Search

Solid mixture of PbS quantum dot and a directly attached emitter penetrating the ligand layer enables photon upconversion from near infrared.

Steric bulkiness – the metric of the robustness of the self-photosensitized, single metal-active-site catalysis, elucidated in CO2 photoreduction.

Efficiency of photon upconversion (UC) from near infrared (NIR) to visible emission by the triplet-triplet annihilation (TTA) mechanism in solid has been limited to be low in spite of its...

A novel mononuclear ruthenium (Ru) complex bearing a PNNP-type tetradentate ligand is introduced here as a self-photosensitized catalyst for the reduction of carbon dioxide (CO2). When the pre-activation of the Ru complex by reaction with a base was carried out, an induction period of catalyst almost disappeared and the catalyst turnover numbers (TONs) over a reaction time of 144 h reached 307 and 489 for carbon monoxide (CO) and for formic acid (HCO2H), respectively. The complex has a long lifespan as a dual photosensitizer and reduction catalyst, due to the sterically bulky and structurally robust (PNNP)Ru framework. Isotope-labeling experiments under 13CO2 atmosphere indicate that CO and HCO2H were both produced from CO2.

We describe a new type of nitrogen‐centered polycyclic scaffold comprising a unique combination of 5‐, 6‐, and 7‐membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1‐naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3‐fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X‐ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density‐functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.

Here, we present single crystalline capsules of a photoresponsive molecule produced by simple recrystallization from organic solutions without direct human processing. During the crystal growth process, a movie was taken of the capsule taking in the organic solution. The capsules responded rapidly (

Realization problems of impulse responses for linear time-invariant (LTI) systems are well-studied. In particular, the realizations with the least order of such systems are said to be minimal. Apart from these problems, parameter estimations of pre-defined LTI models with a specific parametrization of the system matrices are also important. In this paper, we propose a parameter estimation method for such LTI models by transforming a minimal realization obtained through black-box identifications. Our approach is based on the minimal realization theory, exhaustive modelling, and algebraic elimination. Contrary to the existing methods, the proposed method allows polynomial parametrizations of the system.

Diphenylhexatriene and its ring-substituted derivatives act as emitters and show blue-green to green upconverted emission under photoexcitation of 640 nm when mixed with a sensitiser molecule (a palladium complex) in solution in a nitrogen atmosphere.

International audience; We take advantage of the near-resonant enhancement of the third-order nonlinear response to engineer a two-photon polymerization photoinitiator with optimized efficiency in regard with literature benchmarks. We study in detail its linear and resonant third-order nonlinear optical properties, with a particular focus on photoinduced radical generation. Careful choice of peripheral substituents enable its direct solubilization into a mixture of commercial multifunctional acrylic monomers, resulting in homogeneous photoresist with good optical transparency upon simple mixing. When submitted to sub-nanosecond pulsed laser irradiation at 532 nm, the resulting photoresist displays a polymerization threshold up to eight times lower than that obtained with classically used two-photon initiators, giving rise to sub-100 nm linewidth at 250 nm interline separation, and resulting in highly defined threedimensional (3D) structures.

Two-photon-excited fluorescent probes are important for two-photon microscopy for biomedical studies. In contrast to the many examples of probes for cationic species, such as metal ions, there have been fewer reports on the control of two-photon optical properties by anions because in such systems it is difficult to control the associated π-electronic states. This Minireview summarizes anion-responsive molecules that exhibit changes in two-photon optical properties and describes their molecular design and anion-response mechanisms, which are driven by changes in covalent bonds and noncovalent interactions. Results from a recent study of two-photon systems, where geometries and optical properties are modulated by anion binding, are also discussed.

A highly efficient tetradentate PNNP-type Ir photocatalyst, Mes-IrPCY2, was developed for the reduction of carbon dioxide. The photocatalyst furnished formic acid (HCO2H) with 87% selectivity toget...

This perspective article provides a comprehensive but organized tutorial introduction of the kinetics related to photon upconversion (UC) by triplet-triplet annihilation (TTA) (TTA-UC). The field of TTA-UC is multi-disciplinary and rapidly growing with the involvement of researchers from diverse backgrounds. TTA-UC consists of a series of tangled photophysical processes, so a solid understanding of the kinetic features and consequences is important to develop and evaluate materials for TTA-UC. This tutorial starts with an introduction of the standard model of TTA-UC along with the assumptions used in the model. The essential concept of the spin statistics for TTA and how this concept is related to the singlet branching ratio, which directly affects the efficiency of UC, are then explained through step-by-step analyses. Using these foundations, solutions for the steady-state behaviors are derived, featuring the universal curve that describes the excitation intensity dependence of the UC quantum yield for any sample type. Various useful functions for analyzing experimental data are also introduced and summarized. The transient behaviors of TTA-UC are then discussed along with their equations, and the usefulness for analyzing transient experimental data is explained using examples. In this article, self-consistent derivations and relevant references are provided for an easy understanding of the advanced discussion and analyses.

One-directional alignment of Ag nanowires (AgNWs) embedded in silica matrix was achieved by means of the sol-gel fabrication process by stirring the precursor solution consisting of tetramethyl orthosilicate (TMOS) and AgNW during gelation. The parallel orientation of AgNWs along the stirring direction was confirmed in the sliced composite by optical microscopy. The optical function of the obtained composite as polarizer was demonstrated by transmission measurement with polarized light. The polarization response was found to be limited and can be explained with the buckling of AgNWs formed during the condensation reaction.

We fabricated polarized near-infrared (NIR) emitting devices using with the oriented films of a low-band-gap-polymer PTB7 (poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']tithiophene-2,6-diyl-alt...

Herein, triplet-triplet annihilation upconversion (TTA-UC) from near-infrared (NIR, 785 nm) to visible (yellow, centered at 570 nm) regions has been demonstrated in the binary solid of condensed chromophores. Microparticles of the binary solid comprising rubrene as a matrix (emitter) and π-extended Pd-porphyrin as a dopant (sensitizer) in a mole ratio of 1000:1 were obtained by solution casting. Excitation intensity dependence and quantum yield (QY) of the upconverted emission were characterized for individual particles under a microscope and revealed a low threshold intensity (∼100 mW/cm2) as compared to the solution and moderate UC-QY (∼0.5%) in the NIR range. The factors contributing to the UC-QY were investigated by time-resolved and steady-state spectroscopies. It was found that the intersystem crossing of the sensitizer, triplet energy transfer, and TTA occurred efficiently in the binary solid, and the fluorescence QY of the emitter governed the UC-QY.

Linear ladder-type π-conjugated molecules have attracted much interest because of their intriguing physicochemical properties. To modulate their electronic structures, an effective strategy is to incorporate main-group elements into ladder-type π-conjugated molecules. In line with this strategy, a variety of ladder-type π-conjugated molecules with main-group elements have been synthesized to explore their potential utility as organic functional materials. In this context, phosphole-based π-conjugated molecules are highly attractive, owing to their unique optical and electrochemical properties, which arise from the phosphorus atom. Herein, the synthesis and physicochemical properties of doubly thiophene-fused benzodiphospholes, as a new class of phosphole-based ladder-type π-conjugated molecule, are reported. Systematic investigations into the physicochemical properties of doubly thiophene-fused benzodiphospholes revealed their pluripotent features: intense near-infrared fluorescence, excellent two-photon absorption property, and remarkably high electron-transporting ability. This study demonstrates the potential utility of doubly thiophene-fused benzodiphospholes as organic functional materials for biological imaging, nonlinear optics, organic transistors, and organic photovoltaics.

In this work, we report the experimental and theoretical first molecular electronic hyperpolarizability (βHRS) of eleven π-conjugated oxazoles compounds in toluene medium. The Hyper-Rayleigh Scattering (HRS) technique allowed the determination of the experimental dynamic βHRS values, by exciting the compounds with a picosecond pulse trains from a Q-switched and mode-locked Nd:YAG laser tuned at 1064 nm. Theoretical predictions based on time-dependent density functional theory level using the Gaussian 09 program package were performed with three different functionals (B3LYP, CAM-B3LYP, and M06-2X), to calculate both static and dynamic theoretical βHRS values. Good accordance was found between the experimental and theoretical values, in particular for the CAM-B3LYP and M06-2X functionals.

Three new perylenetetracarboxy-3,4:9,10-diimides, bearing 2,6-diisopropylphenyl groups at the imide positions and 4-(R-ethynyl)phenoxy moieties (R = 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole (P2), pyrene (P3) or pyrene-CH2OCH2 (P4)) at the four bay positions, were prepared, along with the known related derivative (R = phenyl (P1)), and well characterized. They have large two-photon absorption (TPA) cross-sections (σ2), as determined by the Z-scan technique, the highest values being reached with P2 which bears a planar π-delocalized donor moiety. P3 is characterized by higher σ2 values than both P1, as expected for the higher π-conjugation of the donor pyrene moiety with respect to phenyl, and P4, due to the presence of the flexible and non-conjugated CH2OCH2 bridge between the pyrene and the ethynyl fragment in the latter compound. The molecular geometry of P1–P4 has been optimized by DFT modeling, showing that in P2 and P3 the bay substituents are stacked due to the π–π interactions of both pyrene and thiophene groups. The LUMO of P1–P4 lies at the same energy and is essentially delocalized on the perylene core whereas the HOMO and HOMO−1 of both P2 and P3 are degenerate and do not show contribution from the perylene core contrarily to that of P1 and P4. The HOMO–LUMO gap is therefore essentially influenced by the HOMO which reflects the electronic charge delocalization on the bay substituents, the lower gaps being observed for P2 and P3, which are characterized by the best TPA properties.

The fluorescence and other photophysical parameters of highly polarized, quadrupolar bis-coumarins possessing an electron-rich pyrrolo[3,2-b]pyrrole bridging unit are highly dependent on the linking position between both chromophores. Delocalization of the LUMO on the entire pi-system results in intense emission and strong two-photon absorption.

Synthesis of novel photoinitiators, spectroscopic (UV vis, fluorescence, steady state and time resolved), electrochemical and EPR studies of their photoinduced radical generation mechanisms, Z-scan measurements of their two-photon absorption cross section, two-photon polymerization at 532 nm, with a pulsed ns laser, material evaluation by scanning electron microscopy

We report the triplet–triplet annihilation (TTA) upconversion (UC) through triplet energy transfer (TET) from a sensitiser fixed on a solid surface to free emitters dissolved in solution. A carboxylic-acid derivative of Pt–porphyrin was used as the sensitiser fixed on an amino-treated surface of continuous nanoporous glass without aggregation. UC emission was observed under photoexcitation of 532 nm for porphyrin-fixed glass immersed in an emitter solution of 9,10-diphenylanthracene (DPA), showing that TET occurs through the solid–liquid interface. The dynamics of TET was analysed through both phosphorescence decay of the sensitiser and UC emission rise from the emitter. Two TET components with different rate constants were found, slower than diffusion-controlled reactions in solution by 1–2 orders of magnitude. Nevertheless, the solid surface TET rates were fast enough to obtain a high quantum yield over the solid–liquid interface. By melting DPA and soaking it into sensitiser-fixed porous glass, we fabricated an all-solid system enabling TTA-UC through the bulk interface.

A highly efficient tetradentate PNNP-type Ir photocatalyst, Mes-IrPCY2, was developed for the reduction of carbon dioxide. The photocatalyst furnished formic acid (HCO

The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications field. Organic compounds have emerged as promising candidates for raw materials to develop nonlinear optical devices, such as optical converters, due to their intrinsic ultra-fast electronic responses. Also, the easy tailoring of organic molecular structures makes organic materials much more appealing than the inorganic ones. In this work, we have performed a linear and nonlinear optical characterization of a set of dibenzylideneacetone derivatives. The nonlinear optical responses investigated correspond to second- and third-order nonlinear processes, namely, first electronic molecular hyperpolarizability and two-photon absorption cross-section, respectively. The value of the first electronic molecular hyperpolarizability, up to 52 cm4&middot, statvolt&minus, 1, could be considered a robust value when compared to the short-sized &pi, electron backbone length of the studied compounds. Such results suggest that these compounds exhibit the potential to be used as optical frequency converters. Quantum chemical calculations were used to predict the theoretical value of the first molecular hyperpolarizability, as well as to simulate the one- and two-photon absorption spectra for all compounds.

Utilization of high density of triplets is important to overcome the dissipation of excitation energy. Triplet–triplet annihilation (TTA) has attracted attention to overcome the conventional limitation for the application of photon upconversion (UC). Synergetic approaches of experimental and computational studies on TTA have been made for efficient TTA-UC in the solid state. Binary solid fabricated by the rapid-drying casting from mixed solution enabled efficient triplet sensitization. Structural modification of emitter molecules has enhanced the performance of TTA-UC in solid. Computational studies clarified the importance of the dimensionality of the exciton diffusion process and orbital overlap in the TTA process. Various extended studies such as solid TTA-UC by near-infrared (NIR) excitation and sensitizer-fixed approach on a solid surface are also presented.

Fluorescent organic molecules have received great attention due to their largest applications, for example, in DNA and RNA spectroscopies studies, development of new photoluminescence bioprobes, an...

Two-photon absorption (TPA) dyes with intense fluorescence can be used to detect small chemical species and as sensors and bioimaging probes for specific analytes. Various TPA dyes responding to a number of external stimuli have been reported. Among them, biologically important anionic species have not been used as agents to control TPA properties because their direct electronic influences on the transition dipole moments of dyes are typically small. In this study, dipyrrolyldiketone BF2 complexes substituted with π-extended units exhibited efficient TPA properties that could be regulated by conformation changes induced by anion binding. The TPA intensity decreased to 1/5 of the original intensity upon anion binding, which was much larger than that observed for one-photon absorption. Anion detection was achieved by a change in the emission intensity of spatially resolved spots of two-photon-excited fluorescence (TPEF) in the sample. Experimental and theoretical studies were performed to understand the mechanism of the TPA property control and showed that the drastic changes in the transition dipole moments upon conformation changes between the straight and bending forms of the π-electronic systems caused the TPA and TPEF intensities drop.

It has been hypothesized that alkyl chains are inactive for electron transport processes through the chains. However, our theoretical study unveiled that loop-like alkyl chains can accelerate the e...

Although the oxidative coupling of disilenides, i.e., the disilicon analogues of vinyl anions, represents a promising route to extend the conjugation between Si═Si double bonds, previously reported synthetic routes to disilenides involve strongly reducing conditions. Herein, we report a novel synthetic route to disilenides from stable disilenes via the selective cleavage of Si(sp2)–Si(sp3) bonds under milder reaction conditions. Using this method, a 1,4-bis(trimethylsilyl)tetrasila-1,3-diene (5) was synthesized from the corresponding silyl-substituted disilene. Moreover, Et3Si-substituted tetrasila-1,3-diene 7 was synthesized via tetrasila-1,3-dien-1-ide 6, which is the first example of a functionalized tetrasila-1,3-diene.

A synthetic entry to novel dyes based on the dipyrrolonaphthyridinedione core was developed via the Heck reaction. These weakly fluorescent compounds bearing double bond linkages between the core and the peripheral units absorbed strongly in the far-red/NIR region and possessed large values of two-photon absorption (TPA) cross-sections (up to 5180 GM). Additionally, analogous dyes bearing triple bond linkages were also efficient TPA materials with relatively large two-photon absorption cross-sections (up to 2840 GM) as well as two-photon brightness (up to 1450 GM). The centrosymmetric nature of both of these families of dyes is responsible for the location of the maxima of two-photon absorption being at much higher energy than the ones corresponding to the double wavelength of the lowest-energy one-photon absorption. Theoretical calculations clarified that the enhancement of the TPA by the peripheral substitutions arose through different mechanisms depending on either the electron-donating or electron-withdrawing ability of a given substituent to the ambipolar core. The change in the electron distribution of HOMO and HOMO-1 by the push-pull effect was found to govern the strength of the lowest-energy TPA-allowed transition. Importantly, compounds from both series possessed a beneficial ratio of σ

Off-resonant excitation of the closed-ring isomer of a photochromic diarylethene derivative at 730 nm induced the efficient cycloreversion reaction with a yield of ∼20%, while the reaction yield was only 2% under one-photon excitation at 365 nm. Excitation wavelength dependence of the one-photon cycloreversion reaction yield under steady-state irradiation in a wide wavelength range showed that the specific electronic state leading to the large cycloreversion reaction yield, which is originally forbidden in the optical transition but partially allowed owing to the low symmetry of the molecule, is spectrally overlapped with the electronic state accessible by the allowed one-photon optical transition in the UV region. Femtosecond transient absorption spectroscopy also revealed that the off-resonant two-photon excitation preferentially pumped the molecule into the specific state, leading to the 10-fold enhancement of the cycloreversion reaction.

Peropyrene is a promising candidate molecule for use in organic solar cells based on singlet fission, because it fulfills the energy matching requirement for singlet fission. We prepare three 2,9-disubstitued peropyrene derivatives and investigate their crystal structures, photophysical properties, and singlet fission phenomenon. Although each derivative shows different molecular overlap motifs in solid state, no singlet fission occurs under normal exciton density conditions due to the substantial stabilization of the first excited singlet (S1) state. In contrast, under high exciton density conditions, singlet fission from highly excited singlet (Sn) states, which is generated by singlet–singlet exciton annihilation, takes place to produce a triplet exciton. We also investigate the reverse process of singlet fission, that is, triplet–triplet annihilation, of peropyrene in solution state to explore the possibility of photon upconversion.

Binary crystalline solids consisting of a sensitizer (Pt-octaethylporphyrin) and an emitter (9,10-diphenylanthracene (DPA) or its alkyl-strapped derivative (C7-sDPA)) were fabricated by solution casting under rapid drying conditions and found to show efficient triplet–triplet annihilation upconversion by the suppression of component segregation. Microspectroscopic studies of individual crystalline particles of the binary solids revealed threshold intensities as low as 5 mW cm−2, close to solar levels, and UC quantum yields of 20% were possible when using C7-sDPA as an emitter, even in air.

In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C&equiv, CPh)(C&equiv, C)(dppe)2 (dppe = Ph2PCH2CH2PPh2) as electron donor (D) and 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole as electron acceptor (A) units in two different arrangement, i.e., A&ndash, D&ndash, A and D&ndash, A&ndash, D, are presented. They were measured in solution by the femtosecond open-aperture Z-scan method. The complexes show moderate two-photon absorption cross-sections &sigma, (2) of several hundred to one thousand GM (here 1 GM = 10&minus, 50 cm4 s molecule&minus, 1 photon&minus, 1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D&ndash, D arrangement are six times higher than that of the A&ndash, A one. This difference can be explained by the number of metal cores (one or two ruthenium centers), the geometrical configurations of the complexes (more or less planar), and the resonance enhancement by lowering the intermediate state.

International audience; We demonstrate an efficient ENZ response in the visible spectral range using organic molecular ultrathin films possessing a Lorentz-type dispersion. For this purpose, two polymethine dyes: sodium [5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulphobutyl)- benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulphobutyl)-benzimidazolium hydroxide] (TDBC), and [2,4-bis[8-hydroxy-1,1,7,7-tetramethyljulolidin-9-yl]squaraine] (HTJSq) were used in spin-coated polymer films at different doping concentrations. By varying the doping concentration in thin films, the real part of highly dispersive permittivity ε1 can be manipulated and tuned such that the spectral width of ENZ region -1 < ε1