Structure and Orientation of 1-Hydroxyl-5-Hexadecyloxy-Naphthalene LB Films Studied By UV-VIS and FTIR Spectroscopy

Ultraviolet-visible (UV-Vis), infrared transmission, and reflection absorption(RA) spectra have been measured for one-and multi-monolayer Langmuir-Blodgett(LB) films of C₁₆H₃₃30Naph(1,5)OH at various temperature to investigate dependencies of the aggregation and phase transitions on the number of monolayers. The UV-vis spectra of the LB films have revealed that the C₁₆H₃₃ONaph(1,5)OH forms aggregates in the LB film. From the temperature dependence of UV-vis absorption spectra, it is clear that the aggregate is gradual converted to monomer upto 80 °C. A comparison of the infrared transmission and RA spectra reveals that the hydrocarbon chains are tilted considerably in the LB film. As for the naphthalene ring part, the result suggest that the ring plane is oriented approximately perpendicular to the substrate surface. The Temperature dependence of infrared transmission spectra have been measured for 1-, 3-, and 11-monolayer LB films to investigate dependence of phase transitions on the number of monolayers. These observations show that the one-monolayer LB films does not have a clear order-disorder transition, while the three-and eleven-monolayer films have a phase transition near 60 °C. Therefore, it seems that the title angles of both the alkyl chain and chromophore part change largely concomitantly with the conversion from the aggregate to the monolayer.