Benzannulation of a ditopic ligand to afford mononuclear and dinuclear Ir(iii) complexes with intense phosphorescence: applications in singlet oxygen generation and bioimaging. Issue 5 (19th January 2022)

• Record Type: Journal Article
• Authors: Shafikov, Marsel Z.; Hodgson, Craig; Gorski, Aleksander; Kowalczyk, Aleksandra; Gapińska, Magdalena; Kowalski, Konrad; Czerwieniec, Rafał; Kozhevnikov, Valery N.
• Is Part Of: Journal of materials chemistry. Volume 10:Issue 5(2022)
• Page Start: 1870
• Page End: 1877
• Publication Date: 2022-01-19
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d1tc05271c
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Benzannulation of a ditopic ligand affords a significant phosphorescence blue-shift and enhanced emission quantum yield of mono- and dinuclear Ir(iii ) complexes. The complexes are excellent oxygen photosensitizers. A use in bioimaging is reported. Abstract : Annulation of the additional aromatic pi-system to the ligand is an effective method of influencing the luminescence of metal complexes. In this contribution, we show the effect of benzannulation of a ditopic ligand on the photophysical properties of a dinuclear Ir(iii ) complex and also utilize it to prepare its mono-nuclear analogue. The new dinuclear complex di-Ir in which the iridium centres are linked by benzo[1, 2- d : 4, 5- d ′]bisthiazole shows drastically improved efficiency of phosphorescence compared to the previously reported complex Ir-2 that has thiazolo[5, 4- d ]thiazole as the linking unit. The new mono-nuclear complex mono-Ir, utilizing the same ditopic ligand as di-Ir, allows tracking the effects of dinuclearity. In degassed dilute dichloromethane solution, the mononuclear complex mono-Ir displays yellow phosphorescence ( λ em = 552 nm) with a quantum yield of Φ PL = 70% and decay time of τ = 7.85 μs, which correspond to the radiative rate of k r = 0.89 × 10 5 s −1 . The dinuclear complex di-Ir displays slightly red-shifted phosphorescence ( λ em = 560 nm) with a quantum yield of Φ PL = 85% and decay time of τ = 4.50 μs corresponding to the radiative rate of k r = 1.90 × 10 5 s −1, which is about two times higher compared to that of the mono-nuclear mono-Ir . The phosphorescence intensity of both complexes is highly sensitive to molecular oxygen, as in the air-equilibrated samples the decay times drop to values τ = 0.73 μs and τ = 0.84 μs for mono-Ir and di-Ir, respectively. Applied as singlet oxygen sensitizers, mono-Ir and di-Ir show very high efficiencies of 78% and 71%, respectively. Such characteristics mean the two complexes are promising materials for optical oxygen sensing and applications associated with singlet oxygen generation.