Infrared transmission, visible absorption, and resonance Raman spectra of 15-monolayer Langmuir-Blodgett (LB) films of 2-(4'-(dioctadocylamino)phenylazo)-N-methylbenzothiazolium perchlorate (Azo 11) have been measured at elevated temperatures, and the order-disorder transition of the films has been investigated. Upward shifts of CH2 antisymmetric and symmetric stretching bands of the hydrocarbon chains suggest that the orderdisorder transition of the tail groups occurs around 70 OC in the films. Prior to the transition, the two CHI stretching bands show broadening (50-70 "C), indicating that the alkyl chain mobility begins to increase before their conformational disorder occurs. The visible absorption and resonance Raman spectra of the LB films of Azo I1 undergo marked changes in the same temperature range as the infrared bands due to the CH2 stretching modes show the broadening. The spectral changes in the visible absorption and resonance Raman spectra are indicative of the conversion from an H-aggregate to monomers in the chromophoric part of Azo 11, and therefore, it seems likely that the conversion is linked with the increase in the mobility of the hydrocarbon chains. Cyclic thermal treatment experiments in the infrared spectra of the Azo I1 LB film show that not only bands due to the chromophoric part but also the CH2 stretching bands do not return to original spectral features after the temperature is cycled to 70 "C. This result indicates that the orientation and/or aggregation in the head groups do not recover upon the cyclic thermal treatment to 70 OC and that the remaining disorder in the head groups hinders reversible order4isorder transition in the alkyl tails.

The self-associations of butan-1-ol, butan-2-ol, and 2-methylpropan-2-ol ( tert-butanol) in the pure liquid state and in carbon tetrachloride solutions have been studied mainly through near-infrared spectroscopic observation at various temperatures. A new analysis assuming a successive association process for the alcohol molecules was applied to the sharp band around 1410 nm (the first-overtone band of the OH stretching vibration mode attributed to free OH monomer and partly to OH polymer); it became clear that the mean association number for each alcohol increases with increasing concentration and decreases with increasing temperature. Comparisons of the association numbers at various constant temperatures for the three kinds of alcohols show that the association abilities are on the order butan-1-ol > butan-2-ol > 2-methylpropan-2-ol.