Effect of Ligands with Extended π-System on the Photophysical Properties of Ru(II) Complexes

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• 作者：Yujie Sun ; Maya El Ojaimi ; Richard Hammitt ; Randolph P. Thummel ; Claudia Turro
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：November 18, 2010
• 年：2010
• 卷：114
• 期：45
• 页码：14664-14670
• 全文大小：254K
• 年卷期：v.114,no.45(November 18, 2010)
• ISSN：1520-5207

文摘

Density functional theory calculations were performed on a series of six ruthenium complexes possessing tridentate ligands: [Ru(tpy)₂]²⁺ (1; tpy = [2,2′;6′,2′′]-terpyridine), [Ru(tpy)(pydppx)]²⁺ (2; pydppx = 3-(pyrid-2′-yl)-11,12-dimethyldipyrido[3,2-a: 2′,3′-c]phenazine), [Ru(pydppx)₂]²⁺ (3), [Ru(tpy)(pydppn)]²⁺ (4; pydppn = 3-(pyrid-2′-yl)-4,5,9,16-tetraazadibenzo[a,c]naphthacene), [Ru(pydppn)₂]²⁺ (5), and [Ru(tpy)(pydbn)]⁺ (6; pyHdbn = 3-pyrid-2′-yl-4,9,16-triazadibenzo[a,c]naphthacene). The calculations were compared to experimental data, including electrochemistry and electronic absorption spectra. The theoretical results reveal that the lowest-lying singlet and triplet states in 4 and 5 are pydppn-based ππ* in character, which are remarkably different from the lowest-lying metal-to-ligand charge transfer (MLCT) states in 1−3. The calculated lowest triplet states in 4 and 5 are consistent with the ³ππ* states observed experimentally. However, although the extended π-system of pydbn⁻ is similar to that of pydppn, the HOMO of 6 lies above those of 4 and 5, resulting in strikingly different spectroscopic properties. Calculations show that the lowest triplet excited state of 6 is a combination of ³MLCT and ³ππ*. This work demonstrates that the electronic structure of the tridentate ligand has a pronounced effect on the photophysical properties of ruthenium(II) complexes and that DFT and TD-DFT methods are a useful tool that can be used to predict photophysical and redox properties of transition metal complexes.