Effect of Microheterogeneity of Different Aqueous Binary Mixtures on the Proton Transfer Dynamics of [2,2′-Bipyridyl]-3,3′-diol: A Femtosecond Fluorescence Upconversion Study

Abstract

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.

Femtosecond Upconversion Study of Interfacial Electron Transfer from Photoexcited CsPbBr3 Perovskite Nanocrystal to Rhodamine 6G

“…The rotational anisotropy study of r6G provides direct proof of NC–r6G complex formation. − Since r6G is sparingly soluble in toluene, one cannot measure the rotational anisotropy of r6G in toluene using a femtosecond upconversion setup. Utilizing the second harmonic of Ti-sapphire laser, we can only excite the sample anywhere between 375 and 430 nm.…”

Unveiling the Interaction of Duplex DNA with Graphene Oxide in the Presence of Two Diverse Binders: A Detailed Photophysical Study

“…Time-resolved anisotropy was performed in the same instrument, and for our setup, the G factor is 0.6. Femtosecond time-resolved experiments were performed on an upconversion setup (FluoroMax, IB Photonics), where a solid-state Ti:sapphire laser (Mai Tai HP, Spectra Physics) was used as an excitation source . In our experiment, we used an 880 nm pulsed laser with a duration of 100 fs and an 80 MHz repetition rate.…”

“…Femtosecond time-resolved experiments were performed on an upconversion setup (FluoroMax, IB Photonics), where a solid-state Ti:sapphire laser (Mai Tai HP, Spectra Physics) was used as an excitation source. 51 In our experiment, we used an 880 nm pulsed laser with a duration of 100 fs and an 80 MHz repetition rate. The fundamental 880 nm beam frequency was doubled to 440 nm in a nonlinear barium borate (BBO) crystal.…”

On the Correlation between Pair Hydrophobicity and Mixing Enthalpies in Water–Alcohol Binary Mixtures

“…Aqueous binary mixtures are often considered as one of the most intriguing systems to study due to their complex nature compared to the pure solvents. − Among other different aqueous binary mixtures, water–alcohol mixtures are a special class of binary systems that have been studied over the years because of their several anomalous behaviors. − Since all alcohols contain a hydrophobic part, the role of “hydrophobic solvation or hydrophobic hydration” is important and unavoidable in such contexts. One of the most debated and old concepts regarding this is the “iceberg theory” proposed by Frank and Evans .…”