Theoretical investigations of the auxochromic effect on novel thermally activated delayed fluorescence (TADF) anthracene derivatives

Abstract

Thermally active delayed fluorescence (TADF) of experimentally synthesized anthracene derivatives is studied. The studied compounds are named as 9-cyano-10-diphenylamino-anthracene (Cy-Anth-1), 9-(N-carbazolyl)-10-cyanoanthracene (Cy-Anth-2), 10-(benzofuro[2,3-b] pyridin-6-yl)-N, N-diphenylanthracen-9-amine (Benzo4-Anth-1), 6-(10-(9H-carbazol-9-yl) anthracen-9-yl) benzofuro[2,3-b] pyridine (Benzo4-Anth-2). Chemical characterization and the structure-TADF relationship were determined using the DFT and TD-DFT techniques. The analysis of frontier molecular orbitals and molecular electrostatic potential indicated that the Benzo4-Anth-1 derivative is a good candidate for TADF due to its spatially separated donor and acceptor groups. The energy gap ΔE (S₁-T₂) of Cy-Anth-1, Cy-Anth-2, Benzo4-Anth-1, and Benzo4-Anth-2 is 0.0057, -0.026, 0.0528, and -0.0635 eV, respectively. While ΔE (T₂-T₁) for Cy-Anth-1, Cy-Anth-2, Benzo4-Anth-1, and Benzo4-Anth-2 is 0.759, 0.790, 1.019, and 0.926 eV, respectively. Donor (D = (N, N-diphenyl)) and acceptor (A = (10-(benzofuro[2,3-b] pyridin-6-yl)) in D-π-A system enhances the ΔE (S₁-S₀) up to 2.837 eV and decreases ΔE (S₁-T₂) to -0.0635 eV by making it good TADF material. Thermodynamic investigation revealed that the rise in temperature from 50–500 K, CV, CP, internal energy (U), enthalpy (H), entropy (S), and ln (Q) increases, but Gibbs free energy (G) decreases.