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

Abstract

C60‐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≡C‐triphenylamine chromophores were used as the light‐harvesting antennas and C60 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 C60 dyads strongly absorb visible light (molar extinction coefficients of up to 118800 M−1 cm−1 at 539 nm) and have a long‐lived triplet excited state (τT=32.3 μs). The photophysical properties of the C60‐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 C60 unit through intramolecular energy transfer. In turn, the triplet excited state of the C60 unit will be populated because of the intrinsic ISC property of C60. As a proof of concept, the dyads were used as heavy‐atom‐free organic triplet photosensitizers for TTA‐based upconversion.

Broadband Visible‐Light‐Harvesting trans‐Bis(alkylphosphine) Platinum(II)‐Alkynyl Complexes with Singlet Energy Transfer between BODIPY and Naphthalene Diimide Ligands

“…This long-lived delayed fluorescence confirmed the upconverted fluorescence emission. [59,66,[83][84][85][86] Similar results were observed for Pt-2 ( Figures S36 and S39 in the Supporting Information).…”

“…Both the singlet energy transfer and the triplet energy transfer can produce the triplet excited state of NDI, because the NDI unit is a "spin converter", that is, the p-conjugated core of NDI is directly attached to the Pt II coordination center, thus, efficient intersystem crossing (ISC) is expected for this coordination moiety. [27,[58][59][60][61]…”

Transition-Metal Complexes for Triplet–Triplet Annihilation-Based Energy Upconversion

“…Recently, lightharvesting fullerene dyads as organic triplet sensitizers for TTA upconversion were reported. Some examples are listed as follows: OS-20 and OS-21 [91], OS-22 and OS-23 [92], OS-24 and OS-25 [93], and OS-26 and OS-27 [94]. …”

Fullerene as Spin Converter

“…Upconversion systems are used in photovoltaics, photocatalysis, nonlinear optics, and luminescent molecular probes [87]. To facilitate upconversion one or two methods are deployed for such as rare-earth materials or two-photon absorption fluorescent dyes [88,89].…”

“…The previously reported triplet photosensitizers are usually transition-metal complexes, such as PtII/PdII porphyrin complexes, IrIII/RuII complexes, or heavy-atom derivatives of organic fluorophores since ISC is facilitated by the heavy atom spin-orbital coupling effect [91][92][93]. Designing these systems via chemical derivatization of a known heavy atom-free organic triplet photosensitizer is not a decisive way to prepare new organic triplet photosensitizers because even simple derivatization of the chromophore may diminishISC [25,26].Heavyatom-freeorganictriplet photosensitizers with absorption in visible range are highly desired and remained rare for TTA upconversion system (Figure 4) [36,87,94]. An intramolecular spin converter is used to overcome the aforementioned challenges.…”