Twisted organic TADF triads based on a diindolocarbazole donor for efficient photoisomerization of stilbene and photo-arylation of heteroarenes

Abstract

Herein we report the design and synthesis of twisted organic thermally activated delayed fluorescence (TADF) triads DI-PF and DI-PI based on diindolocarbazole (DI) as the donor and dibenzo[a,c]phenazine (PF) and phenanthro[9,10-d]imidazole (PI) as the acceptors. The triads DI-PF and DI-PI showed strong charge transfer bands at 590 nm with a 196 nm Stokes shift and 519 nm with a 126 nm Stokes shift, respectively. For effective TADF properties, theoretical and experimental studies revealed small to relatively modest ΔE_ST of 0.01 eV and 0.37 eV for DI-PF and DI-PI, respectively. Transient photoluminescence decay profiles of DI-PF and DI-PI indicated shorter prompt components of 40 ns and 13.38 ns, respectively, and longer delayed components of 6.15 μs and 2.05 μs, respectively, confirming the TADF nature for both compounds. The sufficiently long-lived lifetime components render them suitable for participation in organic photocatalysis. Furthermore, both compounds showed tunable and suitable excited state redox potentials for electron transfer photocatalysis. Accordingly, the triads DI-PF and DI-PI have been employed as photocatalysts in E to Z photoisomerization of stilbene based on their suitable triplet energy levels with reasonably good yields of up to 66% for isomerization products and in arylation of various heteroarenes with up to 86% yields for heteroarene photoarylation products.