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 degrees 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.