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The current investigation demonstrates highly efficient photochemical upconversion (UC) where a long-lived Zr( iv ) ligand-to-metal charge transfer (LMCT) complex serves as a triplet photosensitizer in concert with well-established 9,10-diphenylanthracene (DPA) along with newly conceived DPA–carbazole based acceptors/annihilators in THF solutions. The initial dynamic triplet–triplet energy transfer (TTET) processes (Δ G ∼ −0.19 eV) featured very large Stern–Volmer quenching constants ( K SV ) approaching or achieving 10 5 M −1 with bimolecular rate constants between 2 and 3 × 10 8 M −1 s −1 as ascertained using static and transient spectroscopic techniques. Both the TTET and subsequent triplet–triplet annihilation (TTA) processes were verified and throughly investigated using transient absorption spectroscopy. The Stern–Volmer metrics support 95% quenching of the Zr( iv ) photosensitizer using modest concentrations (0.25 mM) of the various acceptor/annihilators, where no aggregation took place between any of the chromophores in THF. Each of the upconverting formulations operated with continuous-wave linear incident power dependence ( λ ex = 514.5 nm) down to ultralow excitation power densities under optimized experimental conditions. Impressive record-setting η UC values ranging from 31.7% to 42.7% were achieved under excitation conditions (13 mW cm −2 ) below that of solar flux integrated across the Zr( iv ) photosensitizer's absorption band (26.7 mW cm −2 ). This study illustrates the importance of supporting the continued development and discovery of molecular-based triplet photosensitizers based on earth-abundant metals.
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Triplet photodynamic and up-conversion luminescence in donor–acceptor dyads with slip-stacked vs. co-facial arrangement
The design/synthesis and characterization of organic donor–acceptor (D–A) dyads can provide precious data allowing to improve the efficiency of classical photo-induced bimolecular interactions/processes. In this report, two novel triplet D–A dyads (4 and 5) were synthesized and fully characterized. While the optical absorption and emission profiles of these new systems exhibit similar spectral structures as that of the triplet donor/sensitizer quinoidal thioamide (QDN), the transient absorption (TA) spectra of these two dyads produced new features that can be associated with triplet transients and charge transfer species. However, the kinetics of the excited-state processes/dynamics is significantly influenced by the geometrical arrangement(s) of donor/acceptor chromophores. Further analysis of the TA data suggests that the dyad with slip-stack geometry (4) is less effective in undergoing both intra- and inter-dyad triplet energy transfer than the dyad with co-facial geometry (5). Subsequently, triplet sensitization of 9,10-diphenylanthracene (DPA) using both dyads led to upconverted photoluminescence via triplet–triplet annihilation of DPA triplet transients. But, it was found that a maximum upconversion quantum yield could be achieved at a low power density using the co-facial type dyad 5. Altogether, these results provide valuable guidance in the design of triplet donor–acceptor dyads, which could be used for light-harvesting/modulation applications.
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- Award ID(s):
- 2211296
- PAR ID:
- 10329600
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 10
- Issue:
- 18
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 7093 to 7102
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1TC05122A
