Visible-Light-Harvesting Triphenylamine Ethynyl C60-BODIPY Dyads as Heavy-Atom-Free Organic Triplet Photosensitizers for Triplet-Triplet Annihilation Upconversion

C-60-boron dipyrromethene (BODIPY) dyads (C-1 and C-2) were prepared as heavy-atom-free organic triplet photosensitizers for triplet-triplet annihilation (TTA) based upconversion. BODIPY-C equivalent to C-triphenylamine chromophores were used as the light-harvesting antennas and C-60 was used as the singlet energy acceptor and the spin convertor to facilitate the intersystem crossing (ISC) of the dyads from the singlet excited state to the triplet excited state. The C-60 dyads strongly absorb visible light (molar extinction coefficients of up to 118800m 1cm(-1) at 539 nm) and have a long-lived triplet excited state (T= 32.3 ms). The photophysical properties of the C-60-dyads were studied with steady-state and time-resolved spectroscopy. Photoexcitation of the dyad with visible light produces firstly the singlet excited state of the antenna, then the singlet excited state of the C-60 unit through intramolecular energy transfer. In turn, the triplet ex-cited state of the C-60 unit will be populated because of the intrinsic ISC property of C-60. As a proof of concept, the dyads were used as heavyatom- free organic triplet photosensitizers for TTA-based upconversion.