Crystal structure, fluorescence, and nanostructuration studies of the first Zn(II) anthracene-based curcuminoid.

In the following article the coordination properties of a recently reported curcuminoid 9Accm (9Accm = 1,7-(di-9-anthracene)-1,6-heptadiene-3,5-dione) with Zn(II) are reported. Preparation, crystal structure, and fluorescence spectroscopic studies of [Zn(II)(9Accm)(2)(py)] (1) are presented, as well as preliminary AFM and confocal microscopy studies on graphite surfaces. Complex 1 is the first crystallographically characterized Zn-curcuminoid in the literature; the intrinsic features of the complex are contrasted with the free ligand, 9Accm, and [Cu(II)(9Accm)(2)(py)] (2), a similar copper system, which has been recently described by us. It is shown that complex 1 exhibits a chelation enhancement of fluorescence (CHEF) and 2 a chelation enhancement of quenching (CHEQ) with respect to the fluorescence response of the free ligand, demonstrating the highly sensitive response of 9Accm versus these two metals. All studies are supported by density functional theory (DFT) calculations.

Extending the nitrogen-heterosuperbenzene family: the spectroscopic, redox, and photophysical properties of "half-cyclized" N-1/2HSB and Its Ru(II) complex.

Oxidative cyclodehydrogenation is an important process in the formation of the new graphene, N-(1)/(2)HSB 2. This heteropolyaromatic results from the FeCl(3)-catalyzed oxidative cyclodehydrogenation 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)](PF(6))(2) 4 and [Ru(bpy)(2)(1)](PF(6))(2) 3, which differ in the size and planarity of their aromatic ligands. The new ligand 2 and its complex 4 are characterized by (1)H 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 (3)MLCT emission (868 nm, CH(3)CN) as compared to that of [Ru(bpy)(2)(1)](PF(6))(2) 3 (880 nm, CH(3)CN). 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.