Abstract
Coordination abilities of unsymmetrical tridentate ligands, 3,3′-polymethylene-2-(pyrid-2′-yl)-benzo[b]-1,10-phenanthrolines (4) were studied. Reactions of the 3,3′-di- and 3,3′-trimethylene-2-(pyrid-2′-yl)benzo[b]-1,10-phenanthrolines (4b and 4c) with RuCl3 ⋅ 3H2O afforded [Ru(4b)2]2+ and [Ru(4c)2]2+ in 57% and 78% yield, respectively, while reactions of the parent non-bridged ligand (4a), tetramethylene-bridged ligand (4d), and fully aromatized ligand (4e) afforded a messy mixture. Reactions of 4 with Ru(tpy)Cl3 (tpy = 2,2′;6′,2″-terpyridine) afforded [Ru(tpy)(4)]2+ in 61–72% yields. UV absorption spectra of the ligands showed four ligand-centered (LC) π–π* transitions and their Ru complexes showed four LC π–π* transitions and one Ru(dπ) → ligand(π*) MLCT. The ligands showed three major emission maxima (λ emission) in the region of 393–418, 416–445, and 437–471 nm in which λ emission is highly dependent on the length of the methylene bridge connecting C3 of benzo[b]-1,10-phenanthroline and C3 of pyridine. Ru complexes with fully aromatic ligand, [Ru(tpy)(4e)]2+, and the most distorted ligand, [Ru(tpy)(4d)]2+, showed two emission maxima at 410 and 444–446 nm, while the others showed one emission at 410 nm. Each of the emission maxima is bathochromatically shifted from the complex with the most distorted ligand (4d) to the complex with fully aromatized planar ligand (4e) indicating lower energy emission.
Acknowledgment
Financial support from Korean Research Foundation Grant (KRF-2008-521-E00189) is gratefully acknowledged.