New materials for advanced applications : electrochromism, electrocatalysis, and bioimaging

Electrochromic materials have the applications in smart-windows, electrochromic mirrors, and electrochromic display devices. Three Fe(II) bis(terpyridine)-based complexes with thiophene (2.2a), bithiophene (2.2b), and 3,4-ethylenedioxythiophene (2.2c) side chains have been synthesized to provide two terminal active sites for electrochemical polymerization. The thin film of poly-2.2b has been electrodeposited on ITO/glass substrate and was characterized using electrochemistry, X-ray photoelectron spectroscopy, UV-vis spectroscopy and atomic force microscopy. The film exhibited great optical contrast with a change of transmittance of 40% upon applying voltage to it, and a coloration efficiency of 3823 cm²C⁻¹ with a switching time of 1 s. It also demonstrated commonplace stability and reversibility, with a 10% loss in peak current intensity after 200 cyclic voltammetry (CV) cycles and almost no loss in change of transmittance after 900 potential switches between 1.1 V and 0.4 V (vs Fc⁺/Fc). Lanthanide complexes have unique photophysical properties that can be utilized in areas such as bioimaging, bio-sensors, fluoroimmunoassays, and organic light emitting diodes. Our group has previously synthesized the complex-Eu(III) tris-(2-thenoyltrifluroacetonate) 2,6-bis(pyrazoly)pyridine [Eu(bppy)(tta)₃], which has a quantum yield of 60% in dichloromethane solution and 90% in solid state. Various functionalities were introduced on the original bppy ligand, such as carboxyl, hydroxyl, and amino groups to provide the active sites for bioconjugation purpose. Four Eu(III)(R-bppy)(tta)₃ complexes (3.2a-3.2d) were synthesized and their photophysical properties were fully characterized. Their quantum yields range from 20.2% to 45.4% and lifetimes range from 383.9-417.2 [mu]s. Efficiently transforming the greenhouse gas CO₂ into liquid fuels or useful synthetic precursors would have a significant impact on balancing the global carbon cycle. A series of mononuclear Re(I) complexes with dipyrido[3,2-a:2’,3’-c]phenazine (dppz) derived ligands (4.2a-4.2d) were synthesized and investigated as homogeneous electrocatalysts for CO₂ reduction. CV studies showed large enhancements of the cathodic currents under CO₂ atmosphere for the Re(I) complexes, indicating the electrocatalytic reduction of CO₂. CO was confirmed as the only gaseous phase product by gas chromatography. Compared to the Lehn catalyst, a benchmark catalyst for reducing CO₂ to CO, the Re(I) dppz complex with a larger degree of conjugation transformed CO₂ into CO at a lower overpotential.