Elucidation of intriguing methanol-dichloromethane binary solvent mixture: Synergistic effect, analytical modeling, NMR and photo-induced electron transfer studies

Abstract

The present work elucidates the nature of synergistic solvation behavior of methanol (MeOH) – dichloromethane (DCM) binary solvent mixture. The highest degree of solvation has been observed for XMeOH=0.40 in DCM with ETN(30) value of 0.887, which is larger than both pure MeOH (0.762) and pure DCM (0.309). 1H NMR result indicates the presence of MeOH-DCM cluster in the stoichiometric ratio of 1:1.33 in the binary solvent mixture. An analytical solvent exchange model has been used to estimate the extent of synergistic solvation and is found to be 3.5 times larger than the preferential solvation. The disappearance of such cooperative solvation behavior in the excited state of the solvatochromic probe reveals the weak nature of the intermolecular interaction. Photo-induced electron transfer reaction has been employed to estimate the solvent reorganization energy of the mixtures of varying proportions. The slowest rate of electron transfer and highest value of solvent reorganization energy was observed for XMeOH=0.40, where the strongest synergistic effect was observed. All the observed phenomenon has been explained on account of the solvent-solvent interactions through extended hydrogen-bonding network in the solvent mixture.