Chemiluminescence and electrochemiluminescence of water-soluble iridium(III) complexes containing a tetraethylene-glycol functionalised triazolylpyridine ligand

Lifen Chen; Kim Quayle; Zoe M Smith; Timothy U Connell; Egan H Doeven; David J Hayne; Jacqui L Adcock; David J D Wilson; Johnny Agugiaro; Michael L Pattuwage; Natasha S Adamson; Paul S Francis

doi:10.1016/j.aca.2024.342470

Chemiluminescence and electrochemiluminescence of water-soluble iridium(III) complexes containing a tetraethylene-glycol functionalised triazolylpyridine ligand

Anal Chim Acta. 2024 May 22:1304:342470. doi: 10.1016/j.aca.2024.342470. Epub 2024 Mar 22.

Authors

Affiliations

¹ Jiaxing Key Laboratory of Molecular Recognition and Sensing, College of Biological, Chemical Sciences and Engineering, Jiaxing University, Jiaxing, 314001, China.
² School of Life and Environmental Sciences, Faculty of Science, Engineering and Built Environment, Deakin University, Geelong, Victoria, 3220, Australia.
³ Institute for Frontier Materials, Deakin University, Geelong, Victoria, 3220, Australia.
⁴ Department of Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, 3086, Australia.
⁵ School of Life and Environmental Sciences, Faculty of Science, Engineering and Built Environment, Deakin University, Geelong, Victoria, 3220, Australia. Electronic address: paul.francis@deakin.edu.au.

PMID: 38637058
DOI: 10.1016/j.aca.2024.342470

Abstract

Background: Iridium(III) complexes, exhibiting high luminescence quantum yields and a wide range of emission colours, are promising alternatives to tris(2,2'-bipyridine)ruthenium(II) for chemiluminescence (CL) and electrochemiluminescence (ECL) detection. This emerging class of reagent, however, is limited by the poor solubility of many iridium(III) complexes in aqueous solution, and lack of understanding of their remarkably variable selectivities towards different analytes.

Results: Seven [Ir(C^N)₂(pt-TEG)]⁺ complexes, exhibiting a wide range of reduction potentials and emission energies, were examined with six model analytes. For CL, cerium(IV) was used as the oxidant. The alkylamine analytes generally produced greater CL and ECL with the more readily oxidised Ir(III) complexes (C^N = piq, bt, ppy), predominantly through the 'direct' pathway requiring oxidation of both metal complex and analyte. Aniline derivatives that did not also contain secondary or tertiary alkylamines elicited CL from the less readily oxidised complexes (C^N = df-ppy-CF₃, df-ppy) via energy transfer. The most difficult to oxidise complexes (C^N = df(CF₃)-ppy-Me, df(CN)-ppy) gave poor responses due to the limited potential window of the solvent and inefficiency of energy transfer to their high energy excited states. Greater CL and/or ECL intensities were generally obtained for each analyte with at least one Ir(III) complex than with [Ru(bpy)₃]²⁺; superior limits of detection for two analytes were demonstrated.

Significance: This exploration of CL/ECL in which the properties of luminophore, analyte and oxidant are all varied provides a new understanding of the influence of the metal-complex potentials and excited state energy on the light-producing and quenching pathways, and consequently, their distinct selectivity towards different analytes. These findings will guide the development of water-soluble Ir(III) complexes as CL and ECL reagents.

Keywords: Chemiluminescence detection; Electrochemiluminescence detection; Electrogenerated chemiluminescence detection; Iridium(III) complexes.