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.