Photophysics of metal-organic frameworks:A brief overview

Metal-organic frameworks(MOFs),which are self-assembled porous coordination materials,have garnered considerable attention in the fields of optoelectronics,photovoltaic,photochemistry,and photocatalysis due to their diverse structures and excellent tunability.However,the performance of MOF-based optoelectronic applications currently falls short of the industry benchmark.To enhance the performance of MOF materials,it is imperative to undertake comprehensive investigations aimed at gaining a deeper understanding of photophysics and sequentially optimizing properties related to photocarrier transport,recombination,interaction,and transfer.By utilizing femtosecond laser pulses to excite MOFs,time-resolved optical spectroscopy offers a means to observe and characterize these ultrafast microscopic processes.This approach adds the time coordinate as a novel dimension for comprehending the interaction between light and MOFs.Accordingly,this review provides a comprehensive overview of the recent advancements in the photophysics of MOFs and additionally outlines potential avenues for exploring the time domain in the investigation of MOFs.

Aromaticity Concerto in Polycyclic Conjugated Hydrocarbons:Fusion Pattern on Combined Aromaticity Strategy Leads to Distinctive Excited State Photophysics of Dinaphthopentalenes

Understanding the structure-property relationships in polycyclic conjugated hydrocarbons(PCHs)is crucial in controlling their electronic properties and developing new optically functional materials.Aromaticity is a fundamentally important and intriguing property of numerous organic chemical structures and has stimulated a myriad of experimental and theoretical investigations.Exploiting aromaticity rules for the rational design of optoelectronic materials with the desired photophysical characteristics is a challenging yet fascinating task.Herein we present an in-depth computational and spectroscopic study on the structure-property relationships of dinaphthopentalenes(DNPs).Results highlight that the different fusion patterns between 4nπand 4n+2πunits endow these PCHs with the tunable aromaticity in the ground state/excited state,which leads to the diverse electronic structures and consequently the distinctive excited state photophysics.Accordingly,we propose a combined aromaticity design strategy for rationally modulating and tailoring electronic and optical properties of PCH skeletons.These outcomes not only present a full picture of the excited state dynamics of the DNP system and afford a new class of efficient singlet fission-active materials but also provide some basic guidelines for exploiting aromaticity rules to design and develop new optical function materials.

Photophysics,photochemistry and photobiology of hypocrel-lin photosensitizers

Hypocrellins are novel photosensitizers from China, which are demonstrated to have significant anti-tumor and anti-virus activity and to be potential photo-dynamic therapy (PDT) agents. As compared with hemato-porphyrin, the only approved photosensitizer, hypocrellins have several advantages, such as easy preparation and easy purification, high triplet quantum yield, high singlet-oxygen quantum yield, high phototoxicity but low dark toxicity, and rapid clearance from normal issues. This article reviews briefly the photophysics, photochemistry and photobiology of hypocrellins on the basis of the domestic and international research results.

Influence from Thermal Elimination Temperature of Precursor Polymer and Film-forming Methods on the Photophysics of the Poly（2,5-didodecyloxy-p-phenylenevinylene）

A series of poly（p-phenylenevinylene）s （PPVs） with good solubility were synthesized from thermal elimination of precursor poly（2,5-didodecyloxy-p-phenylenevinylene） at different temperature via Wessling method. The polymer photophysics were influenced by the thermal elimination condition, which was consistent with NMR and IR characterizations. The additional absorption peak at longer wavelength and the red-shifted emission maximum both in solution and in film, for PPVs obtained at high elimination temperature, indicated the existence of longer conjugated blocks in these systems. The emission maximum for drop-cast film （436 nm） for PPV obtained under 200 ℃ （PPV200） was 16 nm blue shifted to the spin-coated films （452 nm） or 29 nm to the solution （465 nm）. The SEM study showed drop-cast film had the morphology of isolated conjugated particles in the matrix while blurry linear structure was found for spin-coated film, which was consistent with the photophysics. The discussion about this difference was carried out based on the consideration of the flexibility of the polymer chains and different conjugated length of PPV in different states.

PHOTOPHYSICS STUDIES OF ORCANIC COMPOUNDS (Ⅻ)——THE INVESTIGATION OF THE FLUORESCENCE SPECTRA OF N-SALICYLIDENE-p-(N,N-DIMETHYLAMINO)ANILINE

The fluorescence spectra of N--salicylidene-p-(N,N--dimethylamino)aniline have beeninvestigated in various solvents. Three kinds of fluorescence have been found in the solutionsof various concentrations. They are the excited intermediate (EI) which is formed when theproton transfer has occurred but essentially retains the geometry of the enol tautomer, theexciplex (EX) which consists of a ground monomer and an excited state intermediate and theexcited dimer (ED) which is caused by ground state aggregate. The fluorescence lifetimesof the fluorophores have been measured in tetrahydrofuran (THF). Luminescent mechanismhas been discussed based on the fluorescence spectra and the kinetic data of the compound.

Novel Photo-induced Coupling Reactions of 9-Fluorenylidenemalononitrile or 1,1-Diphenyl-2,2-dicyanoethylene with 10-Methyl-9,10-dihydroacridine. A Study on the Photophysics of the Reaction

9-Fluorenylidenemalononitrile (FDCN) or 1,1 diphenyl 2,2 dicyanoethylene (DPCN) reacted with 10 methyl 9,10 dihydroacridine (AcrH 2) under irradiation ( λ >320 nm) to give couping products. In order to gain further insight into the mechanism of the photo induced reaction, the photophysics of the reactions of FDCN or DPCN with AcrH 2 have been investigated by using UV vis spectroscopy, fluorescence spectroscopy, excitation spectroscopy and time resolved fluorescence spectroscopy, respectively. The results show that FDCN or DPCN interacts with AcrH 2 in the ground states to form a charge transfer complex, which further reacts to give the coupling product upon irradiation.

SILICON-CONTAINING POLY(p-ARYLENE VINYLENE)S:SYNTHESIS AND PHOTOPHYSICS

A series of new silicon-containing poly（p-arylene vinylene）s （PAVs） with anthracene units in the main chain were synthesized by hydrosilylation reaction. The introduction of organosilicon units improved the solubility of the polymers, and the π-π conjugation of polymeric chains was interrupted. These polymers behaved as blue-green light emitters with their fluorescence maximum at 447-499 nm and quantum yields in the range of 0.28-0.30 in solution.

Photophysics studies of organic compounds Ⅷ.Interaction between excited singlet state of pyrene and aromatic amines

The quenching processes of the excited singlet state of pyrene by triphenylamine,diphenyl- amine and N,N-dibenzylaniline in various solvents at room and lower temperature have been stu- died with both static state fluorescence spectroscopy and fluorescence lifetime techniques.On the basis of experimental data,a preliminary quenching mechanism has been discussed.The geome- trical configuration models of the exciplexes formed between the excited pyrene and aromatic ami- nes in nonpolar solvents were proposed.

Synthesis,Crystal Structure,Photophysical and Redox Properties of a Novel Ru(Ⅱ) Complex with Carbazole-grafted 2-(2-Pyridyl)benzimidazole

A novel Ru（Ⅱ） complex [（bpy）2Ru（PBC）]（PF6）2 （PBC = N-[4-（9-carbazole）butyl]-2-（2-pyridyl）benzimidazole） has been synthesized and verified by 1↑H NMR, elemental analysis and X-ray crystallography. The crystal （C48H40F12N8P2Ru, Mr = 1119.89） belongs to the triclinic system, space group P1, with a = 13.128（4）, b = 13.814（4）, c = 14.184（4） A, α = 84.112（6）, β = 88.473（6）, γ = 78.196（6）°, Z = 2, V = 2504.6（13）A^3, Dc = 1.485 g/cm^3, F（000） = 1132, R = 0.0750 and wR = 0.1896. The Ru atom adopts a distorted-octahedral coordination geometry with the bond distances and bond angles falling in normal ranges. The complex shows an intense metal-to-ligand charge transfer （1MLCT） （dπ（Ru） →π＊（L）） transition （ε ~1.2×10^4 dm^3mol^-1cm^-1） at 457 nm in the UV-Vis absorption spectrum and a strong red phosphorescence at 632 nm in the CH3CN solution at ambient temperature. An efficient intramolecular energy transfer process from the carbazole unit to the [（bpy）2Ru（PB）]^2＋ emissive center exists by selective optical-simulation. Its electrochemical behavior shows multiplicate redox processes based on the metal center, the grafting carbazole moiety and the 2-（2-pyridyl）benzimidazole unit.

Influence of Molecular Stacking Pattern on Excited State Dynamics of Copper Phthalocyanine Films

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 withγ∝t^(-1/2).Annihilation rate constants are determined to beγ0=(2.87±0.02)×10^(-20)cm^(3)·s^(-1/2)and(1.42±0.02)×10^(-20)cm^(3)·s^(-1/2)for upright and lyingdown 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.

Elsinochrome A photosensitizers:Alternative drugs for photodynamic therapy

Photodynamic therapy(PDT)has already been a multifunctional modality for various tumors and nontumorous diseases.However,the development of photosensitizers is relatively delayed,compared with the tremendous progress in laser technology.Elsinochrome A(EA),a per-ylenequinonoid pigment from China,has all the typical advantages of perylenequinones.More-over,singlet oxygen quantum yield of EA is superior to other kinds of photosensitizers and EA could be artifially biosynthesized at present,which make it an alternative candidate for PDT.In.this review,the photophysics,photochemistry,photobiology and chemical or biological syntheses of EA photosensitizers are brielty presented.Besides,the future prospects of EA photosensitizers are also proposed.

New insight into the ultra-long lifetime of excitons in organic-inorganic perovskite： Reverse intersystem crossing

Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing （RISC） from the triplet to the singlet state can enhance the quantum yield of pho- toluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △E_st between the singlet state and the triplet state of CH_3NH_3Pbl_3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.

Laser-Induced Recoverable Fluorescence Quenching of Perovskite Films at a Microscopic Grain Scale

Understanding the fundamental properties of metal-halide perovskite materials is driving the development of novel optoelectronic applications.Here,we report the observation of a recoverable laser-induced fluorescence quenching phenomenon in perovskite films with a microscopic grain-scale restriction,accompanied by spectral variations.This fluorescence quenching depends on the laser intensity and the dwell time under Auger recombination dominated conditions.These features indicate that the perovskite lattice deformation may take the main responsibility for the transient and show a new aspect to understand halide perovskite photostability.We further modulate this phenomenon by adjusting the charge carrier recombination and extraction,revealing that efficient carrier transfer can improve the bleaching resistance of perovskite grains.Our results provide future opportunities to attain high-performance devices by tuning the perovskite lattice disorder and harvesting the energetic carriers.

Eu(Ⅲ) Complex-doped PMMA with Fast Radiation Rate and High Emission Quantum Efficiency

Two Eu（Ⅲ） complexes,（tris-4,4,4-trifluoro-1-phenyl-1,3-butanedione）（1,10-phenanthroline）europium（Ⅲ） [Eu（tpb-H） 3（phen）] and（tris-4,4,4-trifluoro-1-phenyl-1,3-butanedione）（2,2＇-bipyridine）europium（Ⅲ）[Eu（tpb-H） 3（bipy）] were synthesized from bi-dental oxygen and nitrogen ligands.Luminescent polymers were fabricated by incorporating deuterated Eu（Ⅲ） complexes in poly（methylmethacrylate）（PMMA） matrixes.Luminescent PMMA containing Eu（tpb-D） 3（phen） exhibited relatively higher quantum yield[Φ,（48.7±4）%],faster radiation rate（k r,7.49×10 2 s-1）,sharper red emission[full width at half maximum（FWHM）,6.3 nm] and larger stimulated emission cross-section（SEC,1.29×10-20 cm 2）.The value of SEC is the same order as that of Nd-glass laser for practical use.Additionally,the thermal properties of Eu（tpb-H） 3（phen）,Eu（tpb-H） 3（bipy）,Eu（tpb-D） 3（phen）-PMMA,and Eu（tpb-H） 3（bipy）PMMA were studied,indicating that the Eu（Ⅲ） complexes and luminescent PMMA can be used for a long-term period in high temperature environment.Prepared luminescent polymers including Eu（tpb-D） 3（phen） have promising applications in novel organic Eu（Ⅲ） devices,such as the high-power laser materials and optical fibers.

PHOTOPHYSICAL STUDY OF SULFONATED POLYSTYRENE

The photophysical properties of a series of sulfonated micromolecule (paratoluenesulfonic acid, HPTS) and macromolecules (linear and crosslinked polystyrene) have been studied by steady-state fluorescence spectra. The results indicate that the ground sulfonated ring associations can form in both the micromolecules and the macromolecules. The fluorescence spectra of the sulfonated crosslinked copolymers appear a red-shift when the copolymers change from hydrogen-type to sodium-type, and some new emission bands appear in the long-wavelength region. These results are explained in terms of synergetic effect of hydrogen bond,π-πinteraction and crosslinking effect.

Synthesis and Photophysical Properties of Dy^(3+) and Gd^(3+) Polymeric Complexes with Functionalized Polybenzimidazole Containing β-Diketone Side Group

The polymeric ligand PBIa （functionalized polybenzimidazole containing β-diketone side group） was successfully synthesized via the reaction of polybenzimidazole （PBI） with 3-Br-acetylacetone in DM SO solvent using Nail as the deprotonation reagent. Its corresponding polymeric complexes of Dy^3＋ and Gd^3＋ were prepared and characterized by FT-IR, ^1H NMR, molar conductance measurements, and thermal analysis. The photoluminescence properties and the probable mechanism of the Dy and Gd complexes were studied. The measurement and analysis of the thermal properties showed that these were thermal stable.

Photophysical Properties of Rare Earth Complexes with 3,4-Furandicarboxylic Acid and 1,10-Phenanthroline

Synthesis, IR spectra, UV vis spectra and photophysical properties of Gd 3+ , Eu 3+ , Tb 3+ complexes with 3,4 furandicarboxylic acid and 1,10 phenanthroline are reported. Intramolecular energy transfer process for these complexes is discussed in detail. It is found that the intramolecular energy transfer efficiency depends on the relative positions between the resonance energy levels of the central rare earth ions and the lowest triplet state energies of ligands.

Conjugate Fluorescent Compound Based on Pyrene-imidazole: Design, Synthesis, Crystal Structure and Fluorescence Property

Pyrenes are an important group of polycyclic aromatic hydrocarbons(PAHs). In order to expand the diversity of conjugate compounds based on pyrene, two new isomeric compounds anti-PyDTPAI and syn-PyDTPAI containing pyrene, imidazole and triphenylamine are synthesized via a one-pot cyclization reaction and characterized. The anti-PyDTPAI is characterized by single-crystal X-ray diffraction which crystallizes in monoclinic, space group P2_1/n with a = 10.132(4), b = 14.997(7), c = 18.968(9) ?, β = 95.543(19)o, V = 2869(2) ?~3, Z = 2, F(000) = 1092, Dc = 1.196 Mg/m^3, Mr = 1033.28 and μ(Mo Kα) = 0.070 mm^(-1). The presence of intermolecular C–H···π interactions results in the stability of the compound. The crystal structure shows a centrosymmetric, coplanar configuration towards pyrene-imidazole segment and a slip-stacked packing mode across the longer molecular axis which is similar to the J-type aggregation. The investigation of UV-vis absorption and fluorescence in solution indicates a strong blue emission under the ultraviolet light excitation. The two isomers also display high thermal stability which is proved by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA). Additionally, the molecular structure and HOMO and LUMO levels are calculated by density functional theory(DFT) at the B3 LYP/6-31 G(d) level.

Synthesis and characterization of X-shaped oligo(para-phenylene) derivatives functionalized with fluorene ethynylene

A series of linear and X-shaped oligo（para-phenylene） derivatives functionalized with fluorene ethynylenes 1,3 and 4 were synthesized through sequent Sonogashira coupling and Suzuki-Miyaura reaction in high yield.The electron-donating group-OCH3 and electron-withdrawing counterparts-CF3 were introduced to tune the spectra properties of compounds 3 and 4.The detail investigation of their photophysical properties in solution and film indicated that the introduction of both -OCH3 and -CF3 makes maximum emission distinct red-shift in comparison with parent compound 1,but the latter more prominently.

Synthesis and photophysical properties of metal anthraquinone phthalocyanine

A novel anthraquinone phthalocyanine AI（Ⅲ） 4 and Co（Ⅱ） 5 were synthesized and characterized by elemental analysis, IR UV/ vis, ^1H NMlL HPLC and MS. The photophysical properties of the two metal complexes were studied and compared by fluorescence spectrum method.