Effect of iodide on the electronic and photoresponsive behaviors of 1D naphthalenediimide-based zinc coordination polymers

Abstract

Four one-dimensional (1D) naphthalenediimide-based zinc coordination polymers, namely, [ZnI₂(4-PMNDI)] (1), [ZnI₂(3-PMNDI)]₂·DMF (2), [ZnI₂(3-PMNDI)]₂·DMA (3), and [ZnI₂(3-PMNDI)]₂·NMP (4) (4-/3-PMNDI = N,N′-bis(4-/3-pyridylmethyl)-1,4,5,8-naphthalenediimide, where DMF = N,N′-dimethylformamide, DMA = N,N′-dimethylacetamide, and NMP = N-methyl pyrrolidone), were synthesized, which exhibited completely different electronic and photoresponsive behaviors. Compared with the optical inertness of 1, 2–4 exhibited noticeable photochromic behaviors, which was attributed to the usage of 3-PMNDI and consequently the formation of different interfacial contacts of electron acceptors (EAs)/electron donors (EDs) as well as the occurrence of new electron-transfer channels (lone pair–π and π–π interactions) in 2–4. Interestingly, the sequential photochromic behaviors of 2–4 (brown to dark brown for 2, light brown to brownish black for 3, and earthy yellow to brownish black for 4) were primarily attributed to the introduction of different electron-rich solvents, which led to the slightly different interfacial contacts of the EAs/EDs. This work provides a new strategy for the manipulation of electronic behaviors from sole intermolecular charge transfer (ICT) to photoinduced intermolecular electron transfer (PIET) and the photoresponsive behaviors from “OFF” to “ON” by adjustment of the interfacial contacts of EAs/EDs for the first time.