Adsorption of a Switchable Industrial Dye on Au(111) and Ag(111)

Abstract

We investigate astraphloxine, an industrial dye, on two metal surfaces, Au(111) and Ag(111). Low-temperature scanning tunneling microscopy with submolecular resolution in comparison to semiempirical calculations reveal that only two of the nine possible conformers of this molecule are adsorbed. The two conformers adsorb via one of their indol groups, which serves as a platform that decouples the rest of the molecule from the surfaces. A change from one to the other conformer is demonstrated by injecting inelastic electrons from the tunneling tip selectively into individual molecules.

Revealing the Presence of Mobile Molecules on the Surface

“…It agrees with the apparent height of the dl -conformer of the molecule imaged by LT-STM on Au(111) at 5 K at a comparable voltage, at 270 pm (see ref ). However, the molecule at 5 K has no black contour . We conclude than that molecule on the terrace is the dl -conformer of astraphloxin and that the diffusive noise results from a mobile molecular gas.…”

“…Both conformers are imaged in low-temperature STM as single protrusions with different apparent heights. 25 On the Cu(111) surface the astraphloxin molecules nicely decorate the step edges at 110 K, similar to the Pc molecules on Ag(100); see Figure 9d. Also, in similarity to the Pc/Ag(100) case, we do not observe the growth of molecular islands from the steps but a black contour around the molecules that is immobilized at the steps.…”

“…Recall that for Pc on Ag(100) the diffusive noise has ∼80% of the apparent height of the Pc molecule. However, the dd- conformer, identified in ref , has a lower apparent height than the dl -conformer. The apparent height of this conformer varies with the surface.…”

“…However, the molecule at 5 K has no black contour. 25 We conclude than that molecule on the terrace is the dl-conformer of astraphloxin and that the diffusive noise results from a mobile molecular gas. Surprisingly, the apparent height of the diffusive noise is only half of the apparent height of the astraphloxin molecule.…”

Unsymmetrical Relaxation Paths of the Excited States in Cyanine Dyes Detected by Time-Resolved Fluorescence: Polymethinic and Polyenic Forms

“…AF has been studied as a model representative of the trimethine polymethine dyes exhibiting highly intensive and selective band in the visible part of the absorption and fluorescence spectra. The advantage of AF is relatively simple molecular structure for quantum-chemical modelling, good solubility in water serving as a highly polar medium, and efficient transcis 21 isomerization. AF molecule dissociates in the water on the positively charged conjugated part with πelectron system and negatively charged counter-ion (Cl -), and main spectral properties of the dye are determined by its conjugated part.…”