Cyclometalated cinchophen ligands on iridium(iii): towards water-soluble complexes with visible luminescence

Abstract

Eight cationic heteroleptic iridium(III) complexes, [Ir(epqc) 2 (N^N)] + , were prepared in high yield from a cyclometalated iridium bridged-chloride dimer bearing two ethyl-2-phenylquinoline-4-carboxylate (epqc) ligands. Two X-ray crystallographic studies were undertaken on selected complexes (where the ancillary ligand N^N = 4,4'-dimethyl-2,2'-bipyridine and 4,7-diphenyl-1,10-phenanthroline) each confirming the proposed formulations, showing an octahedral coordination at Ir(III). In general, the complexes are luminescent (620-630 nm) with moderately long lifetimes indicative of phosphorescence. Hydrolysis of the ethyl ester moieties of the epqc ligands gave the analogous cinchophen-based complexes, which were water-soluble and visibly luminescent (568-631 nm). The spectroscopic and redox characterisation of the complexes was complemented by DFT and TD-DFT calculations, supporting the assignment of dominant 3 MLCT to the emissive character. † Electronic supplementary information (ESI) available: Data collection parameters for the crystallographic studies, electrochemical data for 3a-h, pictorial representations of the calculated frontier orbitals for 3a-h and 4a-h and Cartesian coordinates obtained from DFT calculations. CCDC 907280 and 907282.

Cationic, luminescent cyclometalated iridium(iii) complexes based on substituted 2-phenylthiazole ligands

“…Such an observation has been noted before 12 and is attributed to the reaction conditions and solvent utilised for the complexation: the 2-methoxyethyl groups of [Ir(emptz) 2 -(edppz)](PF 6 ), [Ir(emptz) 2 (piphen)](PF 6 ) and [Ir(emptz) 2 -(ppiphen)](PF 6 ) appeared as broadened triplets around 4.5 and 3.7 ppm together with a singlet ca. Such an observation has been noted before 12 and is attributed to the reaction conditions and solvent utilised for the complexation: the 2-methoxyethyl groups of [Ir(emptz) 2 -(edppz)](PF 6 ), [Ir(emptz) 2 (piphen)](PF 6 ) and [Ir(emptz) 2 -(ppiphen)](PF 6 ) appeared as broadened triplets around 4.5 and 3.7 ppm together with a singlet ca.…”

“…The cyclic voltammograms, measured at a platinum disc electrode (scan rate ν = 200 mV s −1 , 1 × 10 −3 M solutions, 0.1 M [NBu 4 ]-[PF 6 ] as a supporting electrolyte), each (for example, Fig. 16 Related cationic complexes, recorded under identical conditions, that incorporate cyclometalated cinchophen-type ligands 12 for example [Ir(epqc) 2 (bpy)](PF 6 ) (where epqc = ethyl-2-phenylquinoline-4-carboxylate), possess an Ir 3+/4+ couple around +1.40 V. Therefore these results clearly suggest that the Ir(III) ion is relatively stabilised in the emptz variants versus epqc. The comparative potential for [Ir( ppy) 3 ] is +1.0 V/NHE.…”

“…Both dppz-derived species show additional bands at 370 and 390 nm, which are attributed to the extended conjugation of the fused chromophore. 12 The quantum yield for [Ir( ppy) 2 (bpy)](PF 6 ) is higher at ca. These correlate remarkably well with the absorption band at 444 nm calculated using TD-DFT, and thus lend support to the theoretical methodology used.…”

Ligand‐Tuneable, Red‐Emitting Iridium(III) Complexes for Efficient Triplet–Triplet Annihilation Upconversion Performance

“…Our own work into luminescent Ir III complexes has included the development of low‐energy emitting species that luminesce in the red part of the visible spectrum. The requisite cyclometallating ligands are based upon core ligand structures of 2‐phenylquinoline or 2‐phenylquinoxaline, and these can provide interesting species with related pyrene derivatives that also show capability as potent photo‐oxidation sensitisers . Other studies have reported extending the emission wavelengths of Ir III complexes into the near‐infrared (NIR) region…”

A Screen Printed Phenanthroline-Based Flexible Electrochemical Sensor for Selective Detection of Toxic Heavy Metal Ions

“…To make the sensor selective to heavy metals, a selective layer is often used in the CV technique. 1,10-Phenanthroline based compounds are well-known for their effectiveness in binding with metal ions to form inorganic complexes [14][15][16][17][18][19][20][21][22][23][24]. However, the use of their derivatives in the detection of metal ions and other molecular substrates, are not well explored [25][26][27].…”