The Role of Solvent-Molecule Hydrogen Bonding in Polyphenylfluorene-Carbazole Systems: Tuning Molecular Packing Patterns, Crystal Morphologies, and Solid-State Luminescence Efficiency

Abstract

The aggregation-caused quenching (ACQ) phenomenon of organic luminescent molecules in the solid state critically limits the development of organic light-emitting devices. The crystal-induced luminescence or/and stability enhancement (CLoSE) effect, characterized by enhanced luminescence efficiency upon the transition from the amorphous to the crystalline state, offers an effective solution. Herein, we investigated the influence of solvent-molecule hydrogen bonding on molecular self-assembly and the CLoSE effect. The 3-(9-phenyl-9H-fluoren-9-yl)-9H-carbazole (PFCz) molecule, which forms strong N–H···O hydrogen bonds with tetrahydrofuran (THF), yielded two-dimensional (2D) sheet-like crystals whose microcrystalline films exhibited a photoluminescence quantum yield (PLQY) of 27.83%. By contrast, 9-ethyl-3-(9-phenyl-9H-fluoren-9-yl)-9H-carbazole (Et-PFCz), in which these hydrogen bond interactions are blocked, formed one-dimensional (1D) microbelts with larger molecular packing distances and its microcrystal films exhibited a PLQY of 52.21%, substantially exceeding that of its amorphous state (22.00%) and even that of its solution state (47.57%). Concomitantly, the Et-PFCz crystal exhibits markedly enhanced thermal stability compared to that of PFCz. These findings demonstrate that eliminating solvent-molecule hydrogen bonding is a powerful strategy to modulate molecular packing patterns and enhance the thermal stability and the CLoSE effect of crystals, which provides valuable insights for the rational design of high-performance organic light-emitting materials and devices.