We describe a method to detect individual semiconducting nanoparticles (NPs) using the photoelectrochemical (PEC) current measured at an ultramicroelectrode (UME). We use photooxidation of MeOH by TiO2 NPs as a model system of photocatalysis in solution. NPs suspended in MeOH under constant illumination produce valence-band holes that oxidize MeOH. The electrons are collected at the UME, and the current-versus-time data show discrete current changes that are assigned to particle-by-particle interactions of the NPs with the UME. The stepwise changes in the photocurrent denote irreversible attachment of NPs to Pt UMEs (<30 μm diameter). We found that accumulation of electrons in the conduction band by the NPs is not enough to explain the stochastic PEC currents. We propose that the observed anodic steps have a PEC nature and are due to photooxidation of MeOH by the NPs at the electrode surface.

We present the study of dye-sensitized nanoparticles and their agglomerates with stochastic electrochemistry. We use a fluorine doped tin oxide (FTO) ultramicroelectrode (UME) with diameter in the range of 40 to 80 micrometers. To prepare the UME a sheet of perfluoroalkoxy alkane (PFA) is perforated to produce a recessed micro disk of the transparent conductive oxide. We demonstrate that the detection of the colloidal nanoparticles (NPs) sensitized with N719 is achieved via the interactions between agglomerates of the NPs that collide with the FTO. The NPs photooxidize MeOH and we detect the charge transfer from the NPs to the FTO ultramicroelectrode. The interactions between the dye sensitized NPs and the FTO yields oscillations that increase with exposure time. This increment in oscillation amplitude is assigned to changes in the aggregation of the NPs during the illumination even in the presence of 0.1 M supporting electrolyte. The formation of agglomerates is verified by dynamic light scattering and indicates that the agglomerates are able to separate photo-generated electrons and inject the carriers to the UME. We present the study of dye-sensitized nanoparticles (DSNPs) and their agglomerates with stochastic electrochemistry. The field of stochastic electrochemistry for the detection of nanoparticles (NPs) has rapidly gained attention since the initial experiments proposed for the amperometric detection of electrocatalytic NPs by the Bard group 1-3 and others. [4][5][6][7] The stochastic studies have rapidly expanded to include contact, 2,3,8 i.e., irreversible interactions between NPs and the non-contact (reversible) 9,10 interactions between electrodes and NPs of metals. Electrochemical studies of discrete interactions in the "nano-impact" method by Compton 11-16 and co-workers include the complete electrolysis of NPs.17 Single NP detection takes advantage of an electrocatalytic cycle that occurs at the NPs with catalytic NPs interacting with a mostly inert substrate. This enables a large signal amplification that has allowed the trapping and studying of single metal NPs. 18,19 Here, we use an analogous amplification and catalytic cycle that is driven by the interaction of photons with dye-sensitized NP in a colloidal suspension.The use of dyes to modify NPs has been of broad scientific interest since the introduction of nanostructured dye sensitized solar cells (DSSCs) by O'Regan and Gratzel 20 in 1991 sparked interest in the use of nanoparticle films for solar energy conversion. Since then, a large effort has been devoted to improve the efficiency of these devices to meet current energy demand. The study of these events for films or NP ensembles are complicated by electron diffusion within the assembly and mass transport to and within the porous structures. 21Therefore, we are developing the electrochemistry of colloidal semiconductors (SC) to study the electron transfer without complications of transport in and out of the film. This paper describes the detection of collisions of bare TiO 2 NPs sensiti...

The formation of boronic esters lowers the LUMO energy of hexamethoxytriphenylene by $1 V, converting the discotic core archetype from electron-rich to electron-deficient. Cyclic voltammetry gives E 1/2 reduction values (ca. À1.2 V vs. Fc/Fc + ) that are comparable to that of C 60 , the standard electron acceptor in organic electronics. Suitable peripheral functionalization imparts large mesophase temperature ranges. Homeotropic, columnar hexagonal phases with good charge carrier mobilities (up to 8 Â 10 À2 cm 2 V À1 s À1 ) are observed.

We present evidence of the generation of radical ion formation during the oxidation of iodide on a fluorine doped tin oxide (FTO) electrode in acetonitrile. The cyclic voltammograms for the oxidation of iodide and triiodide on FTO are significantly different as in the case of the oxidation of Pt electrode.  These differences are assigned to kinetic differences on the FTO surface that require significant over potentials to drive the oxidation of iodide and triiodide. We propose that at the highly positive potentials the iodine radical intermediate, I·, becomes thermodynamically stable at FTO. The radical nature of the intermediate was verified by the formation of radicals of the usual traps of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2,2,5,5 tetramethyl-1-pyrroline N-oxide (TMPO) when these were added to an electrolyzed solution. Irradiation of an iodine solution causes the homolytic cleavage of I2 and yields the same radical intermediate with TMPO as in the electrolysis experiment. Similar results were obtained from the electrolysis of bromide solutions upon addition of TMPO. Short term electrolysis (< 1 h) gives triiodide as a final product while long-term electrolysis (> 17 h) yields additional byproducts. Byproducts were determined to be organoiodines by gas chromatography-mass spectrometry (GC-MS). Overall, our results are consistent with iodine atoms reacting with the electrolyte during electrolysis at the FTO electrode and with a sequential two-electron transfer process.

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