Janosi Tibor Zoltan, Makkai Geza, Kegl Timea, Matyus Peter, Kollar Laszlo, Erostyak Janos
Institute of Physics, University of Pecs, Ifjusag u. 6, Pecs, H-7624, Hungary.
Szentagothai Research Centre, Spectroscopy Research Group, University of Pecs, Ifjusag u. 20, Pecs, H-7624, Hungary.
J Fluoresc. 2016 Mar;26(2):679-88. doi: 10.1007/s10895-015-1754-3. Epub 2015 Dec 29.
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.
基于相同杯[4]间苯二酚芳烃化合物的穴状配体表现出完全不同的荧光行为。母体化合物四甲基穴状配体（1）的荧光强度在紫外光照射下会缓慢减弱，而上缘带有哒嗪基团的三级穴状配体（5a）在紫外区域激发时荧光发射增强。荧光发射结构（通过激发 - 发射矩阵表征）和5a的吸收保持不变。荧光衰减曲线分析表明存在两个分别对应两个独立发射物种的成分。测量得到的平均寿命和量子产率的显著增加是紫外光诱导5a不同状态之间跃迁的结果。这些观察结果可以用5a和1之间的结构差异来解释。作为仅在上缘带有甲基取代基的裸穴状配体（1）的对应物，5a还有苯、三唑和哒嗪基团三个额外部分。计算研究证明了5a存在两种构象异构体。在紫外光激发下，两种异构体之间会发生从“暗”到“亮”的构象转变。各向异性衰减测量证实了这一假设。
