Promoting intense mechanoluminescence by strengthening C-H?π interactions in thioxanthene derivatives

Pure organic mechanoluminescent (ML) materials are a kind of new environmentally friendly material that can be mechanically stimulated by external force, which has the potential to apply in stress imaging, health moni-toring and structural defect detection. However, the mechanism of ML process in organic materials is still unclear and the molecular designing strategies for these materials remain insufficient. Herein, through simply strengthening intermolecular C-HMIDLINE HORIZONTAL ELLIPSIS pi interactions in the ML-inactive thioxanthene derivatives TxPh, the thio-phene modified compound TxPhTh showed bright ML. The stronger C-HMIDLINE HORIZONTAL ELLIPSIS pi interactions suppressed the non -radiative transition channels during the ML process, and also boosted the photoluminescence quantum yield (PLQY) of crystalline TxPhTh. In addition, the molecular arrangements were switched from centrosymmetric (TxPh) to non-centrosymmetric (TxPhTh). Photophysical studies, detailed single-crystal and TD-DFT calculations were performed. These results provided a new path for designing ML materials and promoted the investigation of ML mechanism.

Automated summary

Pure organic mechanoluminescent materials are environmentally friendly and can be mechanically stimulated by external force. By strengthening intermolecular C-Hπ interactions in the ML-inactive thioxanthene derivatives TxPh, a new compound TxPhTh with bright mechanoluminescence was obtained. The enhanced C-Hπ interactions suppressed non-radiative transition channels and increased the photoluminescence quantum yield of crystalline TxPhTh. This research provides a new approach for designing mechanoluminescent materials and advances the understanding of their mechanism.