Langmuir Monolayers of Azobenzene Derivative with a Urea Head Group

An azobenzene (Az) containing amphiphile having a urea head group [N-(10-{4-[(4-hexylphenyl)azo]phenoxy})decylurea (6Az10-Urea)] was synthesized for the first time, and the spreading behavior, morphology, absorption spectral features, and photoreactivity of this amphiphile at the air–water interface was examined. The features of this monolayer were argued in comparison with those of a carboxylic acid derivative of the homologous structure. Polymer-like stable stable monolayers were formed form 6Az10-Urea both in the trans and cis forms of the Az unit, possibly indicating the formation of intermolecular bifurcated NH···O=C hydrogen bonds of urea heads. Unlike monolayers of simple long alkylureas, the present monolayer did not show a thermal phase transition within the temperature region examined (10—35 °C). In the trans-6Az10-Urea monolayer, the Az unit formed tilted aggregates. In this aggregation state, the trans-to-cis photoisomerization in the 6Az10-Urea monolayer was completely hindered despite the fact that the monolayer was more expanded than that of a corresponding carboxylic acid derivative in which the photoisomerization proceeded.