The electron transfer dynamics in solar cells that utilize sensitized nanocrystalline titanium dioxide photoelectrodes and the iodide/triiodide redox couple have been studied on a nanosecond time scale. The ruthenium and osmium bipyridyl complexes Ru(H 2 L′) 2 (CN) 2 , Os(H 2 L′) 2 (CN) 2 , Ru(H 2 L′) 2 (NCS) 2 , and Os-(H 2 L′) 2 (NCS) 2 , where H 2 L′ is 4,4′-dicarboxylic acid 2,2′-bipyridine, inject electrons into the semiconductor with a rate constant >10 8 s -1 . The effects of excitation intensity, temperature, and applied potential on the recombination reaction were analyzed using a second-order kinetics model. The rates of charge recombination decrease with increasing driving force to the oxidized sensitizer, indicating that charge recombination occurs in the Marcus inverted region. The electronic coupling factors between the oxidized sensitizer and the injected electrons in TiO 2 and the reorganization energies for the recombination reaction vary significantly for the different metal complexes. The charge recombination rates are well described by semiclassical electron transfer theory with reorganization energies of 0.55-1.18 eV. Solar cells sensitized with Ru(H 2 L′) 2 (CN) 2 , Os(H 2 L′) 2 -(CN) 2 , and Ru(H 2 L′) 2 (NCS) 2 have favorable photoelectrochemical characteristics, and iodide is oxidized efficiently. In contrast, iodide oxidation limits the efficiency of cells based on sensitization of TiO 2 with Os(H 2 L′) 2 (NCS) 2 . The observation that charge recombination occurs in the Marcus inverted region has important implications for the design of molecular sensitizers in nanocrystalline solar cells operated under our experimental conditions.

The field of organic electronics has been heavily impacted by the discovery and development of π-conjugated conducting polymers. These polymers show great potential for integration into future optical and electronic devices due to their capacity to transition between semiconducting and conducting states as well as the ability to alter mechanical properties by controlled doping, chemical modification, and stacking or creating composites with other materials. Among π-conjugated polymers, polythiophene and its derivatives has been one of the most extensively studied and is widely investigated computationally and experimentally for use in electronic devices such as light-emitting diodes, water purification devices, hydrogen storage, and biosensors. Various theoretical modeling studies of polythiophene ranging from an oligothiophene approach to infinite chain lengths (periodic boundary conditions) have been undertaken to study a variety of electronic and structural properties of these polymers. In this review, we discuss the recent advances in the understanding of pristine polythiophene and its derivatives from fundamental perspectives to device applications.

A novel approach for the potentiometric detection of saccharides using poly(aniline boronic acid) is presented. A model is described in which the electrochemical potential is sensitive to the change in the pK(a) of the conducting polymer as a result of boronic acid-diol complexation. In this system, boronic acid complexation is the mode of transduction and it is manifested as changes in the electrochemical potential of the polymer with remarkable selectivity. Characteristics of both transient and steady-state response associated with the complexation are discussed. The presence of Nafion and fluoride during the electrochemical polymerization of 3-aminophenylboronic acid are shown to impact the sensitivity and the stability of the electrode response. The sensor sensitivity is improved significantly by increasing the concentration of sodium fluoride during the polymerization. Finally, the nature of the selectivity of the boronic acid-diol reaction under these conditions is explored by using molecular orbital calculations.

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We describe a method for generating a variety of chemically diverse broadly responsive low-power vapor sen-sors. The chemical polymerization of pyrrole in the presence of plasticizers has yielded conducting organic polymer films whose resistivities are sensitive to the identity and concentration of various vapors in air. An array of such sensing elements produced a chemically reversible diagnostic pattern of electrical resistance changes upon exposure to different odorants. Principal component analysis has demonstrated that such sensors can identify and quantity different airborne organic solvents and can yield information on the components of gas mixtures.There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (1, 2). This system is thought to utilize probabilistic repertoires of many different receptors to recognize a single odorant (3, 4). In such a configuration, the burden of recognition is not on highly specific receptors, as in the traditional "lock-and-key" molecular recognition approach to chemical sensing, but lies instead on the distributed pattern processing of the olfactory bulb and the brain (5, 6). We describe herein the construction and characterization of a broadly responsive vapor detection array based on conducting polymer "chemiresistor" elements. Such conducting polymer elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. In addition, these sensors yield a fairly rapid lowpower dc electrical signal in response to the vapor of interest, and their signals are readily integrated with software-or hardware-based neural networks for purposes of analyte identification.Prior attempts to produce a broadly responsive sensor array have exploited heated metal oxide thin film resistors (7-9), polymer sorption layers on the surfaces of acoustic wave resonators (10, 11), arrays of electrochemical detectors (12-14), or conductive polymers (15, 16). Arrays of metal oxide thin film resistors, typically based on SnO2 films that have been coated with various catalysts, yield distinct diagnostic responses for several vapors (7-9). However, due to the lack of understanding of catalyst function, SnO2 arrays do not allow deliberate chemical control of the response of elements in the arrays nor reproducibility of response from array to array. Surface acoustic wave resonators are extremely sensitive to both mass and acoustic impedance changes of the coatings in array elements, but the signal transduction mechanism involves somewhat complicated electronics, requiring frequency measurement to 1 Hz while sustaining a 100-MHz Rayleigh wave in the crystal (10, 11). Electrically conductive organic polymer elements are well-suited for such an array, because swelling of the polymer upon exposure to an analyte will induce changes in the resistivity of the polymer film (17,18). This enables a direct low-power electrical signal readout (the film resistance) to be used as the sensing signal. Some prior work has been pe...