Extending the nitrogen-heterosuperbenzene family:: The spectroscopic, redox, and photophysical properties of "half-cyclized" N1/2-HSB and its Ru(II) complex

Oxidative cyclodehydrogenation is an important process in the formation of the new graphene, N-(1)/2HSB 2. This heteropolyaromatic results from the FeCl3-Catalyzed oxidative cycloclehydrogenation of 1,2-dipyrimidyl-3,4,5,6-tetra-(4- tert-butylphenyl) benzene, Three new C-C bonds are formed that lock the two pyrimidines in a molecular platform comprising eight fused aromatic rings flanked by two remaining "uncyclized" phenyl rings. Mechanistically intriguing is the fact that N-HSB 1, the product of six C-C bond fusions, is co-synthesized with its "half-cyclized" daughter in this reaction, 1 and 2 have the same bidentate N-atom arrangement, This facilitates formation of the heteroleptic Ru(II) complexes, [Ru(bpy)(2)(2)](PF6)(2) 4 and [Ru(bpy)(2)(1)](PF6)(2) 3, which differ in the size and planarity of their aromatic ligands. The new ligand 2 and its complex 4 are characterized by H-1 NMR, IR, ESI-MS, and accurate mass methods. 2 exhibits photophysical properties that are consistent with a reduction of the pi/pi* framework, a concomitant increase in the energy of the LUMO, and a blue-shift of the solvent-dependent fluorescence (lambda(em), = 474 nm, phi(F) = 0.55, toluene) as compared to its parent. Complex 4 absorbs throughout the visible region and borders on near-IR emitter character, exhibiting a slightly blue-shifted (MLCT)-M-3 emission (868 nm, CH3CN) as compared to that of [Ru(bpy)(2)(1)](PF6)(2) 3 (880 nm, CH3CN). Electrochemical analyses permit further elucidation of the intermolecular interactions of 3 and 4. These and the concentration and temperature-dependent NMR spectra of 4 confirm it to be nonaggregating, a direct result of the two uncyclized and rotatable phenyl rings in 2.