Optically Induced Switching of Azobenzene Containing Self Assembling Monolayers Investigated by Kelvin Probe and Scanning Force Microscopy

Abstract

Mol Cn,1. Lly C r y / , VOI. 35s. pp 401-41 I Kcprints avdilable directly fiom the puhlishrr Photocopying permitted by liceme only 0 2001 OPA (Oier\e.c\ I'uhliihcn Awiclanon) N.V. Published by licence under the Gordon and Breach Science Publishers imprint.The light induced switching of self-assembled monolayers containing azobenzenes is observed in situ by the Kelvin probe method. The switching process is optimized by preparing monolayers from mixed solutions of azobenzene thiols and n-alkylene thiols. In a film the efficiency of the E/Zisornerization depends on both the spacer length between azobenzene group and gold surface as well as the free volume in the film, tuned by the n-alkylene thiol fraction in the mixture. An optimum was found in a mixed self-assembling film conlaining 33% 4-fluoromethyl-4'-(lO-carboxy-decyloxy) azobenzene in a dodecane thiol matrix. The structure of the films were characterized by lTIR and AFM.

Optical patterning in azobenzene polymer films

“…Although scanning probe microscopy itself is not able to visualize the process of molecular isomerization or reorientation, it is often used for visualization and inspection of the inscribed nano‐ and micro‐structures (Stiller et al ., 2000, 2001). In this study we have used atomic force microscopy (AFM) not only to visualize the photoinduced structures but also to detect mechanical changes of the optically modulated film surface.…”

Photoemission from Azobenzene Alkanethiol Self-Assembled Monolayers

“…[1][2][3][4] Their electronic and thermal properties make them promising molecular moieties for optical molecular switches, optoelectronic and nonlinear optical applications, as well as for sensors. [1][2][3][4] Combined with the potential of SAMs to modify surfaces, such azobenzene functionalized systems represent invaluable model systems of biological and technological interest. SAMs of alkanethiols are among the most intensively studied systems as they can be easily bound to several relatively inert metal surfaces (e.g., Au, Ag) via reaction with the thiol group.…”

“…This process is reversible, and irradiation with 450 nm light, corresponding to the absorption maximum for the reverse transformation, almost entirely reestablishes the initial film configuration. [2][3][4] This back-and-forth switching has been recently demonstrated by directly measuring the surface potential change over several switching cycles using the Kelvin probe method. 4 The difference in surface potential between the two isomers is related to the net change of the molecular dipole moment (normal component with respect to the surface).…”

Fast optical work-function tuning at an organic/metal interface

“…[2][3][4][5][6][7][8] To extend the idea from a statically modified surface to a responsive surface or interface that is controllable by an external stimulus, the organic layers can be functionalized with molecular switches like the photochromic azobenzene. [9][10][11][12][13][14][15][16][17] Its isomerization from the ground-state trans into the meta-stable cis form can be triggered by UV irradiation whereas illumination with blue light leads to back-switching. 18,19 While the planar inversionsymmetric trans configuration has no static dipole moment, the bent cis isomer is strongly polar.…”

“…So far, in such experiments commonly photon fluxes in the order of 10 16 photons/s cm 2 or less were used, and hence, light-induced changes in the work function required several minutes to attain a photostationary state (PSS). [9][10][11][12][13][14]17 This would be too slow for useful applications. To drive the system into a desired PSS rapidly, we use the tunable interplay of laser light of two wavelengths corresponding to the S 1 and S 2 absorption bands of our azobenzene chromophore.…”