5 research outputs found
Norbornadiene photoswitches anchored to well-defined oxide surfaces: From ultrahigh vacuum into the liquid and the electrochemical environment
Employing molecular photoswitches, we can combine solar energy conversion, storage, and release in an extremely simple single molecule system. In order to release the stored energy as electricity, the photoswitch has to interact with a semiconducting electrode surface. In this work, we explore a solar-energy-storing model system, consisting of a molecular photoswitch anchored to an atomically defined oxide surface in a liquid electrolyte and under potential control. Previously, this model system has been proven to be operational under ultrahigh vacuum (UHV) conditions. We used the tailor-made norbornadiene derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) and characterized its photochemical and electrochemical properties in an organic electrolyte. Next, we assembled a monolayer of CNBD on a well-ordered Co3O4(111) surface by physical vapor deposition in UHV. This model interface was then transferred into the liquid electrolyte and investigated by photoelectrochemical infrared reflection absorption spectroscopy experiments. We demonstrate that the anchored monolayer of CNBD can be converted photochemically to its energy-rich counterpart 2-cyano-3-(4-carboxyphenyl)quadricyclane (CQC) under potential control. However, the reconversion potential of anchored CQC overlaps with the oxidation and decomposition potential of CNBD, which limits the electrochemically triggered reconversion
Solar energy storage at an atomically defined organic-oxide hybrid interface
Molecular photoswitches provide an extremely simple solution for solar energy conversion and storage. To convert stored energy to electricity, however, the photoswitch has to be coupled to a semiconducting electrode. In this work, we report on the assembly of an operational solar-energy-storing organic-oxide hybrid interface, which consists of a tailor-made molecular photoswitch and an atomically-defined semiconducting oxide film. The synthesized norbornadiene derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) was anchored to a well-ordered Co3O4(111) surface by physical vapor deposition in ultrahigh vacuum. Using a photochemical infrared reflection absorption spectroscopy experiment, we demonstrate that the anchored CNBD monolayer remains operational, i.e., can be photo-converted to its energy-rich counterpart 2-cyano-3-(4-carboxyphenyl)quadricyclane (CQC). We show that the activation barrier for energy release remains unaffected by the anchoring reaction and the anchored photoswitch can be charged and discharged with high reversibility. Our atomically-defined solar-energy-storing model interface enables detailed studies of energy conversion processes at organic/oxide hybrid interfaces
Molecular Anchoring to Oxide Surfaces in Ultrahigh Vacuum and in Aqueous Electrolytes: Phosphonic Acids on Atomically-Defined Cobalt Oxide
In this work, we investigated the interaction of phenylphosphonic acid (PPA, C6H5PO3H2) with atomically-defined Co3O4(111) thin films, grown on Ir(100), under ultrahigh vacuum (UHV) conditions and in the electrochemical environment. In the first step, we employed infrared reflection absorption spectroscopy (IRAS) and followed the formation of a saturated monolayer (380 K) in UHV. We observed that the binding motif changes from a chelating tridentate in thesub-monolayer regime to a chelating bidentate at full monolayer coverages. In the electrochemical environment, we analyzed the interaction of PPA with the same Co3O4(111) surface by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) (0.3 VRHE ? 1.3 VRHE). When adsorbed at pH 10 from an ammonia buffered aqueous solution, PPA binds to the surface in form of a fully deprotonated chelating bidentate. With increasing electrode potential, we observed two fully reversible processes. At low buffer concentration, protons are released upon oxidation of surface Co2+ ions and lead to protonation of the anchored phosphonates. At high buffer concentration, most of the protons released are accepted by NH3. Simultaneously, the surface phosphonate changes its adsorption motif from bidentate to tridentate while adopting a more upright geometry.Fil: Bertram, Manon. Universitat Erlangen-Nuremberg; AlemaniaFil: Schuschke, Christian. Universitat Erlangen-Nuremberg; AlemaniaFil: Waidhas, Fabian. Universitat Erlangen-Nuremberg; AlemaniaFil: Schwarz, Matthias. Universitat Erlangen-Nuremberg; AlemaniaFil: Hohner, Chantal. Universitat Erlangen-Nuremberg; AlemaniaFil: Montero, MarÃa de Los Angeles. Universidad Nacional del Litoral. Instituto de QuÃmica Aplicada del Litoral. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Santa Fe. Instituto de QuÃmica Aplicada del Litoral.; ArgentinaFil: Brummel, Olaf. Universitat Erlangen-Nuremberg; AlemaniaFil: Libuda, Joerg. Universitat Erlangen-Nuremberg; Alemani
Phosphonic Acids on an Atomically Defined Oxide Surface: The Binding Motif Changes with Surface Coverage
We
have studied the anchoring mechanism of a phosphonic acid on
an atomically defined oxide surface. Using time-resolved infrared
reflection absorption spectroscopy, we investigated the reaction of
deuterated phenylphosphonic acid (DPPA, C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>D<sub>2</sub>) with an atomically defined Co<sub>3</sub>O<sub>4</sub>(111) surface in situ during film growth by physical
vapor deposition. We show that the binding motif of the phosphonate
anchor group changes as a function of coverage. At low coverage, DPPA
binds in the form of a chelating tridentate phosphonate, while a transition
to a chelating bidentate occurs close to monolayer saturation coverage.
However, the coverage-dependent change in the binding motif is not
associated with a major change of the molecular orientation, suggesting
that the rigid phosphonate linker always maintains the DPPA in a strongly
tilted orientation irrespective of the surface coverage