Shoji Tamura

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.

Langmuir-Blodgett films of amphiphilic cyclodextrins

Abstract Surface pressure-area isotherms for 12 amphiphilic cyclodextrins (CDs) with alkyl chains were recorded. CDs with long alkyl chains of more than eight carbon atoms form stable monolayers at the air-water interface. The limiting areas per molecule depend on the number of glucose units and the substitution of the secondary hydroxy groups. These areas are in good agreement with the values calculated from the model where the base of the cylindrical part of the molecule is packed closely in a two-dimensional layer. Some of the stable condensed monolayers were deposited as Y- or Z-type Langmuir-Blodgett (LB) films. The molecular orientation in the LB films determined by polarized IR spectra supported the above model.

Photopolymerization of a ω-tricosenoyl derivative of β-cyclodextrin in Langmuir-Blodgett films

Abstract Photopolymerization in the LB films of a newly synthesized ω-tricosenoyl derivative of β-cyclodextrin (vinyl-β-CD) and mixtures with ω-tricosenoic acid have been studied by monitoring the change in IR spectra. Vinyl-β-CD formed a stable monolayer with the closest hexagonal packing of cyclodextrin rings parallel to and long alkyl chains perpendicular to the film plane. The polymerization in the LB films was influenced by the mode of deposition and the composition of the mixtures. It has been found that the intermolecular polymerization of vinyl-β-CD can be promoted through the interposition of ω-tricosenoic acid in the blank space between the hexagonally packed molecules of the cyclodextrin derivative. Solvent resistivity of the LB films containing cyclodextrin with specific functions of the cavity was improved by the polymerization.