Solvent impact on the photophysical properties and excited state behavior of p-aminobenzoic acids

Abstract

• The impact of solvent on photo-induced charge transfer is analysed. • The quantum yield of two derivatives is determined in different solvents. • Carbonyl stretching (IR) modes shift in protic solvents. • In methanol there is a thermodynamic barrier, but none in aprotic solvents. The photophysical properties of p -aminobenzoic acid and dimethyl- p -aminobenzoic acid are compared in a range of solvents. The electronic spectra are used to determine quantum efficiencies and evaluate excited state behavior. The latter system is found to undergo a charge transfer following photoexcitation and the thermodynamics for the process are assessed. The strength and type of solvent–solute interaction are important in determining the driving force for the charge transfer, with entropy being dominant in protic solvents and enthalpy in aprotic solvents. Vibrational spectroscopy and calculations provide further insight into the nature of the specific solvent–solute interactions, with shifts in the infrared spectrum observed due to hydrogen bonding interactions with the solvent.