Molecular assembly in ordered mesoporosity: A new class of highly functional nanoscale materials

Assembly of organized molecular structures in ordered mesoporosity has show n to be a very powerful approach to synthesize novel functional nanoscale m aterials. This approach allows rational design of a wide range of material properties, such as pore dimension, surface chemistry, stereochemistry, spa tial distribution of functionality, etc. This paper discusses molecular con formations and assembly mechanisms and illustrates the principles involved in fabricating sophisticated molecular structures in the pore channels. Fir st, an introduction highlights the important progress in synthesizing and u nderstanding ordered mesoporous materials and in incorporating functional m olecules and groups in these mesoporous materials. Next, the molecular conf ormations of simple alkyl chains are discussed as related to chain lengths and pore geometry. The pore size, as well as the uniformity of the porosity , can affect how the long-chain molecules are assembled. Homogeneous molecu lar layers can be formed in 10 nm pores. Smaller pore sizes cause pore clog ging and chain entanglement. Larger pore sizes increase the degree of pore irregularity and produce disordered multilayer coating. Molecules with inte rmediate chain lengths form better molecular layer structures. Detailed mec hanisms of monolayer formation are studied, and a stepwise growth model is proposed. The step-growth mechanism is due to the surface roughness of the pore channels and is believed to be universal in forming "monolayers" invol ving surfaces that are not atomically smooth. Finally, the development of m ultifunctional nanoporous materials is described. Examples include multifun ctionalized catalysts, hierarchical size-and-shape selective nanoporous mat erials with tunable micropatterns and microcavities. The assembly of multif unctional groups and structures will allow us to develop sophisticated nano scale materials with "enzyme mimic" and "biomimic" properties.