# Photogated two conductive pathways of donor-acceptor Stenhouse adducts in single-molecule junctions

## TL;DR

This paper shows how light can control two different electrical pathways in a single molecule, offering new possibilities for molecular electronics.

## Contribution

The study demonstrates light-gated modulation of two distinct conductive pathways in single-molecule junctions using donor-acceptor Stenhouse adducts.

## Key findings

- Two conductive pathways in DASAs are separately controlled via side-chain and main-chain modulation mechanisms.
- Red-light irradiation and dark relaxation enable simultaneous modulation of both pathways in a single-molecule junction.
- Photoisomerization increases through-space electron transport in the cyclic state of DASAs.

## Abstract

Manipulating intramolecular electron transportation can fundamentally modulate the optical property, electromagnetic behavior and chemical reactivity of molecules. Achieving simultaneous control of multiple ( ≥2) transport pathways within a single molecule, however, remains a significant challenge. Herein, we report light-gated modulation of two distinct conductive pathways in single donor-acceptor Stenhouse adduct (DASA) molecules using the scanning tunneling microscopy break-junction (STM-BJ) technique. The donor and π-bridge pathways are separately controlled by designing DASAs with two thiomethyl anchoring sites. In the donor pathway, a side-chain modulation mechanism operates, where linear-to-cyclic isomerization induces electronic redistribution and increases the conductivity. In contrast, the π-bridge pathway is governed by a main-chain modulation mechanism, in which deformation of the π-conjugated backbone decreases the conductivity. By synthesizing DASAs containing three thiomethyl anchoring sites, these two conductive pathways are integrated within a single-molecule junction and can be simultaneously modulated under 635 nm red-light irradiation and dark relaxation. The π-bridge transport in the linear state exhibits mixed through-bond and through-space character, while photoisomerization leads to an increased through-space contribution in the cyclic state driven by cyclopentenone formation. These results highlight DASAs’ potential in understanding molecular electronics and developing photoresponsive molecular-scale devices.

Achieving simultaneous control of multiple transport pathways within single-molecule junctions remains challenging. Here, Sun et al. report light-controlled modulation of two distinct conductive pathways in single donor-acceptor Stenhouse adduct molecule with three thiomethyl anchoring sites.