STUDY OF ELECTRON-TRANSFER INTERACTION BETWEEN HYPOCRELLIN AND N,N-DIETHYLANILINE BY UV-VISIBLE, FLUORESCENCE, ELECTRON-SPIN-RESONANCE SPECTRA AND TIME-RESOLVED TRANSIENT ABSORPTION-SPECTRA

Hypocrellin A (HA) and hypocrellin B (HB) extracted from Hypocrella ba mbusae (B. et. Br) Sacc are perylene quinoid pigments, Quenching of HA or HB fluorescence by N,N-diethylaniline (DEA) results in Stern-Volme r plots; the quenching rate constants in CH3CN are 2.28 x 10(10) M(-1) s(-1) for HA and 2.34 x 10(10) M(-1) s(-1) for HB and are in agreemen t with those calculated from the semiclassical Marcus theory. The valu es of the free energy change Delta G for electron transfer between HA or HB and DEA calculated from Weller's equation are -1.21 eV for HA and -1.24 eV for HB. Electron spin resonance (ESR) signals of semiquin one radical anions of HA or HB have been detected on illumination (lam bda = 550 nm) of HA or HB acid DEA in anaerobic dimethylsulphoxide and CH3CN solutions, indicating that an electron transfer has occurred fr om the ground state of DEA to excited states of HA or HB. The UV-visib le spectra of HA in the presence of DEA in dimethylformamide and the t ime-resolved transient absorption spectra of the interaction of HA and DEA in different concentrations of HA and DEA in CH3CN are examined. The observation of transient absorption of the semiquinone radical ani on of HA (lambda(max) = 620 nm) is also evidence of this electron tran sfer process. The interaction of HA and N-ethylaniline, aniline is als o studied by UV-visible, ESR and fluorescence spectra.