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

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.