Temperature-Insensitive Electron Transfer in Quantum Dot-Molecule Hybrids Driven by Nuclear Quantum Tunneling

Electron transfer (ET) plays a crucial role in many chemical and biological reactions, as well as in optoelectronic devices. Recent studies across different systems often found the ET rates to be insensitive to the temperature, which is beyond the current theoretic framework based on Marcus theory and its modified semiclassical versions and suggests the critical role of nuclear quantum tunneling. Here we formulate a pure quantum tunneling expression of ET rate, which is dictated by the reactant-product vibration wave function overlap of a simplified single quantum mode. This model works remarkably well for describing the weak temperature dependence of ET rate from photoexcited quantum dots to their surface-anchored naphthalene diimides acceptors in both normal and inverted regions, measured from 4 to 300 K. This study underscores the crucial role of nuclear tunneling effects in charge migration at the nano/molecular scales.