Photoinduced electron transfer in donor-acceptor aryl dyads based on N,N,N'N'-tetramethyl-p-phenylenediamine as the donor

The solution-phase photophysics of several electron transfer donor-donor-acceptor assemblies (2 and 3) incorporating N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) derivatized with piperazyl, piperidyl, morpholinyl, and prolinyl groups in the 1- and 4-positions as donors and N,N-dimethyl-4-nitroaniline, anthraquinone, 3,5-dinitrobenzene, and 2,4-dinitrobenzene as accepters are described. In measurements of the model compounds 1 incorporating only the donor moieties, flash photolysis generated the radical cation and triplet species of TMPD as evidenced by the superposition of their transient absorption spectra. Lifetime measurements reveal, as well, a delayed fluorescence derived from triplet-triplet annihilation. In 2 and 3, electron transfer from the lowest excited singlet state of TMPD to the various accepters was established by the following: (1) steady-state emission measurements where the fluorescence of TMPD was drastically quenched by the acceptor, (2) the transient absorption spectra of the radical cation and radical anion of the donor and acceptor, and (3) a single-exponential decay profile in 2 and 3, superseding the biexponential decay observed in the model donor.