Photoinduced intramolecular energy transfer and anion sensing studies of isomeric Ru^IIOs^IIcomplexes derived from an asymmetric phenanthroline–terpyridine bridge

Abstract

Two heterobimetallic Ru(II)-Os(II) complexes of compositions [(bpy)2M(II)(phen-Hbzim-tpy)M'(II)(tpy-PhCH3)](4+), where M(II) = Ru and M'(II) = Os (4) and M(II) = Os and M'(II) = Ru (5), phen-Hbzim-tpy = 2-(4-(2,6-di(pyridin-2-yl)pyridine-4-yl)phenyl)-1H-imidazole[4,5][1,10]phenanthroline, bpy = 2,2'-bipyridine, and tpy-PhCH3 = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine have been synthesized and characterized by elemental analyses, ESI mass spectrometry, and (1)H NMR and UV-vis absorption spectroscopy. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated and compared with that of monometallic model compounds [(bpy)2M(II)(phen-Hbzim-tpy)](2+) [M(II) = Ru (1) and M(II) = Os (2)] and [(phen-Hbzim-tpy)Ru(II)(tpy-PhCH3)](2+) (3). The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations, whereas the monometallic complexes display one-electron oxidation in the positive potential window. Steady state and time-resolved luminescence data at room temperature show that an efficient intramolecular electronic energy transfer takes place from the Ru-center to the Os-based component in both the heterometallic dyads in all the solvents. The complexes under investigation contain an imidazole NH proton which became appreciably acidic due to metal coordination and can be utilized for recognition of selective anions in solution either via hydrogen bonding interaction or by proton transfer. Accordingly, the anion binding properties of the two heterobimetallic complexes as well as parent bridging ligand, phen-Hbzim-tpy, have been studied in solutions using absorption, steady state and time-resolved luminescence spectral measurements. The metalloreceptors act as sensors for F(-), CN(-) and AcO(-) ions. It is evident from sensing studies that in the presence of excess of selective anions, deprotonation of the imidazole N-H proton occurs in all cases.

Light Harvesting and Directional Energy Transfer in Long‐Lived Homo‐ and Heterotrimetallic Complexes of FeII, RuII, and OsII

“…CVs and SWVs of all the trimetallic complexes (3-8) along with the monometallic precursors (1 and 2) are shown in Figure 3 [30] Homotrimetallic RuRuRu (4) and OsOsOs (8) both exhibit a single reversible oxidation, at 1.33 and 0.90 V, respectively, corresponding to three simultaneous M II /M III oxidations at the same potential. Osmium is expected to have higher-energy dp orbitals than ruthenium and hence easier oxidation.…”

“…[30] Herein, we describe the synthesis and characterization of two series of trimetallic complexes of the form [(bpy) =Fe, Ru, Os; bpy = 2,2'-bipyridine). The phen-Hbzim-tpy ligand offers asymmetrical coordination sites in which a bidentate phenanthroline (phen) unit is bridged to a tridentate terpyridine (tpy) moiety.…”

“…The UV/Vis absorption spectra of the free phen-Hbzimtpy ligand and the monometallic Ru II and Os II complexes have been previously reported. [30] The bands at 460 and 426 nm for 1 and at 486 and 435 nm for 2 were assigned as overlapping M(dp)!phen-Hbzim-tpy(p*) and M(dp)!bpy(p*) MLCT transitions.…”

“…The monometallic complexes of composition [(bpy) 2 M(phen-Hbzim-tpy)](ClO 4 ) 2 (M = Ru II , Os II ) were synthesized as described previously by us. [30] All trimetallic complexes 3-8 were purified by column chromatography on neutral alumina followed by recrystallization under weakly acidic conditions. All complexes were characterized by elemental analysis, NMR spectroscopy, and ESI-MS.…”

Double Properties of Novel Acylhydrazone Nanomaterials Based on a Conjugated System: Anion Binding Ability and Antibacterial Activity

“…The intramolecular hydrogen bond did not exist in other compounds (1, 2, 3 and 11). According to the literature [32,33], the existence of an intramolecular hydrogen bond could improve the anion binding ability and so the anion binding ability of compound 6 was the strongest of the synthesized compounds. The above results indicate that multiple hydrogen bonds are important to anion binding ability.…”