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A water-soluble cyclometalated iridium(III) complex for pH sensing based on aggregation-induced enhanced phosphorescence

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Abstract

The novel water-soluble monoanionic Ir(III) complex Na[Ir(ppy)2(SB-COO)] (2; Hppy = phenylpyridine; HSB-COOH = 4-carboxylanilinesalicylaldehyde Schiff base), which was obtained by the reaction of the novel Ir(III) complex [Ir(ppy)2(SB-COOH)] (1) with NaOEt, in its aqueous solution, showed hydrogen ion (H+)-responsive aggregation-induced enhanced phosphorescence (AIEP). Both these complexes exhibited very weak and relatively strong emissions in solution and solid states, respectively. The pH-responsiveness of 2 was evaluated from its emission spectra in aqueous solution in the pH range of 8.7–1.8. Above pH 6, 2 showed weak emission with a maximum at 508 nm. Upon decreasing the pH to 4.7, AIEP with a bathochromic shift to 618 nm was induced by the aggregation of 1, whereby the intensity at 618 nm was increased approximately by 50-fold compared to that at pH 6.0. This enhancement is due to restrictions of the geometrical changes in the six-membered chelate ring of the ancillary ligand (Ir–N–C–C–C–O–) and of the intramolecular rotations in the excited state. The enhanced luminescence originates from spin-forbidden metal-to-ligand–ligand charge transfer (3MLLCT). Below pH 2.8, the emission intensity decreased owing to the decrease in the population of the emissive complex 1 upon dissociation of the ancillary ligand from the Ir(ppy)2 unit.

Graphical abstract: A water-soluble cyclometalated iridium(iii) complex for pH sensing based on aggregation-induced enhanced phosphorescence

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Publication details

The article was received on 10 Dec 2018, accepted on 08 Mar 2019 and first published on 20 Mar 2019


Article type: Paper
DOI: 10.1039/C8DT04861D
Dalton Trans., 2019, Advance Article

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    A water-soluble cyclometalated iridium(III) complex for pH sensing based on aggregation-induced enhanced phosphorescence

    K. Ohno, T. Sakata, M. Shiiba, A. Nagasawa and T. Fujihara, Dalton Trans., 2019, Advance Article , DOI: 10.1039/C8DT04861D

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