Solvent effects on the photophysical and photochemical properties of (E,E,E )-1,6-bis(4-nitrophenyl)hexa-1,3,5-triene
作者:Yoriko Sonoda、Wai Ming Kwok、Zdenék Petrasek、Richard Ostler、Pavel Matousek、Michael Towrie、Anthony W. Parker、David Phillips
DOI:10.1039/b008711o
日期:——
The photophysical and photochemical properties of (E,E,E)-1,6-bis(4-nitrophenyl)hexa-1,3,5-triene [(E,E,E)-1] have been studied in various solvents. The fluorescence emission maxima of (E,E,E)-1 show an increasing Stokes shift with increasing solvent polarity. Picosecond time-resolved fluorescence (TF) and transient absorption (TA) spectra do not show any significant time-dependent shifts in nonpolar solvent whereas, in more polar solvents, large red and blue shifts are observed in the TF and TA spectra, respectively. The fluorescence quantum yield reaches a maximum in moderately polar solvents and the quantum yield of intersystem crossing decreases strongly with increasing solvent polarity. Z–E-Isomerization of triene double bonds is inefficient in all solvents. In contrast, the absorption and fluorescence maxima for (E,E,E)-1,6-bis(4-cyanophenyl)hexa-1,3,5-triene [(E,E,E)-2] are practically solvent-independent. When the solvent polarity is increased, fluorescence quantum yield decreases monotonically and Z–E-isomerization quantum yield increases strongly. The results for (E,E,E)-1 can be understood in terms of an additional charge transfer excited state, which is absent for (E,E,E)-2.
研究了(E,E,E)-1,6-双(4-硝基苯基)六-1,3,5-三烯[(E,E,E)-1]在各种溶剂中的光物理和光化学特性。随着溶剂极性的增加,(E,E,E)-1 的荧光发射最大值显示出越来越大的斯托克斯偏移。在非极性溶剂中,皮秒时间分辨荧光光谱(TF)和瞬态吸收光谱(TA)没有出现任何明显的时间偏移,而在极性较强的溶剂中,TF 和 TA 光谱分别出现了较大的红色和蓝色偏移。在中等极性溶剂中,荧光量子产率达到最大值,而系统间交叉的量子产率则随着溶剂极性的增加而强烈下降。在所有溶剂中,三烯双键的 Z-E 异构化效率都很低。相反,(E,E,E)-1,6-双(4-氰基苯基)六-1,3,5-三烯[(E,E,E)-2]的吸收和荧光最大值实际上与溶剂无关。当溶剂极性增加时,荧光量子产率单调下降,而 Z-E-异构化量子产率则强烈增加。(E,E,E)-1的结果可以通过额外的电荷转移激发态来理解,而(E,E,E)-2不存在这种激发态。