Adrian Guckian

In situ scanning tunnelling spectroscopy of inorganic transition metal complexes

Redox molecules with equilibrium potentials suitable for electrochemical control offer perspectives in nanoscale and single-molecule electronics. This applies to molecular but also towards higher sophistication such as transistor or diode function. Most recent nanoscale or single-molecule functional systems are, however, fraught with operational limitations such as cryogenic temperatures and ultra-high vacuum, or lack of electrochemical potential control. We report here cyclic voltammetry (CV) using single-crystal Au(111)- and Pt(111)-electrodes and electrochemical in situ scanning tunnelling microscopy (STM) of a class of Os(II)/(III)- and Co(II)/(III)-complexes, the former novel molecular electronics. The complexes are robust, with ligand groups suitable for linking the complexes to the Au(111)- and Pt(111)-surfaces via N- and S-donor atoms. The data reflect monolayer behaviour. Interfacial ET of the Os-complexes is fast, kET(0) > or = 10(6) s(-1), while the Co-complex reacts much more slowly, kET(0) approximately (1-3) x 10(3) s(-1). In STM of the Os-complexes shows a maximum in the tunnelling current/overpotential relation at constant bias voltage with up to 50-fold current rise. The peak position systematically the bias voltage and equilibrium potential, in keeping with theoretical frames for two-step electron transfer (ET) of in situ STM of redox molecules. The molecular conductivity behaves broadly similarly. The Co-complex also shows a tunnelling spectroscopic feature but much weaker than the Os-complexes. This can be ascribed much smaller interfacial ET rate constant, again caused by large intramolecular nuclear reorganization and weak electronic coupling to the substrate electrode. Overall the has mapped the properties of target molecules needed for stable electronic switching, possible importance in molecular electronics towards the single-molecule level, in room temperature condensed matter environment.

Novel hybrid sol-gel materials for smart sensor windows

Current sensor trends, such as multianalyte capability, miniaturisation and patternability are important drivers for materials requirements in optical chemical sensors. In particular, issues such as enhanced sensitivity and printablity are key in developing optimised sensor materials for smart windows for bioprocessing applications. This study focuses on combining novel sol-gel-based hybrid matrices with engineered luminescent complexes to produce stable luminescence-based optical sensors with enhanced sensitivity for a range of analytes including oxygen, pH and carbon dioxide. As well as optimising sensor performance, issues such as surface modification of the plastic substrate and compatibility with different deposition techniques were addressed. Hybrid sol-gel matrices were developed using a range of precursors including tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS), ethyltriethoxysilane (ETEOS), n-propyltriethoxysilane (PTEOS), phenyltriethoxysilane (PhTEOS), and n-octyltriethoxysilane (C8TEOS). Oxygen sensing, based on luminescence quenching of ruthenium phenanthroline complexes, has been realised with each of these hybrid materials. Furthermore, the possibility of immobilising pH-indicators for pH and carbon dioxide sensing has been investigated with some success. In the context of in-situ monitoring of bioprocesses, issues such as humidity interference as well as the chemical robustness of the multianalyte platform, were addressed.

Synthesis and characterisation of ruthenium complexes containing a pendent catechol ring

A series of [Ru(bipy)2L]+ and [Ru(phen)2L]+ complexes where L is 2-[5-(3,4-dimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine (HL1) and 4-(5-pyridin-2-yl-4H-1,2,4-triazol-3-yl)benzene-1,2-diol (HL2) are reported. The compounds obtained have been characterised using X-ray crystallography, NMR, UV/Vis and emission spectroscopies. Partial deuteriation is used to determine the nature of the emitting state and to simplify the NMR spectra. The acid-base properties of the compounds are also investigated. The electronic structures of [Ru(bipy)2L1]+ and Ru(bipy)2HL1]2+ are examined using ZINDO. Electro and spectroelectrochemical studies on [Ru(bipy)2(L2)]+ suggest that proton transfer between the catechol and triazole moieties on L2 takes place upon oxidation of the L2 ligand.