Atomic Force Microscopy Studies of Photoisomerization of an Azobenzene Derivative on Langmuir−Blodgett Monolayers

Single Component Self‐Assembled Monolayers of Aromatic Azo‐Biphenyl: Influence of the Packing Tightness on the SAM Structure and Light‐Induced Molecular Movements

“…Significantly, very similar rates of the thermal back reaction have been found for AZO2 SAMs [k ¼ (1.67 AE 0.10) Â 10 À4 s À1 (Au); k ¼ (1.33 AE 0.06) Â 10 À4 s À1 (Pt)] and AZO2 in solution [k ¼ (1.19 AE 0.09) Â 10 À4 s À1 ] suggesting that the switching in the SAMs is not additionally hindered by a lacking free volume [18][19][20][21][22][23][24][25][26]28] and is mostly a property (in the sense of the yield and kinetics) of the individual molecules. This agrees perfectly with a low packing density and orientational order in these films (see below).…”

“…[16,17] The utilization of these proposed functions requires the arrangement of the molecules containing the photoactive azogroup in a medium other than solution, e.g., as either Langmuir-Blodgett (LB) films or self-assembled monolayers (SAMs). However, early studies performed on both LB films [18,19] and SAMs [20,21] of azo-containing compounds showed a poor yield of photoisomerization. This behavior is generally explained by the change in the occupied crosssectional area that is due to isomerization from the almost planar/extended trans-to the non-planar/contracted cisisomer.…”

“…For instance, photoswitchable surfaces have been obtained by lowering the surface pressure during the formation of LB films to get more loosely packed molecular assemblies. [18] Also, photoactive SAMs on Au have been obtained upon ''dilution'' of the azobenzene molecules in a mixed monolayer by using coadsorption from a solution containing the azobenzene derivative and a short ''spacer'' molecule that ''frees up'' volume. [20,24] However, using this method it is difficult to control the ratio between the spacer units and functional azo-molecules in the SAM.…”

Synthesis and characterization of novel azobenzene-based mesogens and their organization at the air–water and air–solid interfaces

“…23 Photo-isomerization kinetics at the air-water interface of the Langmuir monolayers of mesogenic azobenzene dimers have been thoroughly studied by Kumar et al 24 Thin lms of LC mesogens, containing the azobenzene group form promising candidates for the fabrication of devices because the LCs can offer high sensitivity and high control over the architecture using the LB technique. 24,25 Ozaki and his co-workers have reported phase transitions in the LB lms of azobenzene-containing long chain fatty acids based on the spectroscopic studies of H-aggregates. 26,27 In this study, we synthesized new oligomeric mesogens consisting of an azobenzene-based core attached to which are four 4-cyanobiphenyl units via exible alkyl spacers.…”

J-aggregates in matrix stabilized two-dimensional azobenzene derivatives

“…Langmuir monolayers at the air-water interface provide a versatile framework to achieve excellent control of the selfassembly process that converts surfactants from a disordered state into a well-ordered solid state [1][2][3][4] through the formation of interfacially confined, two-dimensional (2D) ordered aggregates [5]. Structured/oriented films are constructed by transferring floating monolayers from the air-water interface to an oriented solid substrate [6][7][8].…”