DUAL FLUORESCENCE OF 2-(4'-(N,N-DIMETHYLAMINO)PHENYL)BENZOTHIAZOLE AND ITS BENZIMIDAZOLE ANALOG - EFFECT OF SOLVENT AND PH ON ELECTRONIC-SPECTRA
DUAL FLUORESCENCE OF 2-(4'-(N,N-DIMETHYLAMINO)PHENYL)BENZOTHIAZOLE AND ITS BENZIMIDAZOLE ANALOG - EFFECT OF SOLVENT AND PH ON ELECTRONIC-SPECTRA
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DOI：
10.1021/j100065a016
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发表时间：
1994-04-07
影响因子：
--
通讯作者：
DOGRA, SK
中科院分区：
文献类型：
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作者：
DEY, J;DOGRA, SK
在不同极性和氢键性质的溶剂中记录了 2-(4'-(N,N-二甲氨基)苯基)苯并噻唑 (DMAPBT) 和 2-(4'-(N,N-二甲氨基)苯基)苯并咪唑 (DMAPBI) 的吸收和荧光光谱。在所有溶剂中，两种化合物均观察到双荧光。正常的斯托克斯位移发射 (B) 源自局部激发的 pi* 电子态，大斯托克斯位移带 (A) 源自扭曲分子内电荷转移 (TICT) 态的发射。即使在非极性溶剂中，观察到的双荧光表明 TICT 态的能量始终低于局部激发态的能量。在 DMAPBT 的情况下，同时形成两种单阳离子，一种在叔氮原子处质子化，另一种在氨基处质子化。前者在非极性溶剂中较稳定，后者在极性溶剂中较稳定。另一方面，DMAPBI 中仅形成一种单阳离子。荧光滴定表明，各个共轭酸碱对的辐射寿命短于质子化/去质子化反应的倒数速率。
The absorption and fluorescence spectra of 2-(4'-(N,N-dimethylamino)phenyl)benzothiazole (DMAPBT) and 2-(4'-(N,N-dimethylamino)phenyl)benzimidazole (DMAPBI) have been recorded in solvents of different polarity and hydrogen-bonding nature. In all the solvents, a dual fluorescence is observed for both the compounds. The normal Stokes-shifted emission (B) originates from a locally excited pi* electronic state, and the large Stokes-shifted band (A) is due to emission from a twisted intramolecular charge-transfer (TICT) state. The dual fluorescence observed, even in nonpolar solvents, indicates that the energy of the TICT state is always lower than that of the locally excited state. Two kinds of monocations, one protonated at the tertiary nitrogen atom and the other protonated at the amino group, are formed simultaneously in the case of DMAPBT. The former is more stable in nonpolar solvents and the latter one in polar solvents. On the other hand, only one kind of monocation is formed in DMAPBI. Fluorimetric titrations have indicated that the radiative lifetimes of the respective conjugate acid-base pairs are shorter than the reciprocal rates of the protonation/deprotonation reactions.