Bodipy-Phenylethynyl Anthracene Dyad: Spin-Orbit Charge Transfer Intersystem Crossing and Triplet Excited-State Equilibrium

Spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) is a promising method to design heavy atom-free triplet photosensitizers (PSs). Herein, a new organic triplet PS, BDP-An (Bodipy-phenylethynyl anthracene dyad) has been synthesized and studied. In polar solvents, charge transfer (CT) emission band was observed, and the singlet oxygen quantum yield (ΦΔ) is up to 95%. From femtosecond transient absorption (fs TA) spectra, SOCT-ISC mechanism was verified, the charge separation (CS) time takes1.6 ps, the lifetime of charge recombination (CR) is 3.8 ns, moreover the triplet state of phenylethynyl anthracene was also observed. In nanosecond transient absorption (ns TA) spectra, long-lived triplet states (τT =108 μs) were observed, which are delocalized on both parts of the dyad, i.e. there is a triplet excited-state equilibrium. This is the first report on the triplet excited-state equilibrium observed in an electron donor/acceptor dyad showing SOCT-ISC. With BDP-An as the triplet donor and perylene as the triplet acceptor, triplet-triplet annihilation upconversion (TTA UC) was performed, the upconversion quantum yield was up to 18.9%, and the lifetime of TTA-based delayed fluorescence was determined as 70.8 μs.

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