Iron(II) and Copper(I) Coordination Polymers: Electrochromic Materials with and without Chiroptical Properties

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Abstract
The electrochemical and optical properties of films prepared from two different Fe(II) coordination polymers (TPT[FeIITPT]n(PF6)2n (TPT = terpyridine−phenyl−terpyridine) and CTPCT[FeIICTPCT]n(PF6)2n (CTPCT = chiral terpyridine−phenyl−chiral terpyridine)) and a coordination polymer based on Cu(I) metal centers (PDP[CuIPDP]n(BF4)n) (PDP = phenanthroline−dodecane−phenanthroline) have been studied. The oxidation of a PDP[CuIPDP]n(BF4)n film coated on an indium−tin oxide (ITO) electrode by stepping the potential from 0.0 to +1.4 V vs Ag/AgCl led not only to the complete bleaching of the absorption in the visible region of the spectrum within 5 min but also to a redox-induced dissociation and dissolution of the polymer. The reverse reaction of binding and reassembling the polymer at the electrode surface, upon stepping the potential back to 0.0 V, occurred with a rate which was at least 1 order of a magnitude slower. In contrast, the bis(2,2‘:6‘,2‘ ‘-terpyridine)iron(II)-based redox polymers TPT[FeIITPT]n(PF6)2n and CTPCT[FeIICTPCT]n(PF6)2n, during similar spectroelectrochemical experiments, not only exhibited a dramatically enhanced switching rate but also displayed symmetric switching kinetics. The films did not show signs of deterioration over 150 switching cycles. Additionally, in an effort to assemble an electrochromic device with chiroptical properties, the electrochromism of films generated from the enantiomerically pure CTPCT[FeIICTPCT]n(PF6)2n polymer was studied through circular dichroism.