Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer.

By the combination of N , N' -bis(carboxymethyl)-pyromellitic diimide (H 2 CMPMD, 1 ) and zinc ions, a novel PMD-based coordination polymer (CP), [Zn(CMPMD)(DMF) 1.5 ]·0.5DMF ( 2 ) (DMF = N , N' -dimethylformamide), has been prepared and characterized. 1 and 2 exhibit completely different photochromic properties, which are mainly reflected in the photoresponsive rate (5 s for 1 vs 1 s for 2 ) and coloration contrast (from colorless to light green for 1 vs green for 2 ). This phenomenon should be attributed to the introduction of zinc ions and the consequent formation of the distinct interfacial contacts of electron donors (EDs) and electron acceptors (EAs) (d n-π = 3.404 and 3.448 Å for 1 vs d n-π = 3.343, 3.359, 3.398, and 3.495 Å for 2 ), suggesting a subtle modulating effect of metal ions on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photochromic behaviors. Interestingly, the photochromic performance of 2 can be enhanced after the removal of coordinated DMF, which might be ascribed to the decrease of the distance of EDs/EAs caused by lattice shrinkage, which further improves the efficiency of PIET. Meanwhile, 2 displays rapid electrochromic behavior with an obvious reversible color change from colorless to green, which can be used in an electrochromic device. This work develops a new type of EA for the construction of stimuli-responsive functional materials with excellent dual photo-/electrochromic properties.