Excited States of Triphenylamine-Substituted 2-Pyridyl-1,2,3-triazole Complexes.

A new 2-pyridyl-1,2,3-triazole (pytri) ligand, TPA-pytri, substituted with a triphenylamine (TPA) donor group on the 5 position of the pyridyl unit was synthesized and characterized. Dichloroplatinum(II), bis(phenylacetylide)platinum(II), bromotricarbonylrhenium(I), and bis(bipyridyl)ruthenium(II) complexes of this ligand were synthesized and compared to complexes of pytri ligands without the TPA substituent. The complexes of unsubstituted pytri ligands show metal-to-ligand charge-transfer (MLCT) absorption bands involving the pytri ligand in the near-UV region. These transitions are complemented by intraligand charge-transfer (ILCT) bands in the TPA-pytri complexes, resulting in greatly improved visible absorption (λmax = 421 nm and ϵ = 19800 M-1 cm-1 for [Pt(TPA-pytri)Cl2]). The resonance Raman enhancement patterns allow for assignment of these absorption bands. The [Re(TPA-pytri)(CO)3Br] and [Pt(TPA-pytri)(CCPh)2] complexes were examined with time-resolved infrared spectroscopy. Shifts in the C≡C and C≡O stretching bands revealed that the complexes form states with increased electron density about their metal centers. [Pt(TPA-pytri)Cl2] is unusual in that it is emissive despite the presence of deactivating d-d states, which prevents emission from the unsubstituted pytri complex.