Water-Mediated Dissolution–Reassembly of a Viologen-Based Coordination Polymer for Activating Multi-stimuli Chromism

Structural reconstruction in coordination polymers (CPs) offers a powerful yet underexplored route to emergent functionality beyond static framework design. Here we report a water-mediated dissolution–reassembly coordination reconstruction process that transforms a tetrahedral Co(II)-based two-dimensional CP (CoVN-1) into two distinct octahedral one-dimensional phases (CoVN-2 and CoVN-3) through dissolution–reassembly. Single-crystal analyses reveal that water coordination induces a tetrahedral-to-octahedral conversion at the metal nodes, accompanied by pronounced conformational reorganization of viologen ligands. This coordination reconstruction activates multi-stimuli chromism such that CoVN-1 remains inactive whereas CoVN-2 and CoVN-3 exhibit reversible photochromic and thermochromic responses and CoVN-3 uniquely displays mechanochromism. The selective mechanical responsiveness is closely associated with enhanced π-conjugation and more favorable intermolecular orbital coupling in the low-torsion conformer. These findings demonstrate that water-mediated coordination-environment modulation can influence charge-transfer pathways and radical generation in CPs, establishing coordination geometry reconstruction as a viable internal lever for adaptive, multi-responsive framework materials.