6,6'-Ditriphenylamine-2,2'-bipyridine: Coordination Chemistry and Electrochemical and Photophysical Properties

Daniel A W Ross; Joseph I Mapley; Andrew P Cording; Roan A S Vasdev; C John McAdam; Keith C Gordon; James D Crowley

doi:10.1021/acs.inorgchem.1c01435

6,6'-Ditriphenylamine-2,2'-bipyridine: Coordination Chemistry and Electrochemical and Photophysical Properties

Inorg Chem. 2021 Aug 16;60(16):11852-11865. doi: 10.1021/acs.inorgchem.1c01435. Epub 2021 Jul 27.

Authors

Daniel A W Ross^{1

2}, Joseph I Mapley^{1

2}, Andrew P Cording¹, Roan A S Vasdev^{1

2}, C John McAdam¹, Keith C Gordon^{1

2}, James D Crowley^{1

2}

Affiliations

¹ Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
² MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand.

PMID: 34311548
DOI: 10.1021/acs.inorgchem.1c01435

Abstract

A 2,2'-bipyridine with bulky triphenylamine substituents in the 6 and 6' positions of the ligand (6,6'-ditriphenylamine-2,2'-bipyridine, 6,6'-diTPAbpy) was generated. Despite the steric bulk, the ligand readily formed bis(homoleptic) complexes with copper(I) and silver(I) ions. Unfortunately, efforts to use the 6,6'-diTPAbpy system to generate heteroleptic [Cu(6,6'-diTPAbpy)(bpy)]⁺ complexes were unsuccessful with only the [Cu(6,6'-diTPAbpy)₂](PF₆) complex observed. The 6,6'-diTPAbpy ligand could also be reacted with 6-coordinate metal ions that featured small ancillary ligands, namely, the [Re(CO)₃Cl] and [Ru(CO)₂Cl₂] fragments. While the complexes could be formed in good yields, the steric bulk of the TPA units does alter the coordination geometry. This is most readily seen in the [(6,6'-diTPAbpy)Re(CO)₃Cl] complex where the Re(I) ion is forced to sit 23° out of the plane formed by the bpy unit. The electrochemical and photophysical properties of the family of compounds were also examined. 6,6'-diTPAbpy exhibits a strong ILCT absorption band (356 nm, 50 mM^-1 cm^-1) which displays a small increase in intensity for the homoleptic complexes ([Cu(6,6'-diTPAbpy)₂]⁺; 353 nm, 72 mM^-1 cm^-1, [Ag(6,6'-diTPAbpy)₂]⁺; 353 nm, 75 mM^-1 cm^-1), despite containing 2 equiv of the ligand, attributed to an increased dihedral angle between the TPA and bpy moieties. For the 6-coordinate complexes the ILCT band is further decreased in intensity and overlaps with MLCT bands, consistent with a further increased TPA-bpy dihedral angle. Emission from the ¹ILCT state is observed at 436 nm (τ = 4.4 ns) for 6,6'-diTPAbpy and does not shift for the Cu, Ag, and Re complexes, although an additional ³MLCT emission is observed for [Re(6,6'-diTPAbpy)(CO)₃Cl] (640 nm, τ = 13.8 ns). No emission was observed for [Ru(6,6'-diTPAbpy)(CO)₂Cl₂]. Transient absorption measurements revealed the population of a ³ILCT state for the Cu and Ag complexes (τ = 80 ns). All assignments were supported by TD-DFT calculations and resonance Raman spectroscopic measurements.