Completely different fluorescence behaviour of cavitands based on a same calix[4]resorcinarene compound was observed. While the fluorescence intensity of the parent compound, tetramethyl-cavitand (1) slowly faded as a result of UV-light exposure, the emission of the three-level cavitand with pyridazine moieties at the upper rim (5a) was enhanced by the excitation in the UV-region. The structure of fluorescence emission (characterized by excitation-emission matrices) and the absorption of 5a remained unaltered. The analysis of fluorescence decay curves reveals the presence of two separated components assigned to two individual emitting species. The measured significant increase of the average lifetime and quantum yield is the consequence of the UV-light induced transition between the different states of 5a. These observations can be explained by the structural difference between 5a and 1. As a counterpart of the naked cavitand (1) with methyl substituents at the upper rim only, 5a has three additional moieties benzene, triazole and pyridazine levels. Computational studies proved the existence of two conformational isomers of 5a. Upon ultraviolet light excitation a “dark” to “light” conformational transition occurs between the two isomers. This hypothesis was confirmed by anisotropy decay measurements.
观察到基于相同杯[4]
间苯二酚化合物的空
配体完全不同的荧光行为。虽然母体化合物四甲基空
配体 (1) 的荧光强度因紫外光照射而缓慢褪色,但上缘具有
哒嗪部分的三级空
配体 (5a) 的发射通过激发而增强。紫外线区域。荧光发射的结构(以激发-发射矩阵为特征)和 5a 的吸收保持不变。荧光衰减曲线的分析揭示了分配给两个单独的发射物种的两个分离的组分的存在。测量到的平均寿命和量子产率的显着增加是紫外光诱导 5a 不同状态之间跃迁的结果。这些观察结果可以通过 5a 和 1 之间的结构差异来解释。作为仅在上边缘具有甲基取代基的裸空穴
配体 (1) 的对应物,5a 具有三个额外的部分苯、三唑和
哒嗪水平。计算研究证明5a存在两种构象异构体。在紫外光激发下,两种异构体之间发生“暗”到“光”构象转变。这一假设得到了各向异性衰变测量的证实。