Conformation-dependent mechanochromic delayed fluorescence of AIE-active tetra-coordinated B–N complexes

Abstract Mechanochromic luminescence (MCL) materials have attracted great attention due to their promising prospect in mechanical sensors, optoelectronic devices and data storage. In this work, two novel molecules bearing electron deficient tetra-coordinated phenylpyridine boron (PPYB) and electron donating phenothiazine (PTZ) are developed, and their thermal stability, optical and electronic structures, electrochemical property, photophysical property and MCL behaviors are investigated. Both molecules display obvious MCL effect with large emission color change from blue to yellow, which are ascribed to the changes of molecular conformation from quasi-axial conformation to quasi-equatorial one. In quasi-axial conformation, they show short fluorescence lifetimes without obvious delayed components, but in quasi-equatorial conformation, they have longer fluorescence lifetimes with prominent delayed components. Moreover, they are weakly fluorescent in solutions, but the emission intensity and delayed components are significantly enhanced in the solid state, demonstrating typical aggregation-induced delayed fluorescence (AIDF) characteristics. The application of both molecules as emitters in organic light-emitting diodes (OLEDs) is also evaluated.