Molecular engineering of octupolar NLO molecules and materials based on bipyridyl metal complexes

Combining very large quadratic and cubic nonlinear optical responses in extended, tris-chelate metallochromophores with six pi-conjugated pyridinium substituents

We describe a series of nine new complex salts in which electron-rich Ru(II) or Fe(II) centers are connected via pi-conjugated bridges to six electron-accepting N-methyl-/N-arylpyridinium groups. This work builds upon our previous preliminary studies (Coe , B. J. J. Am. Chem. Soc. 2005, 127, 13399-13410; J. Phys. Chem. A 2007, 111, 472-478), with the aims of achieving greatly enhanced NLO properties and also combining large quadratic and cubic effects in potentially redox-switchable molecules. Characterization has involved various techniques, including electronic absorption spectroscopy and cyclic voltammetry. The complexes display intense, visible d --> pi* metal-to-ligand charge-transfer (MLCT) bands, and their pi --> pi* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 x 10(5) M(-1) cm(-1). Molecular quadratic nonlinear optical (NLO) responses beta have been determined by using hyper-Rayleigh scattering at 800 and 1064 nm and also via Stark (electroabsorption) spectroscopic studies. The directly and indirectly derived beta values are very large, with the Stark-based static first hyperpolarizabilities beta(0) reaching as high as ca. 10(-27) esu, and generally increase on extending the pi-conjugation and enhancing the electron-accepting strength of the ligands. Cubic NLO properties have also been measured by using the Z-scan technique, revealing relatively high two-photon absorption cross sections of up to 2500 GM at 750 nm.

Facile self-assembly of neutral dendritic metallocycles via oxygen-to-platinum coordination

A new approach for the fabrication of neutral dendritic metallocycles is described. By combining rigid 120 degrees dicarboxylate donor linkers funtionalized with [G0]-[G3] Frechet-type dendrons and complementary rigid 60 degrees and 120 degrees di-Pt(II) acceptor subunits, neutral rhomboidal metallodendrimers and hexagonal metallodendrimers, respectively, were prepared under mild conditions in high yields. The assemblies have well-defined shapes and sizes and were characterized by multinuclear NMR ((1)H and (31)P), mass spectrometry (ESI (+)-TOF-MS and APPI(+)-TOF-MS), and elemental analysis. Isotopically resolved mass spectrometry data support the formation of the neutral [2 + 2] rhomboidal, and [3 + 3] hexagonal metallodendrimers, and NMR data are consistent with the formation of all ensembles. The structures of the [G0] and [G1] neutral rhomboidal metallodendrimers (3a and 3b) were unambiguously confirmed via single-crystal X-ray crystallography. The shape and size of [G3] neutral hexagonal metallodendrimer 5d was established with MMFF force-field simulations.

Synthesis of six-component metallodendrimers via [3 + 3] coordination-driven self-assembly

A new class of 120 degrees dendritic di-Pt(II) acceptor subunits has been designed and synthesized, from which six-component hexagonal metallodendrimers were easily formed with 120 degrees dendritic dipyridine donors via [3 + 3] coordination-driven self-assembly. The structures of all metallodendrimers are confirmed by multinuclear NMR, ESI-TOF-MS/ESI-FTMS, and elemental analysis. MMFF force-field simulations indicates that all metallodendrimers have a hexagonal ring with an internal radius of approximately 1.4 nm.