Non-Traditional Luminescent Polyurethanes of n–π Electron Hybrid Structures with Varying Separation of Aromatic Rings

Detailed structure–activity relationships and molecular design criteria for nonconventional and nonconjugated luminescent polymers are still ambiguous. This work reports n–π electron hybrid polyurethane derivatives (PUs) with varying separation of benzene rings in the backbone. Experimental and computational results show that although through-bond conjugation is not the main source of luminescence, the separated benzene rings still modulate the photophysical properties by affecting the molecular conformation and electron transport. Meanwhile, hydrogen bonds and p–π* interactions exert a significant influence on the emission wavelengths by regulating the aggregated-state structures. In PU1, the excited state is predominantly charge transfer. With an increase in the number of benzene rings along the chain, the energy gap between the acceptor π and π* orbitals is reduced; alongside these effects, the modulation from hydrogen bonds and p–π* interactions promotes a transition to LE-dominated states in PU3, which incorporates terphenyl units. Proof-of-concept applications are demonstrated in information transmission and colorful displays. This work enhances the understanding of the mechanisms underlying the excitation-dependent properties of nonconventional polymers and provides a strategy for tuning and exploiting their intrinsic luminescence.