Photoswitching of azobenzene-containing self-assembled monolayers as a tool for control over silicon surface electronic properties

Abstract

We report on photoinduced remote control of work function and surface potential of a silicon surface modified with a photosensitive self-assembled monolayer consisting of chemisorbed azobenzene molecules (4-nitroazobenzene). It was found that the attachment of the organic monolayer increases the work function by hundreds of meV due to the increase in the electron affinity of silicon substrates. The change in the work function on UV light illumination is more pronounced for the azobenzene jacketed silicon substrate (ca. 250 meV) in comparison to 50 meV for the unmodified surface. Moreover, the photoisomerization of azobenzene results in complex kinetics of the work function change: immediate decrease due to light-driven processes in the silicon surface followed by slower recovery to the initial state due to azobenzene isomerization. This behavior could be of interest for electronic devices where the reaction on irradiation should be more pronounced at small time scales but the overall surface potential should stay constant over time independent of the irradiation conditions.

Understanding of the Kinetic Stability of cis‐ Isomer of Azobenzenes through Kinetic and Computational Studies

“…Azobenzene (AB) derivatives are widely used as photo switchable systems for various applications. [1][2][3][4][5] Most interesting features of ABs are their capability to undergo fast, efficient, and reversible photo-isomerization (trans-! cis-) without sufficient photo bleaching.…”

Self-Assembly-Triggered Cis-to-Trans Conversion of Azobenzene Compounds

“…Azobenzene compounds have been extensively employed in the construction of diversified photoresponsive materials in virtue of their trans–cis conversion triggered by photoirradiation. − It is well-established that the azos undergo trans-to-cis conversion under UV irradiation, while the reverse process occurs under visible light or via thermal relaxation. − In many cases, one can hardly get complete trans isomers in an azo system due to the overlap of the n-π* transition of the trans and the cis isomers. ,, As a result, the azo compounds are always a mixture of the trans and cis isomers in a photostationary state (PSS). ,− Because the cis isomers are nonplanar with larger dipole, they can hardly self-assemble into well-defined structures, which disfavors applications where planar geometry of azos are required. − Although separation of the n-π* transition of the trans and the cis forms via synthetic approaches is possible, ,,, it does not ideally lead to entire trans-to-cis conversion either, which appeals reconsidering the physical insight that governs the photostationary state of azo systems. Herein we show that by viewing the PSS of azos as chemical equilibrium between the trans and the cis azos, the cis-to-trans transition was found to occur simply by inducing the self-assembly of the trans isomers.…”

Photoisomerization of an Azobenzene‐Containing Surfactant Within a Micelle

“…The azobenzene isomerization in (potentially) confining environments, such as in self‐assembled monolayers (SAMs) assembled on planar surfaces [20–22] and on gold nanoparticles, [23] or when azobenzene is confined within a coordination cage, [24] has been addressed by several experimental and theoretical works [25–28] . In some cases the photoswitching cannot be detected, [20,27] whereas in others it has been possible to observe isomerization [22,28] . The parameters such as density of azobenzene units, their orientation, and the substitution pattern appear to be decisive for photoisomerization to take place.…”