Ru-Os dyads based on a mixed bipyridine-terpyridine bridging ligand: modulation of the rate of energy transfer and pH-induced luminescence switching in the infrared domainElectronic supplementary information (ESI) available: Fig. S1-S12. See DOI: 10.1039/c7dt02192e

• Main Authors: Bar, Manoranjan, Maity, Dinesh, Deb, Sourav, Das, Shyamal, Baitalik, Sujoy
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt02192e

A series of heterobimetallic complexes of compositions [(bpy/phen) 2 Ru(dipy-Hbzim-tpy)Os (tpy-PhCH 3 /H 2 pbbzim)] 4+ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, tpy-PhCH 3 = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine and H 2 pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine)), derived from a heteroditopic bpy-tpy bridging ligand, were synthesized and thoroughly characterized in this work. The heterometallic complexes exhibit two successive one-electron reversible metal-centered oxidations corresponding to Os II /Os III at lower potential and Ru II /Ru III at higher potential. All the four dyads exhibit very intense, ligand centered absorption bands in the UV region and moderately intense MLCT bands in the visible region. The dyads also show intense infrared emission with the emission maximum spanning between 734 nm and 775 nm with reasonably long room temperature lifetimes varying between 30 ns and 104 ns. Both steady state and time resolved luminescence spectroscopic investigations indicate that efficient and fast intramolecular energy transfer from the 3 MLCT state of the Ru( ii ) center to the Os-center takes place in all the four dyads. In addition, the rate of energy transfer was found to depend on the terminal ligand on the Os-site. Due to the presence of a number of imidazole NH protons in the dyads, significant modulation of both the ground and excited state properties of the complexes was made possible by varying the pH of the solution. By varying the terminal ligand, pH-induced "on-off", "off-off-on" and "on-off-on" emission switching of the complexes was nicely demonstrated in the infrared region. Ru-Os dyads exhibit intramolecular energy transfer from Ru to the Os-center and pH-induced luminescence switching in the infrared domain.