School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.
Phys Chem Chem Phys. 2012 Jan 7;14(1):218-24. doi: 10.1039/c1cp22329a. Epub 2011 Nov 10.
The excited-state triple proton relay of 7-hydroxyquinoline (7HQ) along a hydrogen-bonded methanol chain in room temperature ionic liquids (RTILs) has been investigated using picosecond time-resolved fluorescence spectroscopy. The rate constant of the proton relay in a methanol-added RTIL is found to be slower by an order of magnitude than that in bulk methanol and to have unity in its kinetic isotope effect. These suggest that the excited-state tautomerization dynamics of 7HQ in methanol-added RTILs is mainly controlled by the solvent reorganization dynamics to form a cyclically hydrogen-bonded complex of 7HQ·(CH(3)OH)(2) upon absorption of a photon due to high viscosity values of RTILs. Because the cyclic complex of 7HQ·(CH(3)OH)(2) at the ground state is unstable in RTILs, the collision-induced slow formation of the cyclic complex should take place upon excitation prior to undergoing subsequent intrinsic proton transfer rapidly.
室温离子液体中 7-羟基喹啉（7HQ）通过氢键连接的甲醇链的激发态三重质子传递已经通过皮秒时间分辨荧光光谱进行了研究。在甲醇添加的室温离子液体中，质子传递的速率常数比在甲醇本体中慢一个数量级，并且其动力学同位素效应为 1。这表明，甲醇添加的室温离子液体中 7HQ 的激发态互变异构动力学主要由溶剂重组动力学控制，由于室温离子液体的高粘度值，在吸收光子后形成 7HQ·（CH（3）OH）（2）的环状氢键复合物。由于基态下 7HQ·（CH（3）OH）（2）的环状复合物在室温离子液体中不稳定，因此在激发态下应该发生碰撞诱导的缓慢形成环状复合物，然后快速进行后续的内在质子转移。
