We report the formation and subsequent topochemical polymerization of semi-fluorinated self-assembled monolayers (SAMs) containing diacetylene groups. The SAMs used were formed via the adsorption of the following derivatives: CF3(CF2)n(CH2)16CtCsCtC(CH2)10SH (n ) 2, 3) and CF3(CF2)n(CH2)11CtCsCt C(CH2)10SH (n ) 9, 12) onto the surface of gold. The polymerization of the monolayers was initiated by UV irradiation and was monitored using resonance Raman spectroscopy. SAMs with short semi-fluorinated portions were found to polymerize more effectively than those with longer portions, indicating that steric factors become important with increasing perfluorinated chain length.

We demonstrate that it is possible to achieve exceptionally fine control over the anchoring of liquid crystals via the use of semi-fluorinated self-assembled monolayers of varying spacer length. We use this approach to map the detailed shape of an anchoring transition surface in thermodynamic phase space and to explore the links between anchoring and orientational wetting phenomena. These results allow one to design a substrate that will place a standard liquid-crystal film arbitrarily close to an anchoring transition between homeotropic and planar anchoring.

We studied the anchoring of 6CB on a series of self-assembled monolayers (SAMs) with a functional group that mimics that of the nematic liquid crystal (LC). The SAMs were first characterized by wetting, Fourier-transform infrared spectroscopy, and surface potential measurements. We found that, in two of these SAMs, the end group dipoles were oriented close to the normal of the surface and that these promoted homeotropic anchoring. In the case of the other SAM, the dipole was oriented parallel to the surface, and planar anchoring was obtained. Raman scattering by adsorbates on thin metal films is enhanced by the electromagnetic fields of surface plasmon polaritons (SPPs). Despite the inherent polarization of SPPs, there have been few reports in which SPP Raman scattering has been used to study molecular orientation. We have developed optical instrumentation to provide efficient excitation and collection of SPP Raman scattered light using attenuated total reflection geometry. The Kretschmann prism coupling configuration was used to excite SPPs on thin (500 A) gold films with adsorbed SAMs of alkanethiols in contact with thin films (50 microm) of the nematic liquid crystal 4'-hexylbiphenyl-4-carbonitrile (6CB, Merck). The anchoring and orientational wetting of the LC 6CB at the interface with omega-functionalized SAMs was studied using this arrangement. In agreement with the results of previous studies, a high-energy surface (-COOH) was found to promote planar anchoring, whereas a low-energy surface (-CF(3)) was found to induce homeotropic anchoring.