Synthesis of Unzipping Polyester and a Study of its Photochemistry.

Preparation of an unzipping polyester is reported. The monomer was prepared from benzoic acid in a four-step sequence. Step growth polymerization of the monomer provides the target polymer. Efficient depolymerization upon irradiation at 254 nm was confirmed with a quantum yield of >0.8. The photolysis mechanism was investigated, and the results of radical trapping experiments are consistent with an initial Norrish type I like homolysis followed by a radical mediated depropagation reaction driven by aromatization.

Study of a two-stage photobase generator for photolithography in microelectronics.

The investigation of the photochemistry of a two-stage photobase generator (PBG) is described. Absorption of a photon by a latent PBG (1) (first step) produces a PBG (2). Irradiation of 2 in the presence of water produces a base (second step). This two-photon sequence (1 + hν → 2 + hν → base) is an important component in the design of photoresists for pitch division technology, a method that doubles the resolution of projection photolithography for the production of microelectronic chips. In the present system, the excitation of 1 results in a Norrish type II intramolecular hydrogen abstraction to generate a 1,4-biradiacal that undergoes cleavage to form 2 and acetophenone (Φ âˆ¼ 0.04). In the second step, excitation of 2 causes cleavage of the oxime ester (Φ = 0.56) followed by base generation after reaction with water.

Design and synthesis of a photoaromatization-based two-stage photobase generator for pitch division lithography.

The synthesis of a two-stage photobase generator (PBG) based on photoinduced aromatization is described. This material was designed for use in resolution-enhanced photolithography. Computer modeling predicts that a delay in the onset of base generation can lead to improved image quality. This delay can be realized by a PBG that must undergo two sequential photoreactions for each molecule of base generated. Toward that end, latent PBGs were designed that are oxime esters of aliphatic acids, which undergo Norrish type II reactions to yield oxime esters of aromatic acids that are efficient PBGs.

Free-floating ultrathin two-dimensional crystals from sequence-specific peptoid polymers.

The design and synthesis of protein-like polymers is a fundamental challenge in materials science. A biomimetic approach is to explore the impact of monomer sequence on non-natural polymer structure and function. We present the aqueous self-assembly of two peptoid polymers into extremely thin two-dimensional (2D) crystalline sheets directed by periodic amphiphilicity, electrostatic recognition and aromatic interactions. Peptoids are sequence-specific, oligo-N-substituted glycine polymers designed to mimic the structure and functionality of proteins. Mixing a 1:1 ratio of two oppositely charged peptoid 36mers of a specific sequence in aqueous solution results in the formation of giant, free-floating sheets with only 2.7 nm thickness. Direct visualization of aligned individual peptoid chains in the sheet structure was achieved using aberration-corrected transmission electron microscopy. Specific binding of a protein to ligand-functionalized sheets was also demonstrated. The synthetic flexibility and biocompatibility of peptoids provide a flexible and robust platform for integrating functionality into defined 2D nanostructures.

Iridium-catalysed direct C-C coupling of methanol and allenes.

Methanol is an abundant (35 million metric tons per year), renewable chemical feedstock, yet its use as a one-carbon building block in fine chemical synthesis is highly underdeveloped. Using a homogeneous iridium catalyst developed in our laboratory, methanol engages in a direct C-C coupling with allenes to furnish higher alcohols that incorporate all-carbon quaternary centres, free of stoichiometric by-products. A catalytic mechanism that involves turnover-limiting methanol oxidation, a consequence of the high energetic demand of methanol dehydrogenation, is corroborated through a series of competition kinetics experiments. This process represents the first catalytic C-C coupling of methanol to provide discrete products of hydroxymethylation.