Intermolecular Halogen Interaction-Induced Efficient Room-Temperature Phosphorescence in Isomer Crystals: A Theoretical Perspective

Introducing intermolecular halogen bonds in room-temperature phosphorescence (RTP) crystals to enhance phosphorescence quantum efficiency (Φ_p) has recently been a common strategy recently. Herein, we focus on exploring the effects of intermolecular halogen bonds on RTP properties through the quantum mechanics/molecular mechanics method using the ONIOM model with the general Amber force field and restrained electrostatic potential charge in three isomer crystal systems. We found that the total contribution of intermolecular halogen bonds to the Hirshfeld surface is related to the Φ_p values of crystals. The isomer crystal with a larger contribution of intermolecular halogen bonds to the Hirshfeld surface would have a higher Φ_p. After investigating the radiative transition process, nonradiative transition process, and quenching process, we discovered that the intermolecular halogen bonds have a remarkable influence on the nonradiative transition rate <i>k</i>_nr. The crystals with a higher intermolecular halogen bond contribution have a higher Φ_p mainly by reducing <i>k</i>_nr. In addition to highlighting the significance of intermolecular halogen bonds in the Φ_p of isomer crystals, this work could also offer theoretical guidelines to boost the Φ_p of RTP crystals with intermolecular halogen bonds.