Mechanistic Regimes of Vibronic Transport in a Heterodimer and the Design Principle of Incoherent Vibronic Transport in Phycobiliproteins

TL;DR

This paper investigates vibronic transport mechanisms in heterodimers, revealing that incoherent vibronic transport, rather than coherent, is more efficient in phycobiliproteins under typical conditions, challenging previous assumptions.

Contribution

It establishes the mechanistic map of vibronic transport in heterodimers and shows incoherent transport is favored in phycobiliproteins, providing a new design principle for light-harvesting materials.

Findings

Incoherent vibronic transport is more efficient than coherent in certain regimes.

Molecular parameters of phycobiliproteins support incoherent transport.

The role of coherent vibronic transport in pigment complexes should be reevaluated.

Abstract

Following the observation of coherent oscillations in non-linear spectra of photosynthetic pigment protein complexes, particularly phycobilliprotein such as PC645, coherent vibronic transport has been suggested as a design principle for novel light harvesting materials operating at room temperature. Vibronic transport between energetically remote pigments is coherent when the presence of a resonant vibration supports transient delocalization between the pair of electronic excited states. Here, we establish the mechanism of vibronic transport for a model heterodimer across a wide range of molecular parameter values. The resulting mechanistic map demonstrates that the molecular parameters of phycobiliproteins in fact support incoherent vibronic transport. This result points to an important design principle: incoherent vibronic transport is more efficient than a coherent mechanism when energetic disorder exceeds the coupling between the donor and vibrationally excited acceptor states. Finally, our results suggest that the role of coherent vibronic transport in pigment protein complexes should be reevaluated.