Abstract: Constructing donor-π-acceptor (D-π-A)-type molecular structures by employing a phenyl as the π-bridge to link donor (D) and acceptor (A) units has been recognized as an effective way to develop highly efficient red thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). However, flexible and relatively planar structures would open potential energy loss channels, such as nonradiative inactivation and aggregation-induced triplet quenching processes. Here, a bulky spiro-9,9′-bifluorene unit is first implemented to serve as a bridging group to construct a D-π-A molecule, enabling it to have higher overall rigidity, more sufficient steric hindrance, prolonged molecule length, and obvious aggregation-induced emission characteristics compared with a common phenyl bridge. As a result, energy dissipation routes are effectively relieved at the unimolecular level, together with mitigated interchromophore quenching, rendering a 100% photoluminescence quantum yield and a larger horizontal dipole ratio of 89%. The OLED based on 3-(2-(diphenylamino)-9,9′-spirobi[fluoren]-7-yl)dibenzo[a,c]phenazine-11,12-dicarbonitrile exhibits an excellent external quantum efficiency of nearly 37% at 612 nm, which is over 1.38-fold enhancement compared with the phenyl bridge-based control molecule. This work provides an instructive solution to design highly efficient red TADF emitters exploiting D-π-A-type molecular structures.
链接：https://onlinelibrary.wiley.com/doi/10.1002/adom.202300368
