Pressure-Induced Emission Enhancement of Multi-Resonance o-Carborane Derivatives via Exciton‒Vibration Coupling Suppression.

Polycyclic multiple resonance (MR) molecules reveal narrowband emission, making them very promising emitters for high color purity display. Nevertheless, they still have challenges such as aggregation-induced emission quenching and spectral broadening. Overcoming these obstacles requires an in-depth understanding of the correlations among the alterations in their geometries, packing structures, and molecular vibrations and their corresponding changes in their photoluminescence (PL) properties. Herein, it is demonstrated that high-pressure infrared, UV-visible absorption, and fluorescence spectroscopies can be combined with computational results to elucidate the influence of the subtle structural variations on the exciton‒vibration couplings and their PL properties. An ortho-carborane-decorated MR emitter (BNC) is a piezochromic molecule and exhibits emission enhancement under high pressure. A thorough analysis of the in situ experimental measurements and calculated results reveals that the pressure-induced changes in the exciton binding energy and exciton‒vibration couplings are responsible for the unusual piezochromism. This research provides insights into the structure‒fluorescence relationship and potential for high-pressure techniques to optimize MR materials for advanced organic light-emitting diodes (OLEDs) applications.