Effects of Protonation on the Spectroscopic Properties of Tetrapyridoacridine (TPAC) Mono- and Dinuclear Ru(II) Complexes in Their Ground and 3MLCT Excited States

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• 作者：Leslie Herman ; Benjamin Elias ; Fré ; dé ; ric Pierard ; Cé ; cile Moucheron ; André ; e Kirsch-De Mesmaeker
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：October 4, 2007
• 年：2007
• 卷：111
• 期：39
• 页码：9756 - 9763
• 全文大小：339K
• 年卷期：v.111,no.39(October 4, 2007)
• ISSN：1520-5215

文摘

The spectroscopic behavior of mono- and dinuclear Ru(II) complexes (P, T, PP and TT, Figure 1) thatcontain the extended planar ligand tetrapyrido[3,2-a:2',3'-c:3' ',2' '-h:2' '',3' ''-j]acridine (TPAC) and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (tap) as ancillary ligands is examined in water andas a function of the pH. These four complexes luminesce in aqueous solution. The analyses of the data inabsorption lead to the pK_a values in the ground state, and the data in emission show that the excited ³MLCTstates are much more basic than the ground state. When the complex contains tap ligands (T and TT), adecrease in pH transforms the luminescent excited basic form into another luminescent excited protonatedspecies, which emits more bathochromically. In contrast, with phen ancillary ligands (P and PP), the protonatedexcited state does not luminesce. The rate constant of first protonation of the ³MLCT state is diffusion controlled,except for the dinuclear PP complex, whose protonation takes place on the nitrogen of the acridine motif.For P, in which the protonation process is the fastest, it would take place on the nitrogen atoms of thenonchelated phen moiety of the TPAC ligand. These results allow also us to gain information on the localizationof the excited electron in the ¹MLCT state populated upon absorption as well as in the relaxed ³MLCT emissivestate. Moreover as these complexes are interesting for their study with DNA, it can be concluded from thesedata that a portion of the excited species in interaction with DNA will be protonated.