Removing H-Bonds of Non-Aromatic Peptidomimetics for Intrinsic Near-Infrared Emission

Peptides and peptidomimetics are promising in diverse biological applications, but intrinsic visible emission without appended fluorophores remains a great challenge due to the lack of π-conjugation in their non-aromatic backbones. Although clusteroluminescence (CL) of nonconjugated materials provides a pathway for intrinsic emission, most non-aromatic clusterolumigens (CLgens) are limited to blue emission, and the underlying factor hindering emission redshift remains unclear. Herein, we identified that intramolecular/intermolecular hydrogen H-bonds between heteroatoms (e.g., –NH2, C=O) compete with through-space conjugation (TSC) and suppress emission redshift. To address this issue, we designed and synthesized ten peptidomimetic polyurethanes (P1-L/H–P5-L) with gradient H-bond densities. Comprehensive characterizations including infrared spectroscopy, femtosecond transient absorption spectroscopy, molecular dynamics simulations, and quantum-chemical calculations confirmed that selective removal of H-bonds enhanced TSC. Notably, H-bond-deficient P4-L and P5-L achieved intrinsic NIR emission at 763 nm and 784 nm, respectively, which is among the longest emission wavelengths reported for non-aromatic CLgens. This work reveals the inhibitory role of H-bonds in TSC and provides a novel strategy for developing intrinsic NIR-emitting peptidomimetics, holding great potential for biological applications.