Inclusion co-crystals based on Tröger's base molecular box for thermally activated delayed fluorescence.

Abstract

Designing thermally activated delayed fluorescence (TADF) emitters via a non-covalent through-space charge transfer (TSCT) is challenging, requiring a delicate balance between molecular geometries and electronic states. Herein, we present an inclusion co-crystal (ICC) strategy to achieve efficient TADF using non-covalent TSCT approach by supramolecularly engineered molecular box-based confined environments that provide sufficient binding ability to aromatic guests. Tröger's base-derived molecular boxes (TB[2]) incorporating mesomeric (meso-TB[2]) and racemic (race-TB[2]) species are designed as electron-rich hosts, which can selectively encapsulate 1,3,5-benzenetricarbonitrile (BTN) and 1,2,4,5-tetra-cyanobenzene (TCNB) among six electron-withdrawing cyanobenzenes, forming three 1:1 binary inclusion CT co-crystals through the synergism of multiple non-covalent interactions. The BTN@meso-TB[2] and BTN@race-TB[2] co-crystals exhibit tunable yellow-green and bright cyan TADF emission due to strong host-guest complexation and weak TSCT interactions. Conversely, TCNB@meso-TB[2] is almost no luminescent as the strong intermolecular CT interaction promotes nonradiative decay processes. The present work offers an efficient strategy for designing TADF emitters by balancing the strength of CT and host-guest complexation.