Electron-proton coupled motion is widespread in both natural and synthetic materials. The best-known mechanism is proton-coupled electron transfer (PCET), which is vital to bioenergetics, cellular respiration, photosynthesis, and nitrogen fixation, and has guided the development of many artificial energy conversion and storage materials. Recently, a new mechanism called proton-coupled singlet energy transfer (PCEnT) has been identified.
Based on prior research on PCET and PCEnT, Prof. WU Kaifeng's team from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences, has addressed a missing link in understanding proton-coupled electronic processes: triplet energy transfer coupled with proton transfer. As another key energy transduction mechanism in natural and synthetic systems, triplet energy transfer is fundamentally distinct from singlet energy transfer.
In a recent study published in Nature Materials , the team identified a novel mechanism called proton shuttle-assisted triplet energy transfer (PS-TET), which occurs from ZnSe-based colloidal quantum dots (QDs) to their surface-anchored phenol-pyridine dyadic acceptors.
The researchers found that upon photoexcitation of ZnSe QDs, hole transfer from ZnSe to phenol is coupled with proton transfer from phenol to pyridine. This is followed by electron transfer from ZnSe to the phenoxyl radical, coupled with back proton transfer from pyridinium. These steps complete a net process of spin-triplet migration from ZnSe QDs to the phenol-pyridine dyads.
Although the proton returns to its original position after PS-TET, this proton shuttle significantly enhances both the rate and efficiency of triplet energy transfer compared to a methylated analog lacking the shuttle. The researchers further observed that adding a strongly electron-withdrawing trifluoromethyl substituent on pyridine can alter the sequence of proton-coupled electron and hole transfer steps.
Furthermore, the temperature insensitivity of the PS-TET rate indicates that the proton shuttle migrates through quantum mechanical tunneling—a finding supported by calculations of proton vibrational wavefunction overlap integrals. These integrals dictate the excited-state relaxation pathways and guide the system toward efficient triplet energy migration. Thus, this study also demonstrates how quantum effects can be harnessed to control charge and energy transduction in complex materials at room temperature.
"The discovery of the PS-TET mechanism has profound implications for many modern molecular technologies involving the spin-triplet excited states of molecules," Prof. WU noted. For instance, enhancing triplet generation efficiency benefits photoredox and environmental catalysis, while organic optoelectronic devices such as solar cells and lasers require the suppression of triplet formation.
This study suggests that creating or eliminating a proton shuttle can enable the on-demand enhancement or suppression of triplet formation, respectively.
Nature Materials
Commentary/editorial
Not applicable
Proton shuttle-assisted triplet energy transfer
9-Mar-2026