Congested position isomerism enhanced mechanoluminescence of triarylboranes†

Abstract

The study of the mechanoluminescence enhancement (MLE) mechanism has been a challenging topic in the field of luminescent materials. Here, we implanted organoboron units with a steric hindrance effect into the molecular backbone and achieved the synthesis of MLE molecules using molecular engineering and crystal engineering. ortho-, meta-, and para-substituted organoboron compounds, namely o-NAB, m-NAB, and p-NAB, were synthesized, where o-NAB showed notable MLE, whereas m-NAB and p-NAB showed decreased fluorescence intensity upon mechanical activation without the assistance of solvent. Our study finds that the steric conformation resulting from different substitution positions plays a decisive role in the fluorescence performance. Grinding releases spatial stress in the o-NAB structure, thereby affecting the process of mechanoresponsive fluorescence transition. Our research provides a congested position strategy for constructing MLE molecules, which not only enhances the fundamental understanding of MLE mechanisms but also bears significant implications for future research.