Photoinduced E to Z isomerization of tetraphenylethylene derivatives within organometallic supramolecular assemblies

Isolation of E-1,2-bis(4-bromophenyl)-1,2-diphenyl-ethylene from the E/Z isomer mixture obtained by a McMurry coupling reaction and reaction of this isomer with imidazole followed by N-alkylation with nBuBr and anion exchange yielded the bisimidazolium tetraphenylethylene (TPE) derivative H-2-E-1(PF6)(2). The reaction of H-2-E-1(PF6)(2) with Ag2O yielded the di-nuclear metallarectangle [Ag-2(E-1)(2)](PF6)(2) where the two bis-NHC donors E-1 bridge two silver atoms. Irradiation of [Ag-2(E-1)(2)](PF6)(2) leads to E/Z isomerization of the di-NHC ligand and formation of Z-1 in the mononuclear complex [Ag(Z-1)]PF6. Demetallation of the di-NHC ligand with NH4Cl/NH4PF6 yielded bisimidazolium salt H-2-Z-1(PF6)(2). The unique isomerization of the E-TPE derivative into its Z-isomer via metal complex formation/irradiation/demetallation cannot be achieved by irradiation of the individual imidazolium salt. The emissive properties of the TPE complexes [Ag-2(E-1)(2)](PF6)(2) and [Ag(Z-1)]PF6 have been investigated.