Oligothiophene-derivatized azobenzene as immobilized photoswitchable conjugated systems

Abstract

Immobilization of an azobenzene-bithiophene compound on a gold surface leads to self-assembled monolayers with photoswitchable electrical properties.

Self‐assembled Azobenzenethiol Monolayer on Electrode Surfaces: Effect of Photo‐switching on the Surface and Electrical Property

“…The oxidation behavior is thought to relate to 1) the work function of the metal electrode involved; 2) the tunneling barrier introduced by the adsorbed species; and 3) the permeability of the adsorbed film which relates to the structural order of the film. From the perspective of work function, the work function measured for the a:C12 modified Au are 5.23 eV and 5.15 eV for trans state and cis state respectively, both of which are lower than the HOMO level of Fe(CN) 6 3-/4-. The work function measured for c:C6 modified Au are 4.59 eV and 4.69 eV for trans state and cis state respectively, both of which are higher than the HOMO level of Fe(CN) 6 3-/4-.…”

“…23 Whereas the traces measured after each UV irradiation (thus the azo moiety in cis state), an increase in current around +0.38~+0.41 V can be observed. This suggests that oxidation of Fe(CN) 6 4can proceed 22 with the azobenzene in the cis state. In contrast, for Au electrode modified with c:C6 monolayer, higher current was observed before UV-irradiation or after each visible light irradiation, suggesting oxidation at around +0.41~+0.42 V proceeds more readily when the azobenzene is in the trans state.…”

“…However, the change in work function is also accompanied by a change of the molecular shape and possibly the film thickness or shielding on the surface, which introduces different barriers for charges transport at the interface. We use the azobenzenethiol-modified Au electrode to probe the interplay of the two factors in the redox behavior of Fe(CN) 6 3-. 22 To avoid the reduction/oxidation behavior of azobenzene moieties, the scan range was set from 0.2 V to 0.7 V. 10,15a,21 Under the above condition without UV or visible irradiation, the CV curves are stable.…”

“…The reversible isomerizations and the physical or electrochemical changes associated with it have also been extended to a wide range of applications, including molecular switches, actuators and sensors. [1][2][3][4][5][6][7][8] The switching between trans-and cis-forms can be activated not only photochemically 9 but also electrochemically. 10 Azobenzene derivatives have also been anchored on various surfaces through silyl or mercapto functional groups to form a monolayer coating to modulate the physical property of the surface through the conformational switching of the azobenzene moiety.…”

Molecular Nanoelectronics

“…A short spacer should favor the electron transfer rate through the junction and increases its conductance, while a longer spacer could improve the decoupling of the azobenzene moiety from the substrate, thus allowing a larger dynamic of the switching event, and thus a larger "on/off" conductance ratio. Recently, we reported the synthesis and the electrical properties of a new molecular switch in which the azobenzene moiety is linked to a bithiophene spacer and a short (4 carbon atoms) alkanethiol [149,150]. Such a design is expected to combine the benefit of a rather long spacer, while preserving a sufficiently high level of current due to the presence of electron-rich bithiophene unit (compared to a fully saturated spacer with the same length).…”