Photo-induced carbocation-enhanced charge transport in single-molecule junctions

Abstract

We report the first example of photo-induced carbocation-enhanced charge transport in triphenylmethane junctions using the scanning tunneling microscopy break junction (STM-BJ) technique.

Light-Driven Charge Transport and Optical Sensing in Molecular Junctions

“…Their approach could be used for probing the reaction kinetics, reversibility, and the occurrence of isomerization during the chemical reaction in MJs. In another recent study, using the STM-BJ technique, Bei et al demonstrated photo-induced carbocation-enhanced charge transport in an MJ composed of malachite green leuco hydroxide (MGOH) [65]. As shown in Figure 2c, in the presence of 302 nm UV light, the MGOH produces malachite green carbocations, thus inducing a minor structural change where the orbital hybridization of the central carbon atom changes from initial sp 3 to sp 2 .…”

Recent Advances in Photochemical Reactions on Single‐Molecule Electrical Platforms

“…For instance, the photo‐driven reaction of malachite green leucoethanol (MGOH) molecules, which are precursors of carbocations, has been studied at the single‐molecule level by using the STM‐BJ technique ( Figure a). [ 100 ] Specifically, in the presence of 302 nm UV light, MGOH efficiently produces malachite green carbocations (MG + ) and hydroxide ions. To confirm the formation of the carbocations, the UV–vis absorption spectra of MGOH before and after UV irradiation are tested.…”

“…b)Schematic representation of the energy level structures for charge transport before and after the formation of a carbocation. Reproduced with permission [100]. Copyright 2019, The Royal Society of Chemistry.…”

Photoconductance from the Bent-to-Planar Photocycle between Ground and Excited States in Single-Molecule Junctions

“…With this in mind, in this work, we presented the first experimental demonstration of monitoring excited-state bent-to-planar motions at the single-molecule scale by photoconductance. The DPAC derivative with SMe anchoring groups ( DPAC-SMe , Figure b) was designed as a molecular prototype, which was utilized to fabricate single-molecule junctions using the scanning tunneling microscope break junction technique (STM-BJ). − By imposing continuous 340 nm light irradiation, the single-molecule junctions of DPAC-SMe exhibited a distinguished and reversible photoconductance of up to ∼200% than that without irradiation, making it one of the largest photoconductance values with high stability among the reported single-molecule junctions, − benefiting from the unique bent-to-planar photocycle between the ground and excited states. This differed significantly from the traditional photoswitching behavior in single-molecule junctions, referring to the steady structural and correspondingly drastic ground-state changes after irradiation, along with resulting irreversible conductances in the absence of other stimuli, such as different wavelengths of light or heat. − The DPAC-SMe -fabricated junctions also exhibited in situ conductance modulation as pulsed 340 nm light irradiation.…”