Mode-selective vibrational control of charge transport in $\pi$-conjugated molecular materials

TL;DR

This study demonstrates that selective excitation of molecular vibrations can modulate photoconductivity in organic electronic devices, revealing a new approach to control charge transport through vibrational dynamics.

Contribution

First experimental demonstration that vibrational excitation can control charge transport in organic materials, enabling mode-specific manipulation of photocurrent.

Findings

Excitation of specific vibrational modes enhances photocurrent.

Vibrations influence trapped charge carriers.

Mode-specific effects are explained by modulation of electronic couplings.

Abstract

The soft character of organic materials leads to strong coupling between molecular nuclear and electronic dynamics. This coupling opens the way to control charge transport in organic electronic devices by inducing molecular vibrational motions. However, despite encouraging theoretical predictions, experimental realization of such control has remained elusive. Here we demonstrate experimentally that photoconductivity in a model organic optoelectronic device can be controlled by the selective excitation of molecular vibrations. Using an ultrafast infrared laser source to create a coherent superposition of vibrational motions in a pentacene/C60 photoresistor, we observe that excitation of certain modes in the 1500-1700 cm$^{-1}$ region leads to photocurrent enhancement. Excited vibrations affect predominantly trapped carriers. The effect depends on the nature of the vibration and its mode-specific character can be well described by the vibrational modulation of intermolecular electronic couplings. Vibrational control thus presents a new tool for studying electron-phonon coupling and charge dynamics in (bio)molecular materials.