Dependences of thermal behaviors on the number of layers in Langmuir-Blodgett (LB) films of 7,8, have been investigated for both morphological and molecular structural aspects by using ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. The temperature-dependent morphological changes have been monitored by the base-line shift in the UV-vis spectra of the LB films. The changes in the base-line in the 450-600 nm region suggest that the domains in the one-layer film decompose progressively with temperature even just above room temperature. In contrast, the domains in the seven-and 11-layer films are stable until 80°C and undergo rather abrupt collapse between 80 and 90°C. These differences in the thermal behaviors of the domain structure between the one-layer film and the seven-and 11-layer films may be attributed to the differences in the film thickness, the effect of the interaction between the first layer and a CaF 2 substrate, and the longitudinal interaction between the domains. The IR spectral measurements for the LB films at elevated temperatures reveal that the order-disorder transition temperature of the one-layer LB film is lower by about 5°C than that of the 11-layer film, which is close to the chain melting point of the bulk material. Of particular interest is that the domain structure of the onelayer film shows the gradual temperature change but that the molecular orientation and structure in the domains experience the clear order-disorder transition.

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The visible and near-infrared excited resonance Raman, infrared, and visible-near-infrared spectra have been measured for six cyanine-7,7,8,8-tetracyanoquinodimethane (TCNQ) anion radical salts. Among them three are insulating simple salts, [DMTzNC][TCNQ], [EMQSeC][TCNQ], and [DETOC][TCNQ] (DMTzNC =3,3'-dimethyl-2,2'-thiazolinocyanine, EMQSeC = l-ethyl-3'-methyl-2,2'-quinoselenacyanine, DETOC = 3,3'-diethyl-2,2'-thiaoxacyanine), and another three are moderately conducting complex salts, [DMTzNC]2[TCNQ]3, [EMQSeC][TCNQ]2, and [DETOC][TCNQ]2. The 1064-nm excited Raman spectra of both the simple and complex cyanine-TCNQ salts are resonance enhanced with a charge transfer transition from TCNQ-to TCNQ-. The simple salts give a spectrum almost identical to that of LPTCNQ-, suggesting the dominance of TCNQ-species in them. In contrast, the complex salts show bands attributed to TCNQO, TCNQ'l2-, and TCNQ-, indicating the coexistence of the species in them. Of particular note is that the spectral patterns of the complex salts are markedly different from each other. Therefore, it seems that the mechanism of the charge transfer differs from one compound to another. The 457.9-, 488.0-, and 514.5-nm excited Raman spectra of the cyanine-TCNQ salts, which are resonance enhanced with a n-n* transition of cyanine dyes, are dominated by their contributions. Comparisons of the spectra with those of iodine salts of the cyanines (DMTzNCT, E M Q S e C T , DETOPI-) suggest that the geometric and electronic structure of the dyes are not perturbed upon complex formation with TCNQ. Although all the infrared spectra of the cyanine-TCNQ salts are characterized by appearances of Ag modes, the spectral patterns of the simple and complex salts can be differentiated by a glance. As in the case of the 1064-nm excited Raman spectra, the infrared spectra of the simple salts exhibit bands due to TCNQ-but do not show those assignable to other species of TCNQ. On the other hand, the infrared spectra of the complex salts are more complicated, showing the coexistence of TCNQ-and TCNQ''2-species. The higher the conducting, the broader the Ag modes and the more remarkable the dips.