Regioisomeric engineering of carbazole–naphthalimide donor–acceptor systems enables efficient triplet generation and room temperature phosphorescence in molecular and nanoaggregated states

-isomers as well as C3-substitution promote more efficient triplet generation through spin-orbit charge-transfer-assisted intersystem crossing, yielding triplet quantum yields approaching unity. Femtosecond and nanosecond transient absorption spectroscopy directly elucidate the singlet-to-triplet conversion dynamics, while TD-DFT calculations and single-crystal X-ray diffraction establish clear relationships between molecular geometry, electronic coupling, and excited-state behaviour. Efficient orange-to-red RTP is observed in benzophenone host-guest matrices as well as in water-dispersed nanoaggregates, suggesting that regioisomeric control can activate persistent phosphorescence in both solid-state and colloidal environments. These findings provide valuable molecular design principles for developing purely organic RTP materials for optoelectronics, time-resolved bioimaging, and photonic applications.