Group Theory-Guided Orbital Symmetry Engineering of cis -Quinacridone: From Symmetry-Forbidden to Dipole-Allowed Transitions for Efficient Narrowband Emissions

Abstract

Abstract Although group theory is widely used to analyze symmetry and electronic transition selection rules in condensed matter physics and coordination chemistry, its use as a predictive design tool for organic light-emitting diodes (OLEDs) remains largely unexplored. This is particularly important for highly symmetric emitters, where orbital-symmetry constraints can render the lowest-energy transition symmetry-forbidden. Herein, guided by quantum-chemical and group-theoretical analyses, we revisit the long-known cis- and trans-quinacridone isomers and reveal that the lowest-energy transition of cis-quinacridone (cis-QA) is symmetry-forbidden, resulting in a negligible transition dipole moment and intrinsically weak emission. We address this limitation through a group theory-guided orbital-symmetry engineering strategy based on carbonyl-to-imine transformation of the cis-QA skeleton. This targeted structural modification reorganizes the frontier orbital symmetry, converting the lowest-energy transition from symmetry-forbidden to dipole-allowed, while preserving the rigid, highly symmetric molecular framework and suppressing excited-state structural relaxation and vibronic coupling. The resulting cis-I2A2 derivatives exhibit high photoluminescence quantum yields (ΦPL) of 70–99% and narrow emission bandwidths with full-widths at half-maximum (fwhm’s) of 20–32 nm. An OLED based on cis-I2A2-3 delivers narrowband yellow electroluminescence with an emission maximum at 550 nm, a maximum external quantum efficiency (EQE) of 32.4%, and substantially mitigated efficiency roll-off relative to conventional cis-quinacridone emitters. This work establishes orbital-symmetry engineering as a rational strategy for decoupling orbital symmetry from overall molecular symmetry, providing a general approach to transforming intrinsically weak luminophores into efficient narrowband emitters.