(556c) Synthesis and Characterization of Bifunctional Silica Imprinted Surfaces

An important capability for enabling several technologies and applications in the future is the nanoscale organization of two different chemical functional groups on a solid surface. Covalent silica imprinting in principle offers a solution to this problem by using a molecular template for organizing chemical functional groups on silica surfaces, on length scales that are generally too small to achieve with conventional lithographic approaches (< 2 nm). The imprinting process consists of immobilizing the imprint molecule, which consists of protected chemical functional groups, and subsequently deprotecting these groups after immobilization has been accomplished, thus leaving behind the desired chemical functional group organization on the surface. Although imprinting has been used for more than sixty years for the preparation of patterned surfaces, it has principally remained limited to the organization of a single type of functional group per site. We demonstrate the first covalent imprinting of two different types of functional groups per site, consisting of an amine and thiol spaced apart by approximately 1 nm, both of which are connected to the silica surface via a propyl tether, but are not connected to each other in any other fashion. This has been accomplished by developing an imprinting approach that relies on thermally labile protecting groups for the amine and thiol. We have successfully synthesized imprints containing a protected thiol-amine pair and have implemented them in both surface-functionalized and bulk imprinted silica synthetic approaches. The nanoscale organization in both surface-functionalized and bulk materials is compared by using a molecular probe that is able to covalently bind to the thiol-amine pairs and thereby produces a chromophore, which is highly specific for the imprinted organization. The results of our studies demonstrate the difficulty of achieving site isolation when using a surface-functionalized synthetic strategy, and the importance of a bulk silica synthesis strategy when imprinting silica with multiple different chemical functionalities. The resulting materials can be used as a versatile scaffold for selective nucleation and preparation of materials with higher levels of organization by utilizing orthogonal coupling strategies, and some of these are demonstrated for materials characterization purposes.