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...

We report the stochastic interactions between dye sensitized anatase nanoparticles, suspended in a colloid, and a Pt ultramicroelectrode (UME) that result in step-wise behavior in the current vs. time response. The stochastic currents are observed in the dark and under illumination. In the dark, the currents are anodic, consistent with the oxidation of the dye N719 at the Pt surface. The electrochemical behavior of the dye was investigated in MeOH and MeCN with a quasireversible cyclic voltammogram (CV) observed at 1 V s. The anodic currents observed in the dark due to nanoparticles (NPs) at the Pt surface are consistent with the CVs in MeOH and MeCN. Under illumination cathodic steps are observed and assigned to the reduction of the oxidized form of the dye generated after electrons are injected into the TiO NPs. The colloidal behavior is a strong function of the history of the colloid with illumination time increasing the size of the agglomerates and with larger agglomerates being less photoelectrochemically active. Agglomerates of ca. 100 nm in diameter are proposed to be photoactive entities with a higher probability of detection that contribute to the staircase photocurrent response.

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.

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