title: Triple phase boundary photovoltammetry: resolving rhodamine B reactivity in 4-(3-phenylpropyl)-pyridine microdroplets.
abstract: Rhodamine B base is employed as a photoactive redox system in a liquid | liquid | electrode triple phase boundary electrochemical experiment. Microdroplets of the water-immiscible 3-(4-phenylpropyl)-pyridine (PPP) containing rhodamine B are deposited onto a basal plane pyrolytic graphite electrode surface which is then immersed into an aqueous solution containing 0.5 M phosphate buffer solution (pH 12). In cyclic voltammetry experiments, it is shown that dark reduction of rhodamine B to leuco-rhodamine B in PPP occurs in two steps--both one electron processes--and the re-oxidation occurs in a single two-electron process. Voltammetric signals are consistent with Na(+) transfer (for the first reduction step) and proton transfer (for the second reduction step) coupled to the electron transfer. A proton-driven disproportionation reaction (with k(dis)=3 mol(-1) dm(3) s(-1) at pH 12) is observed for the one-electron reduced intermediate. In the presence of light, a new photocatalysed oxidation process for the two-electron conversion of leuco-rhodamine B to rhodamine B is observed. Photoexcitation of rhodamine B is shown to trigger an effective photo-comproportionation mechanism. Quantitative insights into the dark and photomechanisms are obtained by comparison of rhodamine B and rhodamine B octadecylester and by applying an approximate numerical simulation procedure based on DigiSim.
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Collins
authors.forename: Xiaohang
authors.initials: X
authors.lastname: Zhang
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Scragg
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Blanchard
authors.forename: Frank
authors.initials: F
authors.lastname: Marken
mesh_terms: D004563:Electrochemistry; D004566:Electrodes; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010777:Photochemistry; D011725:Pyridines / Q000737:chemistry*; D012235:Rhodamines / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011725:Pyridines; D012235:Rhodamines; C029773:rhodamine B; C531278:(4-(3-phenylpropyl)pyridine)