Solvent Effect on the Emission Spectra of Anthracene Sulpho-nates and their Excited State Dipole Moments

Department of Chemistry, Jadavpur University, Calcutta-700 032

Fluorescence and absorption spectra of anthracene-1-sulphonate (1-AS), anthracene­2-sulphonate (2-AS), anthracene-1,5-disulphonate (1,5-AS) and anthracene-1,8-disulpho­nate (1,8-AS) have been studied in a series of polar, protic and aprotic solvents. The ground state (μg) and excited state (µe) dipole moments were estimated according to approximate solvent shift theories for nonspecific interactions. The derived values so obtained are for µg 0.8, 5.8, 0.0 and 3.8 and for µ₈ 4.4, 6.7, 0.0 and 6.7 for 1-AS, 2-AS, 1,5-AS and 1,8-AS, respectively. Intramolecular charge transfer from, π-electronic ring system of anthracene moiety to the SO^-3; group can explain large increase in dipole moment on excitation for 1-AS, 2-AS and 1,8-AS and ∆μ= 0 for 1,5-AS of symmetry C_2h. The diffuse nature of fiuoreseene only for 1-AS in water has been ascribed to exciplex formation. The higher ∆μ value of 1-AS is indicative of rather more polar excited state than other compounds and its low symmetry (C₃) promotes exciplex formation.