Search

Living system involves a plenty of delicate processes where a tiny structural variation of biological substance may lead to drastic change of the fate of the living system. Inspired by this, in artificial photofunctional systems, if tiny structural variation changes the fate of excited states, a new class of advanced material would emerge for optical analysis, sensing, and next‐generation display is reasoned. However, such delicate processes remain rarely explored in photofunctional systems, especially in room temperature organic afterglow systems. Here the attachment/detachment of methoxy group can switch off/on twisted intramolecular charge transfer property in difluoroboron β‐diketonate systems is reported. In addition, structural isomerization triggers afterglow transformation from room temperature phosphorescence to thermally activated delayed fluorescence. These observations are helpful for better photophysical understanding on luminescence systems and advanced material design. [ABSTRACT FROM AUTHOR]

The mechanism of aggregation-induced emission (AIE) for the bis(1-(2,4-difluorophenyl)-1H-pyrazole)(2-(20-hydroxyphenyl)-2-oxazoline)iridium(III) complex, denoted as Ir(dfppz)2(oz), was investigated with use DFT and the TD-DFT level of theory. The mechanism of radiationless deactivation of the triplet state was elucidated. Such a mechanism requires an additional, photophysical triplet channel of the internal conversion (IC) type, which is activated as a result of intramolecular motion deforming the structure of the oz ligand and distorting the iridium coordination sphere. Formally, the rotational movement of the oxazoline relative to the C–C bond in the oz ligand is the main active coordinate that leads to the opening of the triplet channel. The rotation of the oxazoline group and the elongation of the Ir-Nox bond cause a transition between the luminescent, low-lying triplet state with a d / π → π * characteristic ( T 1 (eq) ), and the radiationless d → d triplet state ( T 1 (Ir) ). This transition is made possible by the low energy barrier, which, based on calculations, was estimated at approximately 8.5 kcal/mol. Dimerization, or generally aggregation of the complex molecules, blocks the intramolecular movement in the ligand and is responsible for a strong increase in the energy barrier for the T 1 (eq) ⇝ T 1 (Ir) conversion of triplet states. Thus, the aggregation phenomenon blocks the nonradiative deactivation channel of the excited states and, consequently, contributes to directing the photophysical process toward phosphorescence. The mechanism involved in locking the nonradiative triplet path can be called restricted access to singlet–triplet crossing (RASTC). [ABSTRACT FROM AUTHOR]

The possibilities of emission from the Ã1A″ and ã3A″ excited states of the triatomic halosilylenes, halogermylenes, and halostannylenes (HMX, M = Si, Ge, Sn; X = F, Cl, Br, I) have been explored in a series of extensive ab initio calculations. The triplet states are found to have deep bonding wells supporting an extensive manifold of vibrational levels, which could give rise to observable triplet–singlet phosphorescence. The ã– X ̃ band systems of the halosilylenes are calculated to occur at the red edge of the visible and are likely to be very weak. In contrast, the HGeX and HSnX triplet–singlet spectra are shifted 1000–2000 cm−1 to the higher energy and are expected to be significantly stronger due to increased spin–orbit coupling, making the spectra viable targets for experimental investigations. The Ö X ̃ fluorescence is found to be limited by the possibility of HMX (Ã1A″) → H (2S) + MX (2 Π) dissociation in the excited state, leading to the expectation that HGeF is unlikely to be detectable by laser-induced fluorescence (LIF) spectroscopy. The HSiX and HGeX species with known LIF spectra are found to have deeper à state bonding wells and minimal or no calculated barriers to dissociation. It is generally found that the intensity in their LIF spectra tails off due to a diminution of vibrational overlap rather than the abrupt opening of a dissociation channel. Few of the HSnX species are known experimentally. HSnF and DSnF are found to dissociate very low down in the à state vibrational manifold and are predicted to be unobservable by LIF spectroscopy. The LIF spectrum of HSnCl is expected to consist of only one or two bands, with slightly more activity for DSnCl, precisely as has recently been found experimentally. HSnBr and DSnBr have deeper à state bonding wells, and their LIF spectra are thus likely to be more extensive. Although HSnI and DSnI are calculated to have deep bonding wells with respect to the H + MX dissociation, predictions are complicated by the existence of a global small bond angle minimum and the opening of a second SnH + I dissociation channel. [ABSTRACT FROM AUTHOR]

In this study, the insertion of different monodentate co-ligands on Pt(II) complexes bearing a monoanionic C^N*N luminophore as a tridentate chelator was achieved beyond the previously reported chlorido- ([PtCl(L)]) and cyanido-decorated ([PtCN(L)]) analogues. To investigate the impact of the auxiliary ligand on the photophysical properties, we introduced a neutral carbonyl-ligand and observed a lower photoluminescence quantum yield (ΦL) than with a cyanido moiety. However, the direct substitution of the chlorido co-ligand by a NO-related derivative was not successful. Interestingly, the attempted reduction of the successfully inserted nitrito-N-ligand in [PtNO2(L)] resulted in the oxidation of the Pt(II)-center to Pt(IV), as demonstrated by X-ray diffractometry. For comparison, the trifluoroacetato Pt(II) and chlorido Pt(IV) complexes ([PtTFA(L)] and [PtCl3(L)], respectively) were also synthesized. The photophysical characterization revealed similar photoluminescence profiles for all complexes, indicating a weak effect of the co-ligand on the excited state; in fact, all complexes display emission from metal-perturbed ligand-centered states (even the Pt(IV) species). Nonetheless, longer excited state lifetimes (τav) suggest a reduced thermally-activated radiationless deactivation via metal-centered states upon exchange of the chlorido units for other monodentate entities, yet without significantly improving the overall ΦL at room temperature. The irreversible oxidation waves (measured via cyclic voltammetry) mostly stem from the Pt(II)-center; the co-ligand-related drop of these potentials correlates with the increasing σ-donating capacities of the ancillary ligand. In summary, an enhanced π-acceptor capacity does not necessarily improve the ΦL and can even impair radiative rates by compromising the perturbative participation of the metal center on the emissive triplet state; in addition, strong σ-donor abilities improve the phosphorescence efficiencies by hampering the thermal population of dissociative electronic configurations related to the participation of antibonding d*-orbitals at the metal center. [ABSTRACT FROM AUTHOR]

Absorption, fluorescence, and phosphorescence spectra of single crystals of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and BTBT dispersed in frozen n-nonane, n-hexadecane, and dichloromethane matrices were studied at 5 K. Observation of a new absorption band and related changes in the fluorescence to phosphorescence intensity ratio, when the concentration of BTBT in the matrix increased above 10−4M, indicated the presence of BTBT aggregates. Quantum-chemistry calculations performed for the simplest aggregate, isolated dimer, showed that its structure is similar to the "herringbone" element in the BTBT crystal unit cell and the lowest electronic excited singlet state of the dimer has the intermolecular charge-transfer character. A qualitatively different nature of this state in dimers and in crystals, when compared with the situation in BTBT monomer [locally excited (LE) state], is associated with a decrease in the intersystem crossing yield. The structured vibronic structure of phosphorescence spectra in the studied systems indicated LE character of the triplet states. [ABSTRACT FROM AUTHOR]

We utilize the dopant-matrix strategy and emulsion polymerization to obtain aqueous afterglow dispersions from a liquid precursor, which avoids the processing of solid materials, protects organic triplets and achieves long phosphorescence lifetime of 7.64 s. The aqueous afterglow dispersions display great potential for biomedical applications due to their ultralong-lived excited states. [ABSTRACT FROM AUTHOR]

Phosphorescence of organic materials is highly dependent on intermolecular interactions, for the sensitive triplet excitons toward environment and aggregated structures. However, until now, relationship between phosphorescence and intermolecular interactions is still unclear for complicated influence factors and uncontrollable aggregated behaviors. Herein, taking temperature as the controlled variable, the afterglow can continuously change from blue to green, then to yellow, even achieve the white emission with deuteration process. It is mainly due to the hierarchical architectures of molecular aggregates with rational distribution of intermolecular interactions, as well as gradually unlocking process of interactions with different energies. Accordingly, the one‐to‐one correspondence between the determinate interactions and excited triplet states have been established, guiding accurate design of desirable phosphorescence materials by hierarchical control of aggregated structures. [ABSTRACT FROM AUTHOR]

Developing near-infrared (NIR) TADF emitters is challenging due to the inherent energy gap law. In this work, we designed a set of twelve donor–acceptor1–acceptor2 (D–A1–A2) type NIR pure organic emitter molecules that contain a strong donor (triphenylamine (TPA)), a cyano group substituted anthrathiadiazole (AZ) unit as A1, and fused aromatic/heterocyclic molecules as the A2 unit. The strength of the acceptor part A2 is altered by introducing electron-withdrawing groups (–H, –F, –CN). We studied their geometrical, electronic, and excited state properties using Density functional theory (DFT) and time-dependent DFT methods. Comprehensive analysis of excited state properties obtained from computational methods such as the energy gap between singlet and triplet excited states (ΔEST), spin–orbit coupling (SOC) values, the nature of singlet and triplet excited states, rates of reverse intersystem crossing (kRISC), and radiative and non-radiative emissions (kr and knr) are conducted to acquire insights into the NIR emission in the studied molecules. Our calculated results show that the molecules should possess hybrid localized and charge transfer (HLCT) character dominated by Frenkel-type excitation (LE) in the lowest singlet excited state to achieve faster kr. Furthermore, the strong donor, AZ unit, and moderate acceptor A2 unit provide smaller energy gaps between singlet and triplet states with reasonable SOC values in the higher excited states. In our study, we identify multiple hot-exciton channels to up-convert dark triplet excitons into bright singlet excitons, which might improve the exciton utilization efficiency. [ABSTRACT FROM AUTHOR]

The excited triplet state of a molecule (T1) is one of the principal intermediate products in various photochemical processes due to its high reactivity and relatively long lifetime. The T1 quantum yield ( φ T ) is one of the most important characteristics in the study of photochemical reactions. It is of special interest to determine the φ T of various photoactive compounds (photosensitizer, PS) used in photodynamic therapy (PDT). PDT is an effective medical technique for the treatment of serious diseases, such as cancer and bacterial, fungal and viral infections. This technique is based on the introduction of a PS to a patient's organism and its further excitation by visible light, producing reactive oxygen species (ROS) via electron or energy transfer from the PS T1 state to the biological substrate or molecular oxygen. Therefore, information on the φ T value is fundamental in the search for new and effective PSs. There are various experimental methods to determine φ T values; however, these methods demonstrate a high discrepancy between φ T values. This stimulates the analysis of various factors that can affect the determined φ T . In this study, we analyze the effect of the intensity profile of the exciting laser pulse on the calculation of the φ T value obtained by the Laser Flash Photolysis technique. The φT values were determined by analyzing the variation of a sample transient absorption in the function of the exciting laser pulse intensity, in combination with the spectral and kinetic PS characteristics obtained in nonlinear optical experiments by solving the rate equations of a five-level-energy diagram. Well-studied PSs: meso-tetra(4-sulfonatophenyl) (TPPS4) porphyrins, its zinc complex (ZnTPPS4) and the zinc complex of meso-tetrakis(N-methylpyridinium-4-yl) (ZnTMPyP) were chosen as test compounds to evaluate the proposed model. The φ T values were determined through a comparison with the φ T , T M P y P = 0.82 of meso-tetrakis(N-methylpyridinium-4-yl) (TMPyP), used as a standard. The obtained results ( φ T , T P P S 4 = 0.75 ± 0.02 , φ T , Z n T M P y P = 0.90 ± 0.03) , and φ T , Z n T P P S 4 = 0.89 ± 0.03 ) are highly compatible with the medium φ T values obtained using the known methods. [ABSTRACT FROM AUTHOR]

The chemical stability and the low‐lying singlet and triplet excited states of BN‐n‐acenes (n = 1–7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet‐triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon‐only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet‐triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN‐n‐acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low‐lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron. [ABSTRACT FROM AUTHOR]

The ground, singlet, and triplet excited state structures (S1, S2, T1, and T2) of xanthone have been calculated and characterized in the adiabatic representation by using time‐dependent density functional theory (TDDFT). However, the fast intramolecular transition mechanisms of xanthone are still under debate, and so we perform non‐adiabatic excited state dynamics of the photochemistry of xanthone gas phase and find that it follows El‐Sayed's rule. Electronic transition mechanism of xanthone is sequential from the S2 state: the singlet internal conversion (IC) time from S2 (1ππ*) to S1 (1nπ*) is 3.85 ps, the intersystem crossing (ISC) from S1 (1nπ*) to T2 (3ππ*) takes 4.76 ps, and the triplet internal conversion from T2 (3ππ*) to T1 (3nπ*) takes 472 fs. The displaced oscillator, Franck–Condon approximation, and one‐photon excitation equations were used to simulate the absorption spectra of S0 → S2 transition, with v55 being most crucial for S0 structure; the fluorescence spectra of S1 → S0 transition with v47 for S1; and the phosphorescence spectra of T1 → S0 transition with v4 for T1. Our method can reproduce the experimental absorption, fluorescence, and phosphorescence spectra of gas‐phase xanthone. [ABSTRACT FROM AUTHOR]

Based on models of the electronic kinetics of triplet and singlet states of molecular nitrogen and singlet states of molecular oxygen for the Earth's middle atmosphere, we calculated the intensity profiles of the bands of the first and second positive N2 systems, the Lyman–Birge–Hopfield N2 bands, and the infrared O2 bands in the case of precipitation of high-energy protons during the GLE65, GLE67, GLE69, and GLE70 events of solar cycle 23. Calculations have shown that almost over the entire interval of altitudes of 20–80 km, there is a significant contribution from the processes of quenching some electronically excited states of N2 and O2 during molecular collisions. The kinetics of O2 singlet states at the altitudes of the middle atmosphere during proton precipitation is considered taking into account both direct excitation by high-energy particles and intermolecular processes of electron excitation transfer. [ABSTRACT FROM AUTHOR]

Photophysical processes occurring within organic semiconductors is important for designing and fabricating organic solar cells. Copper phthalocyanine (CuPc) is a typical electron acceptor. In this work, the triplet exciton lifetime is prolonged by altering the molecular stacking pattern of the CuPc film. For CuPc thin films, the excited state decays are mainly determined by the triplet-triplet annihilation process. The ultrafast transient absorption measurements indicate that the primary annihilation mechanism is one-dimensional exciton diffusion collision destruction. The decay kinetics show a clearly time-dependent annihilation rate constant with γ∝t−1/2. Annihilation rate constants are determined to be γ0 = (2.87±0.02)×10−20 cm3·s−1/2 and (1.42±0.02)×10−20 cm3·s−1/2 for upright and lying-down configurations, respectively. Compared to the CuPc thin film with an upright configuration, the thin film with a lying-down configuration shows longer exciton lifetime and higher absorbance, which are beneficial to organic solar cells. The results in this work have important implications on the design and mechanistic understanding of organic optoelectronic devices. [ABSTRACT FROM AUTHOR]

Aqueous afterglow dispersions display promising biomedical applications due to their long‐lived excited states, whereas it is a common problem in the research field that processing and transferring solid‐state afterglow materials into aqueous medium can cause significant drop and even complete loss of their afterglow properties. Here, aqueous afterglow dispersions are fabricated from liquid precursors by dopant–matrix strategy and emulsion polymerization, which avoids the processing procedures on solid‐state materials and achieves 2.4 s long phosphorescence lifetimes in aqueous medium. Luminescent difluoroboron β‐diketonate dopants are first designed with small rate constant of phosphorescence decay and then dissolved in monomers. After emulsion polymerization, the as‐formed polymer latex particles not only assist dopants' intersystem crossing but also provide a glassy microenvironment to largely suppress nonradiative decay of dopants' triplets, leading to in situ formation of aqueous afterglow dispersions. This provides a robust method for constructing afterglow emulsions with long‐term colloidal stability, relatively high solid contents, tunable sizes, and diverse compositions. Through emulsion copolymerization, afterglow emulsions decorated with specific ligands are obtained to exhibit specific protein binding properties. Such decorated afterglow emulsions address the issue that afterglow materials lack biorecognition property and can pave the way for their applications in immunoassay and immunoimaging. [ABSTRACT FROM AUTHOR]

The photochemical reaction of potassium ferrocyanide (K4Fe(CN)6) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K4Fe(CN)6 were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and photoaquation reactions were clarified by comparing the results of 260, 320, 340, and 350 nm excitations. ESED is the path to generate a hydrated electron ( e aq − ). ESED energy barrier varies with the excited state, and it occurs even at the first singlet excited state (1T1g). The 1T1g state shows ∼0.2 ps lifetime and converts into triplet [Fe(CN)6]4− by intersystem crossing. Subsequently, 3[Fe(CN)5]3− appears after one CN− ligand is ejected. In sequence, H2O attacks [Fe(CN)5]3− to generate [Fe(CN)5H2O]3− with a time constant of approximately 20 ps. The 1T1g state and e aq − exhibit strong reducing power. The addition of uridine 5′-monophosphate (UMP) to the K4Fe(CN)6 solution decrease the yield of e aq − and reduce the lifetimes of the e aq − and 1T1g state. The obtained reaction rate constant of 1T1g state and UMP is 1.7×1014 (mol/L)−1·s−1, and the e aq − attachment to UMP is ∼8×109 (mol/L)−1·s−1. Our results indicate that the reductive damage of K4Fe(CN)6 solution to nucleic acids under ultraviolet irradiation cannot be neglected. [ABSTRACT FROM AUTHOR]

High external quantum efficiency (EQE) up to 25% has recently been reported from tetra(t‐butyl)rubrene (TBRb)‐based organic light‐emitting diodes (OLEDs), but its physical origin is still vague. Herein, using the featured responses of the evolution processes of electron‐hole pairs to an external magnetic field, an unreported high‐level reverse intersystem‐crossing (HL‐RISC) from upper‐level triplet to lowest singlet excitons (T2→S1) is observed when T2 is well confined in the active layer of pure TBRb. This HL‐RISC channel becomes stronger with lowering operational temperatures because it is not an endothermic process. Due to the larger separation distance of TBRb molecules with four tert‐butyl groups, the intersystem‐crossing (ISC) process of polaron pairs is stronger than the singlet fission (SF) process existing in pure TBRb, which is markedly different from the behaviors of excited states in pure rubrene (Rb) with negligible ISC and strong SF. More importantly, HL‐RISC is stronger in TBRb than in Rb‐doped systems, which is consistent with the higher EQE frequently reported from TBRb‐doped OLEDs. Thus, this work deepens the physical understanding of microscopic processes in typical organic multi‐functional semiconductors of TBRb or Rb and paves the way for fabricating further high‐efficiency yellow OLEDs. [ABSTRACT FROM AUTHOR]

Nitrenium ions are important reactive intermediates in both chemistry and biology. Although singlet nitrenium ions are well-characterized by direct methods, the triplet states of nitrenium ions have never been directly detected. Here, we find that the excited state of the photoprecursor partitions between heterolysis to generate the singlet nitrenium ion and intersystem crossing (ISC) followed by a spontaneous heterolysis process to generate the triplet p-iodophenylnitrenium ion (np). The triplet nitrenium ion undergoes ISC to generate the ground singlet state, which ultimately undergoes proton and electron transfer to generate a long-lived radical cation that further generates the reduced p-iodoaniline. Ab Initio calculations were performed to map out the potential energy surfaces to better understand the excited state reactivity channels show that an energetically-accessible singlet-triplet crossing lies along the N-N stretch coordinate and that the excited triplet state is unbound and spontaneously eliminates ammonia to generate the triplet nitrenium ion. These results give a clearer picture of the photophysical properties and reactivity of two different spin states of a phenylnitrenium ion and provide the first direct glimpse of a triplet nitrenium ion. Nitrenium ions are highly electrophilic reactive intermediates of formula R−N−R+, nitrogen analogue of carbenes. Here the authors report the detection of a triplet nitrenium ion using time-resolved spectroscopic methods and ab initio computations, allowing a glimpse at the properties and behavior of this important class of intermediates. [ABSTRACT FROM AUTHOR]

We firstly design and synthesize a new facial phosphorescent iridium complex fac‐Ir(NO)3 with three strong electron‐donating N‐embedded π‐conjugation units. It is found that the complex fac‐Ir(NO)3 can display a distinct orange phosphorescence emission (λ=582 nm) with a redshift of 55 nm relative to model complex fac‐Ir(N)3 (λ=527 nm) with three triphenylamine units. Notably, it also exhibits a significantly narrower half‐peak width (FWHM=70 nm) compared with model complex Ir(NO)2acac (FWHM=97 nm) with two N‐embedded π‐conjugation units. In addition, it also shows both distinct intraligand charge transfer (ILCT) and partial unusual ligand‐to‐metal charge transfer (LMCT) excited state properties due to strong electron‐donating capacity of three N‐embedded π‐conjugation units. [ABSTRACT FROM AUTHOR]

Triplet–triplet annihilation (TTA) is a feasible approach for utilizing electrically generated triplet excitons in organic light‐emitting diodes. However, low TTA efficiency is often observed in solids. Owing to the optically inaccessible nature of triplets, the main loss routes of the TTA process remain unknown. In this work, three vibrational emission peaks of the first excited triplet state (T1) are identified in the sensitized room‐temperature phosphorescence of TTA molecules. These peaks provide strong evidence of the loss channels of TTA. It is found that the monomolecular recombination of T1 represents an energy‐loss channel that combines the transient photoluminescence of both upconversion fluorescence and phosphorescence. Moreover, the study demonstrates that low‐energy vibrational T1 acts as an energy‐loss channel with only slight contributions to TTA. This work presents constructive insights into the improvement of TTA efficiency in solid films. [ABSTRACT FROM AUTHOR]

The endoperoxides of β-carotene (βCar-EPOs) are regarded as main products of the chemical deactivation of 1O2 by β-carotene, one of the most important antioxidants, following a concerted singlet-singlet reaction. Here we challenge this view by showing that βCar-EPOs are formed in the absence of 1O2 in a non-concerted triplet-triplet reaction: 3O2 + 3β-carotene → βCar-EPOs, in which 3β-carotene manifests a strong biradical character. Thus, the reactivity of β-carotene towards oxygen is governed by its excited triplet state. βCar-EPOs, while being stable in the dark, are photochemically labile, and are a rare example of nonaromatic endoperoxides that release 1O2, again not in a concerted reaction. Their light-induced breakdown triggers an avalanche of free radicals, which accounts for the pro-oxidant activity of β-carotene and the puzzling swap from its anti- to pro-oxidant features. Furthermore, we show that βCar-EPOs, and carotenoids in general, weakly sensitize 1O2. These findings underlie the key role of the triplet state in determining the chemical and photophysical features of β-carotene. They shake up the prevailing models of carotenoid photophysics, the anti-oxidant functioning of β-carotene, and the role of 1O2 in chemical signaling in biological photosynthetic systems. βCar-EPOs and their degradation products are not markers of 1O2 and oxidative stress but of the overproduction of extremely hazardous chlorophyll triplets in photosystems. Hence, the chemical signaling of overexcitation of the photosynthetic apparatus is based on a 3chlorophyll-3β-carotene relay, rather than on extremely short-lived 1O2. The endoperoxides of β-carotene play a key role in signaling of photooxidative stress in plant cells and are regarded as the products of chemical deactivation of singlet oxygen. The authors show that these compounds are instead formed in a reaction between oxygen and β-carotene in their triplet states, revealing the importance of the triplet states in the photoprotection of photosynthetic apparatus. [ABSTRACT FROM AUTHOR]

The photochemistry of aryl chlorides having a X-SiMe3 group (X = O, NR, S, SiMe2) tethered to the aromatic ring has been investigated in detail, with the aim to generate valuable ϭ,π-heterodiradicals. Two competitive pathways arising from the excited triplet state of the aromatics have been observed, namely heterolysis of the aryl–chlorine bond and homolysis of the X–silicon bond. The former path is found in chlorinated phenols and anilines, whereas the latter is exclusive in the case of silylated thiophenols and aryl silanes. A combined experimental/computational approach was pursued to explain such a photochemical behavior. Graphical abstract [ABSTRACT FROM AUTHOR]

The organic solid-state light-emitting materials have attracted more and more attention owing to their promising applications in displays, lasers and optical communications. In contrast to isolated molecule, there are various weak intermolecular interactions in organic solids that sometimes have a large impact on the excited-state properties and energy dissipation pathways, resulting in strong fluorescence/phosphorescence. It is increasingly necessary to reveal the luminescence mechanism of organic solids. Here, we briefly review how intermolecular interactions induce strong normal fluorescence, thermally activate delayed fluorescence and room-temperature phosphorescence in organic solids by examining changes in geometry, electronic structures, electron-vibration coupling and energy dissipation dynamics of the excited states from isolated to aggregated molecules. We hope that the review will contribute to an in-depth understanding of the excited state properties of organic solids and to the design of excellent solid-state light-emitting materials. [ABSTRACT FROM AUTHOR]

RutheniumII complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ‐(S)‐ and Λ‐(S)‐diastereomers were obtained. The X‐ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ‐(S)‐ and Λ‐(S)‐isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ‐(S)‐isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ‐(S)‐isomer, the six cumulative CH/π interactions suppress further distortion in the T1 state. [ABSTRACT FROM AUTHOR]

The reaction between allenylpyridine (L1) and (Me2S)AuCl resulted in the quantitative formation of the (Indolizy)gold chloride complex 1 (Indolizy = indolizin-2-ylidene). The reaction of 1 with carbazole in the presence of KOtBu affords the corresponding (Indolizy)Au(Cz) complex 2. Both compounds show high air- and temperature stability. The crystal structure of 2 confirmed the linear co-planar geometry. Complex 1 shows an intense low energy absorption of mixed character in the UV-vis spectrum, ascribed to intraligand and (M + Hal)L charge transfer processes, and exhibits bright yellow phosphorescence with an excited state lifetime of 62.8 μs in the crystal and a luminescence quantum yield up to 65%. On the other hand, the carbazolate complex 2 in a polystyrene matrix shows bright red delayed fluorescence at 617 nm with a sub-microsecond excited state lifetime and a quantum yield of 21.6%. [ABSTRACT FROM AUTHOR]

We devised a new generation of halogen-based triplet sensitisers comprising geminal dibromides at the vinyl backbone of a BODIPY fluorophore. Incorporating geminal dibromides into the π-conjugation of BODIPY enhanced intersystem crossing due to the heavy atom effect, which in turn improved the extent of excited triplet states. [ABSTRACT FROM AUTHOR]

In this work nine novel heteroleptic Ir(III) complexes of general formulae [Ir(N∧C#)2(O∧O#)] containing four different cyclometallating and four β‐diketonate ligands were synthesized and fully characterized. Six of them display phosphorescence in the deep red and NIR regions with quantum yields reaching 24.6 % in degassed solution for one of the NIR emitters. Variation in the nature of orthometalating ligands results in dramatic changes in photophysical behavior: the compounds containing 2‐phenylpyridine (N∧C1) and 2‐(benzo[b]thiophen‐2‐yl)pyridine (N∧C2) ligands give non‐emissive complexes, whereas those with methyl 2‐phenylquinoline‐4‐carboxylate (N∧C3) and 6‐(benzo[b]thiophen‐2‐yl)phenanthridine) (N∧C4) are luminescent, but display different character of electronic transitions responsible for absorption and emission. Complexes with the N∧C3 ligand luminesce from 3LC excited state and do not change their emission characteristics upon variations in the nature of β‐diketonates. On the contrary, the compounds based on the N∧C4 cyclometalating ligand emit from the excited state with considerable contribution of 3MLCT character and show systematic bathochromic shift of absorption and emission bands upon increase in electron donicity of O∧O# ligands. This conclusion was supported by DFT and TD‐DFT calculations and by the analysis of correlations between the 13C chemical shift of the diketonate C(H) carbon and emission maxima of the compounds under study. [ABSTRACT FROM AUTHOR]

Energy diagram of various states with fully reduced Iso in the Iso -Tyr281 -Trp277 -Trp338 -Trp382 -Trp384 system of PLEC. [Display omitted] • Interaction system studied was Iso-Tyr281-Trp277-Trp338-Trp382-Trp384 in PLEC. • Iso in the system was in the oxidized form or fully reduced form. • Transition energies of the system in the various electronic states were calculated by MO method. • Proton transfer from Tyr281 to Iso stabilizes the energies in the excited singlet and triplet states. • The produced Tyr anion closely interacted with Iso in the excited singlet and triplet states and other Trps. Photolyases from Escherichia coli. (PLEC) function to repair UV-damaged DNA. Photolyases and cryptochromes (altogether 42 proteins) are found to contain at least one tyrosine (Tyr) residue near the isoalloxazine ring (Iso) of flavin adenine dinucleotide (FAD) within 1.2 nm, Tyr281 in PLEC. Iso in PLEC is surrounded by four Trp residues and one Tyr within 1.2 nm from Iso. Photoinduced charge transfer interactions (PCT) among these chromophores in the Iso-Tyr281-Trp277-Trp338-Trp382-Trp384 system were studied by means of a semi-empirical molecular orbital (MO) method. Structure of the system was extracted from crystal structure of PLEC. In the ground state the PCT interactions between any pairs were negligible. Upon photo-excitation almost one electron transferred from Trp382 to the excited Iso, to which an electron transport chain from Tyr residues at the protein - water interface to Iso is connected. Protonation at N1 or N5 of Iso from Tyr281 markedly stabilized the transition energy in the excited singlet state and triplet state, depending on the polarity of the medium, but not from a source other than Tyr281. In these states, nearly one electron migrates from Tyr281 to Trp382. Effects of the protonation from Tyr281 to the fully reduced Iso were also examined, where total charge of the system was −2. In the ground state the energy of the system was stabilized by the protonation, when the proton was bound to N5 of Iso, but not to N1. In the excited singlet state and triplet state of the fully reduced Iso, the transition energies of the system were also stabilized upon the protonation to N1 or N5 of Iso from Tyr281, but not from a source other than Tyr281. In the ground state almost two negative charges were located at Iso. In the excited singlet state one of two negative charges was mostly localized to Iso and another to Trp277 at the dielectric constant, 3, and to Trp384 at the dielectric constant, 10. In the triplet state without the protonation, one of two negative charges was localized to Iso and another to Trp384 at any dielectric constant. Upon protonation to N1 or N5 of Iso in the triplet state, one of the negative charges was localized to Iso and another to Tyr281 at any value of dielectric constant. Thus Tyr281 closely interacted with Iso in the excited singlet state and triplet state, and other Trp residues in the system through the proton transfer. [ABSTRACT FROM AUTHOR]

There has been controversy surrounding the roles of the metal core (metal–metal interaction) and the shell (metal–ligand interaction) in photoluminescence of ligand‐protected metal nanoclusters. We have discovered aggregation‐induced room‐temperature phosphorescence of a platinum–thiolate complex and its silver ion inclusion complex (a silver‐doped platinum sub‐nanocluster). The inclusion of silver ion boosted the photoluminescent quantum yield by 18 times. Photophysical measurements indicate that the rate of nonradiative decay was slower for the silver‐doped platinum sub‐nanocluster. DFT calculations showed that the LUMO, which had the main contribution from Ag s‐orbital and Pt d‐orbitals, played a critical role in suppressing the structural distortion at the excited state. This work will hopefully stimulate more research on designing strategies based on molecular orbitals of atomicity‐precise luminescent multimetallic nanoclusters. [ABSTRACT FROM AUTHOR]

The combined action of ultraviolet irradiation and microwave heating onto acetonitrile solution of [Re(NN)(CO)3(NCMe)]OTf (NN =phenantroline and neocuproine) afforded cis,trans‐Re(NN)(CO)2(NCMe)2]+ acetonitrile derivatives. Substitution of relatively labile NCMe with a series of aromatic N‐donor ligands (pyridine, pyrazine, 4,4'‐bipyridine, N‐methyl‐4,4'‐bipyridine) gave a novel family of the diimine cis,trans‐[Re(NN)(CO)2(L)2]+ complexes. Photophysical studies of the obtained compounds in solution revealed unusually high absorption across the visible region and NIR phosphorescence with emission band maxima ranging from 711 to 805 nm. The nature of emissive excited states was studied using DFT calculations to show dominant contribution of 3MLCT (dπ(Re)→π*(NN)) character. Electrochemical (CV and DPV) studies of the monocationic diimine complexes revealed one reduction and one oxidation wave assigned to reduction of the diimine moiety and oxidation of the rhenium center, respectively. [ABSTRACT FROM AUTHOR]

Over the last several decades, exploring the pathways to access the triplet excited states of organic chromophores has been a stimulating area of research. Among the numerous photoinduced processes in organic chromophores, analysis of intersystem crossing (ISC) dynamics has received immense attention. The ISC process involves a spin-forbidden horizontal transition from an excited singlet state to a higher vibrational level of the isoenergetic triplet state. Generally, ISC necessitates a strong driving force from efficient spin–orbit coupling (SOC) between the singlet and triplet wavefunctions. The magnitude of SOC can be tuned by the substituent groups (e.g. heavy atoms, carbonyl moieties) or by the out-of-plane vibrational modes in the chromophores. Besides the SOC induced ISC pathway, triplet excited states are also realised in organic chromophores through singlet fission or via charge recombination. Accessing the triplet manifold in π-conjugated systems would also include a possible evolution to more aromatically stable configurations in the excited states, an emerging area that needs attention. In the aforesaid mechanisms, the molecular architecture and/or packing arrangement of the chromophores are vital for the effective population of triplet states. We, herein, present a collection of synthetic, spectroscopic and theoretical investigations that provide insights into the diverse pathways to access triplet excited states in organic chromophores. We believe this tutorial review would prove beneficial for researchers to achieve triplet excited states of organic chromophores for numerous biochemical and optoelectronic applications. [ABSTRACT FROM AUTHOR]

The device lifetime of phosphor mediated TADF OLED, which is composed of three different type of materials such as host, phosphorescence, and TADF emitters in EML, was systematically investigated by a multi‐scale approach from quantum mechanics simulation to kinetic Monte Carlo simulation. The quantum chemical simulations to estimate the chemical stability of materials in atomic scale were clearly showed that the photo‐ or electro‐chemical stability in excited state was good qualitative correlation with device lifetime. From the results, we could figure out the crucial parameters that strongly related with the lifetime of blue TADF devices. Then, the device simulations based on kinetic Monte Carlo method were performed to understand excitonic dynamic. Based on the understanding about both a role of phosphorescence and a mechanism of energy transfer through emitters in EML, we found out that a concentration of triplet exciton around TADF emitters could be a dominant origin of the short lifetime even if TADF would have a sufficient stability condition we expect, and should be reduce to prevent the excitonic stress such as triplet‐triplet annihilation and triplet‐polaron quenching, resulting in the degradation of emitters. Consequently, this work suggests the simultaneous co‐optimization of both the device and its component material, for deep blue OLED device with a longer lifetime. [ABSTRACT FROM AUTHOR]

[Display omitted] • Organic afterglow emulsion exhibiting 2.0 s phosphorescence lifetime is achieved. • The afterglow emulsion features outstanding stability against harsh environments. • The afterglow emulsion exhibits high sensitivity to detect oxygen at low concentration. • All signal changes are fully reversible under degassing and exposing-to-oxygen cycle. The concentration of dissolved oxygen is of vital importance for many biological processes such as cancer occurrence and stem cell development. Aqueous afterglow materials, which feature longer-lived excited states than metal complex-based phosphorescence materials, would possess higher sensitivity in oxygen sensing, and would allow visual and direct observation of oxygen concentration by human eyes and low-cost instrument. However, it remains challenging to fabricate aqueous afterglow materials because of the intrinsic problem of the disruption of rigid microenvironment during processing of solid-state afterglow materials. Here we report the fabrication of aqueous afterglow materials from liquid precursor via emulsion polymerization, which eliminate solid-state afterglow material processing and consequently result in 1.7 s phosphorescence lifetimes (2.0 s in deuterated system) at room temperature. The organic afterglow emulsion exhibits high solid content and colloidal stability, and is robust against large pH change, high salt concentration, and organic solvents. Interestingly, the afterglow emulsion has been found to display oxygen sensing property which can be dually monitored by afterglow intensity and lifetime changes. In-depth study reveals that the oxygen sensing property originates from the labile nature of organic triplets and also the oxygen permeability within the polymer latex in the aqueous emulsion system. [ABSTRACT FROM AUTHOR]

Recently, catalyst-free activation of peroxydisulfate (PDS) via visible light has been extensively investigated. However, the intrinsic relationship between the activation of PDS and the characteristics of pollutants has been largely ignored. This study reports that PDS activation by visible light without any artificial catalyst for the removal of fluoroquinolones (FQs), which reduced the adverse on ecological environment and human health concerns. Importantly, the mechanism of PDS activation by the excited triplet state of FQs (3FQs*) was proposed. Experimental results demonstrated PDS could generate more ∙ OH with the existence of 3FQs*. Meanwhile, the electron transfer pathways from FQs or 3FQs* to PDS were studied. Both radical and non-radical oxidation reactions lead to the degradation of FQs in the Vis/PDS system. The degradation pathways and reactive sites were clarified by QTOF analysis and DFT calculations. Additionally, the degradation experiments of various contaminants demonstrated that the system showed excellent selective oxidation for FQs. [Display omitted] • Transient absorption spectra and DFT calculations confirmed the existence of 3FQs*. • A novel photoexcitation mechanism was investigated via fluorescence and phosphorescence spectra. • Unlike artificial photo-catalysts, this study provided other methods to activate PDS, such as visible light and excited state species. [ABSTRACT FROM AUTHOR]

Energies are reported for the first four singlet and triplet spherically symmetric states of 2e systems confined in an impenetrable sphere. All calculations used explicitly correlated Hylleraas basis sets. These calculations identify a series of level crossings and avoided crossings for Coulombic systems with a positive charge at the center of the sphere. Similar crossings do not occur for the 2e quantum dot. Configuration interaction calculations conducted in parallel provide a description of the system within the more traditional atomic orbital picture. The general shape of the energy versus confinement graphs and the locations of level crossings are shown to be consequences of scaling properties of the interparticle potentials. [ABSTRACT FROM AUTHOR]

An optical thermometry was performed utilizing the intensity ratio between the fluorescence and the phosphorescence of lutecium hematoporphyrin (Lu-HMME). In spite of the large energy level difference between the singlet first excited state (S 1) and the triple first excited state (T 1), the emission intensities of the two channels were on the same order of magnitude, and the resulted luminescence intensity ratio was confirmed to follow the Boltzmann distribution law. The huge difference in population was made up by the intrinsic properties of Lu-HMME that the transition probability of the S 1 state is several orders of magnitude higher than that of T 1. Based on this, Lu-HMME is a candidate for optical high-temperature sensors with high relative sensitivity and good temperature resolution. [Display omitted] • Lu-HMME thermometry was based on the intensity ratio between fluorescence and phosphorescence. • The singlet first excited state and triple first excited state was regarded as the TCLs. • A high relative sensitivity was shown with 2.49% K−1 at 288 K. • An excellent photostability was performed and the temperature resolution could reach 0.07 K at 308 K. [ABSTRACT FROM AUTHOR]

White light: [{Au(L)}3] (L=3‐(2‐thienyl)pyrazolate) gives dual emission, one from an organic chromophore the other from aurophilic stacking interactions. The resulting blue–green and orange–red emissions can be tuned to approach white‐light by modulating the aggregation behavior of the cluster. [ABSTRACT FROM AUTHOR]

[Display omitted] • AIE-active enantiomers show dual-mode afterglows and obvious mechanoluminescence. • Afterglow colour can be linearly tuned from yellow to sky blue by temperature. • Relatively stable warm-white afterglow is observed at around room temperature. • Effects of molecular arrangement on luminescence behaviors are demonstrated. Dual-mode persistent luminescence and helical-array-induced mechanoluminescence (ML) are observed for the first time from two different polymorphs (SC p and SC b) of a pair of AIE-active enantiomers, respectively. The impressive afterglows from the SC p crystals of (R)-ImNCz and (S)-ImNCz are composed of persistent thermally activated delayed fluorescence and ultralong organic phosphorescence, and their colours can be tuned from yellow to sky blue by temperature in a mild window from 0 °C to 100 °C. In particular, the SC p crystals of (S)-ImNCz present relatively stable warm-white afterglows at around room temperature. The generation of dual-mode persistent luminescence from SC p crystals is probably associated with the charge separation and recombination as well as the small Δ E ST values of enantiomer molecules and the strong intermolecular interactions in crystal structures. On the other hand, the conspicuous ML of (R)-ImNCz and (S)-ImNCz from SC b crystals likely results from their helical arrays and notable AIE properties, enabling the formation of crystals with polar space groups and high fluorescence quantum yields. The results from this polymorphic system may provide useful guidance for the development of new organic emitters with innovative applications. [ABSTRACT FROM AUTHOR]

Hydrogen-bonded organic frameworks (HOFs) are the focus of intense scientific research due their potential applications in science and technology. Here, we report on the synthesis, characterization, and photobehavior of a new HOF (T12F-1(124TCB)) based on a dehydrobenzoannulene derivative containing fluorine atoms (T12F-COOH). This HOF exhibits a 2D porous sheet, which is hexagonally networked via H-bonds between the carboxylic groups, and has an interlayers distance (4.3 Å) that is longer than that of a typical π–π interaction. The presence of the fluorine atoms in the DBA molecular units largely increases the emission quantum yield in DMF (0.33, T12F-COOH) when compared to the parent compound (0.02, T12-COOH). The time-resolved dynamics of T12F-COOH in DMF is governed by the emission from a locally excited state (S1, ~0.4 ns), a charge-transfer state (S1(CT), ~2 ns), and a room temperature emissive triplet state (T1, ~20 ns), in addition to a non-emissive triplet structure with a charge-transfer character (T1(CT), τ = 0.75 µs). We also report on the results using T12F-ester. Interestingly, FLIM experiments on single crystals unravel that the emission lifetimes of the crystalline HOF are almost twice those of the amorphous ones or the solid T12F-ester sample. This shows the relevance of the H-bonds in the photodynamics of the HOF and provides a strong basis for further development and study of HOFs based on DBAs for potential applications in photonics. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study to understand the structure and electronic and optical properties of CaMoO4: x Tb3+ (x = 1 mol%, 2 mol%, and 4 mol%) microspheres. The microspheres were prepared by ultrasonic spray pyrolysis and characterized by X-ray diffraction (XRD), field-emission gun scanning electron microscopy (FEG-SEM), micro Raman spectroscopy, and photoluminescence (PL) spectroscopy. First-principles quantum mechanical calculations were performed at the density functional theory level to obtain the geometry and electronic properties of CaMoO 4 : x Tb3+ microspheres in the ground electronic state and excited electronic states (singlet and triplet). These results, combined with XRD patterns, indicate that these crystals have a scheelite-type tetragonal structure. The morphology of the CaMoO 4 : x Tb3+(x = 1 mol%, 2 mol%, and 4 mol%) samples was investigated by FEG-SEM, and a spherical shape was found. The optical properties were investigated by UV–vis spectroscopy and PL spectroscopy, and the chromaticity coordinates of these compounds were obtained. The relationships between the PL properties and the Raman spectra indicate that Tb3+-doped CaMoO4 microspheres constitute promising photoluminescent materials for use in new lighting devices. This also allowed us to understand the charge transfer process that happens in the singlet (s) ground state and the singlet (s*) and triplet (t*) excited states, which generates the photoluminescent emissions of the Tb3+-doped CaMoO 4 microspheres. Image 1 • CaMoO 4 : x Tb3+ (x = 1 mol%, 2 mol%, and 4 mol%) microspheres were prepared by the ultrasonic spray pyrolysis method. • Field emission gun scanning electron microscopy images indicated the formation of microspheres. • Photoluminescence of the CaMoO 4 : x Tb3+ samples reveals the Tb3+ 5D 4.→ 7F J transitions. • The PL spectra are explained on the basis of the localization and characterization of the ground and excited states. [ABSTRACT FROM AUTHOR]

Two silver nitrate complexes with bisphosphines were obtained and characterized: [Ag(dcypm)]2(NO3)2 (1; dcypm = bis(dicyclohexylphosphino)methane) and [Ag(dppm)]2(Me2PzH)n(NO3)2 (n = 1, 2a; n = 2, 2b; dppm = bis(diphenylphosphino)methane, Me2PzH = 3,5-dimethylpyrazole). The steric repulsions of bulky cyclohexyl substituents prevent additional ligand coordination to the silver atoms in 1. Compounds obtained feature the bimetallic eight-member cyclic core [AgPCP]2. The intramolecular argenthophilic interaction (d(Ag···Ag) = 2.981 Å) was observed in complex 1. In contrast, the coordination of pyrazole led to the elongation of Ag···Ag distance to 3.218(1) Å in 2a and 3.520 Å in 2b. Complexes 1 and 2a possess phosphorescence both in the solution and solid state. Time-dependent density-functional theory (TD-DFT) calculations demonstrate the origin of their different emission profile. In the case of 1, upon excitation, the electron leaves the Ag–P bonding orbital and locates on the intramolecular Ag···Ag bond (metal-centered character). Complex 2a at room temperature exhibits a phosphorescence originating from the 3(M + LP+N)LPhCT state. At 77 K, the photoluminescence spectrum of complex 2a shows two bands of two different characters: 3(M + LP+N)LPhCT and 3LCPh transitions. The contribution of Ag atoms to the excited state in both complexes 2a and 2b decreased relative to 1 in agreement with the structural changes caused by pyrazole coordination. [ABSTRACT FROM AUTHOR]

• Two heteloleptic-type cyclometalated iridium(III) complexes coordinated with electron-withdrawing 5,5′-bis(trifluoromethyl)-2,2′-bipyridine (dCF3bpy) ligand [Ir(C^N)2(dCF3bpy)]PF6 {H- C^N = 2-phenylpyridine (Hppy) for [1]PF 6 and 2-(2,4-difluorophenyl)pyridine (HF2ppy) for [2]PF 6 } were developed and successfully characterized. • The combination of experimental and theoretical techniques applied in this study clarified the influence of the CF3 groups at bpy ligands in cyclometalated iridium complexes to their photophysical, electrochemical, and photosensitizing properties. • Complexes [1]PF 6 and [2]PF 6 work as the robust photosensitizers for the photochemical H2 evolution in the presence of K2PtCl4 and TEA under visible light irradiation. Two luminescent cyclometalated iridium(III) complexes coordinated with electron-withdrawing 5,5′-bis(trifluoromethyl)-2,2′-bipyridine (dCF 3 bpy) ligand [Ir(C^N) 2 (dCF 3 bpy)]PF 6 {H- C^N = 2-phenylpyridine (Hppy) for [1]PF 6 and 2-(2,4-difluorophenyl)pyridine (HF 2 ppy) for [2]PF 6 }, which work as the robust photosensitizers, were synthesized and characterized by experimental and theoretical analyses. Obtained [1]PF 6 and [2]PF 6 showed yellow light emissions (559 and 578 nm, respectively) with relatively long lifetimes (728 and 739 nsec, respectively) at room temperature in CH 2 Cl 2. Density functional theory (DFT) calculations clarified that these emissions were assigned as the phosphorescence derived from the mixed metal-ligand-to-ligand charge transfer (MLLCT) excited states. Potential photoredox abilities of [1]PF 6 and [2]PF 6 as the photosensitizers were also closely investigated by cyclic voltammetries (CVs), Stern-Volmer plots, and photochemical hydrogen evolution reactions. The results of these experiments indicated that [1]PF 6 and [2]PF 6 have substantial photosensitizing abilities; (i) reductive quenching of excited states of [1]PF 6 and [2]PF 6 by triethylamine (TEA) were observed in 10% aqueous THF, (ii) the systems involving of [1]PF 6 (or [2]PF 6), K 2 PtCl 4 , and TEA, which were served as the photosensitizer, H 2 evolution catalyst, and sacrificial donor, respectively, showed highly efficient H 2 evolution activities, and (iii) [1]PF 6 and [2]PF 6 have good durabilities in the photochemical H 2 evolution reactions for a long time. The turnover numbers (TONs) of H 2 evolution based on [1]PF 6 and [2]PF 6 at 96 h of irradiation were reached at 758 and 832 TONs, respectively, which were higher than that based on a well-known photosensitizer [Ir(ppy) 2 (bpy)]PF 6 (659 TON). [ABSTRACT FROM AUTHOR]

Delayed fluorescence (DF) is a long-lived luminescence process used in a variety of applications ranging from oxygen sensing in biological tissues to organic Light Emitting Diodes. In common cases, DF results from the de-excitation of the first excited triplet state via the first excited singlet state of the chromophore, which produces a mono-exponential light signal whose amplitude and lifetime give an insight into the probed environment. However, non-linear de-excitation reactions such as triplet-triplet annihilation, which can cause decays to lose their mono-exponential nature, are often neglected. In this work, we derive a global framework to properly interpret decays resulting from a combination of linear and non-linear de-excitation processes. We show why the standard method of using multi-exponential models when decays are not mono-exponential is not always relevant, nor accurate. First, we explain why the triplet de-excitation and light production processes should be analyzed individually: we introduce novel concepts to precisely describe these two processes, namely the deactivation pathway – the reaction which mainly contributes to the triplet state de-excitation – and the measurement pathway – the reaction which is responsible for light production. We derive explicit fitting functions which allow the experimenter to estimate the reaction rates and excited state concentrations in the system. To validate our formalism, we analyze the in vitro Transient Triplet Absorption and DF of Protoporphyrin IX, a well-known biological aromatic molecule used in photodynamic therapy, cancer photodetection and oxygen sensing, which produces DF through various mechanisms depending on concentration and excitation intensity. We also identify the precise assumptions necessary to conclude that triplet-triplet annihilation DF should follow a mono-exponential decay with a lifetime of half the triplet state lifetime. Finally, we describe why the commonly used definitions of triplet / DF lifetime are ill-defined in the case where second-order reactions contribute to the deactivation process, and why the fitting of precise mixed-orders DF kinetics should be preferred in this case. This work could allow the correct interpretation of various long-lived luminescence processes and facilitate their understanding. • Delayed fluorescence / phosphorescence decay kinetics are not always monoexponential. • Second-order de-excitation reactions alter their shape. • We derive explicit decay fit functions for any complex de-excitation scenario. • Precise analysis can give new quantitative insight into chromophore environment. • Photodynamic therapy, cancer detection and oxygen sensing could be improved. [ABSTRACT FROM AUTHOR]