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 (Φp) 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 Φp values of crystals. The isomer crystal with a larger contribution of intermolecular halogen bonds to the Hirshfeld surface would have a higher Φp. 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 knr. The crystals with a higher intermolecular halogen bond contribution have a higher Φp mainly by reducing knr. In addition to highlighting the significance of intermolecular halogen bonds in the Φp of isomer crystals, this work could also offer theoretical guidelines to boost the Φp of RTP crystals with intermolecular halogen bonds.