A new class of crystalline X-ray induced photochromic materials assembled from anion-directed folding of a flexible cation

Electron-deficient viologens are widely used as ligands or structure-directing agents(SDAs)to synthesize crystalline X-ray induced photochromic materials.Here,a new rational strategy of anion-directed fold-ing a flexible cation(H_(2)imb)^(2+)((H_(2)imb)^(2+)=di-protonated 2,3-bis(imidazolin-2-yl)-2,3-dimethylbutane)has been developed.Electron-donating Cl−and(ZnCl4)2−are used to direct folding a flexible electron-deficient(H_(2)imb)^(2+)cation.Three complexes(H_(2)imb)(NO_(3))2(1),(H_(2)imb)Cl2·H_(2)O(2),and(H_(2)imb)ZnCl4(3)have been synthesized in which(H_(2)imb)^(2+)crystallize in an anti-conformation,88.8°-gauche,and 51.8°-gauche,respectively.In contrary to X-ray silent complex 1,X-ray induced photochromism has been achieved in both complex 2 and 3.An intermolecular charge-transfer mechanism has been elucidated and the anion directed folding of(H_(2)imb)^(2+)has been validated to be critical to yield colored long-lived charge-separated states.

A chiral SrSi_(2)(srs)superstructure constructed by a dual interaction system showing isotropic electrical conductivity

Most porous conductive frameworks are highly anisotropic in their structures thus leading to anisotropic charge transport.Here we report a supramolecular self-assembly which is constructed by intermolecular hydrogen bonding andπ···πinteractions.This material features a chiral,porous,cubic framework structure withπ-stacked helical columns along all of the three Cartesian coordinates.As a result,isotropic charge transport with an electrical conductivity(σ)of 2.1×10^(–7)S/cm is achieved.By achieving isotropic charge transport in aπ-stacked supramolecular assembly,these results provide a new type of isotropic conductive framework materials alternative to conductive metal-organic frameworks(MOFs).