Theoretical perspective of the excited state intramolecular proton transfer for a compound with aggregation induced emission in the solid phase

Abstract

In this study, we have investigated the excited state intramolecular proton transfer (ESIPT) for the diphenylethylene-modified 2-(2-hydroxyphenyl)benzothiazole derivative (HBT-d-Ph) with aggregation induced emission (AIE) in the solid phase through a combined quantum mechanics and molecular mechanics (QM/MM) approach and thermal vibration correlation formalism for non-radiative decay rate. In comparison with the molecule in the solid phase, we find that the ESIPT for HBT-d-Ph is prone to occur in toluene due to the intramolecular hydrogen bonding (H-bond). In addition, the rotation of benzene units involved in the low frequency vibration modes (<500 cm⁻¹) is effectively impeded due to the intermolecular interaction in the solid state, thus the energy consumption pathway through the rotation of benzene units could be blocked. Further, a dual fluorescence with blue and green emission in the solid phase could be obtained. Our study could provide some useful information for designing highly efficient emitting materials with ESIPT and AIE features.