VIBRATIONAL DAVYDOV SPLITTING IN 7-(2-ANTHRYL)-1-HEPTANOIC ACID LANGMUIR-BLODGETT FILMS

The IR absorption spectrum of Langmuir-Blodgett multilayers of 7-(2-anthryl)-1-heptanoic acid (I) deposited onto CaF2 substrates was recorded between 1800 cm-1 and 1400 cm-1 using normally incident polarized light. For multilayers deposited from a pH 4.9 subphase the C=O stretch at approximately 1700 cm-1 shows a polarization similar to that observed for the monoclinic forms of single-crystal fatty acids. This band is split by 14 cm-1 into two components that are polarized parallel and perpendicular to the transfer direction. This polarization effect is explained by vibrational Davydov splitting and indicates local order, or island formation, with a preferred, macroscopic orientation induced by the transfer process.