CHARGE-TRANSFER QUENCHING OF SINGLET OXYGEN O-2((1)DELTA(G)) BY AMINES AND AROMATIC-HYDROCARBONS

The quenching rate constants of singlet oxygen O-2((1)Delta(g)) lumine scence at 1.27 mu m by 29 amines and aromatic hydrocarbons were measur ed in acetonitrile and benzene. Quenching occurs via reversible charge transfer with the formation of an exciplex with a partial (delta appr oximate to 0.2 esu) electron transfer. An estimate of the intersystem- crossing rate constant for the exciplex of ca. 10(10) s(-1) is obtaine d, and a modest decrease with increasing exciplex energy is noted. The data predict and it is confirmed that charge transfer plays a signifi cant role in the nonradiative decay of singlet oxygen in solvents as d ifficult to oxidize as toluene-d(8) and mesitylene. It is also confirm ed that N,N,N',N'-tetramethyl-p-phenylene diamine quenches O-2((1)Delt a(g)) nearly exclusively by full electron transfer in D2O, but electro n transfer is not observed in other solvents.