Optimized Photoisomerization on Gold Nanoparticles Capped by Unsymmetrical Azobenzene Disulfides

Abstract

Gold nanoparticles capped by an unsymmetrical azobenzene disulfide, 4-hexyl-4‘-(12-(dodecyldithio)dodecyloxy)azobenzene (C6AzSSC12), were synthesized in order to investigate the efficiency of azobenzene photoisomerization on colloidal gold surfaces. The nanoparticles were synthesized by a two-step method to avoid the direct contact of azobenzene units with a reducing agent. The average size of the particles was determined to be ∼5.2 ± 1.3 nm from transmission electron microscope (TEM) images. The CH2 antisymmetric (∼2919 cm-1) and symmetric (∼2850 cm-1) stretching bands in the FTIR spectra of the nanocomposite confirmed the all-trans conformation of alkyl chains in the C6AzSSC12 on the colloidal gold. The photoisomerization reaction of the C6AzSSC12-capped gold nanoparticles was studied by UV−vis absorption spectroscopy in toluene. The reaction kinetics was identical to that of the free C6AzSSC12 molecules dissolved in toluene, with no deviations from a first-order plot for both trans-to-cis and cis-to-trans photoisomerization, suggesting no steric hindrance throughout the whole reaction process. The free volume guaranteed by the 50% dilution of the dye functions due to the unsymmetrical disulfide structures, as well as their noncompact molecular tails owing to the assembly on the curved colloidal gold, must be responsible for such a highly efficient photoreaction. Sedimentation of the nanoparticles arose in toluene subsequent to the photoisomerization of the capping azobenzene molecules from trans to cis isomers. This phenomenon can be interpreted as resulting from differences in the degree of solvation between the azobenzene isomers.

Using silver nanowire antennas to enhance the conversion efficiency of photoresponsive DNA nanomotors

“…Excited local surface plasmons have been used to elucidate the near-electric-field images of Ag nanoparticles. Although the interaction between azobenzene molecules and metal nanoparticles has been reported (25)(26)(27), for a better understanding of the physical origin of enhanced conversion efficiency, numerical simulations were performed to show near-field behavior of Ag nanoparticles using finite element method-based commercial software. The nanoparticles were simulated with the same morphology and size as those in the experiments.…”

Light Switching of Molecules on Surfaces

“…This demonstrates the importance of conformational restrictions on the photoreactivity of photochromic molecules in addition to electron coupling quenching mechanisms. Asymmetric azobenzene disulfides have been employed in an attempt to realize efficient isomerization on colloidal gold surfaces (61). In the SAMs formed, the free volume for the photoreaction of azobenzenes was provided by the 50% dilution due to the second alkyl leg of the disulfide.…”

Self-assembly of triazatriangulenium-based functional adlayers on Au(111) surfaces

“…7 This is most commonly accomplished by employing mixed monolayers with short-chain spacer molecules. 5,6,[8][9][10][11][12][13][14][15][16][17] More modern approaches to enforce a sufficient free volume employ specially designed molecules, which feature additional bulky spacer groups 6,[18][19][20][21] or molecular tripods [22][23][24][25] as basis. Nevertheless, these types of adlayers also exhibit intrinsic disadvantages such as a comparable low structural order or lack of temporal stability due to phase separation.…”