The solvent dependence of absorption and fluorescence spectra, fluorescence lifetimes (τ Fl ), and quantum yields (q Fl ) of various 3-substituted benzanthrone derivatives have been investigated. A consistent correlation between fluorescence quantum yield and emitting state energy has been found that holds for all 6 derivatives in 11 solvents. The experimental data together with the results of semiempirical quantum chemical calculations indicate that the main quenching channel of the fluorescent S 1 (π,π*) excited state is intersystem crossing to an upper (n,π*) triplet state, T N . The rate constant and efficiency of intersystem crossing between these two states are strongly influenced by the substituent and by the solvent polarity, as both modulate the singlet state energy and the S 1 -T N energy gap. The rate constant of direct S 1 f T 1 intersystem crossing is small in most systems but appears to increase with a decrease in the energy of the S 1 state.

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