Solvatochromic shift studies in LD-425 and LD-423: Estimation of ground and excited state dipole moments

Abstract

The absorption and fluorescence characteristics of 4-methyl-7-(4-morpholinyl)-2H Pyrano [2,3-b] Pyridin-2-one (LD-425) and 1,2,3,8-tetrahydro-1,2,3,3,5-pentamethyl-7H-pyrrolo[3,2-g]quinolin-7-one (LD423) are studied at room temperature in a series of organic solvents and 1,4-dioxane–acetonitrile solvent mixtures. The effects of pure solvents upon the spectral properties are analyzed using Lippert–Mataga polarity function, Richardts microscopic solvent polarity parameter and Kamlet's multiple linear regression approach. Both general solute–solvent interactions and hydrogen bonding interactions are operative in these systems. 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 indicates the intramolecular charge transfer (ICT) character in the emitting singlet state. The solvation studies in 1,4-dioxane–acetonitrile solvent mixtures indicates that these dyes are preferentially solvated by 1,4-dioxane.