Synthesis and properties of a photochromic perinaphthothioindigo conjugated with two porphyrins

Abstract

In this study, we synthesized a new porphyrin-perinaphthothioindigo composite in which two porphyrins are connected to a perinaphthothioindigo dye through ethynyl linkages. The UV-vis absorption spectra of the composite showed an absorption peak originating from the trans-isomer at around 730 nm. Upon photoirradiation at 760 nm, the intensity of this absorption decreased with increasing absorption of the cis-isomer around 500 nm. The HOMO–LUMO absorption of the cis-isomer is blue-shifted by ˜230 nm compared to that of trans-isomer due to lack of [Formula: see text] conjugation. The shift by 230 nm is 100 nm larger than that observed for the monoporphyrin-substituted compound, indicating the expansion of [Formula: see text] conjugation by the additional porphyrin.