Synthesis and stereochemistry of (3α)-6β,7β-dihydroxy- and 6β-hydroxy-8-alkyl-8-azabicyclo[3.2.1]octane-3-spiro-5′-imidazoline-2′,4′-diones

The synthesis of 6β-hydroxy- and 6β,7β-dihydroxy-8-alkyl-8-azabicyclo[3.2.1]octane-3-spiro-5′-hydantoins was stereoselectively achieved by Bucherer-Bergs reaction of the corresponding ketones. An α configuration on C₃ was proposed for all hydantoins on the basis of spectral data.     

Benzothiazolium-π-thiazole-dicyanomethanides: new nonlinear optical chromophores

A series of merocyanines with a benzothiazolylidene donor and a quinoidal thiazole moiety have been synthesized. Experimental results and theoretical calculations show that these compounds have zwitterionic ground states and negative second-order optical nonlinearities. Unlike most merocyanines, the degree of charge transfer does not decrease on increasing the separation between the donor and the acceptor groups, an unexpected feature related to the presence of the proaromatic thiazole fragment.     

Isophorone- and pyran-containing NLO-chromophores: a comparative study

A series of merocyanines containing isophorone or pyran rings in the spacer have been synthesized. For a given pair of donor and acceptor groups, the isophorone derivatives show higher second-order optical nonlinearities, but lower thermal stabilities. The first NLO-chromophores endowed with a dihydropyran fragment in the spacer have also been prepared and studied.     

Fast and stable recording of birefringence and holographic gratings in an azo-polymethacrylate using a single nanosecond light pulse

Pulsed light-induced recording in azobenzene polymers has recently been studied due to its potential use in optical storage applications. In this paper we study the photoinduced birefringence (Deltan) and holographic grating recording in an azobenzene side chain liquid-crystalline polymethacrylate irradiating with a single 4 ns light pulse at 532 nm. For some irradiation conditions, Deltan grows in less than 50 ns reaching an essentially stable value of about 10(-2). Holographic gratings have been registered using intensity and polarization patterns. Fast response and stability, similar to those of Deltan, was observed in the holographic recording process. Both light-induced anisotropy and relief contributions have been found in the case of gratings recorded using intensity patterns, relief being the dominant contribution at high recording energies. Polarization gratings have been recorded using two orthogonally circularly polarized beams. The resultant gratings showed stable efficiencies up to 0.8% (measured at 633 nm in 1-mum-thick films) and no measurable relief was observed.     

Group 11 complexes with the bis(3,5-dimethylpyrazol-1-yl)methane ligand. How secondary bonds can influence the coordination environment of Ag(I): the role of coordinated water in [Ag2(mu-L)2(OH2)2](OTf)2

The complexation properties of the ligand bis(3,5-dimethylpyrazol-1-yl)methane (L) towards group 11 metals have been studied. The reaction in a 1 : 1 molar ratio with [Cu(NCMe)4]PF6 or Ag(OTf) complexes gives the mononuclear [CuL(NCMe)]PF6 (1), with crystallographic mirror symmetry, or dinuclear [Ag2(mu-L)2](OTf)2 (2) (OTf = trifluoromethanesulfonate) in which the ligand bridges both silver centres, an unprecedented mode of coordination for this type of ligands. Compound 2 crystallizes with two water molecules and forms a supramolecular structure through classical hydrogen bonding. The reaction in a 2 : 1 ratio affords in both cases the four-coordinated derivatives [ML2]X (M = Cu, X = PF6 (3); Ag, X = OTf 4). The treatment of [Ag(OTf)(PPh3)] with the ligand L gives [AgL(PPh3)]OTf (5). The gold(I) derivative [Au2(C6F5)2(mu-L)] (6) has also been obtained by reaction of L with two equivalents of [Au(C6F5)(tht)]. These complexes present a luminescent behaviour at low temperature; the emissions being mainly intraligand but enhanced after coordination of the metal. Compounds 1-4 have been characterized by X-ray crystallography. DFT studies showed that, in the silver complex 2, coordination of H2O to Ag in the binuclear complex is favoured by formation of a hydrogen-bonding network, involving the triflato anion, and releasing enough energy to allow distortion of the Ag2 framework.     

Decreased optical nonlinearities upon CF3 substitution on tricyanofuran acceptors

Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3-TCF results in decreased second-order optical nonlinearities in merocyanines bearing a proaromatic 1,3-dithiole donor. The TCF-containing derivatives display exceptionally high mu beta values up to 31,000 x 10(-48) esu, unprecedented for 1,3-dithiole-based NLO-phores.     

Iminium salts of omega-dithiafulvenylpolyenals: an easy entry to the corresponding aldehydes and doubly proaromatic nonlinear optic-phores

A short, high-yielding route to omega-dithiafulvenylpolyenals (1) via the corresponding iminium salts (2) and starting from trimethyl-1,3-dithiolium tetrafluoroborate is reported. The Knoevenagel reactions of either 1 or 2 with isoxazolone-containing acceptors afford merocyanines 7 and 9, in a process that is often accompanied by a vinylene-shortening side reaction. Experimental and theoretical studies reveal that compounds 7 and 9, featuring two proaromatic end groups, are strongly polarized and show good second-order nonlinear optical responses.