Photophysical characteristics of three novel benzanthrone derivatives: Experimental and theoretical estimation of dipole moments

The effect of solvents on absorption and fluorescence spectra and dipole moments of novel benzanthrone derivatives such as 3-N-(N′,N′-Dimethylformamidino) benzanthrone (1), 3-N-(N′,N′-Diethylacetamidino) benzanthrone (2) and 3-morpholinobenzanthrone (3) have been studied in various solvents. The fluorescence lifetime of the dyes (1-3) in chloroform were also recorded. Bathochromic shift observed in the absorption and fluorescence spectra of these molecules with increasing solvent polarity indicates that the transitions involved are π→π⁎. Using the theory of solvatochromism, the difference in the excited-state (μe) and the ground-state (μe) dipole moments was estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and McRae equations by using the variation of Stokes shift with the solvent's relative permittivity and refractive index. AM1 and PM6 semiempirical molecular calculations using MOPAC and ab-initio calculations at B3LYP/6-31 G⁎ level of theory using Gaussian 03 software were carried out to estimate the ground-state dipole moments and some other physicochemical properties. Further, the change in dipole moment value (Δμ) was also calculated by using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter (ETN). The excited-state dipole moments observed are larger than their ground-state counterparts, indicating a substantial redistribution of the π-electron densities in a more polar excited state for all the systems investigated.

Research Highlights► Benzanthrone derivatives which form a part of push-pull systems have interesting chemical and spectral properties. ► Benzanthrone derivatives are widely used as a laser dye, daylight fluorescent pigment and liphophilic fluorescent probe for biochemical and medicinal investigations. ► Knowledge of the dipole moments of electronically excited molecules is quite useful in designing materials with nonlinear optical properties. ► The solvatochromic methods are experimentally much simpler and widely accepted. ► The physicochemical and structural parameters of benzanthrone derivatives would be of great help in the design of new molecules for the best performance for specific applications.