Long‐Distance Rate Acceleration by Bulk Gold

Abstract

We report on avery unusual case of surface catalysis involving azobenzenes in contact with aA u(111) surface.A rate acceleration of the cis-trans isomerization on gold up to af actor of 1300 compared to solution is observed. By using carefully designed molecular frameworks,t he electronic coupling to the surface can be systematically tuned. The isomerization kinetics of molecules with very weak coupling to the metal is similar to that found in solution. Fortheir counterparts with strong coupling,the relaxation rate is shown to depend on the spin-density distribution in the triplet states of the molecules.T his suggests that an intersystem crossing is involved in the relaxation process.A side from their impact on catalytic processes,t hese effects could be used to trigger reactions over long distances.

Diazocine functionalized TATA Platforms

“…The lack of conjugation between azo function and ethynyl spacer of 2 yields in a slightly higher half-life which is in agreement with earlier results. [11]…”

“…We recently discovered a purely organic system in the ground state, whose reaction rate is accelerated from days to seconds by electronic coupling to a bulk gold surface via a conjugated linker over 11 bonds and 14 Å. [11] Thermal cis→trans isomerizations of azobenzenes are usually slow with half-lives of the trans isomer within the range of hours to days at room temperature (parent azobenzene: 4-5 d at 25°C). [12] Rotation around the N=N bond is a symmetry forbidden process and the slow isomerization proceeds via inversion at the N atoms.…”

“…[19][20] The length and electronic nature of the spacer units control the distance from the surface and define the electronic coupling with the metal surface. [11,18] With increasing  conjugation from the azobenzene into the platform, and thus coupling to the gold surface, the activation barrier drops to almost zero (~8 kJ mol -1 ) and the frequency factors (logA) become negative. [11] Vanishing barriers and low frequency factors are typical for non-adiabatic reactions.…”

“…[11,18] With increasing  conjugation from the azobenzene into the platform, and thus coupling to the gold surface, the activation barrier drops to almost zero (~8 kJ mol -1 ) and the frequency factors (logA) become negative. [11] Vanishing barriers and low frequency factors are typical for non-adiabatic reactions. [9] The mechanism was elucidated as a singlet-triplet-singlet spin change process, which is forbidden in solution but mediated by coupling to the conduction band of the bulk gold.…”

Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling

“…Furthermore, honeycomb superstructures may turn out useful to control the density of functional molecules on surfaces. In the context of platform molecules, where a functional unit is attached to a molecular base, the pattern of the platforms is imposed on the functional units.…”