LANGMUIR-BLODGETT-FILM ASSEMBLY OF NOVEL DYE MOLECULES SUBSTITUTED BY A STEROID SKELETON - MOLECULAR DESIGN FOR UNIFORM FILMS

Amphiphiles including dye skeletons such as 7,7,8,8-tetracyanoquinodimethane (TCNQ), p-phenylenediamine (PD), p-quinonediimine (QI), tetrathiafulvalene (TTF), p-benzoquinone (BQ), and anthraquinone (AQ) were newly synthesized to obtain a design rule to produce uniform LB films. The amphiphiles were divided into four groups, based on the differences in hydrophobic tails: monoalkyl derivatives (group 1); tere-dialkyl or tere-tetraalkyl derivatives (group 2), where long alkyl chains were attached to the dye skeleton at separate locations; ortho-dialkyl derivatives where two alkyl chains were attached to the dye skeleton at adjacent locations (group 3); and steroid derivatives (group 4). The amphiphiles including large dye moieties in groups 1 and 2 generally formed unstable monomolecular films on a water surface, if their hydrophilic properties were weak. The latter two groups, whose hydrophobic tails could be closely packed together, yielded stable and condensed monomolecular films. The films for group 3, however, indicated high surface viscosity values (> 1 g/s at 10 dyn/cm), resulting in inhomogeneous LB films. Group 4 molecules yielded less viscous films, resulting in homogeneous LB films. Furthermore, introducing a large and/or strong hydrophilic head into group 3 or 4 compounds was effective for decreasing the viscosity values (10(-1)-10(-2) g/s) and producing homogeneous LB films. The geometric sizes and molecular cohesions of the amphiphiles were found to have great influence on the film-forming properties. Optimum molecular structures for producing uniform dye LB films were discussed.