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We have used scanning tunneling microscopy to investigate the structure and photoswitching behavior of azobenzene molecules functionalized with bulky spacer groups and adsorbed onto Au(111). We find that positioning tert-butyl 'legs' in a canted arrangement on the azobenzene phenyl rings quenches photoisomerizability of the molecule on Au(111). Addition of cyano groups at the para positions changes the molecular self-assembly significantly, but does not alter the quenched photoisomerizability. This behavior likely arises from a combination of molecule-surface interactions, molecule-molecule interactions, and alteration of azobenzene electronic structure resulting from the position-specific addition of tert-butyl groups. [ABSTRACT FROM AUTHOR]

We have investigated the temperature-dependent behavior of thiolated azobenzene molecules on Au(111) using scanning tunneling microscopy. The addition of a thiol functional group to azobenzene molecules leads to increased surface anchoring of single azobenzene molecules to gold. Thiolated azobenzene shows diverse surface morphology and does not form well-ordered structures at low coverage. At elevated temperatures, anchored molecules are observed to spin in place via hindered rotation. By measuring the number of rotating molecules as a function of temperature and using a simple model, we are able to estimate the energy barrier and attempt frequency for thermally induced hindered rotation to be 102±3 meV and 110±2 GHz, respectively. [ABSTRACT FROM AUTHOR]

A route for generating arrays of printable polythiophene-based gas sensor materials suitable for low-cost manufacturing is demonstrated. Materials with complementary sensor responses are synthesized by incorporating functional groups into the molecule, either along the polymer backbone or as end-capping groups. Using these materials as printable sensor inks, a functional, integrated gas sensor array chip is fabricated using additive deposition techniques. The sensor array shows sensitivity to a range of volatile organic compounds down to concentrations of 10 ppm. A three-terminal thin film transistor structure is used, allowing the extraction of multiple parameters that help to elucidate the mechanisms responsible for sensor response and the role of the functional groups in this response. [ABSTRACT FROM AUTHOR]