Photoisomerization of the azobenzenes included in Langmuir-Blodgett films of cyclodextrins

A new type of photochemical Langmuir-Blodgett (LB) film containing azobenzenes (p-phenylazobenzoic acid (PAB), methyl red (MR) and methyl orange (MO)) without long alkyl chains was prepared by the host-guest interaction with an amphiphilic cyclodextrin derivative. The azobenzenes in the LB film of the host- guest complex exhibited an excellent cis-trans photoisomerization, while trans-to- cis photoisomerization was restricted for LB films of long chain azobenzene derivatives alone. The cavity of cyclodextrin provides a favourable environment for the photochemical reaction leading to an increase in the molecular area in the rigid LB film. The half-life times of cis isomers of PAB, MR and MO in the host-guest complex LB films were 35 h, 55 s and 13 min respectively at 20°C.