Spectroscopic properties of aromatic dicarboximides. Part 2.—Substituent effect on the photophysical properties of N-phenyl-1,2-naphthalimide
作者:Attila Demeter、Tibor Bérces、László Biczók、Véronique Wintgens、Pierre Valat、Jean Kossanyi
DOI:10.1039/ft9949002635
日期:——
Absorption and fluorescence spectra, fluorescence decay times, fluorescence quantum yields and triplet yields have been determined for N-phenyl-1,2-naphthalimide and its phenyl-substituted methyl derivatives in different solvents. N-Phenyl-1,2-naphthalimide emits long-wavelength fluorescence in hexane (λmaxf= 550 nm) which is red shifted by methyl substitution at the meta and para positions of the phenyl ring and by using a solvent of higher polarity. The fluorescence decays on the sub-nanosecond timescale. When the N-phenyl-1,2-naphthalimide has o-methyl substituents in the phenyl group, they emit dual fluorescence. The location of the short-wavelength component is constant while that of the long-wavelength component is blue shifted as a result of o-methyl substitution. Ortho substitution also increases the decay time of the long-wavelength fluorescence. The results are explained in terms of vibronic interaction between the S1(ÏÏ*) and S2(nÏ*) excited states (pseudo-JahnâTeller effect) which is enhanced by solvent relaxation and twisting of the phenyl ring towards a coplanar geometry.
测定了 N-苯基-1,2-萘二甲酰亚胺及其苯基取代的甲基衍生物在不同溶剂中的吸收和荧光光谱、荧光衰减时间、荧光量子产率和三重态产率。N-苯基-1,2-萘二甲酰亚胺在正己烷中发出长波长荧光(δ "maxf= 550 nm),甲基取代苯环的元位和对位以及使用极性较高的溶剂会使荧光发生红移。荧光在亚纳秒级衰减。当 N-苯基-1,2-萘二甲酰亚胺的苯基中含有邻甲基取代基时,它们会发出双重荧光。短波分量的位置保持不变,而长波分量则由于邻甲基取代而发生蓝移。正交取代也增加了长波荧光的衰减时间。这些结果可以用 S1(ÏÏ*)和 S2(nÏ*)激发态之间的振子相互作用(伪贾恩泰勒效应)来解释,溶剂松弛和苯环向共面几何扭转增强了这种相互作用。