Photo-induced and thermal reactions in thin films of an azobenzene derivative on Bi(111)

Abstract

Azobenzene is a prototypical molecular switch which can be interconverted with UV and visible light between a trans and a cis isomer in solution. While the ability to control their conformation with light is lost for many molecular photoswitches in the adsorbed state, there are some examples for successful photoisomerization in direct contact with a surface. However, there the process is often driven by a different mechanism than in solution. For instance, photoisomerization of a cyano-substituted azobenzene directly adsorbed on Bi(111) occurs via electronic excitations in the substrate and subsequent charge transfer.In the present study we observe two substrate-mediated trans-cis photoisomerization reactions of the same azobenzene derivative in two different environments within a multilayer thin film on Bi(111). Both processes are associated with photoisomerization and one is around two orders of magnitude more efficient than the other. Furthermore, the cis isomers perform a thermally induced reaction which may be ascribed to a back-isomerization in the electronic ground state or to a phenyl ring rotation of the cis isomer.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New J. Phys. 16 (2014) 053004 C Bronner and P Tegeder New J. Phys. 16 (2014) 053004 C Bronner and P Tegeder 3 New J. Phys. 16 (2014) 053004 C Bronner and P Tegeder 4 New J. Phys. 16 (2014) 053004 C Bronner and P Tegeder 5 New J. Phys. 16 (2014) 053004 C Bronner and P Tegeder 7

Reversible Switching of Spiropyran Molecules in Direct Contact With a Bi(111) Single Crystal Surface

“…This is more than one order higher than for the light‐induced ring opening of a nitro‐SP on Bi(110) . The cross‐section of the photoisomerization of an azobenzene derivate in a ML on the same Bi(111) surface is found as 3.4(3) × 10 −23 cm 2 and therefore even much lower than for the ring opening of SP. Switching of SNP on Bi(111) is thus efficient, compared with other photochromic molecules on surfaces.…”

Long‐Distance Rate Acceleration by Bulk Gold

“…It is known that charge transfer can accelerate the cis-trans isomerization rates of azobenzenes.Azobenzenes that are either oxidized to the corresponding radical cations or reduced to the radical anions exhibit very fast thermal isomerization rates. [17] The low cis-trans activation barriers of azobenzenes directly absorbed on gold nanoparticles [18,19] or lying flat on Au-(111) [20] or Bi(111) [21] surfaces have been explained by atransfer of electron density from the azobenzene to the metal. [19] To investigate if such acharge transfer would be operative in our system, we synthesized azobenzene 6,w here an Au + ion is directly connected to the ethinyl group (Scheme S5).…”

Binding energies of benzene on coinage metal surfaces: Equal stability on different metals

“…We attribute α 2 to desorption from a more densely packed compressed phase, as reported for Bz/Ag(111) 18 or other aromatic organic molecules on noble metal surfaces. 33,34,[47][48][49][50][51] The sub-to monolayer desorption is represented by α 3 . Note that we defined a monolayer to the desorption spectrum shown in red in the inset.…”