Role of the Intramolecular-Locking Strategy in the Construction of Organic Thermally Activated Delayed Fluorescence Emitters with Rotation-Restricted Acceptors

摘要

Constructing highly twisted and rigid donor–acceptor systems is importantfor obtaining highly efficient thermally activated delayed fluorescence (TADF)emitters. In the traditional framework of structurally twisted charge-transferTADF molecular design, increasing the rigidity of the molecule throughconstructing rigid groups guarantees the minimized overlap integral betweentheir highest occupied molecular orbitals and lowest unoccupied molecularorbitals for a small singlet and triplet energy gap, which ensures efficientreverse intersystem crossing. Increasing rigidity also prevents the moleculefrom deforming when in the excited state, effectively suppresses nonradiativeenergy dissipation, and improves the photoluminescence quantumyield. As one of the important fragments for TADF emitters, the developmentof acceptor units with rigid structure deserves in-depth understanding.Therefore, this review offers a comprehensive summary of the designs anddevelopments of rigid TADF acceptors with “intramolecular locks” includingcovalent bonds, coordination bonds, and non-covalent bonds, via the intramolecular-locking strategy. The mechanism of TADF based on results fromdensity functional theory is also described. Finally, the role of the intramolecular-locking strategy in the construction of pure organic TADF emitters withrotation-restricted acceptors and in improving the efficiency of all-organicTADF-based organic light-emitting diodes is discussed.