Self-assembly of photofunctional siloxane-based calix[4]arenes on oxide surfaces

The synthesis of photofunctional calix[4]arenes and the formation and characterization of self-assembled monolayers (SAMs) made from them is described. Two identical 4-(N-piperidinyl)naphthalene-1,8-dicarboximide or perylene-3,4:9,10-bis(dicarboximide) chromophores were covalently attached to the upper rim of calix[4]arene at the 1- and 3-positions, whereas the lower rim was functionalized with four reactive silane groups to ensure strong, covalent multisite binding to hydrophilic oxide surfaces such as quartz and silicon wafers. This strategy allows spatially proximate chromophoric dimers to be attached to surfaces, while offering the flexibility of isolating or diluting these dimer units on the surface. Homo- and heterogeneous nanoscale thin films (1.2-2.1-nm thick) were assembled from solution and characterized using synchrotron X-ray specular reflectivity, advancing contact angle measurements, atomic force microscopy, and optical absorption and fluorescence spectroscopy. Optical spectroscopy of the films show that strong electronic interactions occur between the perylene-3,4:9,10-bis(dicarboximide) dimers, while the 4-(N-piperidinyl)naphthalene-1,8-dicarboximide dimers show little interaction. However, in the latter case, the solvatochromic nature of the chromophore illustrates the low-polarity environment of the films.