Insights into the Efficient Intersystem Crossing of Bodipy-Anthracene Compact Dyads with Steady-State and Time-Resolved Optical/Magnetic Spectroscopies and Observation of the Delayed Fluorescence

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 (CT)-C-1 (charge transfer) state and (LE)-L-1 (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 ((BDP)-B-3) moieties as well as a (CT)-C-3 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