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.