Diversity of electron acceptor groups in donor-acceptor type electrochromic conjugated polymers

Conjugated polymers have been extensively used for optoelectronic applications such as photovoltaics, light-emitting diodes, thin-film transistors and electrochromics. Over the past decade, a large number of donor-acceptor type conjugated polymers with an alternating array of electron donors and acceptors have been designed and synthesised for organic electrochromics application. The selection of proper electron donors and in particular electron acceptors to construct desired conjugated polymers allows scientists to precisely tailor optical and electronic properties of resulting conjugated polymers. In this review, electrochromic conjugated polymers will be summarised based on a category of widely-used electron acceptors including benzothiadiazole, benzoselenadiazole, benzooxazole, benzotriazole, benzoimidazole, quinoxalines and diketopyrrolopyrroles. This paper would help scientists understand how structurally different electron acceptors to control and modulate the highest occupied molecular orbital and the lowest unoccupied molecular orbital by sophisticatedly synthesizing appropriate electron acceptors, thus creating a broad colour palette, and eventually delivering a variety of desired electrochromic parameters such as switching speed, optical contrast, colouration efficiency as well as long-term stability. This summary account will give an insight into design principle and structure-properties relationship of electrochromic conjugated polymers for interested researchers to find optimal performance electrochromic polymeric materials.