Self-Assembled Monolayers of 7-(10-Thiodecoxy)coumarin on Gold:  Synthesis, Characterization, and Photodimerization

Abstract

As is true in solution, irradiation at 350 nm of 7-(10-thiodecoxy)coumarin (1) as a self-assembled monolayer on polycrystalline gold (Au-1) produces [2 + 2] photodimers. In the monolayer, photodimerization is indicated by differences in the grazing angle surface FTIR spectra, sessile drop contact angles, and surface fluorescence spectra before and after irradiation. The photodimerization can be reversed by irradiation at 254 nm, as demonstrated by changes in these same structural probes. Better photochemical reversibility and regioselectivity are observed when the in situ photodimerization is conducted as a dry solid monolayer than when in contact with benzene. A comparison of the structure of a self-assembled monolayer of a syn head-to-head (H-H) dimer of 7-(10-thiodecoxy)coumarin on polycrystalline gold (Au-2) with that of the photodimers generated by irradiation of Au-1 demonstrates that surface reorganization is accomplished in the photodimerization-photoreversion cycle.

Photoreversible Chain Extension of Poly(ethylene glycol)

“…After UVA irradiation, the absorbance at 1 616 cm À1 (C C ring stretch) decreased and the C O stretch shifted from 1 730 to 1 757 cm À1 as a new carbonyl (a to a cyclobutane ring) formed. [39] Figure 10 shows the correlation between the 1 H NMR data (~) and the UV-Vis data (*) for a single dimerization/cleavage cycle. An average of the change in the peak integrals at 7.7, 7.4, 6.8, 6.7 and 6.3 ppm was used to determine the extent of reaction.…”

Reactions and Reactivity in Self-Assembled Monolayers

“…[85] Irradiation at 350 and 254 nm effects dimerization and dissociation of the dimer, respectively.…”

Effect of Alkyl Chain Length on the Fluorescence of 9-Alkylfluorenyl Thiols as Self-Assembled Monolayers on Gold

“…15 Altered photoreactivity is not unique with the stilbenes. Reversible photodimerization is also known for alkyl-appended coumarins, 16 and photodimerization and partial reversion have been reported for substituted anthracenes bound as SAMs. 17 What remains unestablished is whether the photoreactivity differences are a function of packing or local environmental effects or a consequence of electronic coupling with the metal or semiconductor support.…”