Abstract
The effect of thienyl substitution on the intersystem crossing (ISC) of a few arenes was studied using steady state and time-resolved transient absorption and emission spectroscopies, as well as DFT/TDDFT computations. We found that the phenyl and thienyl substituents generally induce red-shifted absorptions for the chromophores, and the DFT/TDDFT computations show that the red-shifted absorption and emission are due to the increased HOMO and the reduced LUMO energy levels. Nanosecond transient absorption spectra indicate the formation of a triplet state, the triplet state lifetime is up to 282 μs, and the singlet oxygen quantum yields (ΦΔ) are up to 60%. DFT/TDDFT computations indicate that introducing the thienyl substituent alters the relative singlet/triplet excited state energy levels, and the energy level-matched S1/T2 states are responsible for the enhanced ISC of the thienyl compounds. This information is useful for the design of heavy atom-free triplet photosensitizers and for the study of the fundamental photochemistry of organic compounds.
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Acknowledgments
We thank the NSFC (21473020, 21673031, 21761142005, 21603021, 21421005, and 21273028), the State Key Laboratory of Fine Chemicals (ZYTS201801), and the Fundamental Research Funds for the Central Universities (Grants DUT16TD25, DUT15ZD224, and DUT2016TB12) for financial support.
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Sadiq, F., Zhao, J., Hussain, M. et al. Effect of thiophene substitution on the intersystem crossing of arene photosensitizers. Photochem Photobiol Sci 17, 1794–1803 (2018). https://doi.org/10.1039/c8pp00230d
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DOI: https://doi.org/10.1039/c8pp00230d