Tailoring the π-system of benzimidazole ligands towards stable light-harvesting cyclometalated iridium(iii) complexes

Abstract

The synthesis, structure, optical and redox properties as well as photovoltaic studies of iridium(III) complexes with cyclometalated 2-arylbenzimidazoles decorated with various polyaromatic fragments and an ancillary aromatic β-diketone are reported....

Rational design of efficient photosensitizers based on cyclometalated iridium(iii) complexes with 2-arylbenzimidazole and aromatic 1,3-diketone ligands

“…The extension of the conjugated aromatic system in the cyclometalated ligands causes a modest bathochromic shift of the absorption maximum at ca. 300 nm (this correlates well with the analogous shift in the spectra of free ligands) along with an increase of the overall absorptivity in the visible region, as evidenced by comparing the spectra of the complexes 1–6 with that of Ir(btbi)(L 1 ) 55 as well as by comparing the spectrum of 12 with those of 10 and 11 (Fig. 3).…”

“…So, the absence of significant conjugation between these rings leads to the fact that the optical properties of this complex are close to those of the unsubstituted analogue and, at the same time, in sharp contrast to the properties of the complex, where the additional phenyl ring is fused with the metalated one. 55…”

“…The use of the more electron-withdrawing diketonate L 2 makes the LUMO+1 fully located on the O^O fragment irrespective of the C^N ligands, whereas the introduction of electron donating L 4 (complex 13 ) leads to the directly opposite effect – the LUMO+1 becomes delocalized over the cyclometalated core. In all the complexes bearing the benzothiophene moiety in the C^N ligands ( 9 , 12 and Ir(btbi) 2 (L 1 ) 55 ), the frontier unoccupied orbitals are completely localized on the cyclometalated fragment, in contrast to the analogues.…”

“…Hydrolysis of the carboxymethyl group of the diketonate in complexes 7 and 9 was performed as described in ref. 55 and 61.…”

Aggregation-induced emission of cyclometalated rhodium(iii) and iridium(iii) phenylpyridine complexes with ancillary 1,3-diketones

“…The presence of the charged complex particles formed owing to the loss of diketonate indicates that the Ir–O bonds are weaker than the other metal–ligand bonds in complexes Ir1–Ir4 , a conclusion reinforced by results for many other cyclometalated iridium( iii ) complexes with 1,3-diketones. 57–61 In turn, the rhodium( iii ) ion seems to form even less stable bonds with oxygen donor atoms although there is a paucity of available data for cyclometalated Rh( iii ) complexes containing β-diketones to support this assumption.…”