Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan.
J Phys Chem A. 2010 Jan 14;114(1):172-82. doi: 10.1021/jp907441p.
The steady-state absorption and fluorescence properties of (E,E,E)-1,6-diaryl-1,3,5-hexatrienes (2, aryl = 2-nitrophenyl; 3, aryl = 3-nitrophenyl; 4, aryl = 4-nitrophenyl) have been investigated in solution and in the crystalline state. The solid-state absorption spectra of 2-4 shifted to longer wavelengths than those in solution. A combination of theoretical calculations and single-crystal X-ray structure analyses shows considerable planarization of molecules in the solid state, which is mainly responsible for the spectral red shifts. The effects of intermolecular interactions on the absorption spectra appeared to be relatively small in these crystals. This is consistent with the monomeric origin of the solid-state emission. Molecule 2 was nonfluorescent in all solvents studied, probably due to the efficient nonradiative deactivation from ionic species produced by excited-state intramolecular proton transfer (ESIPT) along the C-H...O-type hydrogen bonds. The fluorescence of 3, observed only in medium polar solvents, originated from an intramolecular charge transfer (ICT*) state, while that of 4 derived from locally excited (LE*) and/or ICT* states depending on the solvent polarity. All three molecules exhibited LE* fluorescence in the solid state. No observation of ICT* emission in crystals strongly suggests the twisted geometries for ICT* (TICT) of 3 and 4 in solution. The measurable fluorescence from crystal 2 can be attributed to the restricted torsional motions in the solid excited state.
（E,E,E）-1,6-二芳基-1,3,5-己三烯（2，芳基= 2-硝基苯基；3，芳基= 3-硝基苯基；4，芳基= 4-硝基苯基）在溶液中和晶体状态下的稳态吸收和荧光性质已经被研究过。2-4 的固态吸收光谱比在溶液中的吸收光谱向长波长移动。理论计算和单晶 X 射线结构分析的组合表明，分子在固态中具有相当大的平面化，这主要是光谱红移的原因。分子间相互作用对这些晶体吸收光谱的影响似乎相对较小。这与固态发射的单体起源一致。由于激发态分子内质子转移（ESIPT）沿 C-H...O 型氢键产生的离子物种的有效非辐射失活，2 在所有研究的溶剂中均无荧光，可能是由于这个原因。3 的荧光仅在中等极性溶剂中观察到，源自分子内电荷转移（ICT*）态，而 4 的荧光则源自局部激发（LE*）和/或 ICT态，这取决于溶剂的极性。所有三种分子在固态下都表现出 LE荧光。在晶体中没有观察到 ICT发射强烈表明 3 和 4 在溶液中 ICT（TICT）的扭曲构象。晶体 2 中可测量的荧光可以归因于固态激发态中受限的扭转运动。
