Photoswitchable sensitization of porphyrin excited states

Light-driven molecular switches consisting of a porphyrin covalently linked to a fulgimide photochrome antenna have been prepared. Light absorbed by the cyclic form of the fulgimide is transferred to the porphyrin with >= 95% efficiency, generating the porphyrin first excited singlet state. Irradiation with visible light photoisomerizes the fulgimide to the open form, which does not absorb above 450 nm, and antenna function is abolished. UV irradiation converts the fulgimide back into the cyclic form, re-establishing efficient energy transfer. Photoisomerization of the fulgimide thus controls generation of the porphyrin excited state, which may then be used to carry out a variety of useful photochemical processes.