Enhanced nonlinearities in hybrid structure based on nanoporous membrane and a metallohelicate with promising application in nanophotonics and NLO.

The main purposes of this work are designing new hybrid structures based on alumina nanoporous membranes with specific metallosupramolecular structure as well as studies of their usefulness in nonlinear optics (NLO). The NLO studies of the hybrid material is performed on the basis of two methods: the first by the Maker fringe technique, where the second harmonic generation (SHG) signal is recorded by rotating the sample; and the second by SHG imaging microscopy, where the SHG signal is collected point by point on the sample surface. The enhanced SHG signals were obtained without the use of the corona poling method needed during the experiment on thin films in our previous works and clearly shows the efficiency of hybrid materials based on nanoporous membranes as promising materials in devices developed based on NLO.

Mono- and Binuclear Copper(II) and Nickel(II) Complexes with the 3,6-Bis(picolylamino)-1,2,4,5-Tetrazine Ligand.

Four new compounds of formulas [Cu(hfac)2(L)] (1), [Ni(hfac)2(L)] (2), [{Cu(hfac)2}2(µ-L)]·2CH3OH (3) and [{Ni(hfac)2}2(µ-L)]·2CH3CN (4) [Hhfac = hexafluoroacetylacetone and L = 3,6-bis(picolylamino)-1,2,4,5-tetrazine] have been prepared and their structures determined by X-ray diffraction on single crystals. Compounds 1 and 2 are isostructural mononuclear complexes where the metal ions [copper(II) (1) and nickel(II) (2)] are six-coordinated in distorted octahedral MN2O4 surroundings which are built by two bidentate hfac ligands plus another bidentate L molecule. This last ligand coordinates to the metal ions through the nitrogen atoms of the picolylamine fragment. Compounds 3 and 4 are centrosymmetric homodinuclear compounds where two bidentate hfac units are the bidentate capping ligands at each metal center and a bis-bidentate L molecule acts as a bridge. The values of the intramolecular metal···metal separation are 7.97 (3) and 7.82 Å (4). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples 1-4 in the temperature range 1.9-300 K. Curie law behaviors were observed for 1 and 2, the downturn of χMT in the low temperature region for 2 being due to the zero-field splitting of the nickel(II) ion. Very weak [J = -0.247(2) cm-1] and relatively weak intramolecular antiferromagnetic interactions [J = -4.86(2) cm-1] occurred in 3 and 4, respectively (the spin Hamiltonian being defined as H = -JS1·S2). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in 3 and 4 account for their magnetic properties.

Photoactivated Refractive Index Anisotropy in Fluorescent Thiophene Derivatives.

The optical control of anisotropy in materials is highly advantageous for many technological applications, including the real-time modulation of another light signal in photonic switches and sensors. Here, we introduce three thiophene derivatives with a donor-acceptor structure, which feature different positions of an electron-acceptor nitrile group, and both photoalignment and luminescence properties. Quantum chemical calculations highlight the presence of trans-forms stable at room temperature and metastable cis-isomers. Besides photoluminescence peaked at 440-460 nm and 0.4 ns lifetime, the three nonlinear optical chromophores exhibit photoinduced anisotropy of the refractive index closely depending on the specific molecular structure, with higher values of birefringence at lower driving signal being obtained for ortho substitution of the nitrile group. All-optical modulation of an external light beam at rates of hundreds of hertz is demonstrated in the fluorescent systems. This finding opens an interesting route to multispectral photonic switches embedded in the active layers of light-emitting devices.

Crystal structure, Hirshfeld surface analysis and corrosion inhibition study of 3,6-bis-(pyridin-2-yl)-4-{[(3aS,5S,5aR,8aR,8bS)-2,2,7,7-tetra-methyl-tetra-hydro-5H-bis-[1,3]dioxolo[4,5-b:4',5'-d]pyran-5-yl)meth-oxy]meth-yl}pyridazine monohydrate.

In the title compound, C27H30N4O6·H2O, the two dioxolo rings are in envelope conformations, while the pyran ring is in a twisted-boat conformation. The pyradizine ring is oriented at dihedral angles of 9.23 (6) and 12.98 (9)° with respect to the pyridine rings, while the dihedral angle between the two pyridine rings is 13.45 (10)°. In the crystal, O-Hwater⋯Opyran, O-Hwater⋯Ometh-oxy-meth-yl and O-Hwater⋯Npyridazine hydrogen bonds link the mol-ecules into chains along [010]. In addition, weak C-Hdioxolo⋯Odioxolo hydrogen bonds and a weak C-Hmeth-oxy-meth-yl⋯π inter-action complete the three-dimensional structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (55.7%), H⋯C/C⋯H (14.6%), H⋯O/O⋯H (14.5%) and H⋯N/N⋯H (9.6%) inter-actions. Hydrogen-bonding and van der Waals inter-actions are the dominant inter-actions in the crystal packing. Electrochemical measurements are also reported.

Versatile coordination behaviour of the chloro-tetrazine-picolylamine ligand: mixed-valence binuclear Cu(i)/Cu(ii) complexes.

The 3-Cl-6-amino-(2'-picolyl)-1,2,4,5-tetrazine ligand HL1 has been synthesized and structurally characterized. Its versatile coordination behavior has been evidenced through reactions with Cu(Hfac)2 and Cu(triflate)2 precursors, which provided mixed-valence bimetallic Cu1.5Cu1.5 complexes [Cu2(µ-Cl)(L1)2] 2 and [Cu2(µ-triflate)(L1)2] 5. Changing the Cu(ii) precursor and the solvent leads to the formation of mononuclear octahedral Cu(ii) complexes [CuCl2(HL1)2]·2CH3CN 3 and [Cu(Hfac)2(HL1)] 4, in which only the amino-pyridine unit is involved in the coordination of the metal center. In contrast, in complexes 2 and 5, the ligands are deprotonated and bridge the metal centers as pyridine-amido-tetrazine fragments, while a bridging chloride or triflate ligand completes the coordination sphere of the metal ions. The Cu-Cu distances of 2.4313(4) Å in 2 and 2.5198(10) Å in 5 lie among the shorter values within mixed-valence bimetallic Cu complexes. Mixed-valence character is strongly supported by DFT calculations, showing the equal repartition of the unpaired electron between the two metal centers.

Co-existence of ferro- and antiferromagnetic interactions in a hexanuclear mixed-valence CoMnMn cluster sustained by a multidentate Schiff base ligand.

The successful utilization of the "direct synthesis" approach yielded the unprecedented hexanuclear complex of formula [Co2MnMn(L1)4Cl2(µ3-O)2(dmf)4]·2dmf (1) (H3L is the Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol). Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P21/c and it contains a rare mixed-valence {CoMnMn(µ2-O)8(µ3-O)2} core where all metal ions are linked through the phenolato and alkoxo groups of the L3- ligand. Besides the charge balance resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (MnIV-MnII, J2 = +1.10(3) cm-1, J3 = +2.19(3) cm-1; MnII-MnII, j = +0.283(3) cm-1) and antiferromagnetic interactions (MnIV-MnIV, J1 = -17.31(4) cm-1), with the six-coordinate CoIII ions being diamagnetic. DFT type calculations were carried out to substantiate these values. The energy diagram for the different spin states using the best-fit parameters shows the occurrence of six low-lying spin states (S = 0-5) which are close in energy but clearly separated from the remaining ones, with the ground spin state being S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between MnII ions through the long -O-MnIV-O- pathway takes place.

A highly turn-on fluorescent CHEF-type chemosensor for selective detection of Cu2+ in aqueous media.

An efficient "turn on" fluorescence chemosensor Schiff base LH based on the combination of 2-Hydroxy-5-(p-tolyldiazenyl)benzaldehyde and N-(3-Aminopropyl)imidazole was prepared and characterized then evaluated for its selective fluorescent sensing of Cu2+ amongst other metal ions. The CN isomerization inhibition process induced by the Cu2+ binding warrants the chelation-induced enhanced fluorescence (CHEF) effect. In addition, the detection limit sensing of LH for Cu2+ was found to be 1.8 × 10-6 M that is below the WHO recommendation level (20 µM) for drinking water.

All-Optical Switching and Two-States Light-Controlled Coherent-Incoherent Random Lasing in a Thiophene-Based Donor-Acceptor System.

We describe herein the synthesis and characterization of a thiophene-based donor-acceptor system, namely (E)-2-(4-nitrostyryl)-5-phenylthiophene (Th-pNO2 ), which was prepared under Horner-Wadsworth-Emmons conditions. The UV/Vis absorption bands, including the intramolecular charge transfer (ICT) band, were fully assigned using DFT and TD-DFT computations. The results of both efficient third-order nonlinear optical properties and light-amplification phenomena are presented. Investigations of photoinduced birefringence (PIB) in optical Kerr effect (OKE) experiments showed a great potential for this particular compound as an efficient, fully reversible, and fast optical switch. Time constants for the observed trans-cis-trans molecular transitions are in the range of microseconds and give a competitive experimental result for the well-known and exploited azobenzene derivatives. Random lasing (RL) investigations confirmed that this organic system is potentially useful to achieve strong light enhancement, observed as a multimode lasing action. Both RL and OKE measurements indicate that this material is a representative of thiophene derivatives, which can be utilized to fabricate fast all-optical switches or random lasers (light amplifiers).

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination.

The synthesis and full characterization of two tetrathiafulvalene-appended azine ligands, namely 2-([2,2'-bi(1,3-dithiolylidene)]-4-yl)-6-((2,4-dinitrophenyl)hydrazono)methyl)pyridine (L1) and 5-([2,2'-bi(1,3-dithiolylidene)]-4-yl)-2-((2,4-dinitrophenyl)hydrazono)methyl)pyridine (L2) are described. The crystal structure of ligand L1 indicates that the ligand is completely planar with the presence of a strong intramolecular N3-H3···O1 hydrogen bonding. Titration experiments with inorganic anions showed that both ligands are suitable candidates for the sensing of fluoride anions. Ligand L2 was reacted with a Re(I) cation to yield the corresponding rhenium tricarbonyl complex 3. In the crystal structure of the newly prepared electroactive rhenium complex the TTF is neutral and the rhenium cation is hexacoordinated. The electrochemical behavior of the three compounds indicates that they are promising for the construction of crystalline radical cation salts.

Structural, photophysical and magnetic properties of transition metal complexes based on the dipicolylamino-chloro-1,2,4,5-tetrazine ligand.

The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) , prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(II), Cd(II), Mn(II) and Co(II), when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [M(II)-(µ-Cl)2M(II)] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geometries. Moreover, the chlorine atoms, either coordinated to the metal or as a substituent on the tetrazine ring, engage respectively in specific anion-π intramolecular and intermolecular interactions with the electron-poor tetrazine units in the solid state, thus controlling the supramolecular architecture. Modulation of the emission properties is observed in the case of the Zn(II) and Cd(II) complexes when compared to the free ligand. A striking difference is observed in the magnetic properties of the Mn(II) and Co(II) complexes. An antiferromagnetic coupling takes place in the dimanganese(II) compound (J = -1.25 cm(-1)) while the Co(II) centers are ferromagnetically coupled in the corresponding complex (J = +0.55 cm(-1)), the spin Hamiltonian being defined as H = -JSA·SB.

5-Nitro-1,3-bis-(prop-2-yn-yl)-1H-1,3-benzimidazol-2(3H)-one.

The title compound, C13H9N3O3, crystallizes with two identical but differently oriented mol-ecules in the asymmetric unit, the dihedral angle between the fused-ring systems of the two molecules being 64.39 (7)°. The two prop-2-ynyl chains are located on opposite sides of the mol-ecule and are nearly perpendicular to the fused ring plane, as indicated by the C-N-C-C torsion angles in the range 106.0 (3)-113.4 (3)°. In the crystal, the two mol-ecules are linked through C-H⋯O hydrogen bonds into dimers, which are subsequently linked by further C-H⋯O inter-actions, building a three-dimensional network.

1H-Benzotriazol-1-yl 4-{(E)-[4-(dimethyl-amino)-phen-yl]diazen-yl}benzoate.

The title compound, C(21)H(18)N(6)O(2), was obtained as a by-product of a reaction between (E)-4-(4-dimethyl-amino-phenyl-azo)benzoic acid and 2-amino-4-(2-pyrid-yl)-6-(6-pyrid-yl)-1,3,5-triazine, which has a very low solubility, under peptidic coupling conditions, using THF as solvent. The condensation reaction occurred between 1-hy-droxy-benzotriazole and (E)-4-(4-dimethyl-amino-phenyl-azo)benzoic acid. The dihedral angle between the benzene rings in the (E)-diphenyl-diazene fragment is 10.92 (13)° and that between the benzotriazole mean plane and the central benzene ring is 80.57 (7)°. In the crystal, π-π stacking [centroid-centroid distances = 3.823 (2) and 3.863 (2) Å] of similar fragments generates mol-ecular layers parallel to (0-12). The crystal packing also features weak C-H⋯N hydrogen bonds involving N atoms of the benzotriazole ring.

Nonlinear absorption reversing between an electroactive ligand and its metal complexes.

We present the nonlinear absorption investigation of an electroactive ligand and two ruthenium and iron metal complexes under 532 nm, 30 ps laser excitation, by the "open aperture" Z-scan technique. Significant nonlinear optical parameters have in all cases been measured, while the nonlinear attribute has been found to change from saturable to reverse saturable absorption between the initial ligand and its complexes.

Tetrathiafulvalene-triazine-dipyridylamines as multifunctional ligands for electroactive complexes: synthesis, structures, and theoretical study.

The electroactive ligands (2,4-bis-tetrathiafulvalene[6-(dipyridin-2'-ylamino)]-1,3,5-triazine) TTF(2)-tz-dpa (1) and (2-tetrathiafulvalene[4,6-bis-(dipyridin-2'-ylamino)]-1,3,5-triazine) TTF-tz-dpa(2) (2) have been synthesized by palladium cross-coupling catalysis, and the single crystal X-ray structure for 1 was determined. In the solid state the TTF and triazine units are practically coplanar and short intermolecular S···S contacts are established. Two neutral and one tetracationic Zn(II) complexes, formulated as (TTF(2)-tz-dpa)ZnCl(2) (3), [ZnCl(2)(TTF-tz-dpa(2))Zn(H(2)O)Cl(2)] (4), and {[(H(2)O)(2)Zn(TTF-tz-dpa(2))](ClO(4))(2)}(2) (5) have been crystallized and analyzed by single crystal X-ray analysis. A peculiar feature is the evidence for anion-π interactions, as shown by the short Cl···triazine and O(perchlorate)···triazine distances of 3.52 and 3.00 Å, respectively. A complex set of intermolecular π···π, S···S, and hydrogen bonding interactions sustain the supramolecular organizations of the complexes in the solid state. Electronic absorption spectra provide evidence for the intramolecular charge transfer from TTF to triazine, also supported by time-dependent density functional theory (TD DFT) calculations.

Intermolecular interactions in self-assembled monolayers of tetrathiafulvalene derivatives.

The elaboration of mixed self-assembled monolayers (SAMs) of tetrathiafulvalene derivatives allows the modulation of intermolecular interactions and provides evidence of segregated distribution of redox centers.

A neutral zwitterionic molecular solid.

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT-TTF-CO-NH-CH(2)-CO(2)H; 1; EDT-TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT-TTF)(·+)-CO-NH-CH(2)-(CO(2))(-)][(EDT-TTF)-CO-NH-CH(2)-(CO(2)H)]·CH(3)OH (2), a new type of hydrogen-bonded, 1:1 acid/zwitterion hybrid embrace of redox peptidics into a two-dimensional architecture, an example of a system deliberately fashioned so that oxidation of π-conjugated cores toward the radical-cation form would interfere with the activity of the appended ionizable residues in the presence of a templating base during crystal growth. First-principles calculations demonstrate that, notwithstanding preconceived ideas, a metallic state is more stable than the hole-localized alternatives for a neat 1:1 neutral acid/zwitterion hybrid. The inhomogeneous Coulomb field associated with proton-shared, interstacks O-H···O hydrogen bonds between the ionizable residues distributed on both sides of the two-dimensional π-conjugated framework leads, however, to a weak hole localization responsible for the activated but high conductivity of 1 S cm(-1). This situation is reminiscent of the role of the environment on electron transfer in tetraheme cytochrome c, in which the protonation state of a heme propionate becomes paramount, or ion-gated transport phenomena in biology. These observations open rather intriguing opportunities for the construction of electronic systems at the interface of chemistry and biology.

The 8 : 1 : 1 ternary hybrid framework in the system [EDT-TTF +][1,4-bis(iodoethynyl)benzene][Re6Se8(CN)6]4-: dual noncovalent expression of the octahedral halogen-bond hexa-acceptor nanonode.

Complementary shapes of the neutral symmetrical halogen-bond bis-donor core and octahedral inorganic cluster core prevent halogen-bonded polymers developing in more than one direction, favouring further templating by conducting radical cation slabs and yielding an 8 : 1 : 1 phase formulation instead of n : 2 : 1, with a 2D net, or m : 3 : 1, with a pseudo-cubic architecture, which may in principle also be targeted.

Balancing framework densification with charged, halogen-bonded-pi-conjugated linkages: [PPh4]2{[E-TTF-I2][Re6Se8(CN)6]} versus [PPh4]2[EDT-TTF-I]2{[EDT-TTF-I][Re6Se8(CN)6]}.

The ionic character of a set of two redox linkages and strong, directional halogen bonding at the organic-inorganic interface compromise to produce two materials sharing a common two-dimensional net, eventually extended in a third dimension, although two of the six symmetrical halogen bond acceptors ultimately remain uninvolved as a result of charge densification.

Preferential hetero-dimer formation and equilibrium dynamics of self-complementary bifunctional oligo(p-phenylenevinylene) and C60 ureido-pyrimidinone derivatives in solution.

The formation of hetero-dimers of bifunctional oligo(p-phenylenevinylene) and C60 ureido-pyrimidinone derivatives has been observed by 1H-NMR and fluorescence techniques.