Joung Joonyoung F, Kim Sangin, Park Sungnam
Department of Chemistry, Korea University , Seoul 136-701, Korea.
J Phys Chem B. 2015 Dec 17;119(50):15509-15. doi: 10.1021/acs.jpcb.5b09905. Epub 2015 Dec 7.
Coumarin 183 (C183) was used as a photoacid to study excited-state proton transfer (ESPT) reactions. Here, we studied the effect of ions on the ESPT of C183 in aqueous NaCl solutions using a steady-state fluorescence spectroscopy and time-correlated single photon counting (TCSPC) method. The acid dissociation equilibrium of excited-state C183 and the activation energy for the ESPT of C183 were determined as a function of NaCl concentration. The change in the equilibrium constant was found to be correlated with the solvation energy of deprotonated C183. Frequency-resolved TCSPC signals measured at several temperatures were analyzed by using a global fitting analysis method which enabled us to extract all the rate constants involving the ESPT reaction and the spectra of individual species. The activation energy for the ESPT reaction of C183 was highly dependent on NaCl concentration. Quantum chemical calculations were used to calculate the local hydrogen-bond (H-bond) configurations around C183 in aqueous NaCl solutions. It was found that the activation energy for the ESPT was determined by the local H-bond configurations around C183 which were significantly influenced by the dissolved ions.
香豆素183（C183）被用作光酸来研究激发态质子转移（ESPT）反应。在此，我们使用稳态荧光光谱法和时间相关单光子计数（TCSPC）方法研究了离子对C183在NaCl水溶液中ESPT的影响。确定了激发态C183的酸解离平衡以及C183的ESPT活化能与NaCl浓度的函数关系。发现平衡常数的变化与去质子化C183的溶剂化能相关。通过使用全局拟合分析方法对在几个温度下测量的频率分辨TCSPC信号进行分析，这使我们能够提取涉及ESPT反应的所有速率常数以及各个物种的光谱。C183的ESPT反应活化能高度依赖于NaCl浓度。使用量子化学计算来计算NaCl水溶液中C183周围的局部氢键（H键）构型。发现ESPT的活化能由C183周围的局部H键构型决定，而这些构型受到溶解离子的显著影响。
