螺吡喃激发态的反应活性

研究了6′-硝基-1,3,3-三甲基吲(口乃木)苯骈螺吡喃,Ⅰ,和6′-硝基-1-苯基-3,3-二甲基吲(口乃木)苯骈螺吡喃,Ⅱ,的光化学,Ⅰ的直接光解和敏化光解均得到份菁结构的光解产物Ⅲ,量子产率分别是0.42和0.32.Ⅱ直接光解时生成相应的有色光解产物Ⅳ,量子产率是0.40,氮杂蒽酮为敏化剂的敏化光解量子产率是0.58,无疑地,单线态和三线态均参予螺吡喃的发色反应,用这些结果和折算关系式得到,在Ⅰ的直接光解中,Ⅲ主要来自单线态,而在Ⅱ的直接光解中,Ⅳ主要来自三线态.从Ⅰ或Ⅱ的敏化联乙酰燐光实验中求得三线态参数.它们是:φ_ISC^Ⅰ＝0.11,φ_ISC^Ⅱ＝0.48;³K_dt^Ⅰ＝3×10⁴秒^-1,³K_dt^Ⅱ＝9×10⁴秒^-1,类似地,³K_r^Ⅰ＝0.12×10⁴秒^-1,³K_r^Ⅱ＝2.52×10⁴秒^-1,这样,³φ_r^Ⅰ值较小是由于³φ_ISC^Ⅰ值较小,而三线态寿命随结构变动不大.最后,取苯乙烯为模型,用它的电子能量与乙烯双键扭曲角度关系图推断出,来自单线态的双离子具有螺环构型,而来自三线态者具有平面状构型.

THE REACTIVITY OF EXCITED STATES OF THE SPIROPYRANS

The photochemistry of 6’-nitro-1, 3, 3-trimethylindolinobenzopyrylospiran, Ⅰ, and 6’-nitro-1-phenyl-3, 3-dimethylindolinobenzopyrylospiran, Ⅱ, was investigated.Both direct and sensitized photolyses of I afforded the coloured species, the merocyanine, Ⅲ, with quantum yields of 0.42 and 0.32, respectively.Direct irradiation of Ⅱ gave the corresponding merocyanine, Ⅳ, with quantum yield of 0.40, while the quantum efficiency on xanthone sensitization of Ⅱ was determined as 0.58 for the same photoproduct.Undoubtelly, both singlet and triplet were involved in the photocolouration of the spi-ropyrans.These results and the bracketing relationships signified that a considerable fraction of Ⅲ came directly from the excited singlet occured on the direct photolysis of Ⅰ, but 70% of Ⅳ was originated from the excited triplet on the direct photolysis of Ⅱ.The triplet parameters were obtained from the sensitization of biacetyl phosphorescence by Ⅰor Ⅱ at varying biacetyl concentrations.These were:φ_Ⅰ^ISC＝0.11,φ_Ⅱ^ISC＝0.48;³K_Ⅰ^dt＝3×10⁴S^-1,³K_Ⅱ^dt＝9×10⁴S^-1;³K_Ⅰ^r＝0.12×10⁴S^-1,³K_Ⅱ^r＝2.52×10⁴S^-1 Thus, the lower magnitute of ³φ_r^Ⅰ was shown to derive from lower intersystem-crossing quantum yield of Ⅰ and the variation of the triplet life time of Ⅰ and Ⅱ with structure was relatively small.Finally, the electronic energy curves of styrene, a model compound, for twisting of the ethylenie bond were employed to assign that the zwitterion came from the excited singlet had a spiro configuratio and the zwitterion originated from excited triplet had a planar configuration.