Langmuir-Blodgett Films of Retinal Derivatives

We report characterization studies of Langmuir films and Langmuir-Blodgett multilayers of 13-cisretinoic acid, 13-cis-retinal aldehyde, all-trans-retinoic acid, and all-trans-retinol palmitate. We have examined the stability of the floating monolayers prepared on an air-water interface, and the values estimated for the mean molecular areas before collapse are consistent with previous results for other retinal derivatives. After successful transference of the monolayers to form Langmuir-Blodgett films on different solid substrates, we have applied standard infrared spectroscopic techniques to investigate the structural organization of the deposited multilayers of the latter three compounds. By combining the information gathered from the isotherm compression curves of the Langmuir films to the analysis of the relative intensities of characteristic retinal peaks on the grazing angle and attenuated total reflectance spectra of the solid films, we have qualitatively estimated the orientation of the deposited molecules relative to the substrate. We comment on the implication of these results for the use of Langmuir-Blodgett films of retinal derivatives in molecular electronic devices.