Photoinduced Electron and Energy Transfer and pH-Induced Modulation of the Photophysical Properties in Homo- and Heterobimetallic Complexes of Ruthenium(II) and Rhodium(III) Based on a Heteroditopic P

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• 作者：Dinesh Maity ; Chanchal Bhaumik ; Srikanta Karmakar ; Sujoy Baitalik
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：July 15, 2013
• 年：2013
• 卷：52
• 期：14
• 页码：7933-7946
• 全文大小：691K
• 年卷期：v.52,no.14(July 15, 2013)
• ISSN：1520-510X

文摘

Homo- and heterobimetallic complexes of compositions [(bpy)₂Ru^II(phen-Hbzim-tpy)Ru^II(tpy/tpy-PhCH₃/H₂pbbzim)]⁴⁺ and [(bpy)₂Ru^II(phen-Hbzim-tpy)Rh^III(tpy-PhCH₃/H₂pbbzim)]⁵⁺, where phen-Hbzim-tpy = 2-[4-(2,6-dipyridin-2-ylpyridin-4-yl)phenyl]-1H-imidazole[4,5-f][1,10]phenanthroline, bpy = 2,2鈥?bipyridine, tpy = 2,2鈥?6鈥?2鈥?terpyridine, tpy-PhCH₃ = 4鈥?(4-methylphenyl)-2,2鈥?6鈥?2鈥?terpyridine, and H₂pbbzim = 2,6-bis(benzimidazol-2-yl)pyridine, have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and ¹H NMR spectroscopy. The absorption spectra, redox behavior, and luminescence properties of these bimetallic complexes have been thoroughly investigated and compared with those of monometallic [(bpy)₂Ru^II(phen-Hbzim-tpy)]²⁺ and [(tpy-PhCH₃)Rh^III(tpy-Hbzim-phen)]³⁺ model compounds. The electrochemistry of the complexes shows a reversible Ru^II/III oxidation in the anodic region and an irreversible Rh^III/I reduction and several ligand-based reductions in the cathodic region. Steady-state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer from the metal-to-ligand charge-transfer (MLCT) excited state of the [(bpy)₂Ru^II(phen-Hbzim-tpy)] chromophore to the MLCT state of the tpy-containing chromophore [(phen-Hbzim-tpy)Ru^II(tpy/tpy-PhCH₃/H₂pbbzim)] occurs in all three unsymmetrical homobimetallic complexes. On the other hand, for both heterometallic dyads, an efficient intramolecular photoinduced electron transfer from the excited ruthenium moiety to the rhodium-based unit takes place. The rate constants for the energy- and electron-transfer processes have been determined by time-resolved emission spectroscopy. The influence of the pH on the absorption, steady-state, and time-resolved emission properties of complexes has been thoroughly investigated. The absorption titration data were used to determine the ground-state pK values, whereas the luminescence data were utilized for determination of the excited-state acid dissociation constants. In effect, deprotonation of the azole NH moieties of the complexes leads to a substantial lowering of the MLCT absorption and emission band energies.