Fluorescence quenching study on electron transfer from certain amines to excited state triphenylpyrylium ion (TPP+)

The fluorescence quenching of excited singlet state of 2,4,6-triphenylpyrylium tetrafluoroborate (TPPBF4 or TPP+), a very good electron acceptor by amines were investigated in a acetonitrile solution using steady state technique. The bimolecular quenching rate constants lie in the range 2.11-10.26 x 10(10) M-1 s(-1). The driving force (Delta G(et)) for electron transfer process was calculated from the oxidation potential of amines and the reduction potential of TPP+. The observed k(q) values correlated well with the driving force for the electron transfer reactions. Aromatic amines show higher k(q) than aliphatic amines. From the oxidation potential of amines and the quenching rate constant values, a mechanism involving photoinduced electron transfer from amines to excited state TPP is suggested.