Multifunctional naphthalene diimide-based coordination polymers: Ultrafast visible light-induced photochromism, visual detection of blue light, inkless and erasable prints and electrochromism

The development of multifunctional stimuli-responsive materials is of extremely urgency due to their practical applications in gas sensing, anti-counterfeit, inkless and erasable printing, switches and energy conversion. In this work, two novel naphthalene diimide (NDI)-based coordination polymers (CPs), [Zn(CMNDI)1.5(H2O)]·[NH2(CH3)2] (1) and [Cd0.5(CMNDI)]·[NH2(CH3)2] (2) (H2CMNDI = N,N′-bis(carboxymethyl)-naphthalene diimide), have been synthesized by the combination of H2CMNDI with zinc/cadmium ions. The usage of metal ions with different radius and coordination mode leads to a two-dimensional (2D) layer for 1 and a one-dimensional (1D) chain for 2. Both 1 and 2 exhibit ultrafast visible light-induced photochromic properties, which might be attributed to extending the excitonic absorption to the visible light region via charge transfer (CT) caused by π-π interactions. Furthermore, the different photoresponsive behaviors of 1 and 2 are mainly reflected in photoresponse rate, coloration contrast, especially for anti-fatigue/cycle performance (30 cycles for 1 vs. 4 cycles for 2), which should be attributed to the formation of distinct interfacial contacts of electron donors (EDs)/electron acceptors (EAs) through different number and strength of non-covalent interactions. Notably, both 1 and 2 are highly sensitive to the visible-light wavelengths of 400–450 nm, which represents a new category of photochromic materials for the visual detection of blue light. Meanwhile, 1 can be used for inkless and erasable printing media, and the printing-erasing process can be repeated for at least 20 cycles, which is a major breakthrough of photochromic CPs in the anti-fatigue/cycle performance of inkless and erasable printing. Finally, 1 displays outstanding electrochromic property and color change from light yellow to brown by altering the potential from 0 V to −0.8 V, which can be used for the construction of electrochromic device (ECD). This work provides an effective strategy for construction of multifunctional stimuli-responsive materials.