Synthesis, crystal structure, electrochemical properties, and photophysical characterization of ruthenium(II) 4,4′-dimethoxy-2,2′-bipyridine polypyridine complexes

Abstract

A series of ruthenium(II) polypyridine complexes of the type [Ru(tpy)((CH₃O)₂bpy)(4-R-py)]²⁺, where tpy = 2,2′;6′,2″-terpyridine, (CH₃O)₂bpy = 4,4′-dimethoxy-2,2′-bipyridine, and 4-R-py = pyridine (py, 2), 4-methoxypyridine (4-CH₃O-py, 3), 4-aminopyridine (4-NH₂-py, 4), were synthesized and their crystal structures, electronic absorption, luminescence, and electrochemical properties were investigated. The effect of adding electron-donating groups to the bidentate and monodentate ligand was investigated and compared with [Ru(tpy)(bpy)(py)]²⁺ (1) where bpy = 2,2′-bipyridine. While anticipated trends were not observed for the Ru-N(6) bond length as 4-R-py was varied, noticeable modifications of the measured photophysical properties were observed. A red-shift of the metal-to-ligand charge transfer (¹MLCT) is observed from 466 nm in 1 to 474 nm, 478 nm, and 485 nm for 2–4, respectively. Additionally, a red-shift in the luminescence maxima is observed in 2–4 as compared to 1, with 4 exhibiting the greatest shift of more than 100 nm. Complexes 2–4 exhibited luminescence quantum yields of 2.7 × 10⁻⁴, 7.2 × 10⁻⁴, and 7.4 × 10⁻⁴, respectively, which are increased compared to the quantum yield of 2.0 × 10⁻⁴ in 1. These findings demonstrate systematic tuning of absorbance and luminescence properties of ruthenium polypyridine complexes by addition of π-donating substituents to the monodentate and bidentate ligand.

Graphical Abstract

Keywords:

• Ruthenium
• crystal structure
• photophysical tuning
• phosphorescence
• photochemistry

Supplemental material

Supporting information includes ¹H NMR and ¹³C NMR spectra, ESI mass spectra, cyclic voltammograms, and Hammett graphs of 2–6. CCDC 2111562, 2111563, and 2111564 contain the supplementary crystallographic data for 2–4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; Fax: (þ44) 1223–336-033; or E-mail: [email protected].

Acknowledgments

R.N.G. would like to thank the Constance and Miriam Jauchler Jones Endowed Chair. The authors acknowledge the X-ray Crystallographic Facility at the University of Rochester for X-ray data (CHE-1725028). Instrument upgrade and local outreach was made possible through NSF grant CHE-0342508.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the Robert A. Welch Foundation (BN-0032), the University of the Incarnate Word and SUNY Brockport for supporting this research. This work was supported by National Science Foundation.