A new series of metal-free organic chromophores (TPA-TTAR-A (1), TPA-T-TTAR-A (2), TPA-TTAR-T-A (3), and TPA-T-TTAR-T-A (4)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D-π-A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5-5.2 × 10(4) M(-1) cm(-1)). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO2 surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye 3) promotes more vertical dye orientation and denser packing on TiO2 (molecular footprint = 79 Å(2)), thus enabling optimal dye loading. Using dye 3, a DSSC power conversion efficiency (PCE) of 10.1% with Voc = 0.833 V, Jsc = 16.5 mA/cm(2), and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I(-)/I3(-) redox shuttle. Photophysical measurements on dye-grafted TiO2 films reveal that the additional thiophene unit in dye 3 enhances the electron injection efficiency, in agreement with the high quantum efficiency.

In situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) have been used to examine the conformation of a monolayer of polyaniline (PAN) molecules produced on a Au(111) single-crystal electrode by anodization at 1.0 V [vs reversible hydrogen electrode (RHE)] in 0.10 M H(2)SO(4) containing 0.030 M aniline. The as-produced PAN molecules took on a well-defined linear conformation stretching for 500 A or more, as shown by in situ and ex situ STM. The XPS and NEXAFS results indicated that the linear PAN seen at 1.0 V assumed the form of an emeraldine salt made of PAN chains and (bi)sulfate anions. Shifting the potential from 1.0 to 0.7 V altered the shape of the PAN molecules from straight to crooked, which was ascribed to restructuring of the Au(111) electrified interface on the basis of voltammetric and XPS results. In situ STM showed that further decreasing the potential to 0.5 V transformed the crooked PAN threads into a mostly linear form again, with preferential alignment and formation of some locally ordered structures. PAN molecules could be reduced from emeraldine to leucoemeraldine as the potential was decreased to 0.2 V or less. In situ STM showed that the fully reduced PAN molecules were straight but mysteriously shortened to approximately 50 A in length. The conformation of PAN did not recuperate when the potential was shifted positively to 1.0 V.

In situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) were used to examine the electrified interface of Au(111) in 0.1 M H(2)SO(4) containing 0.030 M aniline. In agreement with cyclic voltammogram (CV), which revealed two pairs of peaks at 0.48 and 0.62 V, in situ STM imaging yielded two highly ordered aniline adlattices, (root 19 x 5) at 0.55 V and (3 x 2 root 3)rect at 0.85 V [vs reversible hydrogen electrode, RHE]. According to XPS results obtained with Au(111) emersed at 0.85 V from 0.1 MH(2)SO(4) + 0.030 M aniline, bisulfate anions were coadsorbed in an amount equal to that of aniline. The (3 x 2 root 3)rect-aniline structure was examined carefully by STM using different imaging conditions. Results revealed that imaging with a tunneling current of 10 nA at a -300 mV bias voltage allowed molecular resolution of both aniline admolecules and bisulfate anions. These species could form acid-base pairs and mingled uniformly on the Au(111) electrode. NEXAFS results were also obtained at 0.85 V, showing that the phenyl rings of aniline admolecules on average was tilted away from the Au(I 11) substrate by 47 degrees. At E > 0.95 V, aniline molecules were oxidized to cation radicals, which initiated intermolecular coupling between aniline molecules to form polyaniline (PAN). The as-formed PAN assuming the form of emeraldine salt exhibited distinct linear conformations, which is proposed to derive from a unique head-to-tail arrangement of aniline monomers in the (3 x 2 root 3)rect structure. The coadsorbed bisulfate anions played an important role in the production of surface-bound PAN emeraldine salts, whose high conductivities facilitated molecular resolution STM imaging up to a thickness of four PAN layers

We report in situ scanning tunneling microscopy (STM) results of underpotential deposition (UPD) of copper at well-ordered Pt(111) and Rh(111) electrodes in sulfuric acid solutions. Cyclic voltammograms of Pt(111) at 1 mV/s in 0.05 M H2SO4 and 5 mM CuSO4 reveal two well-defined UPD peaks at 0.65 and 0.61 V, whereas one doublet UPD peak at 0.44 V is observed for Rh(111). Real-time STM imaging revealed that the two sharp UPD features for Pt(111) correspond to the formation of a ( 3 × 3)R30°structure and a disorder phase, respectively. A long-range ordered ( 3 × 7)oblique structure was imaged after a full monolayer of Cu was deposited, tentatively assigned to the (bi)sulfate anions lying atop the Cu adlayer. In contrast, a monolayer of Cu was deposited in a single step on Rh (111), where (bi)sulfate anions also actively participated in the process. In situ STM revealed a well-ordered ( 3 × 7)oblique structure throughout the deposition process, likely because of the coadsorbed (bi)sulfate anions. A series of timedependent in situ STM images were acquired to unveil the deposition processes of Cu. Deposition of Cu preferentially began at defect sites, particularly upper step ledges. Lateral growth and coalescence of Cu islands followed to cover nearly the whole surface. Decreasing potential to the bulk deposition region led to the formation of local Cu islands with a thickness of 4-5 layers of Cu, on which a well-ordered ( 3 × 7)oblique structure was still observed. All the STM results indicate that sulfate anions were heavily involved in the UPD processes of Cu at these two electrodes. The different adsorption energies of Cu adatoms on Pt and Rh electrodes also affect the deposition processes.

The adsorption of 3-mercaptopropanesulfonate (MPS) molecule on a Pt(111) single-crystal electrode and its effect on the deposition of Cu have been examined using in situ scanning tunneling microscopy (STM). MPS admolecules were irreversibly adsorbed in a largely disordered adlayer on bare Pt(111) in 0.1 M HClO(4), irrespective of the presence of chloride, the concentration of MPS, and the applied potential. In comparison, the MPS admolecules readily formed a highly ordered molecular structure identified as (4x2 root 3)rect on Pt(111) precoated with a monolayer of Cu adatoms. The MPS admolecules were adsorbed upright on Pt(111). The cyclic voltammetric results show that the MPS adlayer on Pt(111) would inhibit Cu deposition because the addition of 10 mu M MPS to the electrolyte of 0.1 M HClO(4)+1 mM KCl+1 mM Cu(ClO(4))(2) reduced the amount of the Cu deposit by half, even in the presence of chloride. The texture of the Cu deposit also varied with the surface state of the Pt(111) electrode as the Cu film grew in three-dimensional islands and smooth flakelike morphology on the MPS-modified and Cu-coated Pt(111) electrodes, respectively. In situ STM results indicated that the MPS admolecules stayed afloat rather than buried by the Cu deposit

Surface modification for biosensors has focused attention for improvement of their sensitivity and specificity, particularly for the detection in complex medium. In this work, we have synthesized zwitterionic carboxybetaine-thiols (CB-thiols) and sulfobetaine-thiols (SB-thiols) for modification of gold substrates to form a functional self-assembled monolayer (SAM) for the immunoassay in a surface plasmon resonance (SPR) biosensor. X-ray photoelectron spectroscopy (XPS), contact angle goniometer, and cyclic voltammetry were applied for characterizations of elemental composition, surface wettability, and packing density, respectively. The antifouling properties of the SAMs were accessed by quantitative analysis of protein and bacterial adsorption. The results from the SAMs with a single component indicated that the SB-thiol SAM provides better surface hydrophilicity, fouling resistance, and packing density as compared to the CB-thiol SAM, likely due to the ionic association of CB moieties. However, the CB-thiol with the functional carboxylate group plays a critical role in postmodification of biomolecules via commercially available amine coupling chemistry. Thus, the mixed SAMs were prepared to integrate the unique characteristics from CB- and SB-thiols to control compositions and surface properties. The immunoassay was performed in the SPR biosensor, showing that the zwitterionic mixed SAM enables immobilization of biorecognition elements (BREs), and improved sensitivity and specificity. Consequently, the work reveals excellent and attractive versatility, antifouling, and functionalizable properties of zwitterionic mixed SAMs comprising CB- and SB-thiols for biosensing applications. This surface chemistry is expected to be applicable to monitor specific molecular recognition events.

In situ scanning tunneling microscopy (STM) has been used to examine underpotential deposition (UPD) of Cu at Pt(111) electrodes in the solutions of 0.01 M HCl and 1 mM Cu(ClO4)2. Cyclic voltammetry reveals two well-defined features at 0.72 and 0.55 V (vs RHE), where a tailing phenomenon is noted for the former peak. In situ STM imaging reveals a disorder-to-ordered transition of the adlayer, as the electrochemical potential of Pt(111) was stepped from 0.8 to 0.7 V to facilitate the deposition of a sub-monolayer of Cu adatoms. The ordered adlattice can be approximately characterized as (4 × 4), whose irregular intensity modulation of the STM atomic features indicates its incommensuratity. Toward the end of the first UPD feature, deposition of Cu continues, resulting in reconstruction of the (4 × 4) adlattice to (√7×√7)R19.1°. The latter structure is then stable toward further negative potential stepping to the end of the second UPD wave. In situ STM imaging turns fuzzy when the electrochemical potential of Pt(111) is made more negative to the Nernst value. Varying the operation parameters of the STM can result in atomic structures of not only the upper layer of chloride but also the lower metallic adlayer or the Pt(111) substrate.

New branched alkyl tetrathienothiophene (TTAR)-based organic sensitizers with power conversion efficiency up to 11%.