Solvatochromic studies of biologically active iodinated 4-aryloxymethyl coumarins and estimation of dipole moments

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The steady state absorption and emission spectra of biologically active iodinated 4-aryloxymethyl coumarins 4-(4-iodo-phenoxymethyl)-benzo[h]coumarin (4IPMBC) and 4-(4-iodo-phenoxymethyl)-6-methoxy coumarin (4IPMMC) are studied at room temperature in a series of solvents and 1,4-dioxane–acetonitrile solvent mixture. The effect of pure solvents upon the spectral properties are analyzed using Lippert–Mataga polarity function, Reichardt's microscopic solvent polarity parameter, Kamlet's and Catalan's multiple linear regression approaches. General solute–solvent interactions and hydrogen bonding interactions are operative in these systems. However, the contribution of later interaction is less. The solvatochromic data is used to estimate excited state dipole moment using experimentally determined ground state dipole moment. The bathochromic shift of emission spectra and increase in dipole moment after excitation indicate the intramolecular charge transfer (ICT) character in the emitting singlet state. The solvation studies in 1,4-dioxane–acetonitrile solvent mixture suggest that these dyes are preferentially solvated by 1,4-dioxane.