White Light Emission via Dual Thermally Activated Delayed Fluorescence from a Single-Component Phenothiazines–Diphenyl Quinoline Conjugate

White light emission (WLE) via dual thermally activated delayed fluorescence (TADF) from a single-component-based organic system remains challenging as a result of the difficulty in design. Here, we introduce a conformational isomerization approach to achieve WLE from a twisted donor-acceptor (PTzQP1) that comprises two phenothiazines covalently attached to the 6,8-isomeric positions of 2,4-diphenyl quinoline via two C-N single bonds. Spectroscopic studies and quantum chemistry calculations revealed that PTzQP1 shows WLE via simultaneous blue TADF and orange TADF covering the visible range (420-800 nm) with a photoluminescence quantum yield of 45 ± 2% and Commission Internationale de l'Éclairage (CIE) coordinates of 0.30, 0.33. The dual TADF features with high rates of reverse intersystem crossing (k_RISC1 = 1.38 × 10⁷ ± 0.24 s^-1 and k_RISC2 = 5.04 × 10⁶ ± 0.32 s^-1) are realized as a result of the low singlet-triplet gaps (S1^EQ-T1^EQ = 0.04 eV and S1^QA-T1^QA = 0.05 eV) of the quasi-axial (QA) and quasi-equatorial (QE) conformers. This finding is expected to provide a new direction for designing high-energy-efficient WLE emitters.