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 (λ_max = 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