Primary Processes in the Photoreduction of Acridine in Various Alcohols

Abstract

Abstract The effect of the addition of biacetyl on the quantum yield of photoreduction of acridine in methanol, ethanol, n- and iso-propanol has been studied under the aerated and deaerated conditions. From the analysis of the results, the quantum yields for four mechanisms ΦMS(S means that a reactive state is singlet excited states, S*, and M denotes a molecular mechanism), ΦMS (R denotes a radical mechanism), ΦMT (T indicates that a reactive state is a state other than S* and T(π–π*), most likely T(n–π*) and ΦRT have been decided, assuming that oxygen does not deactivate T(n–π*). The values are 5&for methanol, & &Φ_M^S(0.027) & &Φ_R^S(0.039) & &Φ_M^T(0.006) & &Φ_R^T(0.057) &for ethanol, & &Φ_M^S(0.043) & &Φ_R^S(0.067) & &Φ_M^T(0) & &Φ_R^T(0.019) &for n-propanol, & &Φ_M^S(0.030) & &Φ_R^S(0.036) & &Φ_M^T(0) & &Φ_M^T(0.022) &for isopropanol, & &Φ_M^S(0.03) & &Φ_R^S(0.058) & &Φ_M^T(0) & &Φ_R^T(0) The quenching constants of biacetyl on the fluorescence of acridine have been found to agree with the ones on the reaction at S* in all alcohols; the rate constants approximate diffusion controlled. In addition it has been confirmed by a flash method that biacetyl does not attack the T(π–π*) nor the semi-reduced acridine; this justifies the present method of analysis.