Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties

Abstract

Self-assembled monolayers (SAMs) containing azobenzene moieties are very attractive for a wide range of applications, including molecular electronics and photonics, bio-interface engineering and sensoring. However, very little is known about the aggregation and photoswitching behavior that azobenzene units undergo during the SAM formation process. Here, we demonstrate that the formation of thiol-based SAMs containing azobenzenes (denoted as AzoSH) on gold surfaces is characterised by a two-step adsorption kinetics, while a three-step assembly process has been identified for dithiolane-based SAMs containing azobenzenes (denoted AzoSS). The H-aggregation on the AzoSS SAMs was found to be remarkably dependent on the time of self-assembly, with less aggregation as a function of time. While photoisomerization of the AzoSH was suppressed for all different assembly times, the reversible trans-cis photoisomerization of AzoSS SAMs formed over 24 hours was clearly observed upon alternating UV and Vis light irradiation. We contend that detailed information on formation kinetics and related optical properties is of crucial importance for elucidating the photoswitching capabilities of azobenzene-based SAMs.

Surface Molecular Tailoring Using pH-Switchable Supramolecular Dendron-Ligand Assemblies

“…The S (2p) spectra for all the surfaces show doublet peaks at 163.4 eV (S (2p 1/2 )) and 162.2 eV (S (2p 3/2 )), which are assignable to the thiolate-type sulfur bound to the gold surface. 29 …”

A bistren cryptand with a remote thioether function: Cu(ii) complexation in solution and on the surface of gold nanostars

“…The dialdehyde 1 was obtained following the procedures reported in literature. 18 Reagent 2 was prepared modifying a described procedure: 19 2-hydroxy-1,4-benzenedicarboxaldehyde (0.2 g, 1.33 mmol), K 2 CO 3 (0.40 g, 2.93 mmol) and 2-chloroethyl methyl sulfide (0.26 mL, 2.66 mmol) were suspended in 5 mL DMF, and refluxed for 24 hours in inert atmosphere. The orange mixture was then cooled and filtered.…”

“…Dialdehydes 1 and 2 were easily obtained modifying described procedures. 18,19 By this approach, we obtained an aza-cryptand featuring an ethyl methyl sulfide chain covalently linked on one of the three p-xylyl spacers. R-S-R or R-S-R 0 dialkyl sulphides (i.e.…”

Synthesis and Light‐Mediated Structural Disruption of an Azobenzene‐Containing Helical Poly(isocyanide)

“…The direction of this shift is in line with literature reports of azobenzene units with similar substituents in the para-position. [31,32] In addition to the prominent band around 350 nm, a less intense absorption band around 455 nm was also visualized in the UV-Vis spectra. As reported in the literature, the minor band corresponds to the symmetry forbidden n-π* transition of the azobenzene unit.…”

“…[9,[35][36][37] The λ min at around 350 nm corresponds to the π-π* transition of the trans azobenzene unit along the polymer side-chains. [31,32] Next, the cuvette was irradiated for ten minutes with a handheld UV lamp at 365 nm. The sample was then returned to the CD spectrophotometer.…”