Photo-excited nanodiamonds can efficiently emit electrons due to their negative electron affinity, making them promising candidates for photoinduced electron injection into liquid water. The emitted electron can become solvated, enabling high-energy redox reactions. This study investigates the initial photoexcitation and charge-transfer dynamics using adamantane–water clusters as a model system. The charge-transfer mechanism involves excitons, which feature HOMO-to-LUMO transitions from adamantane to water. Water structures with disrupted hydrogen bonding and large dipole moments stabilize the photoexcited electron. Similar charge-transfer process in bulk water is confirmed through molecular dynamics and LR-TDDFT simulations. The exciton properties are benchmarked using DFT, LR-TDDFT, and many-body perturbation theory (GW/BSE). Amino functionalization of adamantane is further explored as a promising material design strategy to reduce the energy gap of adamantane and enhance charge transfer. Nevertheless, excessive modification can reduce electron emission. Overall, this work clarifies how nanodiamond surface properties govern photoexcitation-driven charge transfer and electron solvation in liquid water.
