Coupled Bond Relaxation at Organic-Aqueous Interfaces: A Spectroscopic and Computational Study.

Understanding the coupled evolution of interactions at organic-aqueous interfaces is crucial for predicting and controlling interfacial phenomena. Here, we reveal a general, cooperative relaxation mechanism by integrating concentration-dependent Raman spectroscopy with ab initio molecular dynamics (AIMD) simulations across DMSO-, THF-, and DMF-water systems. The spectroscopic results consistently identify a "one-redshift, two-blueshifts" signature, corresponding to the weakening of the central intermolecular O:H nonbond (evidenced by a Raman redshift) and the simultaneous strengthening of the adjacent water H-O and solute polar covalent bonds (S═O, C═O, or C-O), both exhibiting distinct blueshifts. The AIMD simulations corroborate these findings by providing direct structural evidence: the elongation of the nonbond and the contraction of the adjacent covalent bonds. To rationalize the cooperative effect, we propose a coupled three-oscillator model, which provides a physical basis for the observed spectral signature. This work establishes a general framework for how macroscopic perturbations translate into collective changes in bond character, offering a predictive tool for tuning covalent properties via noncovalent interactions at complex interfaces.