Controlled intermolecular proton-coupled electron transfer process: a novel design strategy for highly sensitive piezo-chromic fluorescent materials

Abstract

Highly sensitive piezochromic fluorescent (PCF) materials were successfully synthesized via a controlled intermolecular proton-coupled electron transfer (IPCET) process in a single-benzene π-system. Upon a record-low pressure of 0.3 MPa, a blue shift of 105 nm (4642 cm⁻¹) from green to blue emission appears and strengthens with an increase of PLQY from 19.6% to 43.7%. A mechanistic study combining time-resolved fluorescence analysis, X-ray diffraction analysis, and theoretical calculations revealed that the IPCET process in the S₁ state on/off switching plays a key role in this abnormal phenomenon. A change in the intermolecular hydrogen bond distance in the dimer structure from 1.760 Å to 2.183 Å turns on or off the IPCET process, leading to a switch between the charge transfer (CT) state and the local excited (LE) state. This work enriches the underlying mechanism of the highly sensitive PCF materials and provides an ideal model to study the IPCET process.