The synthesis and application of thionated donor-acceptor chromophores as triplet photosensitizers Anna Wright, Benson M. Kariuki, Yi-Lin Wu Cardiff University, UK Triplet photosensitisers (PSs), where excitation followed by intersystem crossing (ISC) generate long-lived triplet species that are necessary for applications such as photocatalysis, [1,2] photon up conversion [3] and photodynamic therapy. [4] In recent years, organic PSs have seen reinvigorated attention owing to their atomic abundance and versatility in comparison to their inorganic counterparts. [2,5,6] However, triplet formation in organic PSs often lacks predictability and requires complex structural design. Based on this, our research aims include the development of a renovated molecular design for organic PSs and to understand their mechanism of triplet formation. To achieve our aims, we have exploited the underutilised thiocarbonyl photochemistry to generate a series of donor-acceptor (D-A) triplet-forming chromophores with strong visible-light absorption ( ε ≥ 1.8 x10 4 M -1 cm -1 ) [7] and fast ISC from 1 (n-π*) to 3 (π-π*) as determined by singlet oxygen formation (Φ Δ ≥ 52 %) [7] and DFT calculations. [4,8,9] The D and A moieties allow for the PSs to participate in both oxidative and reductive electron transfer reactions, where we have demonstrated that our PSs can be used as electrochemically amphoteric photocatalysts. And the D-A structural design mildly decouples the mechanisms of ISC and optical absorption, allowing for the modification of the later without affecting triplet formation. Where we have tuned our PSs through structural modification to outcompete the traditional inorganic photosensitiser Ru(bpy) 3 Cl 2 in both energy and electron transfer reactions. In conclusion, we have established a structural design for sustainable organic PSs with predictable properties that have been tuned to increase triplet efficiency. Their success as electrochemically amphoteric photosensitisers suggests that further studies will uncover the full potential of this novel PSs design. This has led us to develop new chromophores with the same design motifs that also pose as promising organic PSs for sustainable photocatalysis and further applications. References 1. N. A. Romero, D. A. Nicewicz, Chem. Rev. 2016 , 116 , 10075–10166. 2. C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev. 2013 , 113 , 5322–5363. 3. L. Huang, E. Kakadiaris, T. Vaneckova, K. Huang, M. Vaculovicova, G. Han, Biomaterials 2019 , 201 , 77–86. 4. J. Tang, L. Wang, A. Loredo, C. Cole, H. Xiao, Chem. Sci. 2020 , 11 , 6701–6708. 5. K. Behm, R. D. McIntosh, ChemPlusChem 2020 , 85 , 2611–2618. 6. S. Ye, E. H. Song, Q. Y. Zhang, Adv. Sci. 2016 , 3 , 1600302. 7. A. I. Wright, B. M. Kariuki, Y. L. Wu, Eur. J. Org. Chem. 202 , 2021 , 4647–4652. 8. J. R. Palmer, K. A. Wells, J. E. Yarnell, J. M. Favale, F. N. Castellano, J. Phys. Chem. Lett. 2020 , 11 , 5092–5099. 9. A. Maciejewski, R. P. Steer, Chem. Rev. 1993 , 93 , 67–98.
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