Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
J Phys Chem A. 2010 Oct 21;114(41):10929-35. doi: 10.1021/jp1054827.
The series of linear-shaped phenylacetylenyl- and (phenylacetylenyl)phenylacetylenyl-substituted aromatic enediynes 1-3 were synthesized as pure trans and cis isomers and their photochemistry explored. With expansion of the π-electron system, the absorption spectra red-shifted and the molar extinction coefficients dramatically increased up to 122000 M(-1) cm(-1) for trans-3. The absorption spectra of cis-2 and cis-3 consisted of two independent absorption bands. The fluorescence quantum yields of the molecules were high, even for the cis isomers (Φ(f) = 0.39-0.61). The fluorescence decay of each of the compounds was analyzed as a single exponential and the wavelength dependence of time constants was not observed, indicating a single emitting state in all cases. All isomers exhibited mutual cis-trans photoisomerization. The quantum yield of both trans-to-cis and cis-to-trans photoisomerization considerably decreased in 2 and 3, presumably due to an increased number of photochemical processes that yield nonreactive excited species and which result in nonradiative deactivation. Three energy minima exist in the excited triplet state, where the energy of planar conformation decreased with the extension of the phenyl acetylenyl chain, resulting in the promotion of nonradiative processes without conformational change.
一系列线性苯乙炔基和（苯乙炔基）苯乙炔基取代的芳香二烯 1-3 被合成为纯的顺式和反式异构体，并对其光化学进行了研究。随着π-电子体系的扩展，吸收光谱红移，摩尔消光系数急剧增加，最高可达 122000 M(-1) cm(-1)（反式-3）。顺式-2 和顺式-3 的吸收光谱由两个独立的吸收带组成。这些分子的荧光量子产率很高，即使是顺式异构体（Φ(f) = 0.39-0.61）。各化合物的荧光衰减均被分析为单指数衰减，且未观察到波长依赖性，表明在所有情况下均存在单一发射态。所有异构体均表现出相互的顺反光致异构化。顺式-反式和反式-顺式光致异构化的量子产率在 2 和 3 中均显著降低，这可能是由于增加了光化学反应的数量，这些反应产生非反应性激发态，并导致非辐射失活。在激发三重态中存在三个能量最小值，其中平面构象的能量随苯乙炔基链的延长而降低，从而在不发生构象变化的情况下促进非辐射过程。
