CONTROL OF MOLECULAR-ORIENTATION AND AGGREGATION OF SQUARYLIUM DYES IN THE MONOLAYER BY SUBSTITUTED ALKYL SUBSTITUENTS - FABRICATION OF THE LANGMUIR-BLODGETT-FILMS CONTAINING J-AGGREGATES AND H-AGGREGATES

We have synthesized a wide variety of squarylium dyes 2-[4-(dialkylamino)phenyl]-4-[4-(dialkyliminio)-2, 5-cyelohexadienylidene]-3-oxo-l-cyclobuten-l-olate with different lengths of alkyl substituents. π-A isotherms and UV-Vis. absorption spectra were measured for these dye monolayers on water surface. It has been found that orientation and aggregation of the dyes in the monolayers can be controlled by combination of the alkyl substituents. J-aggregates of squarylium dyes were obtrained in the monolayers of bis[4-(N-propylalkyl-amino)phenyl]squaryliumdye s (when alkyl substituent is longer than propyl) on water surface. It is very interesting that two propyl substituents at both ends of the chromophore facing to water side cause to form the J-aggregete. On transfering to solid substrates by Langmuir-Blodgett method, these J-aggregates formed on water surface easily transform to other kinds of aggregates. However, LB-films containing J-aggregate can be deposited successively with mixed monolayer of Cd-icosanoate and bis[4-(dipropylamino) phenyl] squarylium dye in the molar ratio of 1:1 at the surface pressure of 30 mN/m. In these conditions, the monolayer of squarylium dye at higher compression undergoes transition resulting in a multiplied (mainly triple) structure, where the J-aggregates of dye are stabilized by the surrounding monolayer of the Cd-icosanoate. In the monolayer of bis[4-(dibutylamino)phenyl]squarylium dye, reversible change of absorption spectra were observed among J-aggregete, H-aggregate and monomeric species by the compression and the expansion of the monolayer at the subphase temperature of 5°C. Almost pure H-aggregates were formed at 20°C. LB-films containing H-aggregates were deposited at the surface pressure of 20 mN/m at 20°C. These results indicate that aggregation forms of squarylium dye in LB-films can be controlled by the position and the length of the alkylsubstituents. The LB-films of J-and H-aggregates of squarylium dyes are expected to exhibit advanced functions for organic thin film devices, such as photoelectric devices, chemical sensors using fluorescence and so on. © 1990, The Chemical Society of Japan. All rights reserved.