MOLECULAR-ORIENTATION IN LB FILMS OF AZOBENZENE-CONTAINING LONG-CHAIN FATTY-ACIDS AND THEIR BARIUM SALTS STUDIED BY FT-IR TRANSMISSION AND REFLECTION ABSORPTION-SPECTROSCOPY

Molecular orientations in Langmuir-Blodgett films of four kinds of azobenzene-containing long-chain fatty acids and their barium salts are quantitatively evaluated by Fourier transform infrared transmission and reflection-absorption spectroscopy. The effects of carbon chain length of the tail and spacer portions, the number of monolayers, and the head group difference between the carboxyl and carboxylate groups on the molecular orientation are examined. It is concluded that the barium salts are more highly oriented as compared with the corresponding acids. This tendency is remarkable between barium salts with an eight-carbon tail and their acids. These results are consistent with our previous results obtained by UV absorption spectroscopy. Further, the orientation of the hydrocarbon chain and the azobenzene chromophore is found to be almost independent of the number of monolayers, but the tilt angle of the symmetrical axis of the carboxylate group in the first monolayer is larger than those in the upper monolayers. This fact may arise from the difference in the mode of barium ion binding between the first and upper monolayers. © 1990, American Chemical Society. All rights reserved.