Photoisomerization and optical behavior study of a subphthalocyanine-bisazobenzene-subphthalocyanine triad with visible-light response

The synthesis and characterization of a subphthalocyanine-bisazobenzene-subphthalocyanine triad are reported. Evidence for E,E <-> E,Z isomerization of the linking bisazobenzene moiety is observed in the optical and NMR spectra when the subphthalocyanine rings are used as light-harvesting units. Electronic coupling and communication between the two para-azo units decrease the photoisomerization efficiency. An obvious decrease in fluorescence intensity is observed on moving from E -> Z with a recovery in intensity observed on moving back from Z -> E that can be attributed to a change in the rate of non-radiative decay.