Conformational Effect of Catechol-Terephthalonitrile Emitters Leading to Ambient Violet Phosphorescence
Raktim Deka, Suvendu S. Dey, Manoj Upadhyay, Sakshi Chawla, Debdas Ray
Abstract
Organic ambient violet phosphorescent (AVP) materials are of great interest due to their involvement of high energy and longer-lived triplet excitons. Here, we show three fused ring functionalized donor–acceptor–donor (D–A–D/D–A–D′) emitters ( BPT1–BPT3 ), in which two catechol-based donors (3,4-dihydroxybenzophenone, catechol, or 3,5-di tert -butylcatechol) are covalently fused to the terephthalonitrile acceptor via four O–C single bonds. Spectroscopic analysis revealed that all the molecules show AVP (∼390–394 nm, τ AVP = 73–101 μs) with phosphorescence quantum yields (ϕ P ) of 1.8–27.4% due to low singlet–triplet gaps (0.036–0.046 eV) and conformational effects. BPT3 with bulky tert -butyl groups increases AVP (ϕ P = 27.4%). Quantum chemistry calculations reveal flat (F1) and twisted (F2) conformers (ground state) with a low energy difference (∼4–5 kcal/mol) for all molecules; the F1 conformer is responsible for efficient AVP, while weak blue thermally activated delayed fluorescence with longer-lived delayed components is realized from the F2 conformer. This approach may provide important clues for the design of high-energy organic phosphorescent materials.