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Theoretical studies on complexes [Ru(phen)2 (9,9′-2R-dpq)]2+ (phen=1,10-phenanthroline; dpq=dipyrido[3,2-d:2′,3′-f]quinoxaline; R=NH2,OH,H and F) were carried out using the density functional theory (DFT) method. The results show that the 9,9′-site-substituents in intercalative ligand(dpq) have very important effects on the frontier molecular orbitals and related properties of the complexes. The HOMO, NHOMO, LUMO and NLUMO energies are gerenally decreased with increase of π electron-withdrawing ability of R except the LUMO energy of complex II (R–OH) being the lowest due to the rather strong intramolecular hydrogen-bonds in complex II. Both the π electron-pushing groups (NH2,OH) and the electron-withdrawing (F) can make red shifts in the max (λ) electronic absorption bands of the substitution derivates, in particular, OH group can lead to this effect more. Moreover, both electron-withdrawing group(F) and the electron-pushing groups (NH2,OH) can all make the LUMOs of the corresponding derivatives predominantly populate on π-orbitals of their main ligands, whereas the LUMO of the parent complex [Ru(phen)2(dpq)]2+ is almost equally populated on the π-orbitals of three ligands. In addition, the coordination stabilities of the four complexes are reduced with increase of π electron-withdrawing ability of R. The above theoretical results can be applied to reasonably analyze the trend in DNA-binding of the complexes, and thus they will be useful references for designs of new DNA-probes and photoreagents. |
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