Long-lived photoproduced radical ions in tetrathiafulvalenes covalently tethered to C-60

C-60 or [60]fullerene, a reversible one- to six-electron acceptor with mode rate first electron. affinity, was covalently linked, via a 1,3-dipolar add ition reaction using azomethine ylides and two flexible insulating sigma-ch ains of different lengths, to a tetrathioalkyltetrathiafulvalene, a reversi ble one- to two-electron donor with low first ionization potential, yieldin g molecules 1 and 2. The electrochemical oxidation and reduction waves are the same as those of the separate components; UV-VIS spectra indicate no ap preciable charge transfer in the ground state between the donor and accepto r moieties of these D-sigma-A systems 1 and 2: there is only a weak shoulde r at 800 nm (epsilon approximate to 200 L mol(-1) cm(-1)), which could be t he intervalence transfer band. These same molecules, as well as their donor and acceptor components taken separately, were electrochemically oxidized/reduced in liquid solutions, an d also irradiated with laser light in low-temperature glasses. The electron paramagnetic resonance (EPR) spectra revealed photoexcited electron transf er at 77 K, with resulting S = 1/2 radical cation and radical anion states. In a glass at 77 K these radical signals survive a long time (up to severa l days) after the end of light irradiation. This may be separately solvated pairs of long-lived radicals D.+-sigma-A and D-sigma-A(.-) or, less likely , a long-lived excited-state zwitterionic biradical D.+-sigma-A(.-) with in creasing temperature and the onset of diffusional motion, the EPR signals d isappear.