Photoswitching of Azobenzene-Functionalized Molecular Platforms on Au Surfaces

Abstract

The photo-and thermally induced switching of well-ordered molecular arrays of free-standing functional groups, formed by self-assembly on Au surfaces, were studied by photoelectrochemical methods (cyclic voltammetry, chronoamperometry) and surface plasmon resonance spectroscopy. These molecular adlayers exhibit azobenzene functions mounted vertically on the surface via molecular platforms on the basis of triazatriangulenium. Detailed quantitative studies of the switching kinetics revealed that the photoinduced trans−cis isomerization of the azobenzene groups in these adlayers proceeds very fast and highly reversible. Cis−trans backisomerization by thermal relaxation occurs surprisingly 4−5 orders of magnitude faster than in solution. A rapid thermal cis−trans relaxation that dominates over the photoinduced processes is also supported by the pronounced increase of the cis fraction in the adlayers with irradiation intensity and the weak dependence of the isomerization time constants on the intensity. In complementary density functional theory calculations of the cis isomer on a Au cluster, no significant electron density depletion of the azo moiety, but strong electronic coupling of the switchable group with the Au substrate, were found. We propose that the latter leads to a spin exchange between conduction electrons in the metal and the azo moiety, enabling a relaxation mechanism that is forbidden for the free molecule.

Comparison of the periodic slab approach with the finite cluster description of metal–organic interfaces at the example of PTCDA on Ag(110)

“…In most of these applications the structure of the metal cluster was taken from experimental bulk data (see Refs. for exceptions where the cluster structure was partially relaxed). Furthermore, the “outer” metal atoms were generally described with large core pseudopotentials such that only the 4s orbitals or not even these carried electrons and basis sets.…”

Optical properties of azobenzene-functionalized self-assembled monolayers: Intermolecular coupling and many-body interactions

“…[7][8][9][10][11][12] Unfortunately, such systems come with a substantial drawback: The photo-isomerization rate is drastically suppressed due to steric hindrance or excitonic coupling. 13,14 A number of experimental strategies have been suggested to overcome this problem, such as replacing the aliphatic linker by an aromatic one 15 or even bulkier groups, [16][17][18] or diluting the azobenzene moieties in densely-packed alkanethiolate SAMs. 14,[19][20][21][22] From a theoretical viewpoint the issue of hindered photo-isomerization in densely-packed azobenzenefunctionalized SAMs has been addressed by a few works, mainly focused on the excitonic coupling between the chromophores, 23,24 as well as on the effects of a metal substrate.…”

Thiocyanate Anchors for Salt-like Iron(II) Complexes on Au(111): Promises and Caveats

“…Bulging head groups are accommodated best if they can enter into lateral interactions, such as π-π stacking [8]. A complementary approach to accommodate bulging head groups employs voluminous anchor groups [9], sometimes with multiple surface-binding functions [10]. The coating of (near-)spherical gold nanoparticles, whose curved surface alleviates the 'space problem' caused by bulging head groups, with suitably functionalised transition metal complexes, has recently been reviewed [11].…”