FT-infrared and pyroelectric studies on calix[8]arene Langmuir-Blodgett films.

Pyroelectric activity is exhibited by materials which possess a spontaneous temperature-dependent electric polarisation. These materials generate a current as their temperature is changed. Many classes of organic materials exhibit pyroelectric activity but only if processed in such a way that a non-centrosymmetric arrangement of dipole results. When deposited as alternate layers by the Langmuir-Blodgett (LB) technique a macroscopically polar assembly is formed. To date, the best performance has been achieved by alternately depositing two materials, one containing acid groups and the other containing amine groups. Calixarenes are one family of materials which are particularly good vehicles for the acid and amine groups. Alternate layer LB films of acid- and amine-substituted calixarenes have high pyroelectric coefficients and form extremely robust films. Fourier transform infrared (FTIR) spectroscopy is a useful tool in examining the properties of thin film samples. Using the FTIR techniques of attenuated total reflection (ATR) and reflection-absorption infrared spectroscopy (RAIRS) it is possible to study the behaviour of the acid and amine groups within the pyroelectric samples.This thesis describes the pyroelectric properties of a series of calix[8]arenes. The dependence of the pyroelectric coefficient on temperature, film thickness and substituent chain length is analysed. The infrared spectra show that the acid and amine groups interact by proton transfer but also that the remaining acid groups form either facing dimers with the amine or sideways dimers between themselves. The spectra do not change with temperature. This demonstrates that the films are thermally stable. Additionally, this invariance shows that the pyroelectric activity in these films does not arise from a change in the proton transfer as has been previously postulated. Theoretical calculations undertaken predict that the source of the dipole change required for the level of pyroelectric activity seen is likely to be a change in distance between the acid and amine groups. Further observations, quantitatively examined by curve fitting techniques, show that the greater the number of proton-transferred pairs, the lower the pyroelectric coefficient. Thus, only the temperature-dependent separation of the acid and amine pairs which have not undergone proton transfer is responsible for the pyroelectric activity in these systems.