Leiderman Pavel, Gepshtein Rinat, Uritski Anna, Genosar Liat, Huppert Dan
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Israel.
J Phys Chem A. 2006 May 4;110(17):5573-84. doi: 10.1021/jp060170j.
Time-resolved emission and steady-state fluorescence techniques are used to study the excited-state intermolecular proton transfer from 8-hydroxypyrene-1,3,6-trisulfonate (HPTS or pyranine) to water in the presence of inert salts, NaCl and MgCl(2). At low salt concentrations, up to about 0.5 M MgCl(2) or about 0.8 M NaCl, the time-resolved emission of both the photoacid and conjugate base can be quantitatively fitted by our diffusion-assisted geminate recombination model. In this concentration range, the proton transfer and geminate recombination rate constants are almost independent of the salt concentrations whereas the proton diffusion constant decreases as the salt concentration increases. At higher salt concentrations, the proton-transfer rate constant decreases while the recombination rate constant increases slightly. For the saturated solution of MgCl(2) (about 5 M at room temperature), the steady-state emission consists of only a single band of the protonated photoacid. Careful examination of the time-resolved emission of HPTS in the presence of a large concentration of MgCl(2) shows that the quality of the fit to the geminate recombination model is rather poor and we fail to find adjustable parameters for a good quality fitting. For this large concentration range of MgCl(2) we were able to get a good fit of the experimental data with a model based on a distribution of proton-transfer rates. The model is consistent with an inhomogeneous water environment next to the excited HPTS molecule in such concentrated solutions.
利用时间分辨发射和稳态荧光技术，研究了在惰性盐氯化钠和氯化镁存在下，8-羟基芘-1,3,6-三磺酸盐（HPTS或吡喃）到水的激发态分子间质子转移。在低盐浓度下，高达约0.5M的氯化镁或约0.8M的氯化钠，光酸和共轭碱的时间分辨发射都可以用我们的扩散辅助双分子复合模型进行定量拟合。在此浓度范围内，质子转移和双分子复合速率常数几乎与盐浓度无关，而质子扩散常数随盐浓度增加而减小。在较高盐浓度下，质子转移速率常数降低，而复合速率常数略有增加。对于氯化镁的饱和溶液（室温下约5M），稳态发射仅由质子化光酸的单一谱带组成。仔细研究在高浓度氯化镁存在下HPTS的时间分辨发射表明，与双分子复合模型的拟合质量相当差，我们未能找到用于高质量拟合的可调参数。对于这个大浓度范围的氯化镁，我们能够用基于质子转移速率分布的模型很好地拟合实验数据。该模型与这种浓溶液中激发态HPTS分子附近的非均匀水环境一致。
