Synthesis of Ni-Based Metallo-Supramolecular Polymer with Bis-NNO-Tridentate Ligand for Electrochromic Devices

Abstract

An imine-based bis-NNO-tridentate ligand (L1) was prepared by condensation of a salicylaldehyde derivative with 8-aminoquinoline. L1 formed a 1:1 complex with Ni(II) ions with a high coordination constant. A one-dimensional, Ni-based metallo-supramolecular polymer (polyNiL1) was synthesized via the 1:1 complexation of Li with Ni(II) ions in DMF at 60ºC. L1 and polyNiL1 were characterized by IR absorption spectroscopy. In the IR spectrum of polyNiL1, a shift of the C=N absorption peak based on the complexation was observed. In UV-vis spectroscopy of polyNiL1, a strong absorption appeared at 505 nm, which is attributed to the metal-to-ligand charge transfer (MLCT) band from Ni(II) ions to L1. In a cyclic voltammogram of polyNiL1 in a DMF solution, a reversible redox wave was observed at +0.58 V. PolyNiL1 in a film state exhibited electrochromism between reddish-orange and green color by applying-2.5 V and +2.5 V, respectively. The green color in the oxidation state comes from the ligand-to-ligand charge transfer (LLCT) of a radical cation between the phenyl ring and the quinoline ring in polyNiL1. Since the radical cation of L1 was stabilized by a Ni(II) ion in the complex, this electrochromism showed good reversibility about 10 times under ambient conditions.

Electrochromic Behavior of Donor-Acceptor Polymers Containing Diketopyrrolopyrrole Unit

“…From a materials point of view, it is significant to understand the structureproperty relationship that determines the colors in both the neutral and doped states and their switching rates [22][23][24][25][26][27][28]. However, as already mentioned, examples of electrochromic DPP-based polymers are limited, and most of them are composed of alternating structures of thiophene-based donors and DPP acceptors.…”