Effect of the solvent composition in methanol-pentane and methanol-acetonitrile mixtures on the quantum yield of proton transfer and reactions of transient species in the photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline

The photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline in binary MeOH-C₅H₁₂ and MeOH-MeCN mixtures was studied in dependence on the solvent composition by steady state and pulse photolysis. The photoinduced proton transfer from the N-H bond to the C(3) carbon atom of the heterocycle does not occur up to the methanol concentration of 0.25 (1 vol %) and 2.5 mol l⁻¹ (10 vol %) in the MeOH-C₅H₁₂ and MeOH-MeCN mixtures, respectively. The trends in the increase in the relative quantum yield of the proton transfer reaction (Q _mix/Q _MeOH) and the decay rate constant for 2,2,4,6-tetramethyl-2,3-dihydroquinoline, the product of the proton transfer reaction, in dependence on the composition differ significantly for these binary mixtures. The results are interpreted in terms of peculiarities in the aggregation of methanol and the distribution of the DHQ molecules and transient species in the mixtures.