一种新型的可见光诱导电子转移生酸体系的研究

对 4种分子内共轭的电荷转移化合物和取代的双 (三氯甲基 ) 2 ,4,6 三嗪分子间的光诱导电子转移和光生酸反应进行了详细研究 .通过荧光猝灭和体系荧光随时间的变化可看到作为电子受体的三嗪分子和作为电子给体电荷转移化合物间的光诱导电荷转移作用 .在对体系酸度的测定中 ,可清楚地看到体系经光照后所发生的变化 .对所研究生酸体系引发酚醛树脂 六甲氧基甲基三聚氰胺交联反应的能力进行了初步研究 .对可能发生的反应机制进行了讨论     

具有荧光发射能力有机化合物的光物理和光化学问题研究

有机化合物的结构、构象和环境效应对发光化合物的荧光发射具有重要的影响.本文从化合物激发态的衰变过程出发,侧重于过程的光化学与光物理问题对发光行为和机制进行讨论.如:化合物分子结构的受阻和桥键化对发光的影响;光激发下的光诱导电子和电荷转移及其相互转化;化合物扭曲的分子内电荷转移(TICT);溶剂分子和发光化合物分子间不同的相互作用及对发光的影响;在发光过程中存在着最佳的发光构象等.对于这些问题的研究和掌握,将有利于设计和合成具有高荧光量子产率的发光化合物,更好地解释在研究中出现的种种现象和在实际工作中应用它们.文章还引用了大量发光化合物作为实例,对工作中所得的结果进行了详细讨论.     

“马鞍型”环八四噻吩-三嗪体系的合成与聚集诱导发光(AIE)性质研究

以"马鞍型"环八四噻吩(COTh)与1,3,5-三嗪为构筑模块,通过Kumada类型反应有效地制备了三种分别含有1~3个COTh结构单元的环八四噻吩-三嗪衍生物,即2,4-二甲氧基-6-(5,8,11-三甲基硅基)-环八[1,2-b:4,3-b':5,6-b':8,7-b'']四噻吩-1,3,5-三嗪(1),2-甲氧基-4,6-二{(5,8,11-三甲基硅基)-环八[1,2-b:4,3-b':5,6-b':8,7-b'']四噻吩}-1,3,5-三嗪(2)和2,4,6-三{(5,8,11-三甲基硅基)-环八[1,2-b:4,3-b':5,6-b':8,7-b'']四噻吩}-1,3,5-三嗪(3).理论计算表明了该类化合物的长波长的两个吸收峰来自于分子内的电荷转移(CT)吸收.在溶液相它们发射分子内电荷转移(ICT)态荧光,峰位在560~570nm.而在冻结态下呈双荧光发射,即短波长的环八四噻吩本征态发光(400 nm)与长波长的ICT发光(480~500 nm).在四氢呋喃(THF)-H2O二元溶剂体系中,该类化合物产生聚集诱导发光(AIE)现象,可能与化合物分子同时受分子内旋转受阻(RIR)与分子内振动受阻(RIV)机制控制有关.单晶数据表明,化合物1分子内噻吩环与三嗪环之间呈现近平面构象.相邻分子之间噻吩环上的碳原子与三嗪环上的碳原子存在C-C相互作用,制约着连接分子内噻吩环与三嗪环之间单键的自由旋转,从而一定程度上制约了非辐射失活过程,有利于AIE现象的产生.     

以吖啶染料荧光猝灭为基础的卤素阴离子检测研究

合成了两种吖啶及吖啶橙盐类小分子化合物和带有吖啶盐的三元共聚物.研究了它们在溶液中的荧光被卤素离子猝灭的问题.发现它们能强烈地被碘离子所猝灭而不易被氯离子猝灭,表明这类化合物有可能用于在有氯离子存在条件下对碘、溴离子的检测.对荧光猝灭机理进行的研究发现,卤素离子的猝灭能力并不和它们对发光化合物的系间窜越和三重态的生成等有关,而是和阴离子对极化分子的作用减弱了分子内的电荷转移能力相关.     

2,4,6-三萘基-1,3,5-三嗪的合成与光谱行为

本文通过Suzuki偶联反应高效合成了两种三萘基三嗪化合物,即2,4,6-三(1-萘基)-1,3,5-三嗪(T1NT)和2,4,6-三(2-萘基)-1,3,5-三嗪(T2NT). 考察了介质的极性、温度以及THF-H₂O二元溶剂体系中的溶解性等因素对它们吸收和发射光谱行为的影响.研究发现, 由于T1NT比T2NT具有更好的分子平面性,其激发态下分子内电荷转移的程度较大,导致其在溶液中吸收光谱、发射光谱比T2NT呈现显著红移.冻结态下,分子平面性较差的T2NT显示出较短波长的发光.     

1,3,5-三芳基-2-吡唑啉化合物光物理行为的研究

近年来，在分子内电荷转移化合物发光行为的研究中，对分子激发态非辐射衰变通道问题的研究有了较大的进展［‘－’］．在分子结构和所处环境两因素对激发分子非辐射衰变过程影响的研究中，在结构方面已经认识到如化合物分子内双键的特性、杂原子的存在以及分子的几何构象等都可能对化合物的发光行为带来很大影响［’－’1．特别是分子立体几何构象问题，自F6rster－Hoffmarm提出他们的模型以来同，最近迅速发展起来的所谓“扭曲的分子内电荷转移（TICT）”概念同，使分子构象问题在荧光、激光染料的光物理研究中占有十分重要的位置．按…     

3,6-二(蒽醌-2-乙烯基)-N-乙基咔唑的合成及光谱性质研究

利用N-乙基咔唑和2-甲基蒽醌合成了一种A-π-D-π-A分子内电荷转移型化合物3,6-二(蒽醌-2-乙烯基)-N-乙基咔唑,并对该化合物的光化学和光物理行为进行了研究。荧光光谱表明,该化合物的发光行为对溶剂的极性非常敏感,随着溶剂极性的增大,其荧光最大发射峰有明显红移,并在强极性溶剂乙腈中出现了双荧光现象。该化合物的激发态和基态的偶极矩差值△μ为3.014D,发生了从给体(咔唑基)的N原子到分子两端受体(蒽醌)的羰基的分子内电荷转移。     

痂囊腔菌素A与咔唑化合物间的光致电子转移

研究了咔唑、咔唑-9-乙酸、3-溴-咔唑-9-乙酸在缺氧条件下对天然苝醌化合物痂囊腔菌素A(简记为EA)的荧光猝灭行为;由竹红菌甲素(HA)和乙素(HB)的荧光寿命估算了EA在乙腈中的荧光寿命,并进而计算了三个咔唑化合物的双分子猝灭速度常数.结果表明,三个咔唑化合物在EA的可见光吸收区无光吸收,据此推测其对EA的荧光猝灭作用归因于咔唑化合物作为电子给体而EA作为电子受体的光致电子转移作用.三个咔唑化合物的Stern-Volmer猝灭常数分别为698、704和1 063L·mol-1;乙酸基对咔唑环的光致电子转移速率几乎没有影响,而溴原子取代能够增加咔唑化合物对EA的荧光猝灭程度和光致电子转移速率.此外,EA在乙腈中的荧光寿命为1.98ns,而三个咔唑化合物的双分子猝灭速率常数分别为3.52×1011,3.56×1011和5.37×1011 L·mol-1·s-1.     

分子内电荷转移化合物的光谱和光物理

近年来,分子内电荷转移化合物光物理行为的研究受到了广泛的注意,这是由于这类化合物分子的发光性能强烈地受其周围溶剂性质的影响.它们常被考虑作为研究溶剂-溶质间相互作用以及溶剂分子弛豫的有效探针化合物.Loutfy等曾对被束缚的及未被束缚的N,N-二甲基氨基苄叉二腈类化合物的光物理行为作过详细研究.指出它们的荧光量子产率和该类化合物分子的刚性以及和母体环境的粘度、温度及物理化学性质等密切有关,它们     

不同位置取代的三氰基乙烯基蒽的光谱行为的研究

本文设计合成了两个典型的共轭的电子给体与电子受体(D-A)化合物:2-三氰基乙烯基蒽(2-TCVA)与9-三氰基乙烯基蒽(9-TCVA),通过极性效应,温度效应对它们基态与激发态的光谱行为进行了表征。研究表明:这两个化合物均表现出显著的电荷转移(CT)吸收峰,分子受光激发后,9-TCVA只能在非极性溶剂中产生分子内电荷转移(ICT)态荧光,而2-TCVA在极性与非极性溶剂中都能从ICT态发光。另外,温度效应显示冻结态下,2-TCVA只发射ICT态荧光,而9-TCVA既发射类蒽(anthracene-like)荧光又发射ICT态荧光,造成这一现象的主要原因可能是2-TCVA与9-TCVA分子平面性上的差异而引起分子内电荷转移相互作用不同所致。文中还利用了Bilot-Kawski公式估算了化合物2-TCVA在激发态与基态时偶极矩的差值为18.8D。     

一种新型红光敏感光交联体系

研究了Oxonol在不同溶剂中的吸收和荧光光谱,观察到反常的溶致变色行为.研究了由Oxonol和双 (三氯甲基)三腈化合物所组成体系在不同环境中的光诱导电子转移生酸反应和其褪色效应,发现这一体系可在红光照射下灵敏地引发某些预聚物而发生光交联反应.对Oxonol在胶束体系中的荧光发射进行了研究,比较了它们的荧光量子产率,并对出现这种现象的原因进行了初步讨论.     

Quantum chemical study on excited states and charge transfer of oxazolo[4,5-b]-pyridine derivatives

The excitedstate intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The sub-stituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.     

Photoinduced intramolecular charge transfer and S2 fluorescence in thiophene-pi-conjugated donor-acceptor systems: experimental and TDDFT studies

Experimental and theoretical methods were used to study newly synthesized thiophene-pi-conjugated donor-acceptor compounds, which were found to exhibit efficient intramolecular charge-transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert-Mataga models. We found that intramolecular charge transfer in these donor-acceptor systems is significantly dependent on the electron-withdrawing substituents at the thienyl 2-position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge-transfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric conformations. In addition, a novel S(2) fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S(2) fluorescence. We demonstrate that S(2) fluorescence can be explained by the calculated energy gap between the S(2) and S(1) states of these molecules. Furthermore, nonlinear optical behavior of the thiophene-pi-conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.     

Tuning the Nature of the Fluorescent State: A Substituted Polycondensed Dye as a Case Study

An extensive spectroscopic analysis is presented of an elongated polycondensed dye with a donor–acceptor substitution. The charge‐transfer (CT) state, polarized along the long molecular axis, is close in energy to a local excitation (LE) of the polycondensed system, roughly polarized along the short molecular axis, which makes this system particularly suitable to investigate the subtle LE/CT interplay. An essential‐state model is presented that quantitatively reproduces absorption and fluorescence spectra, as well as fluorescence emission and excitation anisotropy spectra collected in solvents of different polarity and viscosity, which sets a sound basis for the understanding of how solvent polarity and solvent relaxation affect the nature of low‐lying excitations. The markedly different fluorescence emission and excitation anisotropy spectra measured in glassy and liquid polar solvents unambiguously demonstrate the major role played by solvent relaxation in the definition of fluorescence properties of the dye.     

STUDIES ON FLAVINS IN ORGANIC SOLVENTS-I*. SPECTRAL CHARACTERISTICS OF RIBOFLAVIN,RIBOFLAVIN TETRABUTYRATE AND LUMICHROME

Abstract— The absorption and fluorescence spectra of riboflavin, riboflavin tetrabutyrate and lumichrome have been studied in organic solvents of different polarity including ethanol, acetone, dioxane, pyridine, acetic acid and in cyclohexane-dioxane mixtures. The molar extinction coefficients of the compounds were measured and the character of solvent sensitive changes observed in the absorption spectra are discussed. The effect of hydrogen bonding and/or intramolecular charge transfer complex are proposed as possible explanation. Changes in the shape of fluorescence emission spectra are less evident; in the case of riboflavin tetrabutyrate, mirror symmetry to the shape of the longest wavelength maximum was observed in low-polar solvents. Quantum yields of fluorescence are higher the lower the polarity of the solvent used; the value for riboflavin tetrabutyrate is greater than for riboflavin. Changes were also observed in the fluorescence emission spectra of lumichrome in solvents of different polarity. Fairly good agreement was demonstrated for positions of the observed absorption maxima of riboflavin in 98% dioxane, riboflavin tetrabutyrate and lumichrome in 80% cyclohexane in mixture with dioxane and the values calculated from energies of molecular orbitals of flavins computed by B. Pullman and A. Pullman.     

STUDY ON THE PROTONATION MECHANISM OF 2,6-DIMETHYL NAPHTHALENE DICARBOXYLATE

By the study of absorption and fluorescence spectra and the lifetime of fluorescence at room and low temperatures of 2,6-dimethyl naphthalene dicarboxylate (DMN) in different concentrations of sulfuric acid, different interactions between molecules of DMN and sulfuric acid have been observed. These interactions have been revealed by the absorption spectra of charge transfer complex in the ground state, emission of exciplex, absorption spectra of hydrogen bonding interaction, absorption and emission spectra after proton transfer and different lifetimes before and after protonation. The interaction mechanism of DMN and sulfuric acid through first the CT complex and exciplex then hydrogen bonding and finally proton transfer is proposed.     

Photophysical Property of Photoactive Molecules with Multibranched Push-Pull Structures

The structure-property characteristics of a series of newly synthesized intramolecular charge-transfer (ICT) compounds, single-branch monomer with triphenylmethane as electron donor and 2,1,3-benzothiadiazole as acceptor, the corresponding two-branch dimer and three-branch trimer, have been investigated by means of steady-state and femtosecond time-resolved stimulated emission fluorescence depletion (FS TR-SEP FD) techniques in different polar solvents. The TD-DFT calculations are further performed to explain the observed ICT properties. The interpretation of the experimental results is based on the comparative stud-ies of the series of compounds which have increased amount of identical branch moiety. The similarity of the absorption and fluorescence spectra as well as strong solvent-dependence of the spectral properties for the three compounds reveal that the excited state of the dimer and trimer are nearly the same with that of the monomer, which may localize on one branch. It is found that polar excited state emerged through multidimensional intramolecular charge transfer from the donating moiety to the acceptor upon excitation, and quickly relaxed to one branch before emission. Even so, the red-shift in the absorption and emission spectra and decreased fluorescence radiative lifetime with respect to their monomer counterpart still suggest some extent delocalization of excited state in the dimer and trimer upon excitation. The similar behavior of their excited ICT state is demonstrated by FS TR-SEP FD mea-surements, and shows that the trimer has the largest charge-separate extent in all studied three samples. Finally, steady-state excitation anisotropy measurements has further been carried out to estimate the nature of the optical excitation and the mechanism of energy redistribution among the branches, where no plateau through the ICT band suggests the intramolecular excitation transfer process between the branches in dimer and trimer.     

Synthesis and Spectral Properties of 4‐(2,5‐Dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO)

An interesting flourophore, 4‐(2,5‐dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) was synthesized by mixing an equivalent molar quantity of hippuric acid and 2,5‐dimethoxybenzaldehyde in acetic anhydride in the presence of anhydrous sodium acetate. The absorption and fluorescence characteristics of 4‐(2,5‐dimethoxy‐phenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) were investigated in different solvents. DMPO dye exhibits red shift in both absorption and emission spectra as solvent polarity increases, indicating change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMPO gave strong excimer like emission at 630 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B‐type class of Steven's Classification. DMPO displayed fluorescence quenching by triethylamine via nonemissive exciplex formation.     

Charge‐Transfer Interactions in Tris‐Donor–Tris‐Acceptor Hexaarylbenzene Redox Chromophores

Symmetric‐ and asymmetric hexaarylbenzenes (HABs), each substituted with three electron‐donor triarylamine redox centers and three electron‐acceptor triarylborane redox centers, were synthesized by cobalt‐catalyzed cyclotrimerization, thereby forming compounds with six‐ and four donor–acceptor interactions, respectively. The electrochemical‐ and photophysical properties of these systems were investigated by cyclovoltammetry (CV), as well as by absorption‐ and fluorescence spectroscopy, and compared to a HAB that only contained one neighboring donor–acceptor pair. CV measurements of the asymmetric HAB show three oxidation peaks and three reduction peaks, whose peak‐separation is greatly influenced by the conducting salt, owing to ion‐pairing and shielding effects. Consequently, the peak‐separations cannot be interpreted in terms of the electronic couplings in the generated mixed‐valence species. Transient‐absorption spectra, fluorescence‐solvatochromism, and absorption spectra show that charge‐transfer states from the amine‐ to the boron centers are generated after optical excitation. The electronic donor–acceptor interactions are weak because the charge transfer has to occur predominantly through space. Moreover, the excitation energy of the localized excited charge‐transfer states can be redistributed between the aryl substituents of these multidimensional chromophores within the fluorescence lifetime (about 60 ns). This result was confirmed by steady‐state fluorescence‐anisotropy measurements, which further indicated symmetry‐breaking in the superficially symmetric HAB. Adding fluoride ions causes the boron centers to lose their accepting ability owing to complexation. Consequently, the charge‐transfer character in the donor–acceptor chromophores vanishes, as observed in both the absorption‐ and fluorescence spectra. However, the ability of the boron center as a fluoride sensor is strongly influenced by the moisture content of the solvent, possibly owing to the formation of hydrogen‐bonding interactions between water molecules and the fluoride anions.