Garramone Gaetano, Pietrangeli Daniela, Ricciardi Giampaolo, Conoci Sabrina, Guascito Maria Rachele, Malitesta Cosimino, Cesari Daniela, Casilli Serena, Giotta Livia, Giancane Gabriele, Valli Ludovico
Dipartimento di Chimica, Università della Basilicata, Via N. Sauro, 85, Potenza, Italia.
J Phys Chem B. 2008 Sep 18;112(37):11517-28. doi: 10.1021/jp803418b. Epub 2008 Aug 22.
Thin films of a newly synthesized iron(III) porphyrazine, LFeOESPz ( L = ClEtO, OESPz = ethylsulfanylporphyrazine), have been deposited by the Langmuir-Schafer (LS) technique (horizontal lifting) on ITO or gold substrates. Before deposition, the floating films have been investigated at the air-water interface by pressure/area per molecule (pi/ A) experiments, Brewster angle microscopy (BAM) and UV-vis reflection spectroscopy (RefSpec). The complex reacts with water subphase (pH 6.2) forming the mu-oxo dimer, which becomes the predominant component of the LS films ( LS-Fe) as indicated by optical, IR, XPS, and electrochemical data. LS-Fe multilayers exhibit, between open circuit potential (OCP) and +0.90 V (vs SCE), two independent peak pairs with formal potentials, E surf (I) and E surf(II) of +0.56 V and +0.78 V, respectively. According to dynamic voltammetric and coulometric experiments the peak pair at +0.56 V is attributed to one-electron process at the iron(III) centers on the monomer, while the peak pair at +0.78 V is associated to a four-electron process involving mu-oxo-dimer oligomers. LS-Fe films prove to be quite stable electrochemically between OCP and +0.90 V. The electrochemical stability decreases, however, when the potential range is extended both anodically and cathodically outside these limits, due to formation of new species. Upon incubation with TCA solutions, LS-Fe films show remarkable changes in the UV-vis spectra, which are consistent with a significant mu-oxo dimer --> monomer conversion. Addition of TCA to the electrochemical cell using a LS-Fe film as working electrode, results in a linear increase of a cathodic current peak near -0.40 V as the TCA concentration varies in the 0.1-2.0 mM range. This behavior is interpreted in terms of TCA inducing a progressive change in the composition of the LS-Fe films in favor of the monomeric iron(III) porphyrazine, which is responsible for the observed increase in the cathodic current near -0.40 V.
一种新合成的铁（III）卟啉，LFeOESPz（L = ClEtO，OESPz = 乙硫基卟啉）的薄膜已通过朗缪尔-谢弗（LS）技术（水平提拉）沉积在氧化铟锡（ITO）或金基底上。在沉积之前，通过每分子压力/面积（π/A）实验、布鲁斯特角显微镜（BAM）和紫外-可见反射光谱（RefSpec）在空气-水界面研究了漂浮膜。该配合物与水亚相（pH 6.2）反应形成μ-氧二聚体，光学、红外、X射线光电子能谱（XPS）和电化学数据表明，该二聚体成为LS膜（LS-Fe）的主要成分。LS-Fe多层膜在开路电位（OCP）和 +0.90 V（相对于饱和甘汞电极（SCE））之间表现出两对独立的峰，其形式电位E surf（I）和E surf（II）分别为 +0.56 V和 +0.78 V。根据动态伏安法和库仑法实验，+0.56 V处的峰对归因于单体上铁（III）中心的单电子过程，而 +0.78 V处的峰对与涉及μ-氧二聚体低聚物的四电子过程相关。LS-Fe膜在OCP和 +0.90 V之间电化学上相当稳定。然而，当电位范围在阳极和阴极方向上扩展到超出这些极限时，由于形成了新的物种，电化学稳定性会降低。在用三氯乙酸（TCA）溶液孵育后，LS-Fe膜在紫外-可见光谱中显示出显著变化，这与μ-氧二聚体向单体的显著转化一致。在以LS-Fe膜作为工作电极的电化学池中加入TCA，随着TCA浓度在0.1 - 2.0 mM范围内变化，在 -0.40 V附近的阴极电流峰线性增加。这种行为被解释为TCA诱导LS-Fe膜的组成逐渐变化，有利于单体铁（III）卟啉，这导致了在 -0.40 V附近观察到的阴极电流增加。
