Dual enhancement of absorption redshift and oscillator strength via an asymmetric CNNH bridge and integrated orbital engineering

Developing organic chromophores that simultaneously exhibit a narrow bandgap and a high oscillator strength in the near-infrared (NIR) region remains a formidable challenge due to the inherent trade-off in conventional donor-π-acceptor designs. Here, we propose a paradigm-shifting strategy: integrating orbital and symmetry engineering into a single, asymmetric bridging unit. The rationally designed C N-NH bridge establishes an intrinsic push-pull system that elevates the HOMO level and narrows the HOMO-LUMO gap. This electronic configuration ensures a fully allowed and highly pure lowest-energy transition, simultaneously yielding a substantial redshift and enhanced oscillator strength. Using this as a programmable platform, we decipher a “spatial polarization matching” rule: functional group position outweighs number, with asymmetric modification near the acceptor end maximizing the intramolecular charge-transfer driving force. This principle enables precise design of a molecule absorbing at 580 nm with an oscillator strength of 0.64, with the absorption tail extending toward the NIR edge (f ≈ 0.1 at 800 nm from Gaussian broadening). Importantly, preliminary experimental validation was performed by synthesizing a derivative (CNN-2) bearing the same C N-NH core, which exhibited a 100 nm redshift relative to HNS, a low laser ignition threshold (10 W, 8 ms) under pressed conditions, a thermal decomposition temperature of 279 °C, and an impact sensitivity >40 J. These results provide initial experimental support for the optical advantage of the C N-NH bridge, establishing it as a promising platform for future optimization toward NIR photonic and energetic applications.