Ultra-High-Response, Multiply Twisted Electro-optic Chromophores: Influence of π-System Elongation and Interplanar Torsion on Hyperpolarizability.

The systematic synthesis, structural, optical spectroscopic, and second-order nonlinear optical (NLO) characterization of a series of donor-acceptor poly-arylene chromophores which have heretofore unachieved π-extension and substantial twisting from planarity, are reported: specifically, two-ring 2TTMC, dicyano(4-(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-3-methylphenyl)methanide; three-ring 3TTMC, dicyano(4'-(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-2,2',3',5',6'-pentamethyl[1,1'-biphenyl]-4-yl)methanide; and four-ring 4TTMC, dicyano(4″-(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-2,2',3″,6,6'-pentamethyl[1,1':4',1″-terphenyl]-4-yl)methanide. Single-crystal X-ray diffraction, DFT-optimized geometries, and B3LYP/INDO-SOS analysis identify three key features underlying the very large NLO response: (1) For ring catenation of three or greater, sterically enforced π-system twists are only essential near the chromophore donor and acceptor sites to ensure large NLO responses. (2) For synthetic efficiency, deletion of one ortho-methyl group from o,o',o″,o‴-tetramethylbiaryl junctures, only slightly relaxes the biaryl twist angle from 89.

An acido-triggered reversible luminescent and nonlinear optical switch based on a substituted styrylpyridine: EFISH measurements as an unusual method to reveal a protonation-deprotonation NLO contrast.

Diphenyl-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (DPVPA) constitutes a novel acido-triggered reversible luminescent and nonlinear optical switch. Remarkably, for the first time the Electric-Field Induced Second Harmonic generation (EFISH) technique is used to reveal a protonation-deprotonation NLO contrast.

Synthesis and characterisation of cobalt, nickel and copper complexes with tripodal 4N ligands as novel catalysts for the homogeneous partial oxidation of alkanes.

Four new compounds of the general formula [M(L)(CHCOO)][PF], where L is a tetradentate tripodal ligand such as tris[2-(dimethylamino)ethyl]amine (L1) or (2-aminoethyl)bis(2-pyridylmethyl)amine (L2) and M is Co(II), Ni(II) or Cu(II), have been prepared employing a simple two-step synthesis. The compounds have been characterised by elemental analysis, mass spectroscopy, IR spectroscopy and X-ray diffraction. The catalytic properties of the derivatives containing the aliphatic ligand L1 have been investigated in particular toward the oxidation of cyclohexane and adamantane in the presence of the sacrificial oxidant -CPBA (-chloroperbenzoic acid).

Switching of emissive and NLO properties in push-pull chromophores with crescent PPV-like structures.

We report on a series of novel homologous push-pull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, bearing, respectively, 1, 2 and 3 p-phenylenevinylene units in direct linear conjugation (compounds 7-9). The three compounds exhibit striking differences in their linear and nonlinear optical properties. The shorter compound 7 exhibits aggregation-induced emission with a strong luminescence in the solid state (blue emission, photoluminescence quantum yield 38%), and it is nonemissive in solution; the more extended conjugated systems 8 and 9 show classical aggregation-caused quenching in the solid state, while high quantum yield photoluminescence (21 and 93% in toluene) is restored in diluted solutions, through mechanisms involving intramolecular charge transfer in the excited states.

Efficient crystallization induced emissive materials based on a simple push-pull molecular structure.

Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view. Aggregation caused quenching (ACQ) processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing higher emission intensity in the solid state than in solution.

Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains.

New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties.

Tuning second-order NLO responses through halogen bonding.

As a function of the ability of the solvent to behave as acceptor of halogen bonding, the NLO-phores under study give rise to microbeta(lambda) values ranging from +192 x 10(-48) esu to -465 x 10(-48) esu.