3.2: Singlet‐Triplet Splitting Energy Management via Acceptor Substitution: Complanation Molecular Design for Deep‐Blue Thermally Activated Delayed Fluorescent Organic Light‐Emitting Diodes. (28th November 2018)

• Record Type: Journal Article
• Authors: Cai, Xinyi; Gao, Bin; Li, Xiang-long; Su, Shi-Jian
• Is Part Of: Digest of technical papers. Volume 49(2018)Supplement 1
• Page Start: 16
• Page End: 21
• Publication Date: 2018-11-28
• Subjects: deep-blue -- organic light-emitting diode -- thermally activated delayed fluorescent -- organic electronics; Information display systems -- Congresses; 621.3815422
• DOI: 10.1002/sdtp.12627
• Languages: English
• ISSNs: 0097-966X

Abstract

Abstract : Hardly reached balance between weak intramolecular‐charge‐transfer (ICT) and small singlet‐triplet splitting energy (ΔEST ) for reverse intersystem crossing (RISC) from non‐emissive triplet state to radiative singlet state impedes the realization of deep‐blue thermally activated delayed fluorescent (TADF) materials. By discarding twisted‐ICT framework for flattened molecular backbone and introducing strong acceptor possessing n‐π* transition character, blue‐shifted color, large radiative rate (kF ) and small ΔEST are achieved simultaneously. Six molecules with 9, 9‐dimethyl‐10‐phenyl‐9, 10‐dihydroacridine (i‐DMAc) donor were synthesized and investigated. Coinciding with time‐dependent density function theory (TD‐DFT), the reduced dihedral angles between donor (D) and acceptor (A) weaken ICT from dispersed charge density and capacitate large kF from increased FMOs overlap. Despite the separated highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) population, the intercalation of phenyl‐bridges between D‐A increases kF but significantly lowers the locally triplet excited state, indicating small HOMO and LUMO overlap is not sufficient but necessary condition for reduced ΔEST . Integrating short conjugation length and carbonyl or 1, 3, 5‐triazine acceptors into the complanation molecules, deep‐blue TADF‐OLEDs demonstrated maximum external quantum efficiencies of 11.5% and 10.9% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.16, 0.09) and (0.15, 0.11), respectively, which is quite close to the stringent National Television System Committee (NTSC) blue standard.