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Published on: June 10, 2021
Conformationally controlled thermally activated delayed fluorescence in a nitro-substituted phenothiazine: a combined
Lewei Bian1, Yi Shen1, Qiongxiang Zhou1
1School of Chemistry and Chemical Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, PR China.
Abstract:
Thermally activated delayed fluorescence (TADF) can convert triplet excitations into emissive singlet states through reverse intersystem crossing (rISC), but nitro groups usually promote nonradiative decay. Here, the photophysics of 4'-nitro-10-phenylphenothiazine (NPh-PTZ) was investigated by steady-state and time-resolved spectroscopy, including nanosecond transient absorption and temperature-dependent photoluminescence, together with (TD)DFT calculations. In cyclohexane, NPh-PTZ shows a prompt and an oxygen-sensitive delayed emission component with overlapping spectra, consistent with TADF; its measured fluorescence quantum yield is 0.015. Calculations suggest distinct roles for the axial and equatorial conformations: the former has stronger calculated spin-orbit coupling, whereas the latter has a smaller calculated singlet-triplet gap. Delayed emission is suppressed in the more polar solvent 1,4-dioxane. These results establish the photophysical behavior of NPh-PTZ and motivate comparative studies of structurally related nitro-substituted phenothiazines.
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