Caging of phenazine by 4,4′-bis(dimethylamino)diphenylmethane: a comparative study with phenazine-N,N-dimethylaniline

Phenazine (PZ) forms exciplexes with the aromatic amines, N,N-dimethylaniline (DMA) and 4,4′-bis(dimethylamino)diphenylmethane (DMDPM), of which the latter may be considered as two DMA units linked by a methylene group. Laser flash photolysis has been used to identify the radical ion species that are formed by the photoinduced electron transfer from the amines to PZ. The much higher absorbance of the DMDPM radical cation compared to the DMA radical cation suggests that in DMDPM both the DMA units participate in the electron transfer process. Thus we can visualize that in the charge transfer complex, DMDPM acts like a tweezer and cages the PZ molecule. A careful study of the transient absorption spectra of the amine radical cations in different hydroxylic and nonhydroxylic solvents of comparable polarity provides further evidence for this caging.