Development of pH-Sensitive Spin-Crossover Complex Film and Direct Observation of Proton Flow

在高质子传导性Nafion膜中，[FeII(Diamsar)]@Nafion(diamsar=1，8-二氨基磺酸)是一种pH敏感的自旋-交叉铁(II)络合物，它的自旋状态可以通过电场诱导的质子浓度梯度进行时空调控。[Fe(II)(Diamsar)]在酸性条件下具有Fe(II)的高自旋(HS)态，而在碱性条件下由于其末端氨基的质子化/去质子化与颜色变化有关而具有低自旋(LS)态。外加电压可逆地诱导了[Fe(II)(Diamsar)]@Nafion的时变颜色变化，对应于[Fe(II)(Diamsar)]的动态自旋交叉行为。通过这种方式，我们首次使用对pH敏感的自旋交叉络合物作为颜色指示剂来可视化Nafion膜中的质子流动。

The spin state of a pH-sensitive spin-crossover iron(II) complex in highly proton-conductive Nafion membrane, [FeII(diAMsar)]@Nafion (diAMsar = 1,8-diaminosarcophagine), was spatiotemporally manipulated by electric field-induced proton concentration gradient derived from applied voltage. [Fe(II)(diAMsar)] has the high-spin (HS) state of Fe(II) in acidic condition, whereas it has the low-spin (LS) state in basic condition due to the protonation/deprotonation of the terminal amino groups of diAMsar being associated with color change. Applied voltage reversibly induced the time-variable color change of [Fe(II)(diAMsar)]@Nafion, corresponding to the dynamical spin-crossover behavior of [Fe(II)(diAMsar)]. In this way, we visualized the proton flow in Nafion membrane by using the pH-sensitive spin-crossover complex as a color indicator for the first time.