Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
Chemphyschem. 2010 Sep 10;11(13):2862-70. doi: 10.1002/cphc.200000094.
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.
罗丹明 B 碱基被用作液-液-电极三相边界电化学实验中的光活性氧化还原体系。罗丹明 B 的疏水性 3-(4-苯基丙基)-吡啶（PPP）微滴沉积在基底平面热解石墨电极表面，然后浸入含有 0.5 M 磷酸盐缓冲溶液（pH 12）的水溶液中。在循环伏安实验中，表明罗丹明 B 在 PPP 中暗还原为无色罗丹明 B 分两步进行——均为单电子过程——而重新氧化发生在单个双电子过程中。伏安信号与 Na(+)转移（对于第一步还原）和质子转移（对于第二步还原）与电子转移偶联一致。观察到单电子还原中间产物的质子驱动歧化反应（在 pH 12 时 k(dis)=3 mol(-1) dm(3) s(-1)）。在光的存在下，观察到无色罗丹明 B 到罗丹明 B 的两电子转化的新光催化氧化过程。证明罗丹明 B 的光激发引发了有效的光复合机制。通过比较罗丹明 B 和罗丹明 B 十八烷基酯，并应用基于 DigiSim 的近似数值模拟程序，获得了对暗和光机制的定量见解。
