Photoluminescence and electrochemical studies of tetranuclear ruthenium(II) polypyridyl complexes of benzimidazolyl functionalised pyrenylcalix[4]resorcinarene

Abstract

We report the hitherto unreported pyrene footed calix[4]resorcinarene (P1) supramolecular assembly and its tetranuclear Ru(II) polypyridyl complexes, [{Ru(phen)2}4(L)](ClO4)8 (CP1), [{Ru(bpy)2}4(L)](ClO4)8 (CP2), and [{Ru(P2)2}4(L)](ClO4)8 (CP3) [where, L = 2,8,14,20-tetra(pyren-1-yl)-5,11,17,23-tetrakis((2-(pyridin-2-yl)-1H-benzimidazol-1-yl)methyl)-4,6,10,12,16,18,22,24-octahydroxy-calix[4]resorcinarene and P2 = 2-(pyridin-2-yl)-1H-benzimidazole]. The single crystal structure of 2,8,14,20-tetra(pyren-1-yl)-4,6,10,12,16,18,22,24-octahydroxycalix[4]-resorcinarene (P1) possesses all cis configuration and a boat like conformation with pyrene rings occupying the axial positions. The tetranuclear complexes, CP1, CP2 and CP3, show decreasing energy of 3MLCT luminescence at 298 K but the intensity is increased at 77 K in frozen acetonitrile due to lowering of energy gap between π* of the ligand and the d orbital of ruthenium metal ion. The luminescence quantum yield has also been increased considerably in all the complexes when the temperature is decreased from 298 K to 77 K due to the lowering of nonradiative decay pathways. The complexes exhibit a single exponential decay profile in acetonitrile at 298 K. The cyclic voltammograms of the complexes show simultaneous four single electron quasireversible redox processes.