Halogen-Substitution Tuning of Room-Temperature Phosphorescence in Tetraphenylene Derivatives: A Multiscale Theoretical Study from Molecular to Aggregated States

Organic room-temperature phosphorescent (RTP) materials have attracted a great deal of attention in recent years. Incorporating halogen atoms into molecular frameworks offers a rational strategy for developing RTP materials with long-lived lifetimes and high efficiency. However, the mechanism and extent to which halogen substitution regulates luminescence are insufficiently understood. Here, we systematically investigate the photophysical properties of halogen-substituted tetraphenylene (TeP) derivatives through theoretical analyses of geometric and electronic structures, intermolecular interactions, and exciton dynamics processes, in both solution and solid phases, to elucidate the origins of their experimental performance variations and derive molecular design principles. The calculated results indicate that halogen atoms tune frontier molecular orbital energy levels via a synergistic interplay between inductive and conjugative effects. Moreover, the highly distorted, bird-shaped configuration of TeP derivatives enhances spin-orbit coupling, facilitating efficient RTP. In the solid phase, fluorine substitution substantially suppresses exciton nonradiative decay due to compact molecular packing. In contrast, chlorine- and bromine-substituted derivatives exhibit markedly increased reorganization energies, attributed to molecular stretching vibrations and relatively looser packing induced by σ-hole repulsion─particularly prominent in the heavy-atom-contained TeP-Br. These findings provide critical insights into structure-performance relationships and offer theoretical guidance for tuning the photophysical properties of materials through halogen functionalization.