Particle–Hole Symmetry Breaking in Nitrogen-Decorated Triphenylmethyl Radical Emitters

Organic radical emitters have recently emerged as promising alternatives to conventional singlet emitters, as they circumvent spin-statistical limits and can, in principle, achieve unity internal quantum efficiency in OLEDs. Here, we study the photophysics of a series of nitrogen-decorated triphenylmethyl radicals using the Pariser–Parr–Pople (PPP) model within the Restricted Active Space Configuration Interaction (RASCI) framework. By exploiting the PPP particle–hole difference operator introduced in J. Phys. Chem. C 2024, 128, 18158–18169, we quantify particle–hole symmetry breaking and relate it to the oscillator strength of the first absorption band. Systematic nitrogen substitution at the meta positions of the phenyl rings leads to increasingly bright doublet states. We further show that an effective difference operator value can be computed using ground-state DFT energies, enabling a fast and practical screening protocol for identifying potentially emissive radicals. Our results provide simple design rules and predictive indicators for engineering bright organic radicals through controlled particle–hole symmetry breaking.