Role of Solvation Dynamics in Excited State Proton Transfer of 1‐Naphthol in Nanoscopic Water Clusters Formed in a Hydrophobic Solvent

Abstract

Excited state proton transfer (ESPT) in biologically relevant organic molecules in aqueous environments following photoexcitation is very crucial as the reorganization of polar solvents (solvation) in the locally excited (LE) state of the organic molecule plays an important role in the overall rate of the ESPT process. A clear evolution of the two photoinduced dynamics in a model ESPT probe 1-naphthol (NpOH) upon ultrafast photoexcitation is the motive of the present study. Herein, the detailed kinetics of the ESPT reaction of NpOH in water clusters formed in hydrophobic solvent are investigated. Distinct values of time constants associated with proton transfer and solvent relaxation have been achieved through picosecond-resolved fluorescence measurements. We have also used a model solvation probe Coumarin 500 (C500) to investigate the dynamics of solvation in the same environmental condition. The temperature dependent picosecond-resolved measurement of ESPT of NpOH and the dynamics of solvation from C500 identify the magnitude of intermolecular hydrogen bonding energy in the water cluster associated with the ultrafast ESPT process.

Different mechanisms of ultrafast excited state deactivation of coumarin 500 in dioxane and methanol solvents: experimental and theoretical study

“…1A) was a typical 7-aminocoumarin dye that was widely used as a uorescence probe doped into varied systems and has been researched using many steadystate and transient-state spectroscopic methods. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] A few years back, Nad et al studied the photophysical properties of C500 in a series of solvents, from nonpolar solvents to polar solvents and alcoholic solvents. They measured the optical absorption and uorescence spectra of C500 in different solvents and the results indicated that C500 exhibited unusual spectral behaviors in nonpolar solvents.…”

Solvatofluorochromism of polyethyleneimine-encapsulated Ag nanoclusters and their concentration-dependent fluorescence

“…Moreover, the use of THF, as a hydrogen bond acceptor solvent, will also benet this process. 27 In the case of EGME, although strong transition dipole moments are also present, because of the different conformation of PEI and the hydrogen bond effect of EGME, the slow mobility of this environment makes the change of electron transfer dependent on time. In particular, we further proved that such special solvent effects could not be ascribed to the formation of dimers or aggregated Ag nanoclusters in THF or EGME by comparing the UV-vis spectra of Ag nanoclusters at higher concentrations (vide infra).…”

The change in excited-state proton transfer kinetics of 1-naphthol in micelles upon the binding of polymers: The influence of hyaluronan hydration

“…The excited state proton transfer fluorescence probe 1-naphthol exhibits dual fluorescence with emission peaks of neutral form (NpOH) at ∼350 nm and an emission peak of anionic form (NpO − ) at ∼450 nm. The emission of NpO − is dominant in a water environment and NpOH emission is dominant in a hydrophobic environment or in alcohols (Lee, Robinson, Webb, Philips, & Clark, 1986;Rakshit, Saha, Verma, & Pal, 2012). In bulk water, 1-naphthol undergoes excited state proton transfer in 35 ps and almost the entire excited state population is in anionic form.…”