# Synthesis, Photophysical and TD-DFT Evaluation of Triphenylphosphonium-Labeled Ru(II) and Ir(III) Luminophores

## TL;DR

This paper describes the synthesis and evaluation of new phosphorescent compounds containing triphenylphosphonium units and their photophysical properties.

## Contribution

The novel contribution is the development and characterization of TPP+-labeled Ru(II) and Ir(III) luminophores with detailed photophysical and structural analysis.

## Key findings

- The TPP+ unit moderately quenches phosphorescence in Ru(II) and Ir(III) complexes.
- X-ray crystal structures revealed distorted octahedral coordination and spatial relationships in TPP+ complexes.
- Phosphorescence in the red region was observed with 3MLCT or 3MLCT/3LLCT character.

## Abstract

The chemistry of
5-acetamido derivatized 1,10-phenanthroline was
developed to yield a series of pro-ligands (L

1–4
) and related triphenylphosphonium (TPP+) appended cationic variants (L

5–8
). The resulting heteroleptic complexes [Ru­(bipy)2(L

1–8
)]
n+ (where bipy = 2,2′-bipyridine) and cyclometalated
species [Ir­(tmq)2(L

1–8
)]
n+ (where tmq = 2,6,7-trimethyl-3-phenylquinoxaline)
were isolated and fully characterized using a range of analytical
and spectroscopic methods, including electrochemistry and time-resolved
photophysics. Multinuclear NMR spectroscopies were used to characterize
the compounds, including 31P NMR showing δP 21.3–24.4 ppm for the phosphonium species. Two X-ray crystal
structures were successfully obtained on TPP+ functionalized
Ru­(II) and Ir­(III) species: key features include the distorted octahedral
coordination spheres, and the defined spatial relationships between
the complex core and the TPP+ unit. All Ru­(II) and Ir­(III)
complexes were phosphorescent in the red region with 3MLCT
or 3MLCT/3LLCT character, respectively. Comparison
across the series suggest the presence of the TPP+ unit
induced moderate quenching of the complex phosphorescence. A comparison
with quaternary ammonium analogues suggests this may be due to differences
in ion pairing and solvation phenomena in the TPP+ complexes.