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.