Photonic Control of Photoinduced Electron Transfer via Switching of Redox Potentials in a Photochromic Moiety

A porphyrin (P) has been covalently linked to a photochromic dihydroindolizine moiety (DHI) to form a P-DHI dyad. When the dihydroindolizine is in its closed, spirocyclic form (DHIc), the photophysics of the attached porphyrin are unaffected. Irradiation with UV light opens the photochromic moiety to the betaine form (DHIo), which has a significantly higher reduction potential than DHIc. Light absorption by the porphyrin moiety of P-DHIo is followed by rapid (50 ps) photoinduced electron transfer to yield the P.+-DHIo(.-) charge-seperated state. This state recombines in 2.9 ps to give the ground state. Irradiation of P-DHIo with light at wavelengths > 590 nm induces photoisomerization back to P-DHIc. Thermal closing can also be achieved. Thus, light is used to switch photoinduced electron transfer on or off. These principles may be useful in the design of molecular optoelectronic devices.