Magnetic field effect on photoinduced electron transfer between dibenzo[a,c]phenazine and different amines in acetonitrile - water mixture

Abstract

Unlike the simple phenazine (PZ) molecule, one of its derivatives, dibenzo[a,c]phenazine (DBPZ) forms a charge-transfer complex in the triplet state ((ECT)-E-3) with different amines, e.g., N,N-dimethylaniline (DMA), 4,4'-bis(dimethylamino)diphenylmethane (DMDPM), and triethylamine (TEA). Formation of the (ECT)-E-3 and radical ion pairs (RIPs) due to electron transfer is identified by laser flash photolysis. The RIPs are much more abundant in the cases of DMA and DMDPM rather than in TEA. Interestingly, a prominent magnetic field effect (MFE) is observed in both the cases of (ECT)-E-3 and RIPs in homogeneous acetonitrile-water (MeCN/H2O) mixtures. This rare observation of the (ECT)-E-3 and MFE in non-viscous medium could be explained by considering the extended planar structure of DBPZ and inter-radical hydrogen bonding, mediated by the intervening water molecules. The magnetic field behavior is consistent with the hyperfine mechanism; however, the low B-1/2 value for DBPZ-TEA system is ascribed to fast electron exchange due to the close proximity of the corresponding radical ions.