Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK.
Dalton Trans. 2010 Jan 7(1):200-11. doi: 10.1039/b918086a. Epub 2009 Nov 20.
The trinuclear complexes {(R2bipy)2Ru}3(mu3-HHTP)3 [1(PF6)3, R = H; 2(PF6)3, R = 4-tBu] contain three {Ru(R2bipy)2}2+ fragments connected to the triangular tris-chelating ligand hexahydroxytriphenylene (H6HHTP). This bridging ligand contains three dioxolene-type binding sites, each of which can reversibly convert between dianionic catecholate (cat), monoanionic semiquinone (sq) or neutral quinone (q) redox states. The bridging ligand as a whole can therefore exist in seven different redox states from fully reduced [cat,cat,cat]6- through to fully oxidised, neutral [q,q,q]. Cyclic voltammetry of 1(PF6)3 in MeCN reveals six redox processes of which the three at more positive potentials (the sq/q couples) are reversible but the three at more negative potentials (the sq/cat couples) are irreversible with distorted wave shapes due to the insolubility of the reduced forms of the complex. In contrast, the more soluble complex 2(PF6)3 displays six reversible one-electron redox processes making all components of a seven-membered redox chain accessible. UV/Vis/NIR spectro-electrochemical studies reveal rich spectroscopic behaviour, with--in particular--very intense transitions in the near-IR region in many of the oxidation states associated with Ru(II)-->(dioxolene) MLCT and bridging ligand centred pi-pi* transitions. TDDFT calculations were used to analyse the electronic spectra in all seven oxidation states; the calculated spectra generally show very good agreement with experiment, which has allowed a fairly complete assignment of the low-energy transitions. The strong electrochromism of the complexes in the near-IR region has formed the basis of an optical window in which a thin film of 1(PF6)3 or 2(PF6)3 on a conductive glass surface can be reversibly and rapidly switched between redox states that alternate between strongly absorbing or near-transparent at 1100 nm, with--for 2(PF6)3--the switching being stable and reversible in water over thousands of cycles.
三核配合物{(R2bipy)2Ru}3(mu3-HHTP)3 [1(PF6)3, R = H; 2(PF6)3, R = 4-tBu] 中包含三个通过三齿螯合配体六羟基三苯（H6HHTP）连接的{Ru(R2bipy)2}2+片段。该桥连配体包含三个二氧戊环型配位位，每个位都可以在阴离子邻苯二酚（cat）、单阴离子半醌（sq）或中性醌（q）氧化还原态之间可逆转换。因此，桥连配体整体可以存在七种不同的氧化还原态，从完全还原的[cat,cat,cat]6-到完全氧化、中性的[q,q,q]。1(PF6)3 在 MeCN 中的循环伏安法显示出六个氧化还原过程，其中三个在更正电位（sq/q 对）是可逆的，但三个在更负电位（sq/cat 对）是不可逆的，由于复合物还原形式的不溶性，呈现出扭曲的波形状。相比之下，更具可溶性的 2(PF6)3 显示出六个可逆的单电子氧化还原过程，使七个成员的氧化还原链的所有组成部分都可以访问。紫外可见近红外光谱电化学研究揭示了丰富的光谱行为，特别是在许多与 Ru(II)-(二氧戊环) MLCT 和桥连配体中心 pi-pi*跃迁相关的氧化态中存在非常强的近红外区域跃迁。TDDFT 计算用于分析所有七个氧化态的电子光谱；计算光谱通常与实验非常吻合，这使得对低能跃迁进行了相当完整的分配。复合物在近红外区域的强电致变色特性已成为光学窗口的基础，在该光学窗口中，导电玻璃表面上的 1(PF6)3 或 2(PF6)3 薄膜可以在强吸收或近透明的氧化还原态之间快速可逆切换，对于 2(PF6)3，在数千个循环中，水的开关稳定且可逆。
