Role of structural flexibility in the fluorescence and photochromism of salicylideneaniline: the general scheme of the phototransformations

The mechanism of light-induced transformation in the salicylideneaniline molecule was studied by semiempirical PM3 calculations. The structures and energies of the minima and saddle points (transition states) on the S₀, S₁ and T₁ potential energy hypersurfaces (PESs) were obtained, together with the gradient lines on the PESs. The structure-energy scheme was compared with the experimental findings. According to the results obtained, the following principle processes are observed: fast S₁ excited state intramolecular proton transfer (ESIPT), followed by typical ESIPT fluorescence; the formation of two S₁ twisted intramolecular charge transfer (TICT) structures which quench the ESIPT fluorescence; the diabatic formation of two ground state metastable coloured “post-TICT” structures responsible for photochromism.     

Photophysics properties of 4-formacyl-triphenylamine and 4,4''''-bisformacyl-triphenylamine

The photophysical processes of 4-formacyl-triphenylamine (FTA) and 4,4'-bisformacyl-triphenyl-amine (BTA) have been studied. The fluorescences of FTA and BTA with donor (triamine) and acceptor (formacyl) moieties show the twisted intramolecular charge transfer (TICT) emission in polar solvents and photoinduced charge transfer (ICT) emission in nonpolar solvents. These could be supported by the solvent effect, temperature effect and the quenching process by strong electron-deficient compounds.     

Effect of K4FE(CN)6 and K3FE(CN)6 on TICT Dual Fluorescence of Sodium p-Dimethylaminobenzoate in Cetyltrimethylammonium Chloride Micelle. Identification of the Magenetic Effect in TICT Process

Comparison of the effects of K₄Fe(CN)₆ and K₃Fe(CN)₆ on TICT dual fluorescence of sodium p-dimethylaminobenzoate (SDMAB) in cetyltrimethyl ammonium chloride (CTAC) micelle yields a conclusion that the presence of a magnetic effect un favors the TICT process, which is verified by inserting the sample in a stationary magnetic field of 100G in which a decrease in the relative quantum yield of TICT state is observed.     

Radiative decay channel assessment to understand the sensing mechanism of a fluorescent turn-on Al3+ chemosensor

The turn-on luminescent chemosensor [2-Hydroxy-1-naphthaldehyde-(2-pyridyl) hydrazone] (L), selective to Al³⁺ ions, was studied by means of density functional theory (DFT) and time-dependent-DFT quantum mechanics calculations. The UV-Vis absorption and the radiative channel from the adiabatic S₁ excited state were assessed in order to elucidate the selective sensing mechanism of L to Al³⁺ ions. We found that twisted intramolecular charge transfer (TICT) and photoelectron transfer (PET), which alter the emissive state, are responsible for the luminescence quenching in L. After coordination with Al³⁺, the TICT is blocked, and PET is no longer possible. So, the emission of the coordination complex is activated, and a fluorescence effect enhanced by chelation is observed. For compounds with Zn²⁺ and Cd²⁺, the luminescence quenching is caused by PET, while for Ni²⁺, ligand to metal charge transfer is the prominent mechanism. To go into more detail, the metal-ligand interaction was analyzed via the Morokuma-Ziegler energy decomposition scheme and the natural orbital of chemical valence.     

Quantitative Design of Bright Fluorophores and AIEgens by the Accurate Prediction of Twisted Intramolecular Charge Transfer (TICT)

Inhibition of TICT can significantly increase the brightness of fluorescent materials. Accurate prediction of TICT is thus critical for the quantitative design of high‐performance fluorophores and AIEgens. TICT of 14 types of popular organic fluorophores were modeled with time‐dependent density functional theory (TD‐DFT). A reliable and generalizable computational approach for modeling TICT formations was established. To demonstrate the prediction power of our approach, we quantitatively designed a boron dipyrromethene (BODIPY)‐based AIEgen which exhibits (almost) barrierless TICT rotations in monomers. Subsequent experiments validated our molecular design and showed that the aggregation of this compound turns on bright emissions with ca. 27‐fold fluorescence enhancement, as TICT formation is inhibited in molecular aggregates.     

Electron Energies, Dipole Electric Moments, and Distribution of the Laurdan Molecule over the Conformation States of Methyl Groups

Using the methods of molecular simulation and HyperChem v.5.0 programs (PM3 method), we carried out calculations of the principal spectroscopic characteristics and of the structure of the laurdan molecule in the ground and the first excited electronic states. The thermal static distribution of molecules over various possible orientations of the plane of methyl groups relative to the plane of the naphthalene bicycle was taken into account. The energies and dipole moments of these electronic states have been calculated as functions of the torsion angle of methyl groups. The existence of an additional mechanism of electronic spectrum broadening is shown; it is associated with thermal mismatch of the equilibrium orientations of the rotational fragment of the molecule and with the dependence of the electron transition frequency on the degree of deviation of the angle from the equilibrium value. The dependence of dipole moments on this angle has been found and calculated. This dependence is the strongest for the ground state. The maximum values of dipole moments in the ground and excited states are 4.0 and 7.6 D.     

具有空穴传输基团的超支化聚合物发光材料的结构与光谱性质

利用A2 B3反应,合成了带有空穴传输基团——三苯胺为联接单元,以1,3,5-三苯基苯为核的超支化聚合物（TPA-TPP）,并对这类聚合物的合成方法、结构、光物理性质进行了系统的研究。通过溶剂效应观察到了TICT（分子内电荷转移态）,发射谱为宽而无结构的带谱,且发射波长随溶剂极性的增大而明显红移。因而可利用此特性来调节发光波长。研究结果表明,以三苯基苯为核心,引入三苯胺基团作为连接基团,加大了空间位阻,使由溶液到固体膜状态的发射光谱红移减小。     

DMABN测定含溴化钠或正丁醇水溶液中表面活性剂的临界胶团浓度

以对二甲氨基苯甲腈(DMABN)为探针, 测定它在含NaBr或n-C4H9OH的表面活性剂十二烷基三甲基溴化铵(C12TABr)、季铵盐Gemini表面活性剂C12-3-C12·2Br和十二烷基硫酸钠(SDS)水溶液中的第二重荧光对应的强度(Ia)和特征波长(λa)对表面活性剂浓度(c)曲线. 由Ia-c曲线的转折点或λa-c曲线对应的一阶导数极小点可以获得临界胶团浓度(cmc), 扩展了DMABN探针测定表面活性剂cmc的适用性.     

Time‐dependent density functional theory study on the hydrogen bonding‐induced twisted intramolecular charge‐transfer excited states of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine

In this work, the time‐dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen‐bonded intramolecular charge‐transfer excited state of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine (DMAPIP) in methanol (MeOH) solvent. All the geometric conformations of the ground state and locally excited (LE) state and the twisted intramolecular charge‐transfer (TICT) state for isolated DMAPIP and its hydrogen‐bonded complexes have been optimized. At the same time, the absorption and fluorescence spectra of DMAPIP and the hydrogen‐bonded complexes in different electronic states are also calculated. We theoretically demonstrated for the first time that the intermolecular hydrogen bond formed between DMAPIP and MeOH can induce the formation of the TICT state for DMAPIP in MeOH solvent. Therefore, the two components at 414 and 506 nm observed in the fluorescence spectra of DMAPIP in MeOH solvent were reassigned in this work. The fluorescence peak at 414 nm is confirmed to be the LE state. Furthermore, the red‐shifted shoulder at 506 nm should be originated from the hydrogen‐bonded TICT excited state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

伴随着分子内电荷分离的分子内转动模型的时间分辨荧光光谱研究

本文采用时间分辨荧光光谱方法,考查了两种7-胺基香豆类素衍生物分子在不同溶剂中的荧光辐射弛豫过程,研究了环境因素对伴随着分子内电荷转移的分子内转动激发态(TICT)弛豫过程的影响。结果说明TICT态是非刚性香豆素分子激发态无辐射弛豫路径之一,这一过程受到环境介质的极性、粘度和温度的影响。并指出了在考虑粘度影响时,须对DSE理论进行修正,同时提出了TICT态存在位垒的观点。