Charge-Transfer Quenching of Singlet Oxygen O2(1¢g) by Amines and Aromatic

The quenching rate constants of singlet oxygen O2(1¢g) luminescence at 1.27 ím by 29 amines and aromatic hydrocarbons were measured in acetonitrile and benzene. Quenching occurs via reversible charge transfer with the formation of an exciplex with a partial (ä 0.2 esu) electron transfer. An estimate of the intersystem-crossing rate constant for the exciplex of ca. 1010 s-1 is obtained, and a modest decrease with increasing exciplex energy is noted. The data predict and it is confirmed that charge transfer plays a significant role in the nonradiative decay of singlet oxygen in solvents as difficult to oxidize as toluene-d8 and mesitylene. It is also confirmed that N,N,N′,N′-tetramethyl-p-phenylene diamine quenches O2(1¢g) nearly exclusively by full electron transfer in D2O, but electron transfer is not observed in other solvents