Spectroscopic investigation of preferential solvation of N-confused tetraphenylporphyrinin binary mixtures of dichloromethane with organic cosolvents.

Spectroscopic behaviour of porphyrin is known to be sensitive to the choice of the solvent and has been used to probe solvation phenomena. The UV-visible spectra of N-confused tetraphenylporphyrin are observed in a series of binary solvent mixtures - (dichloromethane + diethyl ether), (dichloromethane + chlorobenzene) and (dichloromethane + ethyl acetate). The resulting E scale for NCTPP solvation indicates nonlinear behaviour and preferential solvation by a solvent-solvent complex in all the three solvents - with the dichloromethane + ethyl acetate system showing the largest deviation from ideality. The data is fitted to the model based on solvent exchange equilibria for determining the preferential solvation parameters which are specific to the probe as well as the identity of solvents in the binary mixture. Further analysis using polarity parameters from literature indicate that the solvation of NCTPP in the (dichloromethane + ethyl acetate) mixture is dependent on the hydrogen bond accepting capacity and polarizability of the medium. Excess spectra derived from ATR-FTIR measurement of dichloromethane + ethyl acetate solutions lead to important inferences about the structure and role of solvent-solvent interactions responsible for the preferential solvation.