Enhancing reverse intersystem crossing of intermolecular exciplexes by peripheral spatial-block for highly efficient narrowband blue OLEDs

Thermally activated delayed fluorescence (TADF) exciplexes, constituted of donor-acceptor moieties, have garnered mounting interest because of their promising potential to obtain high-performance electroluminescent devices. However, the moderate reverse intersystem crossing (RISC) of current reported exciplex systems and the lack of clear molecular design concepts to improve this situation have distinctly hindered the further use of exciplexes in organic light-emitting diodes (OLEDs). Herein, we conduct an exploration of exciplex systems founded upon [2,2]paracyclophane (PCP)-containing donor molecules and a triazine acceptor, which exhibit very fast RISC processes with a rate constant (kRISC) up to 8.3 × 106 s−1 benefiting from the efficient interactions between the donor and acceptor fragments induced by the peripheral spatial-blocking of PCP group. Utilizing these deep-blue exciplexes as hosts and a multiple resonance (MR) molecule as emitter, pure-blue narrowband OLEDs with CIE coordinates of (0.124, 0.137), a full-width at half-maximum (FWHM) of 23 nm, and a high external quantum efficiency (EQE) of around 30% are accessed. This study paves the way for developing blue OLEDs using PCP-based exciplex materials with an enhanced RISC process.