STRUCTURAL CHARACTERIZATION OF LANGMUIR-BLODGETT-FILMS DERIVED FROM MULTISULFUR HETEROCYCLES

A novel multisulfur heterocyclic compound with alkyl chains, C3S5(C18H 37)(2) (4,5-bis(octadecylthio)-1,3-dithiole-2-thione), has been synthe sized and fabricated into Langmuir-Blodgett (LB) films. The structure of this film on SiO2 slides has been studied using X-ray photoelectron spectroscopy (XPS) and SR and UV transmission linear dichroism (LD) m easurements. From the isotherm, it is known that the Langmuir film at the air-water interface is a bilayer. Angle-resolved XPS of films tran sferred to SiO2 show that the alkyl chains of the molecule form the to pmost layer of the film, with the C3S5 ring underneath the alkyl layer . Electronic structure calculations indicate that the transition momen t associated with the observed UV band lies coincident with the C-2 ax is of the C3S5 ring group. In order to properly interpret the polarize d absorption data, a simple model addressing The local field effect in LD measurements was developed. Incorporating measured information on the polarizability of the chromophore, UV and IR LD measurements showe d the ring plane and the chains to be stacked at 69 degrees and 20 deg rees, respectively, relative to the surface normal. These data coupled with the XPS results permitted a structural model to be constructed w hich accounts for the multilayer structure of the transferred film.