Photoswitchable azobenzene-appended iridium(iii) complexes

Abstract

Iridium(iii) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended 2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(iii) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and (1)H-NMR spectroscopy permitted us to conclude that the light-induced trans-to-cis isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(iii) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH2- or -OCH2-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes.

Structure-switching M3L2 Ir(iii) coordination cages with photo-isomerising azo-aromatic linkers

“…[Ir III (C^N) 2 (A) n ] + species where A is either two monodentate or one bidentate ligand(s) represent an important subclass of emissive materials, 34 and azobenzenes can themselves be weakly emissive. Freixa et al showed that [Ir III (C^N) 2 (A) n ] + complexes bearing cyclometallated 35 or bipyridyl appended 28 AZB units have negligible luminescence owing to competitive electron transfer from the mixed CT triplet to the azo group. The emission properties of cages C1 , C1-Me , C2 and C3 were determined in DCM solution, Fig.…”

Azobased iminopyridine ligands and their rhenium metal complexes: Syntheses, spectroscopic, trans-cis photoisomerization and theoretical studies

“…Clearly, the photoisomerization dynamics is strongly influenced by the conjugation pathway and modified upon coordination of a metal to the azobenzene containing conjugated ligand, as previously demonstrated by Fillaut and coworkers for a series of Ruthenium(II) tris(bipyridine) complexes [16]. More recently Freixa and coworkers reported Iridium(III) cyclometalated complexes, in which the use of an aliphatic spacer unit between the azobenzene and the coordinating unit of the ligand allowed the electronic communication to be disrupted and the observation of photochromic properties for these coordination complexes [2].…”

“…Of course, the photoinduced isomerization of azobenzene and its derivatives is one of the most and well-studied light driven processes. The location of the azobenzene unit in the ligands has A C C E P T E D M A N U S C R I P T been established as an important factor to influence the photochromic properties of azobenzene containing transition metal complexes [2][3][4][5]. The isomerization is assumed to take place from intraligand excited states localized on the azobenzene unit.…”

Bromination and C–C Cross-Coupling Reactions for the C–H Functionalization of Iridium(III) Emitters

“…These reactions are one of the most efficient tools to modify and enlarge the application range of phosphorescent emitters. ,, Thus, they have been employed to convert iridium­(III) complexes bearing cyclometalated 2-phenylpyridines or related ligands into emissive polymers and dendrimers . Freixa and co-workers have appended azobenzene moieties to the phenyl group, to study the influence of the extended conjugation and substitution on the photochromic properties of the resulting systems . Williams’ group has assembled multimetallic broad-band light emitters, through coupling of mononuclear bis-terpyridyl complexes with extended conjugation …”