AUTHOR]

Water can be vitrified if it is cooled at high rates, which makes it possible to outrun crystallization in so-called no man's land, a range of deeply supercooled temperatures where water crystallizes rapidly. Here, we study the reverse process in pure water samples by flash melting amorphous ice with microsecond laser pulses. Time-resolved electron diffraction reveals that the sample transiently crystallizes despite a heating rate of more than 5 × 106 K/s, even though under the same conditions, vitrification can be achieved with a similar cooling rate of 107 K/s. Moreover, we observe different crystallization kinetics for amorphous solid water and hyperquenched glassy water. These experiments open up new avenues for elucidating the crystallization mechanism of water and studying its dynamics in no man's land. They also add important insights into the laser melting and revitrification processes that are integral to the emerging field of microsecond time-resolved cryo-electron microscopy. [ABSTRACT FROM AUTHOR]

The rotational relaxation behavior of D2(1,12) in a D2–N2 mixture was investigated using coherent anti-Stokes Raman scattering (CARS) technique. The rovibrational level v = 1 and J = 12 of D2 was selectively excited through stimulated Raman pumping while monitoring the temporal evolution of population for D2(1, J ≤ 12) molecules using time-resolved CARS spectroscopy. The results demonstrate that the rotational relaxation processes of D2(1,12) encompass both multi-quantum relaxation and continuous single-quantum relaxation. When α, the molar ratio of N2, is less than 0.5, D2(1,12) predominantly undergoes a single quantum relaxation process transition. However, when α ≥ 0.5, the multi-quantum relaxation mechanism gradually predominates. The total rotational relaxation rate coefficients of D2(1,12) collisions with N2 and D2 at 295 K were determined to be 3.974 × 10−14 and 1.179 × 10−14 cm3 s−1, respectively. The temperature dependence of rotational relaxation rate of D2(1,12) was investigated within the temperature range of 295–453 K. With increasing temperature, the dominant relaxation process exhibited an accelerated behavior, while the minor relaxation process remained largely unaffected. The rotational temperature of the D2 molecule at various N2 molar ratios was determined through the utilization of Boltzmann plots. The rotational temperature undergoes a rapid decline within 2 μs, corresponding to the near-resonant rotation–vibration relaxation process of D2(1,12) collisions with N2. The system reaches a quasi-equilibrium state when the delay time is 3 μs. The findings of this study can serve as a valuable empirical basis for further validation of the kinetic theory and simulation. [ABSTRACT FROM AUTHOR]

The rotational relaxation behavior of D2(1,12) in a D2–N2 mixture was investigated using coherent anti-Stokes Raman scattering (CARS) technique. The rovibrational level v = 1 and J = 12 of D2 was selectively excited through stimulated Raman pumping while monitoring the temporal evolution of population for D2(1, J ≤ 12) molecules using time-resolved CARS spectroscopy. The results demonstrate that the rotational relaxation processes of D2(1,12) encompass both multi-quantum relaxation and continuous single-quantum relaxation. When α, the molar ratio of N2, is less than 0.5, D2(1,12) predominantly undergoes a single quantum relaxation process transition. However, when α ≥ 0.5, the multi-quantum relaxation mechanism gradually predominates. The total rotational relaxation rate coefficients of D2(1,12) collisions with N2 and D2 at 295 K were determined to be 3.974 × 10−14 and 1.179 × 10−14 cm3 s−1, respectively. The temperature dependence of rotational relaxation rate of D2(1,12) was investigated within the temperature range of 295–453 K. With increasing temperature, the dominant relaxation process exhibited an accelerated behavior, while the minor relaxation process remained largely unaffected. The rotational temperature of the D2 molecule at various N2 molar ratios was determined through the utilization of Boltzmann plots. The rotational temperature undergoes a rapid decline within 2 μs, corresponding to the near-resonant rotation–vibration relaxation process of D2(1,12) collisions with N2. The system reaches a quasi-equilibrium state when the delay time is 3 μs. The findings of this study can serve as a valuable empirical basis for further validation of the kinetic theory and simulation. [ABSTRACT FROM AUTHOR]

Ultrafast optical spectroscopy is a powerful technique for studying the dynamic processes of molecular systems in condensed phases. However, in molecular systems containing many dye molecules, the spectra can become crowded and difficult to interpret owing to the presence of multiple nonlinear optical contributions. In this work, we theoretically propose time-resolved spectroscopy based on the coincidence counting of two entangled photons generated via parametric down-conversion with a monochromatic laser. We demonstrate that the use of two-photon counting detection of entangled photon pairs enables the selective elimination of the excited-state absorption signal. This selective elimination cannot be realized with classical coherent light. We anticipate that the proposed spectroscopy will help simplify the spectral interpretation of complex molecular and material systems comprising multiple molecules. [ABSTRACT FROM AUTHOR]

In this work, charge photogeneration and recombination processes of PM6:IDIC-4F and PM6:IDIC blend films were investigated by the steady-state and time-resolved spectroscopies, as well as the time-dependent density functional theory calculations. The peaks in absorption and photoluminescence (PL) spectra of IDIC and IDIC-4F solutions were assigned by combining the experiment and the simulation of UV–vis absorption and PL spectra. For neat acceptor films, the exciton diffusion length of neat IDIC and IDIC-4F films was estimated as ∼28.9 and ∼19.9 nm, respectively. For PM6-based blend films, we find that the fluorine substitution engineering on the IDIC acceptor material can increase the phase separate size of acceptor material in blend films, resulting in the reduction of dissociation efficiencies of acceptor excitons. In addition, we find that the charge recombination in PM6:IDIC-4F is dominated by bimolecular recombination, in comparison to geminate type carrier recombination in PM6:IDIC blend films. In addition, we find that thermal annealing treatment has a weak influence on carrier recombination but slightly reduces the exciton dissociation efficiency of acceptor in PM6:IDIC blend films, leading to a slightly reduced power conversion efficiency of PM6:IDIC solar cells. These results may shed light on the design of high-performance semiconductor molecules for application in solar cells. [ABSTRACT FROM AUTHOR]

The photophysics of thiobases—nucleobases in which one or more oxygen atoms are replaced with sulfur atoms— vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I− · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88 eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16 eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14 eV pulses. Excitation at 3.88 eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16 eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide–nucleobase clusters. [ABSTRACT FROM AUTHOR]

The manipulation of the ultrafast quantum dynamics of a molecular system can be achieved through the application of tailored light fields. This has been done in many ways in the past. In our present investigation, we show that it is possible to exert specific control over the nonadiabatic dynamics of a generic model system describing ultrafast charge-transfer within a condensed dissipative environment by using frequency-chirped pulses. By adjusting the external photoexcitation conditions, such as the chirp parameter, we show that the final population of the excitonic and charge-transfer states can be significantly altered, thereby influencing the elementary steps controlling the transfer process. In addition, we introduce an excitation scheme based on double-pump time-resolved fluorescence spectroscopy using chirped-pulse excitations. Here, our findings reveal that chirped excitations enhance the vibrational system dynamics as evidenced by the simulated spectra, where a substantial signal intensity dependence on the chirp is observed. Our simulations show that chirped pulses are a promising tool for steering the dynamics of the charge-transfer process toward a desired target outcome. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The morphology of the active layer plays a crucial role in the performance of organic photovoltaics. Although volatile additives are commonly used to manipulate the morphology, their mechanism of action remains poorly understood. In this study, we conducted a systematic exploration of the mechanism of the traditional volatile additive 1‐CN in film formation kinetics of typical PM6:Y6 system. We found that 1‐CN induces a secondary aggregation effect, improving film morphology and promoting face‐on crystalline orientation. Through elucidating its impact on exciton dynamics, we established a link between morphology optimization and increased exciton diffusion length and accelerated charge separation. Our findings unveil the unique mechanism of action of volatile additive, providing a new perspective for improving the morphology and enhancing the performance of organic photovoltaic devices. [ABSTRACT FROM AUTHOR]

Polydisperse edge‐fused nickel(II) porphyrin nanoribbons have been synthesized by Yamamoto coupling followed by gold(III)‐mediated fusion, with average degrees of polymerization of up to 37 repeat units (length 31 nm). Time‐resolved optical‐pump terahertz spectroscopy measurements indicate that photo‐generated charge carriers have dc mobilities of up to 205 cm2 V−1 s−1 in these nanoribbons, exceeding the values previously reported for most other types of nanoribbon or π‐conjugated polymer. [ABSTRACT FROM AUTHOR]

The scarcity of suitable high-throughput screening technology for hydrogen sulfide (H2S) donors has hampered the discovery of H2S donors. In this study, a long-lived cyclometalated iridium complex was rationally designed as a mitochondria-targeted H2S probe to monitor the real-time dynamic change of H2S. By using the time-resolved emission spectroscopy (TRES) technique, an anti-interference high-throughput screening system was developed to monitor H2S in living cells with decreased false negative results. As a proof-of-concept, three natural products were identified as potential H2S donors from a natural product library using the developed TRES probe. Notably, the discovery of allicin and diallyl trisulfide demonstrated the feasibility of this screening platform, while garlic-derived allyl methyl sulfide was explored as a H2S donor candidate. The results were further validated by a commercial assay. We anticipate this high-throughput platform could facilitate the discovery of H2S donors by discriminating the endogenous interfering fluorescence from biological systems. H2S donors in living cells are essential for modulating H2S levels and have been proposed to be relevant for managing hepatic disorders, but conventional platforms to screen for H2S donors are plagued by interference by endogenous background fluorescence signals. Here, the authors develop a luminogenic probe—based on an Ir(III) complex with a 1,10-phenanthroline-5,6-dione moiety—capable of selective response to mitochondrial H2S, and set up an anti-interference high-throughput screening system capable of distinguishing target signals from complex background autofluorescence in living cells. [ABSTRACT FROM AUTHOR]

The selective photoreduction of CO2 in aqueous media based on earth-abundant elements only, is today a challenging topic. Here we present the anchoring of discrete molecular catalysts on organic polymeric semiconductors via covalent bonding, generating molecular hybrid materials with well-defined active sites for CO2 photoreduction, exclusively to CO in purely aqueous media. The molecular catalysts are based on aryl substituted Co phthalocyanines that can be coordinated by dangling pyridyl attached to a polymeric covalent triazine framework that acts as a light absorber. This generates a molecular hybrid material that efficiently and selectively achieves the photoreduction of CO2 to CO in KHCO3 aqueous buffer, giving high yields in the range of 22 mmol g−1 (458 μmol g−1 h−1) and turnover numbers above 550 in 48 h, with no deactivation and no detectable H2. The electron transfer mechanism for the activation of the catalyst is proposed based on the combined results from time-resolved fluorescence spectroscopy, in situ spectroscopies and quantum chemical calculations. The selective CO2 photoreduction in water mediated by earth-abundant photocatalysts remains highly challenging. Here the authors present the coordinative anchorage of molecular catalysts on a pyridine-armed covalent triazine framework for CO2 photoreduction to CO in fully aqueous solutions. [ABSTRACT FROM AUTHOR]

In this study, we comprehensively investigate thermal lens (TL) spectroscopy, known for its ultra-sensitivity in probing molecular properties through nonlinear heating responses to femtosecond lasers. Using time-resolved TL spectroscopy and numerical simulations, we focus on the influence of convection on heat generation and the resulting phase shift in the probe beam. We examined single-beam, dual-beam same wavelength, and dual-beam different wavelength scenarios, systematically investigating power dependence, pump beam spot size, and sample length limitations. Our findings reveal a direct relationship between the TL effect and pump power, resulting in decreased probe beam transmittance with increasing convection. Additionally, the TL strength grows within the Rayleigh regime as the sample length increases. Utilizing the same wavelength for the probe beam enhances the TL effect in dual-beam setups. Notably, tight focusing of the pump beam substantially reduces the lag between convection and conduction. Our empirical results closely match the experimental data, providing a thorough explanation of the TL process and its underlying principles. These insights can be applied to design and optimize TL-based optical devices and systems for higher sensitivity, highlighting the potential of TL spectroscopy in advanced molecular property probing. [ABSTRACT FROM AUTHOR]

The "New Journal of Chemistry" published by the Royal Society of Chemistry features a variety of research articles in the field of chemistry. The latest issue includes papers on topics such as the synthesis of acyclic analogues of adenosine sulfonamides, construction of covalent organic frameworks, and studies on various chemical compounds and reactions. The journal aims to connect the global chemistry community and invest profits back into the field of chemistry. [Extracted from the article]

In this study, we examined the photophysical properties of an azacrown–iridium(III) complex while focusing on its interactions with calcium ions (Ca2+). We explored the dynamic processes within the complex combining time-dependent density functional theory (TDDFT) calculations and time-resolved spectroscopies. In the presence of Ca2+, the complex exhibits significant shifts in absorption and emission profiles, from 494 nm to 375 nm, aligning with theoretical predictions. Notably, we observed the ultrafast photo-ejection of Ca2+ within 70 femtoseconds, followed by its recapture in 250 nanoseconds, revealing a 10-million-fold timescale difference between the two phenomena. These behaviors confirm the established photophysical properties of polypyridyl iridium(III) complexes and their intrinsic sensitivity to their surrounding environment. Our comprehensive kinetic analysis highlights the azacrown moiety's competitive binding and photo-release capabilities, suggesting its potential for practical sensing applications. The versatile properties of these iridium(III) complexes offer promising prospects for their application as stimuli-responsive materials and in advanced optoelectronic devices, targeted imaging, and biomedical ion sensors and delivery systems. [ABSTRACT FROM AUTHOR]

Accelerated diagnostic of plasma plays a significant role in controlling and optimizing plasma-mediated processing, particularly for plasma with higher temporal and spatial gradients, such as laser produced plasma (LPP). In the present work, two advanced machine learning (ML) algorithms, random forest regression, and gradient boosting regression are integrated with noninvasive collisional radiative (CR) model-based optical diagnostics to facilitate accurate diagnostics. A comprehensive fine-structure resolved CR model framework is developed by incorporating our consistent cross section data obtained from the Relativistic Distorted Wave method [Suresh et al., "Fully relativistic distorted wave calculations of electron impact excitation of gallium atom: Cross sections relevant for plasma kinetic modelling," Spectrochim. Acta B: At. Spectrosc. 213, 106860 (2024)]. An extensive dataset of CR model simulated intensities is created to train and test the ML methods. The present CR model is applied to characterize the Gallium LPP coupling with the optical emission spectroscopic measurements of Guo et al. ["Time-resolved spectroscopy analysis of Ga atom in laser induced plasma," Laser Phys. 19, 1832–1837 (2009)] at different delay times. Further, a detailed correlation study of the line intensity ratios is performed to observe the qualitative behavior of the plasma parameters. The electron temperature results obtained from the CR model, ML, and line ratio methods were compared and found to be in excellent agreement. Overall, the present study demonstrates diagnostic approaches that can benefit the LPP community significantly by providing a rapid understanding of the plasma behavior across various operating conditions. [ABSTRACT FROM AUTHOR]

This document is a profile of Jinfa Chang, a new editorial board member of Frontier Reporters for the Chinese Journal of Chemistry. Chang is a professor at Northeast Normal University in China and has a background in chemistry, with a focus on electrocatalytic hydrogen energy-electric energy conversion. Chang's research aims to design and develop cost-effective, high-performance catalysts to accelerate the commercialization of hydrogen-related energy storage and conversion technologies. The lab pays particular attention to the electrocatalytic performance of electrode materials for fuel cells and water electrolysis under real-service conditions, with a specific interest in the reaction mechanism and structure-performance relationship. [Extracted from the article]

Optically pumped spintronic terahertz emitters (STEs) have, in less than a decade, strongly impacted terahertz (THz) source technology, by the combination of their Fourier‐limited ultrafast response, their phononless emission spectrum and their wavelength‐independent operation. However, the intrinsic strength of the inverse spin Hall effect governing these devices introduces a challenge: the optical‐to‐terahertz conversion efficiency is considerably lower than traditional sources. It is therefore primordial to maximize at least their electromagnetic efficiency independently of the spin dynamics at play. Using a rigorous time‐domain treatment of the electromagnetic generation and extraction processes, an optimized design is presented and experimentally confirmed. With respect to the strongest reported spintronic THz emitters it achieves a 250% enhancement of the emitted THz field and therefore an 8 dB increase of emitted power. This experimental achievement brings STE close to the symbolic barrier of mW levels. The design strategy is generically applicable to any kind of ultrafast spin‐to‐charge conversion (S2C) system. On a broader level, our work highlights how a rigorous handling of the purely electromagnetic aspects of THz spintronic devices can uncover overlooked aspects of their operation and lead to substantial improvements. [ABSTRACT FROM AUTHOR]

ABSTRACT This work reports the S‐branch Raman linewidths of N2 broadened by H2O vapour at temperatures 870–1900 K determined using the picosecond time‐resolved pure rotational coherent anti‐Stokes Raman scattering (RCARS) approach. The coherent dephasing time constant of nitrogen in a binary mixture was determined from the time trace fitting of the RCARS signal. Raman linewidths of N2 for four different binary mixture compositions up to 20% H2O were obtained for each temperature and the N2‐H2O broadening coefficient was determined. The decay of nitrogen broadened by water vapour is faster than that of self‐broadened nitrogen for all temperatures leading to a higher Raman linewidth. Respectively, the S‐branch Raman linewidths of N2‐H2O deviate significantly in magnitude and slope from the Q‐branch Raman linewidth calculated by the modified energy gap (MEG) law. Therefore, taking into account the broadening effect of water molecules in nitrogen has the potential to significantly improve thermometry and species concentration determination. The determined S‐branch Raman linewidths and broadening coefficient will therefore find application in combustion and reactive flow diagnostics. [ABSTRACT FROM AUTHOR]

In the past decade, organic electrosynthesis has emerged as an atom‐ and energy‐efficient strategy for harvesting renewable electricity that provides exceptional control over the reaction parameters. A profound and fundamental understanding of electrochemical interfaces becomes imperative to advance the knowledge‐based development of electrochemical processes. The major strategy toward an efficient electrochemical system is based on the advancement in material science for electrocatalysis. Studies on the complex interplay among electrode surface, electrolyte, and transformation intermediates have only recently started to emerge. It involves acquiring atomic‐scale insights into the electrochemical double layer, for which the identity and concentration of composing ions play a crucial role. In this study, we present how the identity and concentration of alkali cations impact the selectivity of aldehyde functionality electroreduction. As a case‐study transformation, we set the electrochemical conversion of 5‐hydroxymethylfurfural (HMF), a promising biomass‐derived feedstock for the sustainable production of polymer or fuel precursors. Our findings reveal a consistent trend of the selectivity shift towards 2,5‐bis(hydroxymethyl)furan (BHMF) as a function of cation size and concentration, rationalized by specific cation adsorption at the glassy carbon (GC), followed by the increase in the electrode surface charge density. [ABSTRACT FROM AUTHOR]

Incorporation of the trimethoxyphenyl group at position 7 of flavin can drastically change the photophysical properties of flavin. We show unique fast singlet 1(π,π*) excited state deactivation pathway through nonadiabatic transition to the 1(n,π*) excited- state, and subsequent deactivation to the ground electronic state (S0), closing the photocycle. This mechanism explains the exceptionally weak fluorescence and the short excited–state lifetime for the flavin trimethoxyphenyl derivative and the lack of excited triplet T1 state formation. Full recovery of flavin in its ground state takes place within a 15 ps time window after photoexcitation in a polar solvent such as acetonitrile. According to quantum chemical calculations, the C(2)-O distance elongates by 0.16 Å in the 1(n,π*) state, with respect to the ground state. Intermediate–state structures are predicted by theoretical ab initio calculations and their dynamics are investigated using broadband vis-NIR time-resolved transient absorption and fluorescence up-conversion techniques. [ABSTRACT FROM AUTHOR]

Unlike traditional group‐6 transition metal dichalcogenides (TMDs), group‐10 TMDs such as PtSe2 and PdTe2 possess highly tuneable indirect bandgaps, transitioning from semiconducting in the near‐infrared to semimetal behavior with a number of monolayers (MLs). This opens up the possibility of TMD‐based mid‐infrared and terahertz optoelectronics. Despite this large potential, the optical properties of such materials have shown an extremely large disparity between that predicted and measured. For example, simulations show that a few MLs is required for the semiconductor–semimetal transition, whilst tens of MLs is found experimentally. This is a result of widely used optical extrapolation methods to determine bandgaps, such as the Tauc plot approach, that are not adapted here owing to i) nearby direct transitions, ii) the material dimensionality and iii) large changes in the non‐parabolic bandstructure with MLs. Here, uniquely combining optical ellipsometry to determine the complex permittivity, terahertz time resolved spectroscopy for the complex conductivity and in‐depth density functional theory (DFT) simulations, it is shown that the optical properties and bandstructure can be determined reliably and demonstrate clearly that the semiconductor‐semimetal transition occurs for PtSe2 layers ≈5 MLs. The microscopic origins of the observed transitions and the crucial role of the Coulomb interaction for thin semiconducting layers, and that of interlayer van der Waals forces for multilayer semimetallic samples are also demonstrated. This work of combining complimentary experimental techniques and extensive simulations avoids the application of constrained extrapolation methods to determine the optical properties of group‐10 TMDs, and will be of importance for future mid‐infrared and terahertz applications. [ABSTRACT FROM AUTHOR]

Fluorescing proteins emitting in the near-infrared region are of high importance in various fields of biomedicine and applied life sciences. Promising candidates are phytochromes that can be engineered to a small size and genetically attached to a target system for in vivo monitoring. Here, we have investigated two of these minimal single-domain phytochromes, miRFP670nano3 and miRFP718nano, aiming at a better understanding of the structural parameters that control the fluorescence properties of the covalently bound biliverdin (BV) chromophore. On the basis of resonance Raman and time-resolved fluorescence spectroscopy, it is shown that in both proteins, BV is deprotonated at one of the inner pyrrole rings (B or C). This protonation pattern, which is unusual for tetrapyrroles in proteins, implies an equilibrium between a B- and C-protonated tautomer. The dynamics of the equilibrium are slow compared to the fluorescence lifetime in miRFP670nano3 but much faster in miRFP718nano, both in the ground and excited states. The different rates of proton exchange are most likely due to the different structural dynamics of the more rigid and more flexible chromophore in miRFP670nano3 and miRFP718nano, respectively. We suggest that these structural properties account for the quite different fluorescent quantum yields of both proteins. [ABSTRACT FROM AUTHOR]

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored. In this study, femtosecond infrared spectroscopy was used to investigate the dynamics of 4-AP in methanol and acetonitrile after excitation at 350 and 300 nm, which promoted 4-AP to the S1 and S2 states, respectively. The excited 4-AP in the S1 state relaxed to the ground state, while 4-AP in the S2 state relaxed via the S1 state without the occurrence of ESIPT. The enol form of 4-AP (Enol 4-AP) in the S1 state was calculated to be ~10 kcal/mol higher in energy than the keto form in the S1 state, indicating that keto-to-enol tautomerization was endergonic, ultimately resulting in no observable ESIPT for 4-AP in the S1 state. Upon the excitation of 4-AP to the S2 state, the transition to Enol-4-AP in the S1 state was found to be exergonic; however, ESIPT must compete with an internal conversion from the S2 to the S1 state. The internal S2 → S1 conversion was significantly faster than the solvent-assisted ESIPT, resulting in a negligible ESIPT for the 4-AP excited to the S2 state. The detailed excitation dynamics of 4-AP clearly reveal the molecular mechanism underlying its negligible ESIPT, despite the fact that it forms a favorable structure for solvent-assisted ESIPT. [ABSTRACT FROM AUTHOR]

Using fluorinated mono‐alcohols, in particular hexafluoro‐isopropanol (HFIP), as a solvent can enhance chemical reaction rates in a spectacular manner. Previous work has shown evidence that this enhancement is related to the hydrogen‐bond structure of these liquids. Here, we investigate the hydrogen‐bond dynamics of HFIP and compare it to that of its non‐fluorinated analog, isopropanol. Ultrafast infrared spectroscopy experiments show that the dynamics of individual hydrogen‐bonds is about twice as slow in HFIP as in isopropanol. Surprisingly, from dielectric spectroscopy we find the opposite behavior for the dynamics of hydrogen‐bonded clusters: collective rearrangements are 3 times faster in HFIP than in isopropanol. This difference indicates that the hydrogen‐bonded clusters in HFIP are smaller than in isopropanol. The differences in cluster size can be traced to changes in the hydrogen‐bond donor and acceptor strengths upon fluorination. The smaller cluster size can boost reaction rates in HFIP by increasing the concentration of reactive, terminal OH‐groups of the clusters, whereas the fast collective dynamics can increase the rate of formation of hydrogen‐bonds with the reactants. The longer lifetime of the individual hydrogen‐bonds in HFIP can enhance the stability of the hydrogen‐bonded clusters, and so increase the probability of reactant‐solvent hydrogen‐bonding. [ABSTRACT FROM AUTHOR]

The ultrafast photochemical reaction mechanism, transient spectra, and transition kinetics of the human blue cone visual pigment have been recorded at room temperature. Ultrafast time-resolved absorption spectroscopy revealed the progressive formation and decay of several metastable photo-intermediates, corresponding to the Batho to Meta-II photo-intermediates previously observed with bovine rhodopsin and human green cone opsin, on the picosecond to millisecond timescales following pulsed excitation. The experimental data reveal several interesting similarities and differences between the photobleaching sequences of bovine rhodopsin, human green cone opsin, and human blue cone opsin. While Meta-II formation kinetics are comparable between bovine rhodopsin and blue cone opsin, the transition kinetics of earlier photo-intermediates and qualitative characteristics of the Meta-I to Meta-II transition are more similar for blue cone opsin and green cone opsin. Additionally, the blue cone photo-intermediate spectra exhibit a high degree of overlap with uniquely small spectral shifts. The observed variation in Meta-II formation kinetics between rod and cone visual pigments is explained based on key structural differences. [ABSTRACT FROM AUTHOR]

A systematic investigation of the photoinduced [6π]‐electrocyclization reaction of diphenylamine and N‐methyldiphenylamine has been carried out under steady‐state and time‐resolved conditions in homogeneous (cyclohexane, acetonitrile and methanol) and micellar solutions (sodium dodecyl sulfate ‐SDS, cetyltrimethylammonium chloride‐CTAC and polyethylene glycol monododecyl ether‐Brij P35). The photolysis of such compounds in both homogeneous and micro‐heterogeneous media afforded the corresponding carbazoles in almost quantitative yield under oxidative conditions. Furthermore, the relative rate of formation of the photoproducts increases when moving from homogeneous media to micellar solution, due to the environmental confined and hydrophobic micellar core as highlighted by 1D and 2D NMR (NOESY and DOSY) spectroscopic analyses. [ABSTRACT FROM AUTHOR]

In this work, a green protocol for the synthesis of new para‐Azaquinodimethane (pAQM) small molecules, functionalized with anisole (An) or bithiophene (TT) moieties on the central unit and with different alkoxy groups as lateral substituents is developed and reported. The alkoxy lateral substituents are found to strongly impact the solubility and processability of the chromophores. On the other hand, the steady–state and time‐resolved spectroscopic results show completely different spectral and photophysical features for the An‐ and TT‐ derivatives. Only for the TT‐compounds, the nanosecond and femtosecond transient absorption experiments reveal low efficiency of triplet production in solution as well as ultrafast (≈1 ps) and efficient (≈200%) singlet fission (SF) in thin film. The yellow An‐containing molecules are instead used to sensitize the purple SF‐active TT‐compounds via quantitative FRET in mixed thin films, which interestingly exhibit panchromatic absorption extending in the entire visible spectral range. With this study, the synergy between FRET and SF is exploited at the intermolecular level in the solid‐state for the first time by considering unconventional and stable SF chromophores, opening intriguing new possibilities for solar energy harvesting. [ABSTRACT FROM AUTHOR]

Abstract Incorporation of the trimethoxyphenyl group at position 7 of flavin can drastically change the photophysical properties of flavin. We show unique fast singlet 1(π,π*) excited state deactivation pathway through nonadiabatic transition to the 1(n,π*) excited- state, and subsequent deactivation to the ground electronic state (S0), closing the photocycle. This mechanism explains the exceptionally weak fluorescence and the short excited–state lifetime for the flavin trimethoxyphenyl derivative and the lack of excited triplet T1 state formation. Full recovery of flavin in its ground state takes place within a 15 ps time window after photoexcitation in a polar solvent such as acetonitrile. According to quantum chemical calculations, the C(2)-O distance elongates by 0.16 Å in the 1(n,π*) state, with respect to the ground state. Intermediate–state structures are predicted by theoretical ab initio calculations and their dynamics are investigated using broadband vis-NIR time-resolved transient absorption and fluorescence up-conversion techniques.

Abstract Porphyrins are acknowledged for their efficacy as photosensitizers and show potential for the treatment of water contaminated with diverse dyes. This research emphasizes the use of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) as a photosensitizer for purifying water contaminated with rhodamine B. Investigations were conducted under homogeneous conditions using visible light irradiation, revealing the efficacy of the porphyrin in the decolorization of rhodamine B strongly depends on pH of the solution. This study demonstrated that within 120 min, the decolorization process rapidly removed about 95% of RhB at an initial pH of 3.0, while at pH 6.0, the removal rate was significantly lower, at only 12%. An extensive photophysical study of the TPPS was carried out at pH 6.0 and pH 3.0 including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields in order to explain difference in the efficiency of RhB discoloration. A thorough investigation into mechanism revealed that neither reactive oxygen species nor singlet oxygen played a role in RhB decolorization within this system. Instead, the predominant route was found to be the electron transfer from photoexcited TPPS to RhB, followed by proton transfer at pH 3.0, leading to the generation of a colorless leuco form.

Abstract Besides many efforts on the detection and quantification of reactive oxygen and nitrogen species (RONSs) in the aqueous media activated by the cold atmospheric plasma, to get a better insight into the dominant mechanism and reactive species in medical applications, a challenge still remains in monitoring the real-time evaluation of them. To this end, in the present work, relying on the photonic technology based on the time-resolved phosphorescence spectroscopy, real-time tracking of RONSs concentration in treated aqueous media is achieved by following the dissolved oxygen (DO) production/consumption. Using a photonic-based dissolved oxygen sensor, the dependence of real-time RONS concentration evaluation of plasma activated medium on plasma nozzle distance, non-thermal plasma jet exposure time, various culture media, and presence of cells is investigated. Analyzing the results, the activation parameters including the time of reaching maximum RONS concentration after treatment and defined activation parameter $$\epsilon\:$$ of the treated media for each case is measured and compared together. Moreover, employing the scavengers related to two involved ROSs, the dominant chemical reactions as well as ROS contributed in the DMEM medium is determined. As a promising result, the obtained correlation between the real-time DO level and viability and toxicity of the cancer cells, MCF-7 breast cancer cells, could enable us to exploit the present photonic setup as an alternative technique for the biological assessment.

Abstract Meta-tetra(hydroxyphenyl)chlorin (m-THPC) is among the most potent photosensitizers, known for its high singlet oxygen generation efficiency. However, its clinical effectiveness in photodynamic therapy (PDT) is compromised by its propensity to aggregate in aqueous solutions, adversely affecting its photophysical properties and therapeutic potential. A series of spectroscopic techniques, including UV-Vis absorption, fluorescence spectroscopy, and laser flash photolysis, revealed that m-THPC exhibits significant aggregation, particularly in MeOH-PBS mixtures with MeOH content below 30%. This aggregation adversely affects its photophysical properties leading to reduced fluorescence quantum yield and most importantly reducing its singlet oxygen quantum yield. This study introduces the use of bovine serum albumin (BSA) to counteract the aggregation of m-THPC, aiming to enhance its solubility, stability, and efficacy in physiological settings. Through advanced spectroscopic analyses we demonstrated that the m-THPC@BSA complex exhibits restored photophysical properties characteristic for monomeric form. Notably, the complex showed a significant restoration of the singlet oxygen quantum yield (ΦΔ = 0.21) compared to aggregated m-THPC. These results underscore the potential of BSA to preserve the monomeric form of m-THPC, mitigating aggregation-induced losses in singlet oxygen production. Our findings suggest that BSA-mediated delivery systems could play a crucial role in optimizing the clinical utility of hydrophobic photosensitizers like m-THPC.

This study introduces a compact, portable femtosecond fibre laser system designed for synchronization with SPring-8 synchrotron X-ray pulses in a uniform filling mode. Unlike traditional titanium–sapphire mode-locked lasers, which are fixed installations, our system utilizes fibre laser technology to provide a practical alternative for time-resolved spectroscopy, striking a balance between usability, portability and cost-efficiency. Comprehensive evaluations, including pulse characterization, timing jitter and frequency stability tests revealed a centre wavelength of 1600 nm, a pulse energy of 4.5 nJ, a pulse duration of 35 fs with a timing jitter of less than 9 ps, confirming the suitability of the system for time-resolved spectroscopic studies. This development enhances the feasibility of experiments that combine synchrotron X-rays and laser pulses, offering significant scientific contributions by enabling more flexible and diverse research applications.

Porphyrins are acknowledged for their efficacy as photosensitizers and show potential for the treatment of water contaminated with diverse dyes. This research emphasizes the use of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) as a photosensitizer for purifying water contaminated with rhodamine B. Investigations were conducted under homogeneous conditions using visible light irradiation, revealing the efficacy of the porphyrin in the decolorization of rhodamine B strongly depends on pH of the solution. This study demonstrated that within 120 min, the decolorization process rapidly removed about 95% of RhB at an initial pH of 3.0, while at pH 6.0, the removal rate was significantly lower, at only 12%. An extensive photophysical study of the TPPS was carried out at pH 6.0 and pH 3.0 including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields in order to explain difference in the efficiency of RhB discoloration. A thorough investigation into mechanism revealed that neither reactive oxygen species nor singlet oxygen played a role in RhB decolorization within this system. Instead, the predominant route was found to be the electron transfer from photoexcited TPPS to RhB, followed by proton transfer at pH 3.0, leading to the generation of a colorless leuco form. [ABSTRACT FROM AUTHOR]

A series of Pr,La:CaF2 single crystals grown using the temperature gradient technique (TGT) method were presented systematically with a detailed spectroscopic investigation. The results indicate that the distinct Pr3+-La3+ cluster types have replaced the original Pr3+-Pr3+ clusters after introducing La3+ into the Pr:CaF2 crystal, as demonstrated by density functional theory-based first principles calculation and spectral analysis. This cluster evolution has led to a drastic increase in the Pr3+ emission quantum efficiency as the La3+ concentration increases. Evaluation of the impacts of multiphonon relaxation and cross-relaxation processes on quantum yields also revealed that cross-relaxation processes persisted in the Pr, La codoped samples, which led to not high quantum yields as expected. The incorporation of La3+ substantially manipulated the local structure of Pr ions in the CaF2 crystal lattice. Low temperature absorption and selective-site spectroscopy, and time resolved emission spectroscopy were applied to investigate the local structure symmetries of Pr ions in the Pr3+,La3+:CaF2 crystal. Despite a lower degree of discrepancy, two types of centers were observed in TRES, all of which showed cubic symmetry of these locations based on the cluster simulation. [ABSTRACT FROM AUTHOR]

The development of artificial biomimetic systems with real-world applications relies on a profound understanding of all photophysical and photochemical processes taking place upon light absorption by a chromophoric unit. Efficient photoinduced charge separation in photosensitizers or specialized photocatalysts is the process triggering most of the chemical reactions in the production of solar fuels, and hence, its proper characterization is of utmost importance. In this work, we investigated photoinduced charge separation processes in a perfluorinated Zn-tetraphenylporphyrin photosensitizer (ZnF20). Ascorbate and 1,4-diazabicyclo[2.2.2]octane (DABCO) were used as reversible electron donors for nanosecond-resolved pump–probe experiments using both optical absorption and resonance Raman scattering as probes. Our results indicate that in spite of similar charge separation efficiencies, the DABCO-containing system exhibits a much faster kinetics of charge-separated state formation and decay. This is attributed to its inherent ability to coordinate to the metal center. Time-resolved resonance Raman measurements allow for the detection of vibrational modes specific to both the triplet excited state of ZnF20 and its reduced state, complementing transient absorption data to fully characterize the charge separation process. [ABSTRACT FROM AUTHOR]

Norbornadiene‐based photoswitches have emerged as promising candidates for harnessing and storing solar energy, holding great promise as a viable solution to meet the growing energy demands. Despite their potential, the effectiveness of their direct photochemical conversion into the resulting quadricyclanes has room for improvement owing to (i) moderate quantum yields, (ii) poor overlap with the solar spectrum and (iii) photochemical back reactions. Herein, we present an approach to enhance the performance of such molecular solar thermal energy storage (MOST) systems through the triplet‐sensitized conversion of aryl‐substituted norbornadienes. Our study combines deep spectroscopic analyses, irradiation experiments, and quantum mechanical calculations to elucidate the energy transfer mechanism and inherent advantages of the resulting MOST systems. We demonstrate remarkable quantum yields using readily available sensitizers under both LED and solar light irradiation, significantly surpassing those achieved through direct excitation with photons of higher energy. In contrast to the conventional approach, light‐induced back reactions of the high‐energy products do not play any role, allowing quantitative switching within minutes. These results not only underscore the potential of triplet‐sensitized MOST systems to leverage the high energy storage capabilities of multistate photoswitches but they might also stimulate the broader usage of sensitization strategies in photochemical energy conversion. [ABSTRACT FROM AUTHOR]

Ultrafast spectroscopy can be used to study dynamic processes on femtosecond to nanosecond timescales, but is typically used for photoinduced processes. Several materials can induce ultrafast temperature rises upon absorption of femtosecond laser pulses, in principle allowing to study thermally activated processes, such as (catalytic) reactions, phase transitions, and conformational changes. Gold–silica core–shell nanoparticles are particularly interesting for this, as they can be used in a wide range of media and are chemically inert. Here we computationally model the temporal and spatial temperature profiles of gold nanoparticles with and without silica shell in liquid and gas media. Fast rises in temperature within tens of picoseconds are always observed. This is fast enough to study many of the aforementioned processes. We also validate our results experimentally using a poly(urethane‐urea) exhibiting a temperature‐dependent hydrogen bonding network, which shows local temperatures above 90 °C are reached on this timescale. Moreover, this experiment shows the hydrogen bond breaking in such polymers occurs within tens of picoseconds. [ABSTRACT FROM AUTHOR]

We introduce an extreme ultraviolet (XUV)-beamline designed for the time-resolved investigation and coherent control of attosecond (as) electron dynamics in atoms and molecules by polarization-shaped as-laser pulses. Shaped as-pulses are generated through high-harmonic generation (HHG) of tailored white-light supercontinua (WLS) in noble gases. The interaction of shaped as-pulses with the sample is studied using velocity map imaging (VMI) techniques to achieve the differential detection of photoelectron wave packets. The instrument consists of the WLS-beamline, which includes a hollow-core fiber compressor and a home-built 4f polarization pulse shaper, and the high-vacuum XUV-beamline, which combines an HHG-stage and a versatile multi-experiment vacuum chamber equipped with a home-built VMI spectrometer. The VMI spectrometer allows the detection of photoelectron wave packets from both the multiphoton ionization (MPI) of atomic or molecular samples by the tailored WLS-pulses and the single-photon ionization (SPI) by the shaped XUV-pulses. To characterize the VMI spectrometer, we studied the MPI of xenon atoms by linearly polarized WLS pulses. To validate the interplay of these components, we conducted experiments on the SPI of xenon atoms with linearly polarized XUV-pulses. Our results include the reconstruction of the 3D photoelectron momentum distribution (PMD) and initial findings on the coherent control of the PMD by tuning the spectrum of the XUV-pulses with the spectral phase of the WLS. Our results demonstrate the performance of the entire instrument for HHG-based photoelectron imaging spectroscopy with prototypical shaped pulses. Perspectively, we will employ polarization-tailored WLS-pulses to generate polarization-shaped as-pulses. [ABSTRACT FROM AUTHOR]

We report on spectroscopic and photometric observations of the AM Canum Venaticorum (AM CVn) system ASASSN-21br, which was discovered in outburst by the All-Sky Automated Survey for Supernovae in 2021 February. The outburst lasted for around three weeks, and exhibited a pronounced brightness dip for |$\approx$| 4 d, during which the spectra showed a sudden transition from emission- to absorption-line dominated. Only |$\approx$| 60 AM CVn systems with derived orbital periods are found in the Galaxy, therefore increasing the sample of AM CVn systems with known orbital periods is of tremendous importance to (1) constrain the physical mechanisms of their outbursts and (2) establish a better understanding of the low-frequency background noise of future gravitational wave surveys. Time-resolved photometry taken during the outburst of ASASSN-21br showed modulation with a period of around 36.65 min, which is likely the superhump or orbital period of the system. Time-resolved spectroscopy taken with the Southern African Large Telescope did not show any sign of periodicity in the He  i absorption lines. This is possibly due to the origin of these lines in the outbursting accretion disc, which makes it challenging to retrieve periodicity from the spectral lines. Future follow-up spectral observations during quiescence might allow us better constrain the orbital period of ASASSN-21br. [ABSTRACT FROM AUTHOR]

Few-cycle laser pulses at a high repetition rate with a stable carrier-envelope phase are required for next-generation attosecond time-resolved spectroscopies. One way to generate these pulses is the nonlinear compression of laser pulses via gas-filled hollow-core fibers. Recently, an alternative approach based on multi-pass cells (MPCs) has been shown to be very efficient for post-compression of turn-key, industrial-grade, high average power Yb-doped solid-state laser amplifiers. However, to expand the system for exploring strong-field laser applications, its carrier-envelope phase stability needs to be demonstrated in the compressed pulses. In this Letter, we present the generation of carrier-envelope phase-stabilized 40 fs pulses with 380 μJ energy at 50 kHz by compressing the output of a Yb:KGW amplifier in a gas-filled MPC. Comparable short-term carrier-envelope phase errors of 412 and 435 mrad root mean square were observed from the amplifier and MPC, respectively, indicating that the phase stability of the amplified pulses is well-maintained during pulse compression in the MPC. [ABSTRACT FROM AUTHOR]

Organic/inorganic hybrid systems offer great potential for novel solar cell design combining the tunability of organic chromophore absorption properties with high charge carrier mobilities of inorganic semiconductors. However, often such material combinations do not show the expected performance: while ZnO, for example, basically exhibits all necessary properties for a successful application in light‐harvesting, it was clearly outpaced by TiO2 in terms of charge separation efficiency. The origin of this deficiency has long been debated. This study employs femtosecond time‐resolved photoelectron spectroscopy and many‐body ab initio calculations to identify and quantify all elementary steps leading to the suppression of charge separation at an exemplary organic/ZnO interface. It is demonstrated that charge separation indeed occurs efficiently on ultrafast (350 fs) timescales, but that electrons are recaptured at the interface on a 100 ps timescale and subsequently trapped in a strongly bound (0.7 eV) hybrid exciton state with a lifetime exceeding 5 µs. Thus, initially successful charge separation is followed by delayed electron capture at the interface, leading to apparently low charge separation efficiencies. This finding provides a sufficiently large time frame for counter‐measures in device design to successfully implement specifically ZnO and, moreover, invites material scientists to revisit charge separation in various kinds of previously discarded hybrid systems. [ABSTRACT FROM AUTHOR]

Molecular charge accumulating systems that act as both, photosensitizer and electron storage unit, are of interest in the context of multielectron redox processes, e. g. in solar fuel production. To this end, the photophysical properties of RuL1, a ruthenium tris‐diimine complex with an alloxazine‐based ligand as bioinspired structural motif, were investigated. The study includes absorption, emission, resonance Raman and transient absorption spectroscopy in combination with quantum chemical simulations to determine the light‐driven reactivity of the complex. Moreover, spectroelectrochemistry was employed for an in‐depth characterization of the optical properties of the reduced complex. Finally, a photolysis experiment using triethanolamine as electron source, in conjunction with redox titrations, demonstrated that visible light irradiation triggers the formation of the doubly‐reduced singly‐protonated derivative of RuL1, where both redox equivalents are stored on the alloxazine‐based ligand. [ABSTRACT FROM AUTHOR]

Sagittally focusing x-ray crystal spectrometers with elliptical profiles in the meridional (x-ray dispersion) plane are proposed for plasma diagnostics in experiments accompanied by high neutron yields. The spectrometers feature a variable sagittal radius of curvature to ensure the sagittal focusing of rays for each photon energy in a chosen detection plane. The detector is placed after the ray crossing point at the second ellipse focus, and the source-to-detector distance is maximized to reduce the neutron-induced background. The elliptical shape imposes a limitation on the spectrometer geometry such that the influence of the source size on the spectral resolution can be avoided only for a demagnifying spectrometer (the source-to-crystal distance is larger than that of crystal-to-detector). Hence, two designs are proposed. The first design, featuring high magnification and limited spectral resolution can be suitable for x-ray continuum spectroscopy. The second design of high demagnification is optimized for spectral resolution, and can be used for time-resolved spectroscopy of plasma's characteristic emission lines using streak cameras. The key performance characteristics of the two designs are verified using ray tracing. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are promising light absorbers for multijunction photovoltaic applications because of their remarkable bandgap tunability, achieved through compositional mixing on the halide site. However, poor energy‐level alignment at the interface between wide‐bandgap mixed‐halide perovskites and charge‐extraction layers still causes significant losses in solar‐cell performance. Here, the origin of such losses is investigated, focusing on the energy‐level misalignment between the valence band maximum and the highest occupied molecular orbital (HOMO) for a commonly employed combination, FA0.83Cs0.17Pb(I1‐xBrx)3 with bromide content x ranging from 0 to 1, and poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA). A combination of time‐resolved photoluminescence spectroscopy and numerical modeling of charge‐carrier dynamics reveals that open‐circuit voltage (VOC) losses associated with a rising energy‐level misalignment derive from increasing accumulation of holes in the HOMO of PTAA, which then subsequently recombine non‐radiatively across the interface via interfacial defects. Simulations assuming an ideal choice of hole‐transport material to pair with FA0.83Cs0.17Pb(I1‐xBrx)3 show that such VOC losses originating from energy‐level misalignment can be reduced by up to 70 mV. These findings highlight the urgent need for tailored charge‐extraction materials exhibiting improved energy‐level alignment with wide‐bandgap mixed‐halide perovskites to enable solar cells with improved power conversion efficiencies. [ABSTRACT FROM AUTHOR]

Highly-crystallized carbon nitride (HCCN) nanosheets exhibit significant potential for advancements in the field of photoelectric conversion. However, to fully exploit their potential, a thorough understanding of the fundamental excitonic photophysical processes is crucial. Here, the temperature-dependent excitonic photoluminescence (PL) of HCCN nanosheets and amorphous polymeric carbon nitride (PCN) is investigated using steady-state and time-resolved PL spectroscopy. The exciton binding energy of HCCN is determined to be 109.26 meV, lower than that of PCN (207.39 meV), which is attributed to the ordered stacking structure of HCCN with a weaker Coulomb interaction between electrons and holes. As the temperature increases, a noticeable reduction in PL lifetime is observed on both the HCCN and PCN, which is ascribed to the thermal activation of carrier trapping by the enhanced electron–phonon coupling effect. The thermal activation energy of HCCN is determined to be 102.9 meV, close to the value of PCN, due to their same band structures. Through wavelength-dependent PL dynamics analysis, we have identified the PL emission of HCCN as deriving from the transitions: σ *–LP, π *– π, and π *–LP, where the π *–LP transition dominants the emission because of the high excited state density of the LP state. These results demonstrate the impact of high-crystallinity on the excitonic emission of HCCN materials, thereby expanding their potential applications in the field of photoelectric conversion. [ABSTRACT FROM AUTHOR]

Two novel covalently linked triads containing one 3-pyrrolyl BODIPY unit and two BODIPY units were synthesized over a sequence of steps using meso-(p-formylphenyl)-3-pyrrolyl BODIPY as a key precursor. Both triads were thoroughly characterized and studied by using HRMS, 1D and 2D NMR spectroscopy, X-ray crystallography, absorption, steady-state and time-resolved fluorescence, cyclic voltammetry, and DFT/TD-DFT techniques. X-ray structural analysis of these triads revealed that the dipyrrin units of both meso-BODIPY and 3-pyrrolyl BODIPY were oriented in the same plane whereas the dipyrrin unit of the α-BODIPY unit was oriented almost perpendicular to that of the 3-pyrrolyl BODIPY unit. Both triads showed two well-separated absorption bands corresponding to BODIPY and 3-pyrrolyl BODIPY units in the 510–675 nm region. In these triads, the BODIPY unit absorbs in the higher energy region and acts as an energy donor whereas the 3-pyrrolyl BODIPY unit absorbs in the lower energy region and acts as an energy acceptor. Steady-state and time-resolved fluorescence studies of these triads indicated the possibility of intramolecular singlet–singlet energy transfer with almost 98% efficiency from the BODIPY units to the 3-pyrrolyl BODIPY unit upon selective excitation of the BODIPY unit in both triads. DFT and TD-DFT investigations corroborated the experimental findings. [ABSTRACT FROM AUTHOR]

Owing to the diverse biological application, photophysical behaviour of Hoechst 33258 (H33258) is an important topic in biophysical research. Here, we have reported the photophysical behavior of H33258 in model biomembrane mimicking micellar microenvironment. In order to understand the molecular mechanism of the interaction of H33258 with micelles, we have used cationic (Hexadecetyltrimethyl ammonium bromide (CTAB)), anionic (sodium dodecyl sulphate (SDS)), and non‐ionic (t‐octylphenoxypolyoxyethanol, Triton‐X100 (TX 100)) micelles. From the steady‐state emission study the evaluated apparent binding constant (Kb) values for the complex formation between H33258 and CTAB, SDS and TX 100 micelle were (1.45±0.42)×105, (31.95±4.89)×105 and (3.10±0.73)×105 M−1, respectively. Thus, it was found that the Kb value was greater in the case of anionic micelle than non‐ionic and cationic micelles. Such differences in Kb values were due to the electrostatic interaction and hydrogen bond formation between the probe molecule and micelles. In addition, time‐resolved fluorescence decay and time‐resolved fluorescence anisotropy studies were performed to understand the dynamical behavior of H33258 in presence of micelles. The interaction of H33258 with micelles might be useful to study the structure and dynamics of different bio‐membranes and to formulate new drug delivery system. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The problem of molecular diffusion in the soup of chemical reactions attracts mounting interest across fields ranging from chemistry to biophysics to material science. Chemical reactions involve bond breakup and formation, whose time scale is typically on the orders of fs to ps, while molecular diffusion occurs at time scales of μs to ms. The two processes are often considered orthogonal, given the vastly different scales. The serial results show that the enzyme's diffusion is enhanced in a substrate‐dependent manner, which was further extended to small molecule reaction systems, challenging this classical paradigm. However, the results from different groups using different techniques do not quantitatively agree, and a general mechanism is yet to be understood. We summarize experimental studies on diffusion problems and seek to reconcile the interpretation with understanding the limits of measurement tools and the chemical nature of reaction systems. Understanding molecular diffusion in chemical reactions will provide fresh thoughts in designing chemical systems such as molecular machines that harvest work at the nanoscale in a controllable manner. [ABSTRACT FROM AUTHOR]

Carbene‐metal‐amides (CMAs) are emerging delayed fluorescence materials for organic light‐emitting diode (OLED) applications. CMAs possess fast, efficient emission owing to rapid forward and reverse intersystem crossing (ISC) rates. The resulting dynamic equilibrium between singlet and triplet spin manifolds distinguishes CMAs from most purely organic thermally activated delayed fluorescence emitters. However, direct experimental triplet characterization in CMAs is underutilized, limiting our detailed understanding of the ISC mechanism. In this work, we combine time‐resolved spectroscopy with tuning of state energies through environmental polarity and metal substitution, focusing on the interplay between charge‐transfer (3CT) and local exciton (3LE) triplets. Unlike previous photophysical work, we investigate evaporated host : guest films of CMAs and small‐molecule hosts for increased device relevance. Transient absorption reveals an evolution in the triplet excited‐state absorption (ESA) consistent with a change in orbital character between hosts with differing dielectric constants. Using quantum chemical calculations, we simulate ESAs of the lowest triplet states, highlighting the contribution of only 3CT and donor‐moiety 3LE states to spectral features, with no strong evidence for a low‐lying acceptor‐centered 3LE. Thus, our work provides a blueprint for understanding the role of triplet excited states in CMAs which will enable further intelligent optimization of this promising class of materials. [ABSTRACT FROM AUTHOR]