Tunable Chromic Properties of Viologen-Metal Polymers Modulated by Coordination Modes for Inkless Erasable Printing

Inkless and erasable printing (IEP) based on chromic materials holds great promise to alleviate environmental and sustainable problems. Metal-organic polymers (MOPs) are bright platforms for constructing IEP materials. However, it is still challenging to design target MOPs with excellent specific functions rationally due to the intricate component-structure-property relationships. Herein, an effective strategy was proposed for the rational design IEP-MOP materials. The stimuli-responsive viologen moiety was introduced into the construction of MOPs to give it potential chromic behaviors and two different coordination models (i. e. bilateral coordination model, M₁ ; unilateral coordinated model, M₂ ) based on the same viologen ligand were designed. Aided by theoretical calculations, model M₁ was recommended secondarily as a more suitable system for IEP materials. Along this line, two representative viologen-Zn^II MOPs 1 and 2 with models M₁ and M₂ were synthesized successfully. Experiments exhibit that 1 does have quicker stimuli response, stronger color contrast and longer radical lifetime compared to 2. Significantly, the obtained 1-IEP media brightly inherits the excellent chromic characteristics of 1 and the flexibility of the paper at the same time, which achieves most daily printing requirements, as well as enough resolution and durability to be used in identification by smart device.