Hammett Type Correlations for Intramolecular Charge Transfer (ICT) Dipole Moments of 4’-Substituted 9-Styrylacridines in the Ground State and in the Excited State

Abstract

9-Styrylacridine(1a) and a series of 4'-substituted 9-styrylacridines (1b-f) (substituent: Me, OMe, NMe 2 , Cl, NO 2 ) have been prepared to study their spectroscopic properties in several solvents of different dipolarity. They show strong Stokes shifts from the ground state to the S 1 excited state (Δ ν - 5400 to -8700 cm - 1 ) which denotes an important change of conformation in the fluorescing state. AM1 calculations suggest that the coplanarity increases in the S 1 state. The fluorescence spectra exhibit a positive solvatochromism, allowing the determination of excited state dipole moment (μ E ). Hammett correlations between σ p and μ G (ground state dipole moments) and μ E respectively, show that the electronic influence of substituent on the internal charge transfer (ICT) is ca. 3 times stronger in the S 1 excited state than in the ground state.