Disentangling congested charge transfer manifolds with electronic-vibrational spectroscopy

Authors:
Publisher website
Google Scholar
Abstract
Efficient charge separation at donor-acceptor interfaces underpins organic photovoltaics and related optoelectronic technologies, yet the ultrafast vibronic processes enabling this remain incompletely understood. Charge-transfer (CT) excitons form and evolve on ultrafast timescales within a congested manifold of states strongly coupled to vibrational modes. Directly resolving such dynamics requires spectroscopies that correlate electronic and nuclear motion. Here, we present quantum-dynamical simulations of a donor-acceptor system with four CT states coupled to a high-frequency tuning mode. Using the Hierarchy Equations of Motion, we compute two-dimensional electronic spectroscopy (2DES) and two-dimensional electronic–vibrational spectroscopy (2DEV) signals. The 2DES maps show rapid exciton-to-CT transfer within ∼100-200 fs, accompanied by vibrational coherences near 940 cm−1, though spectral congestion obscures individual state contributions. By contrast, 2DEV disentangles these overlaps, revealing distinct cross-peaks that track vibronic wavepacket motion across the CT landscape. Oscillatory features at ∼1467 cm−1 highlight long-lived vibrational coherence persisting for several hundred femtoseconds. These results demonstrate that 2DEV provides vibrationally resolved fingerprints of CT dynamics inaccessible to 2DES alone. The predicted coherence signatures offer concrete experimental observables and suggest that targeted vibrational couplings can transiently promote charge separation. More broadly, this work establishes combined 2DES/2DEV approaches as powerful probes of vibronic dynamics and points to new design strategies for tuning vibrational couplings to optimise energy conversion in donor-acceptor systems.
Funding Information
  • Engineering and Physical Sciences Research Council ((V011359/1 (P))
  • Ningbo International Science and Technology Cooperation (2023H009)
  • Yongjiang talents program (2022A-094-G; 2023A-158-G)
  • National Natural Science Foundation of China (12274247; 12404310)
  • National Key Research and Development Program of China (2024YFA1409800)

This publication has 49 references indexed in Scilit: