Deep-blue emission and thermally activated delayed fluorescence via Dimroth rearrangement of tris(triazolo)triazines

Abstract

Three luminescent donor–acceptor compounds were prepared based on the Dimroth rearrangement of tris(triazolo)triazines (TTT). In comparison to the non-rearranged TTT isomers, the Dimroth isomer (TTTD) exhibits a substantial blue-shift in emission while maintaining thermally activated delayed fluorescence (TADF) properties. Out of the series of emitters, TTTD-3HMAT exhibits deepest blue emission with CIE(x, y) < (0.16, 0.03) and unity quantum yield in toluene, a narrower emission band, and highest two-photon cross-section of 1001 GM owing to the nature of the planarized HMAT donor. TTTD-3tBu also exhibits unity quantum yield and deep-blue emission with CIE(x, y) < (0.16, 0.05) in toluene. Finally, TTTD-3ACR exhibits TADF with blue-shifted emission and prolonged delayed lifetime due to the slightly larger ΔE_ST of 0.26 eV in comparison to the non-rearranged isomer. Overall, this work demonstrates a practical strategy to convert TTT-based donor–acceptor materials to their Dimroth isomers, opening the door to deeper blue-emitting TADF materials with TTT-type acceptors.