Synthesis, photophysical, and electrochemical properties of six Ru(II) complexes: asymmetric ligands composed of 6-phenyl substituted 2,2′-bipyridine and 4,5-diazafluorene derivatives

<p>Six asymmetric ligands, 6-[(4,5-diazafluoren-9-ylimino)methyoxyphenyl]-2,2′-bipyridine (L¹), 4-[(4,5-diazafluoren-9-ylimino)methyoxyphenyl]-6-phenyl-2,2′-bipyridine (L²), 6-[4-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-2,2′-bipyridine (L³), 4-[4-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-6-phenyl-2,2′-bipyridine (L⁴), 6-[2-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-2,2′-bipyridine (L⁵) and 4-[2-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-6-phenyl-2,2′-bipyridine (L⁶), and corresponding Ru(II) complexes [(bpy)₂Ru(L^1–6)](PF₆)₂ (bpy = 2,2′-bipyridine) were synthesized. All six ligands have two kinds of nonequivalent chelating sites: one involving the 6-phenyl substituted 2,2′-bipyridine moiety, and the other involving the 4,5-diazafluorene moiety. All six Ru(II) complexes have metal-to-ligand charge transfer absorptions around 447 nm and one Ru(II)-centered oxidation around 1.35 V <i>versus</i> SCE in CH₃CN solution at room temperature. These complexes are non-emissive in CH₃CN solution at room temperature. The emission intensities of [(bpy)₂Ru(L¹)]²⁺ and [(bpy)₂Ru(L²)]²⁺ are stronger than that of [(bpy)₂Ru(L^3–6)]²⁺ in EtOH-MeOH (4 : 1, v/v) glassy matrix at 77 K.</p

Three trinuclear Ru(II) complexes containing 4,5-diazafluorene and 2,2′-bipyridine: synthesis, absorption spectrum, luminescence, and redox behavior

<div><p>Three heterotopic ligands L¹, L², and L³ have been prepared by the reaction of 4,4′-bis(bromomethyl)-2,2′-bipyridine with 4,5-diazafluoren-9-oxime, 9-(2-hydroxy)phenylimino-4,5-diazafluorene, and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively, in DMF. The three ligands consist of two 4,5-diazafluorene units and one 2,2′-bipyridine unit. Ru(II) complexes [{Ru(bpy)₂}₃(μ₃-L¹⁻³)](PF₆)₆ (bpy = 2,2′-bipyridine) were prepared by refluxing Ru(bpy)₂Cl₂·2H₂O and the ligands in 2-methoxyethanol. The three Ru(II) complexes display metal-to-ligand charge-transfer absorption at 445–450 nm and one Ru(II)-centered oxidation at 1.32 V in CH₃CN solution at room temperature. Upon excitation into the metal-to-ligand charge-transfer band, the emission intensities of [{Ru(bpy)₂}₃(μ₃-L²)]⁶⁺ and [{Ru(bpy)₂}₃(μ₃-L³)]⁶⁺ are almost equal to that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in CH₃CN solution at room temperature, but weaker than that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in EtOH–MeOH (4 : 1, v/v) glassy matrix at 77 K.</p></div

Monomer-Promoting Asymmetric Kinetic Resolution-Alternating Copolymerization To Afford AAB-Type Copolyesters

Living copolymerization of mixed monomers can enrich the diversity of copolymer materials with well-defined performance via controlling both monomers and stereosequences. However, periodic sequence-controlled living copolymerization of same-type monomers with more than two components in synthetic polymer science remains a challenge. In this work, a new method of monomer-promoting asymmetric kinetic resolution-alternating copolymerization can let a tricomponent mixture of l-lactide (S,S-LA or l-LA) and two enantiomeric isomers of racemic tropic acid cyclic esters (tropicolactone) be polymerized into sequence-controlled −(ASASBS)n– type biodegradable copolyesters (the subscript S presents the configuration and A and B present lactic acid units and tropic acid units, respectively), and diblock copolymers of −(ASASBS)n-b-(ARARBR)n– can further be obtained upon addition of R,R-LA (d-LA). Compared to previous asymmetric kinetic resolutions of racemic chemicals via polymerization or organic reactions, no enantiopure catalyst/initiator is required in this system. After the resolution and alternating copolymerization of S,S-LA and rac-tropicolactone, the ee value of unreacted tropicolactone can reach 99.4%. The alternating probability between tropicolactone and lactide monomers is more than 96% in periodic sequence polymers of −(ASASBS)n–. The tetracomponent mixture of rac-lactide and rac-tropicolactone can be copolymerized into an alternating copolymer with a −((ASASBS)x-ran-(ARARBR)y)n– structure, in which the stereoselective linkage probability of 95% after S,S-lactide (R,R-lactide) followed by S-tropicolactone (R-tropicolactone) keeps very high too