Two photochromic Cd(II)-CPs were obtained based on the viologen ligand using different synthetic routes, named {[Cd₄(p-BDC)₄(CPB)₂(H₂O)₂]·2H₂O·EtOH}_n (1) and {[Cd(p-BDC)(CPB)(H₂O)]·(L)·DMF}_n (2) (p-H₂BDC = 1,4-benzene-dicarboxylate, HCPB·Cl = 1-(4-carboxyphenyl)-4,4′-bipyridinium·Cl, L = 2,4-dinitrochlorobenzene, and DMF = N,N-dimethylformamide), respectively. Due to different coordination modes, the two Cd(II)-CPs show different structures. Compound 1 exhibits a three-dimensional (3D) framework with bimetallic nodes, while compound 2 displays a 2-fold interpenetrated (4,4) net topology. Notably, the two Cd(II)-CPs exhibit substantial disparities in photo/thermochromism, which can be attributed to variations in donor–acceptor (D–A) distances arising from structural differences. Compound 1 showed visually sensitive photo- and thermochromic behavior due to multi-pathway electron transfer and short D–A distances, which is relatively rare in electron-transfer type photochromic systems. In contrast, 2 only demonstrates insensitive photochromic behavior, with a slight deepening of the color observed after 2 hours of UV light, which is due to the mono-pathway electron transfer and long D–A distance. Moreover, we first combined Cd(II)-viologen CPs with polydimethylsiloxane (PDMS) to prepare a 1@PDMS flexible UV imaging film. 1@PDMS exhibits excellent bendability and stretchability and maintains good photochromic properties after 100 bending cycles. To demonstrate the rapid color response and distinct color contrast of 1, its application in anti-counterfeiting is also demonstrated.

中文翻译：

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通过配位模式调节Cd(II)-紫罗碱配位聚合物的可调节光/热致变色性能，用于柔性成像薄膜和防伪

以紫罗碱为配体，采用不同的合成路线，得到了两种光致变色的Cd( II )-CPs，命名为{[Cd ₄ ( p -BDC) ₄ (CPB) ₂ (H ₂ O) ₂ ]·2H ₂ O·EtOH} _n ( 1 ) 和 {[Cd( p -BDC)(CPB)(H ₂ O)]·(L)·DMF} _n ( 2 ) ( p -H ₂ BDC = 1,4-苯二甲酸，HCPB·Cl分别为：1-(4-羧基苯基)-4,4'-联吡啶鎓·Cl、L=2,4-二硝基氯苯、DMF= N , N-二甲基甲酰胺)。由于配位方式不同，两种Cd( II )-CP表现出不同的结构。化合物1表现出具有双金属节点的三维 (3D) 框架，而化合物2表现出 2 重互穿 (4,4) 网络拓扑。值得注意的是，两种 Cd( II )-CP 在光/热致变色方面表现出巨大的差异，这可归因于结构差异引起的供体-受体 (D-A) 距离的变化。由于多途径电子转移和短D-A距离，化合物1表现出视觉敏感的光致变色和热致变色行为，这在电子转移型光致变色系统中相对罕见。相比之下，2仅表现出不敏感的光致变色行为，在紫外线照射 2 小时后观察到颜色略有加深，这是由于单途径电子转移和长 D-A 距离。此外，我们首先将Cd( II )-紫罗碱CPs与聚二甲基硅氧烷(PDMS)结合，制备了1 @PDMS柔性紫外成像薄膜。1 @PDMS 表现出优异的弯曲性和拉伸性，并在 100 次弯曲循环后仍保持良好的光致变色性能。为了证明1的快速颜色响应和鲜明的颜色对比度，还演示了其在防伪方面的应用。