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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A series of new dyes based on the N-analogue of Pechmann hybrid dyes were prepared by the condensation of different 5-aryl derivatives of pyrrolinone ester (phenyl, 4-bromophenyl, thienyl, and biphenyl) with isatin. N-Alkylated derivatives were also prepared using bromoethyl acetate. Full 1 H and 13 C NMR assignment was performed. All prepared dyes were soluble in most organic solvents: N-alkylated derivatives had better solubility than non-alkylated derivatives. The UV-vis absorption spectra of the derivatives under study are quite similar and exhibit maxima in the 509-526 nm range. No E/Z photoisomerisation is observed. The dyeing process, dye exhaustion on polyester, and the fastness properties of the dyes were examined.

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