Regulation of π⋯π stacking interactions between triimidazole luminophores and comprehensive emission quenching by coordination to Cu(ii)

Abstract

Eight Cu(II) coordination compounds with cyclic triimidazole, triimidazo[1,2-a:1′,2′-c:1′′,2′′-e][1,3,5]-triazine (L₁), its positional isomer, triimidazo[1,2-a:1′,2′-c:1′′,5′′-e][1,3,5]-triazine (L₂), and two pyridine derivatives of L₁, 3-(pyridin-2-yl)triimidazo[1,2-a:1′,2′-c:1′′,2′′-e][1,3,5]triazine (L₃) and 3-(pyridin-4-yl)triimidazo[1,2-a:1′,2′-c:1′′,2′′-e][1,3,5]triazine (L₄) are reported. All compounds represent neutral Cu(II) discrete complexes or coordination polymers comprising luminophore triimidazole molecules and charge-compensated anions. Starting from copper(II) acetate monohydrate with the paddle-wheel geometry, two binuclear complexes [Cu₂(CH₃COO)₄(L₁)₂] (1) and [Cu₂(CH₃COO)₄(L₃)₂] (2), a mixed-dimensional 0D/1D coordination compound {[Cu₂(CH₃COO)₄(L₂)]₂[Cu₂(CH₃COO)₄(H₂O)(L₂)]·2(H₂O)}_n (3), all with binuclear paddle-wheel [Cu₂(CO₂)₄] secondary building units, and a mononuclear complex [Cu(CH₃COO)₂(L₂)₂] (4) with square-planar N₂O₂ Cu(II) coordination, were obtained. Starting from copper(II) nitrate trihydrate, three mononuclear complexes [Cu(NO₃)₂(L₂)₄]·2CH₃CN (5), [Cu(NO₃)₂(L₂)₄]·1.5(dmf) (6), and [Cu(NO₃)₂(H₂O)₂(L₄)₂]·2H₂O (7) with Cu(II) distorted octahedral N₄O₂ and N₂O₄ coordination cores, and 1D coordination polymer [Cu(NO₃)₂(L₃)]_n (8) with the distorted square pyramidal N₂O₃ Cu(II) coordination geometry were obtained. In the mono- and binuclear complexes, luminophores L₁–L₄ coordinate as monodentate terminal ligands. In the coordination chain 3 the L₂ ligand acts as a bidentate-bridging exo-ligand, while in 8 the L₃ ligand acts as a bidentate-chelate one, and the structure extension to 1D is achieved via the bridging nitrate-anions. The compromise between the hydrogen bonds and π⋯π stacking interactions defines the stacking patterns of bulky luminophores coordinated to the metal center that vary from the dimeric associates to the infinite 2D motifs with the different overlapping areas of the stacking ligands. The strong aggregation-induced emission demonstrated by pure luminophores was nearly quenched in the reported Cu(II) coordination compounds in the solid state.