Pressure-induced emission enhancement by restricting chemical bond vibration

In this work, we found that the pressure-induced emission enhancement (PIEE) phenomenon can be produced by the restriction of intramolecular chemical bond vibration, which differs from the mechanism of restricting intramolecular motion (RIM). Dibenzo[b,d]thiophene 5,5-dioxide (DBTS) is an aggregation-induced emission enhancement (AIEE) material. In the crystal state of DBTS, the high pressure strengthens intermolecular C-H center dot center dot center dot O=S hydrogen bonds, which greatly restricts the vibration of C-H and S=O bonds and then rigidifies the molecular skeleton, thereby suppressing the non-radiative process and promoting emission enhancement. In situ high-pressure infrared spectroscopy and angle-dispersive X-ray diffraction analysis combined with reorganization energy and Hirshfeld surface theory calculation provide clear evidence that the restriction of the deformation vibration C-H bonds plays an essential role in PIEE, and S O bonds can act as the powerful controller that enhances intermolecular C-H center dot center dot center dot O=S hydrogen bonds. This study introduces a new AIEE and PIEE fluorophore and provides deep insights into the influence of intermolecular interactions on intramolecular chemical bond vibration and luminescence, which will play an important role in the development of precision optical sensors.