Strategy for the Construction of Diverse Poly-NHC-Derived Assemblies and Their Photoinduced Transformations.

A series of supramolecular assemblies of types [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 , obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H4 -L(PF6 )4 and AgI ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H4 -L(PF6 )4 . Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag4 (L)2 ](PF6 )4 or [Ag8 (L)4 ](PF6 )8 stoichiometry. The molecular structures of selected [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 assemblies were determined by X-ray diffraction analyses. While H4 -L(PF6 )4 does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC-metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.