EFFECTS OF AGGREGATION AND MESOMORPHIC ORDER ON THE PHOTOPHYSICAL PROPERTIES OF 4-ALKYL-N-(P-CYANOPHENYL)PIPERIDINES. MOLECULES CAPABLE OF FORMING INT RAMOLECULAR CHARGE TRANSFER STATES
EFFECTS OF AGGREGATION AND MESOMORPHIC ORDER ON THE PHOTOPHYSICAL PROPERTIES OF 4-ALKYL-N-(P-CYANOPHENYL)PIPERIDINES. MOLECULES CAPABLE OF FORMING INT RAMOLECULAR CHARGE TRANSFER STATES
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DOI：
10.1021/ja00093a008
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发表时间：
1994-07
影响因子：
15
通讯作者：
B. M. Sheikh-ali;R. Weiss
中科院分区：
文献类型：
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作者：
B. M. Sheikh-ali;R. Weiss
用静态吸收光谱、荧光光谱和皮秒时间域发射光谱研究了4-烷基-JV-(/？-氰基苯基)哌啶(I)在稀溶液、浓溶液、纯熔体和向列相中的光物理性质。1的分子中含有一个能够形成分子内电荷转移(ICT)激发态的生色团。I在极性溶剂中的稀溶液表现出类似于/>；-(MA-二甲氨基)苯甲腈(DMABN)的双发射。在浓正己烷溶液以及I的液晶和熔融相中，已经获得了几个基态和激发态物种的证据，其中包括两个不同的络合物和I的电荷转移激发态。在对I的戊基和庚基同系物1/1(wt/wt)混合物的向列相和熔体相的向列相和熔体相的向列相和熔体相的时间域实验中，来自最低能量吸收带红边激发的荧光“瞬时”上升，衰减可符合三指数函数。相应的时间分辨发射光谱表现出随时间的斯托克斯漂移，这是由于电荷转移为主的激发态物种的驰豫所致。相反，当在发射波段的长波长侧监测发射时，在最低能量吸收最大值附近的激发会导致具有可测量上升时间的荧光，而当在波段的短波长侧监测时，会产生“瞬时”上升。提出了与这些观测结果相一致的动力学模型。结果表明，I或其配合物的激发单重态的能量跃迁对电荷转移物种的布居没有重要贡献。
The photophysical properties of 4-alkyl-jV-(/?-cyanophenyl) piperidines (I) in dilute and concentrated solutions and in neat melt and nematic phases have been studied by means of their static absorption and fluorescence spectra and by picosecond time-domain emission measurements. Molecules of 1 contain a chromophore which is capable of forming intramolecular charge-transfer (ICT) excited states. Dilute solutions of I in polar solvents exhibit dualemission similar to that of/>-(MA-dimethylamino) benzonitrile (DMABN). Evidence for several ground-and excited-state species, including two distinct complexes and a charge-transfer excited state of I, has been obtained in concentrated hexane solutions as well as in theneat liquid-crystalline and melt phases of I. In the time domain experiments on nematic and melt phases ofa 1/1 (wt/wt) mixture of the pentyl and heptyl homologues of I, fluorescence from excitation at the red edge of the lowest energy absorption band rises “instantaneously” and the decay can be fit to a triple exponential function. The corresponding time-resolved emission spectra exhibit a time-dependent Stokes shift due to relaxation about a charge-transfer dominated excited-state species. In contrast, excitation near the lowest energy absorption maximum leads to fluorescence with a measurable rise time when emissionis monitored at the long wavelength side of the emission band and an “instantaneous” rise when monitored at the short wavelength side of the band. A kinetic modelconsistent with these observations is proposed. It is shown that energy hopping from the excited singlet of I or its complexes is not an important contributor to the population of the charge-transfer species.