Self-assembly and photoisomerization of azobenzenealkanethiol derivatives on gold films: Infrared reflection absorption studies

Self-assembly and photoisomerization of 4-(4'-(phenylazo) phenoxy) undecane-1-thiol and its fluoro- and methoxy-phenylazo derivatives on evaporated gold films have been characterized by infrared reflection absorption spectroscopy. The infrared measurements as a function of self-assembling time show that their self-assembling proceeds through Langmuir adsorption with a settlement in alignment of the azobenzene moiety and the aliphatic long chain. Moreover, photoisomerizations of these compounds from trans to cis and vice versa are very, limited in their close-packed monolayer films in contrast to the molecules in solution. However, such restrictions are somewhat relaxed for a self-assembly film of the cis-form methoxy-phenylazo derivative. This effect of preferential cis-form assembling is also demonstrated by the changes in the alignment of 4-cyano-4'-pentylbiphenyl (5CB) nematic liquid crystalline molecules caused by conformational changes of the underlying self-assembled molecules.