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• A new viologen complex was successfully synthesized and characterized. • Under UV irradiation, the samples heated at 120 and 180℃showed different colors. • We construct a "AND" logic-gate strategy, different inputs lead to disparate results. Electron transfer is crucial for the rapid response of viologen-based complexes and investigating the factors that affect electron transfer has always been a major challenge. Herein, a new viologen-based complex, formulated as {[Zn 5 (cbbbc) 3 (BTC) 3 (μ 1 , 1 -OH)(H 2 O) 5 ]·22H 2 O} n , with a three-dimensional framework was successfully designed and synthesized by viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy), trimesic acid (H 3 BTC) and Zn(NO 3) 2 ·6H 2 O. In particular, complex 1 does not exhibit photochromic properties. However, samples of complex 1 heated at 120 and 180 ℃ display tunable colors under UV light irradiation. The experimental results indicate that the compound's light response is less sensitive with higher water content in the lattice. The polarity and hydrogen bonding ability of lattice water in viologen-based complexes can interact with the donor of viologen, leading to a reduction in electron transfer. This study demonstrates the impact of lattice water on electron transfer in viologen-based complexes and offers insights for designing faster response complexes in the future. The light response of the complexes becomes less sensitive as the water content in the lattice increases. This is because the lattice water hinders the electron transfer of the complexes. [Display omitted] [ABSTRACT FROM AUTHOR]

A Naphthalenediimide-based photochromic 2D MOF was successfully synthesized. After irradiation and immersion in acetonitrile solution, the single-crystal-to-single-crystal transition occurred, and 1-P and 1@MeCN were obtained, respectively. 1-P is a rare example of structural visualization during the formation of free radicals after NDI-based photochromism. 1@MeCN improves the photochromic performance of the system by introducing solvent molecules. Finally, for the first time, 1@MeCN was combined with organic glass for practical applications in ink-free printing, purple light detection/filtering, and information anti-counterfeiting. [Display omitted] • A photochromic MOF (1) based on the NDI ligand was synthesized and characterized. • Captured a rare process of structural visualization of free radical formation in 1-P. • The effect of solvent on the photochromic properties (1@MeCN) was revealed. • 1 and 1@MeCN were first used to selectively detect and filter 395 nm purple light. • The 1@MeCN glass was prepared for the first time. It is still a great challenge to understand the structural variation during the photochromic process, to rationally regulate the photochromic performance, and to expand the practical application of NDI-based photochromic materials. Herein, we found a 2D NDI-type photochromic MOF (1). When illuminated by 395 nm purple light, 1 underwent a single-crystal-to-single-crystal (SCSC) transition, resulting in 1-P , which is a rare structural visualization phenomenon during the formation of free radicals. In addition, it was demonstrated for the first time that the introduction of solvent molecules into the system (1@MeCN) can modulate the photochromic ability caused by electron transfer. It was found that 1 and 1@MeCN have the most sensitive response to 395 nm purple light, and are ideal candidates for detecting and filtering purple light. Finally, a photochromic glass based on 1@MeCN was reported, which is first applied in ink-free printing, purple light detection/filtering, and information anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Organic molecules and some coordination polymers that are responsive to external stimuli (such as light, electrical potential, heat, guest inclusion or pressure) often generate structural isomerization, such as ring-opening/closing, tautomerism and cis-trans isomerization. While for viologen derivatives, generally, electron transfer occurs upon the photoirradiation without a significant structural change. Herein we present a new viologen-based Zn-complex (1) which undergoes single-crystal-to-single-crystal (SCSC) transformation to 1G upon crushing. Both 1 and 1G could change to 1Y when stored under air in the dark at ambient for one week. The colorless crystal 1 undergoes a two-step color change to pink (1P) and brown (1Z) upon irradiation with UV for 40 s and 15 min, respectively. More importantly, the complex 1G also has a two-step coloring phenomenon under UV light. The colorless crystals of 1G change into blue (1Q) after irradiation for 15 s and finally become brown (1Z′) with the increase of irradiation time. While 1Y only undergoes one coloration from colorless to cyan 1Y′ after UV irradiation. The possible pathways for electron transfer were confirmed to be through intermolecular hydrogen bonding according to the results of crystal structure and the photochromic behavior of the ground samples. 1Z and 1Z′ could change color to yellow 1H and 1H′ in the dark, respectively. Only the changes between 1 and 1P , 1Z and 1H , 1G and 1Q , 1Z′ and 1H′ , 1Y and 1Y′ are reversible, which implies that the crystal structures varied upon photoirradiation because 1Z and 1Z' can revert to neither the original crystals 1 and 1G , nor the intermediate 1P and 1Q. These findings help to understand multiple photochromism and variations of crystal structures under different external stimuli via SCSC transformations. In addition, complex 1 shows high selectivity for primary aromatic amine aniline among various amines. [Display omitted] • Complex 1 undergoes a single-crystal to single-crystal transformation to 1G upon crush with structure change. • Both 1 and 1G could undergo a two-step coloring phenomenon under UV light. • 1 and 1G change to 1Y when stored in the dark for one week. • Complex 1 shows high sensitivity to aniline. • The pathways for electron transfer of the two-step were discussed in detail. [ABSTRACT FROM AUTHOR]