The synthesis of ruthenium piano-stool complexes for nonlinear optics

Abstract

A range of novel compounds of general formula [RuIICl(arene)(L–L)]n+ (L–L = 4,4ʹ-disubstituted bpy derivative, n = 1 or 3); n = 1, arene = p-cymene, L–L = 4,4-bis[(E)-2-(methoxycarbonyl)vinyl]-bpy, 1, and 4,4-bis[(E)-(p-ethoxycarbonyl-styryl)]-bpy, 2; n = 3, L–L = 4,4-bis[(E)-2-(N-methyl-4-pyridyl)vinyl]-bpy, 3, 4,4′-bis{(E)-2-[N-(2,4-dinitrophenyl)-4-pyridyl]vinyl}-2,2′-bpy 4, 4,4′-bis[(E,E)-4-(N-methyl-4-pyridyl)buta-1,3-dienyl]-2,2′-bpy 5, and 4,4′-bis[(E,E)-2-{4-[2-(N-methyl-4-pyridyl)vinyl]phenyl}-vinyl]-2,2′-bpy 6; ); n = 1, arene = hmb, L–L = 4,4-bis[(E)-2-(methoxycarbonyl)vinyl]-bpy, 7, and 4,4-bis[(E)-(p-ethoxycarbonyl-styryl)]-bpy, 8; n = 3, L–L = 4,4-bis[(E)-2-(N-methyl-4-pyridyl)vinyl]-bpy, 9 and [RuIIpy(hmb)(mcpv2bpy)][PF6]2 have been successfully synthesised in good yields and which all gave acceptable results when assessed by CHN analyses All the compounds were isolated as [PF6]− salts. A series of techniques, including1H NMR, ES-MS, MALDI-MS spectrometry, and elemental analysis, were used to study and probe the structure of these complexes. Crystals suitable for X-ray diffraction analysis were grown for RuII (hmb) complex salts 7 – 10. The single crystal structures of complex 9 contains two different Ru molecules. Whereas the asymmetric unit cell of 10 has identical molecules. All single crystal structures of these RuII (hmb) complexes present centrosymmetric packing, thus they may not have potential for bulk nonlinear optical effects in the solid state. The electronic absorption spectra were recorded in MeCN and characterized by a weaker absorption in the visible region and more intense bands in the UV region and the assignment of these bands has been supported by TD-DFT calculations. Indeed, the electrochemical measurements demonstrate that all complex salts 1 – 3, 6 – 8, show a quasi-reversible Ru-based oxidation wave, making these compounds particularly interesting in terms of redox switching of nonlinear optical responses. According to TD-DFT calculations, the low-energy bands contain two main transitions and involves a mixture of MLCT, LLCT character. Whereas the high-energy absorptions involve charge-transfer π → π* within the bipyridine ligands. The first static hyperpolarizability b response of the compounds were calculated using different level of theory and the results show that the β response increases as the bpy ligand becomes more extended.

Date of Award	23 May 2022
Original language	English
Awarding Institution	The University of Manchester