Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Phys Chem A. 2012 Nov 8;116(44):10786-92. doi: 10.1021/jp309019g. Epub 2012 Oct 25.
The photochemistry of the rotor probe 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was studied to elucidate a curious effect of fluid flow previously reported. The apparent sensitivity to fluid motion observed in CCVJ but not in the closely related molecule 9-(dicyanovinyl)julolidine (DCVJ) is found to be an indirect effect of a photoisomerization reaction. The results presented here demonstrate that it is this isomerization, rather than the commonly assumed TICT process, that confers viscosity-sensing ability on these fluorophores. In micromolar solutions in hydroxylic solvents CCVJ exists primarily in the carboxylate form. Only the E isomer of this anion is initially present in solutions prepared from the solid, but in room light such solutions rapidly achieve a photostationary state in which the E isomer and an essentially nonfluorescent Z isomer exist in comparable concentrations. The Z isomer is metastable in S(0) such that in the absence of light the solution reverts slowly to pure E. Unlike DCVJ where only a single isomer is possible, the production of long-lived photoproducts in CCVJ and other asymmetrically substituted styryenyl probes complicates their fluorescence response. Considerable care is needed when such fluorphores are used as steady-state sensors of environmental fluidity are used.
转子探针 9-(2-羧基-2-氰基乙烯基)乔利定（CCVJ）的光化学性质被研究，以阐明先前报道的一种奇特的流体流动效应。在 CCVJ 中观察到的对流体运动的明显敏感性，而在密切相关的分子 9-(二氰基乙烯基)乔利定（DCVJ）中则没有观察到，这被发现是光异构化反应的间接效应。这里呈现的结果表明，正是这种异构化，而不是通常假设的 TICT 过程，赋予了这些荧光团对粘度的感应能力。在羟基溶剂中的微摩尔溶液中，CCVJ 主要以羧酸形式存在。只有这种阴离子的 E 异构体最初存在于从固体制备的溶液中，但在室温光线下，这些溶液迅速达到光稳定状态，其中 E 异构体和一种基本上非荧光的 Z 异构体以可比浓度存在。Z 异构体在 S(0)中是亚稳态的，因此在没有光的情况下，溶液会缓慢地恢复为纯 E。与 DCVJ 不同，其中只有一种异构体是可能的，CCVJ 和其他不对称取代的苯乙烯探针中的长寿命光产物的产生使它们的荧光响应复杂化。当这些荧光团被用作环境流动性的稳态传感器时，需要非常小心。
