Photophysical characteristics of biologically active 4-aryloxymethyl coumarins 4PTMBC and 1IPMBC

• Effect of solvents on spectral properties of biologically active coumarins is studied.
• The double linear correlation of spectral properties with ETN is observed.
• Dipole moment of dyes is more in excited state compared to ground state.

The absorption and fluorescence characteristics of biologically active coumarin derivatives 4-p-tolyloxymethyl-benzo[h]coumarin (4PTMBC) and 1-(4-iodo phenoxymethyl)-benzo[f]coumarin (1IPMBC) are studied at room temperature in a series of organic solvents and 1,4-dioxane – acetonitrile solvent mixture. The effect of pure solvents on 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. Both general solute – solvent interactions and hydrogen bonding interactions are operative in these systems. However, the contribution of hydrogen bonding interactions is less compared to general solute–solvent interactions. The solvatochromic correlations are used to estimate excited state dipole moment using experimentally determined ground state dipole moment. The bathochromic shift of the emission spectra and the increase in excited state dipole moment 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.

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