Electrochemical oxidation and ex-situ STM observations of bis(4-dimethylamino-2-dihydroxyphenyl)squaraine dye layers on HOPG electrodes

Adsorption Morphology, Light Absorption, and Sensitization Yields for Squaraine Dyes on SnS2Surfaces

“…In an earlier electrochemical study, we showed that potentials for the oxidation and rereduction of 1-1OHSQ dye layers adsorbed on HOPG electrodes depended on the identity and concentration of the electrolyte anions . If this is also the case on an SnS 2 substrate, the recombination rate of photoinjected electrons would be affected and influence the observed photocurrent quantum yield.…”

“…In an earlier electrochemical study, we showed that potentials for the oxidation and rereduction of 1-1OHSQ dye layers adsorbed on HOPG electrodes depended on the identity and concentration of the electrolyte anions. 64 If this is also the case on an SnS 2 substrate, the recombination rate of photoinjected electrons would be affected and influence the observed photocurrent quantum yield. However, changing the supporting electrolyte from LiCl to NaBr, NaI, or Na 2 SO 4 (1 M), all with 10mM H 2 Q used as the regenerator, had no strong effect on the quantum yield and shape of the photocurrent-voltage curves.…”

“…In the HOPG study, the redox potentials of the surface-confined dye layers were influenced because of anion incorporation into and expulsion from the dye layers that was necessary to maintain electrical neutrality in the film when large areas of dye molecules were oxidized or rereduced. 64 On the other hand, the photoelectrochemical oxidation process involves only individual dye molecules at any given time and the rapid regeneration reaction makes the lifetime of the oxidized dye very short. In addition, the migration of the photogenerated hole in the dye layer to a more stable site is also possible.…”

“…62,63 We also discovered a large hysteresis and electrolyte anion dependent peak potentials in cyclic voltammograms of squaraine layers on HOPG, associated with the formation of ordered aggregates. 64 Together with these findings, further studies on the morphologies of squaraine dye molecules and their photosensitization properties should reveal interesting insights into the structure-property relationships of the dye sensitization process. SnS 2 single-crystal surfaces are an excellent choice for the purposes of this study.…”

“…In the solid state, squaraines exhibit a broad absorption spectrum extending into the near-IR region and also exhibit high photoconductivities due to strong intermolecular interactions within the crystal. These attributes make squaraines attractive for use as organic photoconductors in laser printers , and as nonlinear optical materials. − Studies concerning the application of squaraines for photovoltaic cells and photosensitizers for semiconductors were also reported, but the efficiencies measured in these studies were rather low. − Recent STM studies from our laboratory on a family of squaraines with various alkyl chain lengths revealed highly ordered structures on highly oriented pyrolytic graphite (HOPG) surfaces with many of the molecules exhibiting several different 2D polymorphs. , We also discovered a large hysteresis and electrolyte anion dependent peak potentials in cyclic voltammograms of squaraine layers on HOPG, associated with the formation of ordered aggregates . Together with these findings, further studies on the morphologies of squaraine dye molecules and their photosensitization properties should reveal interesting insights into the structure−property relationships of the dye sensitization process.…”