Département de chimie moléculaire

A family made of four bis(pyridyl)triazine ligands with appended aryl rings, including three fused arom. rings, were synthesized, and their corresponding homoleptic Ru(II) and Zn(II) complexes were prepd. and characterized by several means. The free ligands 2,4-di(2-pyridyl)-6-phenyl-1,3,5-triazine (L1); 2,4-di(2-pyridyl)-6-(1-naphthyl)-1,3,5-triazine (L2); 2,4-di(2-pyridyl)-6-(9-phenanthryl)-1,3,5-triazine (L3); and 2,4-di(2-pyridyl)-6-(1-pyrenyl)-1,3,5-triazine (L4) were formed in triazine ring-forming reactions from the reactions of the cyano-functionalized arom. rings with LiNMe2 followed by the addn. of 2 equiv of 2-cyanopyridine. The metal complexes examd. in this study are the homoleptic Ru(II) complexes Ru(L1)22+ (2a), Ru(L2)22+ (2b), Ru(L3)22+ (2c), and Ru(L4)22+ (2d) and Zn(II) complexes Zn(L1)22+ (3a), Zn(L2)22+ (3b), Zn(L3)22+ (3c), and Zn(L4)22+ (3d). Also, crystallog. data for the free ligands and Zn(II) and Ru(II) complexes were obtained in some cases. The redox behavior and absorption spectra of all the species were studied, together with the luminescence properties of the free ligands at room temp. in fluid soln. and of the Ru(II) complexes both at room temp. in fluid soln. and at 77 K in rigid matrix. The redox data indicate that the free ligands are reduced twice at relatively mild potentials ({\textless} -2.30 V vs. SCE), with the first redn. almost independent of the nature of the substituted aryl group. The UV absorption spectra of all the compds. are dominated by intense spin-allowed $π$-$π$* transitions mainly centered on the bis(pyridyl)triazine moiety; however, in L2-L4, moderately intense intraligand charge-transfer (ILCT) bands are also present. Such bands are red shifted in the Zn(II) compds., while they are obscured in the Ru(II) species by the more intense spin-allowed metal-to-ligand charge-transfer (MLCT) bands. The free ligands exhibit interesting emission properties, ranging from fluorescence from $π$-$π$* states to excimeric (in L4) and ILCT (in L2 and L3) emission. In the Ru(II) complexes, strong emission is found at 77 K from triplet MLCT states. For 2c and 2d, the emissive MLCT states are mixed with low-lying triplet ligand-centered states. [on SciFinder(R)]