Understanding Electrogenerated Chemiluminescence Efficiency in Blue‐Shifted Iridium(III)‐Complexes: An Experimental and Theoretical Study |
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| Authors: | Dr Gregory J Barbante Dr Egan H Doeven Emily Kerr Timothy U Connell Dr Paul S Donnelly Prof Jonathan M White Thais Lópes Sarah Laird Dr David J D Wilson Dr Peter J Barnard Dr Conor F Hogan Prof Paul S Francis |
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| Affiliation: | 1. Centre for Chemistry and Biotechnology, Faculty of Science, Engineering and Built Environment, Deakin University, Waurn Ponds, Victoria 3216 (Australia), Fax: (+61)?3‐5227‐2356;2. School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne 3010 (Australia);3. Present address: Department of Chemistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul 97.105‐900 (Brazil);4. Department of Chemistry, La Trobe Institute for Molecular Sciences, La Trobe University, Victoria 3086 (Australia) |
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| Abstract: | Compared to tris(2‐phenylpyridine)iridium(III) (Ir(ppy)3]), iridium(III) complexes containing difluorophenylpyridine (df‐ppy) and/or an ancillary triazolylpyridine ligand 3‐phenyl‐1,2,4‐triazol‐5‐ylpyridinato (ptp) or 1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25–60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with Ir(ppy)3] and Ir(df‐ppy)3], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri‐n‐propylamine (TPA) as a co‐reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M+) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M+ LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue‐shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, Ir(df‐ppy)2(ptb)]+ was most attractive as a blue‐emitter for ECL detection, featuring a large hypsochromic shift (λmax=454 and 484 nm), superior co‐reactant ECL intensity than the archetypal homoleptic green and blue emitters: Ir(ppy)3] and Ir(df‐ppy)3] (by over 16‐fold and threefold, respectively), and greater solubility in polar solvents. |
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| Keywords: | density functional calculations electrochemiluminescence electrochemistry iridium luminescence |
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