Dinuclear transition-metal terpyridine complexes with a dithienylcyclo- pentene bridge directed toward molecular electronic applications.

A series of dinuclear metal terpyridine (M-tpy; M = Ru, Os, Fe, and Co) complexes with a photochromic dithienylethene bridge were designed and synthesized through either a convergent or a divergent approach. The open forms of the complexes containing RuII and FeII centers were found to be inert to ultraviolet photoirradiation but could be cyclized electrochemically as revealed by a cyclic voltammetric study. On the contrary, the CoII complex underwent efficient photochemical but not electrochemical cyclization.

Electrospun light-emitting nanofibers.

We have electrospun light-emitting nanofibers from ruthenium(II) tris(bipyridine)/polyethylene oxide mixtures. The electroluminescent fibers were deposited on gold interdigitated electrodes and lit in a nitrogen atmosphere. The fibers showed light emission at low operating voltages (3-4 V), with turn-on voltages approaching the band gap limit of the organic semiconductor.

Observation of electroluminescence and photovoltaic response in ionic junctions.

Electronic devices primarily use electronic rather than ionic charge carriers. Using soft-contact lamination, we fabricated ionic junctions between two organic semiconductors with mobile anions and cations, respectively. Mobile ionic charge was successfully deployed to control the direction of electronic current flow in semiconductor devices.

Identification of a quenching species in ruthenium tris-bipyridine electroluminescent devices.

We have used matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and micro-Raman spectroscopy to identify a quenching species that is formed during operation of [Ru(bpy)3]2+ electroluminescent devices. We identify this performance-degrading product to be the oxo-bridged dimer [(bpy)2(H2O)RuORu(OH2)(bpy)2]4+ and show this dimer to be an effective quencher of device luminescence. This work is the first to detect a specific chemical degradation product formed during iTMC OLED operation.

Stepwise self-assembly of ordered supramolecular assemblies based on coordination chemistry.

Ultrathin multilayers based on transition metal complexes have been prepared by successive deposition and self-assembly. Dendrimer layers were deposited onto SiO2 wafers by alternately immersing the substrate into a solution of terpyridyl (tpy)-pendant poly(amido amine) (PAMAM) dendrimers (dend-n-tpy; n = 8, 16) dissolved in CH2Cl2, followed by the interfacial coordination reaction with cobalt (Co2+) from aqueous solution. The films derived from this simple assembly method have been characterized by electrochemical methods, synchrotron-based X-ray reflectivity (XRR), and X-ray fluorescence (XRF) recorded under grazing incidence.

Ruthenium molecular wires with conjugated bridging ligands: onset of band formation in linear inorganic conjugated oligomers.

We have prepared and characterized a series of multimetallic oligomers of Ru using the pi-conjugated bridging ligand tetra-2-pyridyl-1,4-pyrazine (tppz), as well as mixed-ligand complexes with terpyridine end caps, and analyzed their electrochemical and spectroscopic properties, comparing them with modern computational electronic structure methods. The results suggest that the high degree of metal-metal interunit communication in these linear oligomers yields low HOMO-LUMO gaps, high delocalization, and the onset of "quasi-band" features, all indicative that these compounds should be excellent molecular wire materials. Recent spectroscopic and excited-state analyses of these and related compounds focus on optically accessible states, which ignore optically silent frontier electronic states more relevant to nanoelectronic applications.