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Spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) is of particular interest for preparation of heavy atom-free triplet photosensitizers. Up to now, examples for SOCT-ISC dyads are limited and electron donor/acceptor SOCT-ISC dyads showing strong visible-light harvesting are rare. Herein, we studied the photophysics of a series of Bodipy-anthracene (BDP-An) compact dyads, especially the triplet state electron spin dynamics with the time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The electronic coupling matrix elements ( V DA * ) between the 1 CT (charge transfer) state and 1 LE (locally excited) state are in the range 773–1545 cm –1 . For one dyad, we observed three triplet states simultaneously with TREPR, that is triplet states confined on the anthracene ( 3 An) and the Bodipy ( 3 BDP) moieties as well as a 3 CT state. Based on the electron spin polarization of these three triplet states and the optical experiments, the SOCT-ISC mechanism is confirmed and the radical pair-ISC mechanism as the main ISC channel was excluded. Triplet–triplet annihilation-induced delayed fluorescence was observed for the dyads, which is rare for Bodipy fluorophores.
Wang et al. (Thu,) studied this question.