In this article, we have investigated the excited-state intramolecular double proton transfer dynamics of [2,2′-bipyridyl]-3,3′-diol, BP(OH)₂, in three alcohol–water binary mixtures, namely, ethanol (EtOH)–water, n-propanol (PrOH)–water, tert-butyl alcohol (TBA)–water, and dimethyl sulfoxide (DMSO)–water utilizing the femtosecond fluorescence upconversion technique. We have found that in alcohol–water binary mixtures the proton transfer (PT) pathway of BP(OH)₂ is sequential and the anomalous slowdown in PT dynamics is observed in mole fraction (χ) ranges χ_EtOH = 0.04–0.07, χ_EtOH = 0.23–0.28, χ_PrOH = 0.17–0.30, χ_TBA = 0.12–0.21, and χ_TBA = 0.40–0.46. Our study sheds light on the involvement of water network in the PT dynamics. Reduction in water accessibility due to the involvement of water molecules in cluster formation results in hindered PT dynamics, and this retardation is more for the TBA–water binary mixture compared to that for the other two mixtures. Additionally, we have found two anomalous regions for the DMSO–water binary mixture in ranges χ_DMSO = 0.12–0.16 and χ_DMSO = 0.26–0.34. However, most interestingly, beyond χ_DMSO = 0.40, we do not find any growth component in the femtosecond fluorescence upconversion trace, which may be due to the change in the PT mechanism from a sequential water-mediated pathway to a concerted intramolecular pathway.

中文翻译：

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飞秒荧光上转换研究不同水性二元混合物的微观异质性对[2,2'-联吡啶基] -3,3'-二醇质子转移动力学的影响

在本文中，我们研究了[2,2'-联吡啶基] -3,3'-二醇BP（OH）₂在三种醇水二元混合物即乙醇中的激发态分子内双质子转移动力学（EtOH）-水，正丙醇（PrOH）-水，叔丁醇（TBA）-水和二甲基亚砜（DMSO）-水均采用飞秒荧光上转换技术。我们已经发现，在醇-水的二元混合物的质子转移（PT）BP的途径（OH）₂是连续的，在PT动力学异常放缓摩尔分数（χ）中观察到的范围χ_的EtOH = 0.04-0.07，χ _EtOH中= 0.23-0.28，χ_异丙醇= 0.17-0.30，χ _TBA= 0.12-0.21，和χ _TBA = 0.40-0.46。我们的研究揭示了水网络在PT动力学中的作用。由于水分子参与团簇形成而导致的水可及性降低，导致PT动力学受阻，与其他两种混合物相比，TBA-水二元混合物的阻滞作用更大。此外，我们已经发现了两个反常区域为在范围χ的DMSO-水二元混合物_DMSO = 0.12-0.16和χ _DMSO = 0.26-0.34。然而，最有趣的是，超越χ _DMSO = 0.40，我们在飞秒荧光上转换迹线中未找到任何生长成分，这可能是由于PT机制从顺序的水介导途径变为分子内协同途径的变化所致。