붕소 기반 열활성 지연 형광 물질의 계산 및 실험 연구

Abstract

1. Experimental and computational study on Multiple-resonance (MR) TADF including carborane The unique structure of Multiple-Resonance thermally activated delayed fluorescence (MR-TADF) emitters, with the HOMO and LUMO localized on different atoms, results in short-range charge transfer (SRCT) transitions, leading to narrowband emissions. This implies that the electronic coupling between the carborane and the B,N-doped MR-emitting core will differ from that observed in conventional caroborane luminophores. Furthermore, introducing carborane into either the dominant HOMO or LUMO position may have distinct effects on the excited-state properties. To investigate the impact of carborane on the photophysical and electroluminescent properties of MR-TADF emitters, we present two carborane-appended MR-TADF emitters, 2CB-BuDABNA (1) and 3CB-BuDABNA (2), along with a reference emitter, BuDABNA (3). Our findings demonstrate that the emission characteristics of the MR-emitting core are retained and can be fine-tuned by the carborane substitution, without inducing charge transfer (CT) emission.

2 Computational study on Donor-Acceptor TADF The photophysical properties of three donor-acceptor-type TADF emitters (PXZBAO (1), PXZBTO (2), and PXZBPO (3)) are herein investigated using time-dependent density functional theory (TDDFT) calculations. Photoluminescence experiments revealed that the emitters exhibit the red (1) to orange (3) emissions with an increase in the π-expansion in the BCO acceptors. This unusual emission color shift can be explained by the LUMO energy level of TADF emitter, which is attributed to the strength of local aromaticity for the π-expanded unit of BCO acceptors, for which the squared effective ring electron density (ERED2) was evaluated as a descriptor for the local aromaticity of a ring over all Kekulé structures based on WFRT analysis. Also, To provide photophysical insights of their TADF processes, we evaluated the spin orbit coupling matrix elements (SOCME) between the S1 and Tn(n = 1 and 2) excited states. The SOCME between the S1 and T2 states is much larger than that between the corresponding S1 and T1 states for all compounds, as expected by El-Sayed rule.