Belén Villacampa

The first tetrathiafulvalene derivatives exhibiting second-order NLO properties

Abstract The second order NLO properties of push-pull TTF derivatives have been studied for the first time. The effect of modifying both the acceptor and the donor moieties on the μβ values has been studied by experimental (EFISH) and theoretical techniques.

4H-Pyran-4-ylidenes: Strong Proaromatic Donors for Organic Nonlinear Optical Chromophores

Merocyanines where a polyenic spacer separates a 4H-pyran-4-ylidene moiety and different strong organic acceptors have been synthesized. According to NMR studies and X-ray diffraction data, these compounds have weakly alternated structures and remarkably zwitterionic ground states, with a partial aromatic character that is compared to those of other pyran derivatives. The proaromaticity of the 4H-pyran-4-ylidene donor lies behind the cyanine-like behavior and low (positive or negative) second-order optical nonlinearities of the shorter derivatives. On the other hand, lengthening the pi-spacer gives rise to rapidly increasing mubeta(1907) values up to 17,400 x 10(-48) esu.

Aromatic/Proaromatic Donors in 2‐Dicyanomethylenethiazole Merocyanines: From Neutral to Strongly Zwitterionic Nonlinear Optical Chromophores

Push-pull compounds, in which a proaromatic electron donor is conjugated to a 2-dicyanomethylenethiazole acceptor, have been prepared, and their properties compared to those of model compounds featuring an aromatic donor. A combined experimental (X-ray diffraction, (1) H NMR, IR, Raman, UV/Vis, nonlinear optical (NLO) measurements) and theoretical study reveals that structural and solvent effects determine the ground-state polarisation of these merocyanines: whereas 4H-pyran-4-ylidene- and 4-pyridylidene-containing compounds are zwitterionic and 1,3-dithiol-2-ylidene derivatives are close to the cyanine limit, anilino-derived merocyanines are essentially neutral. This very large range of intramolecular charge transfer (ICT) gives rise to efficient second-order NLO chromophores with μβ values ranging from strongly negative to strongly positive. In particular, pyranylidene derivatives are unusual in that they show an increase in the degree of ICT on lengthening the π-spacer, a feature that lies behind the very large negative μβ values they display. The linking of the formally quinoidal 2-dicyanomethylenethiazole moiety to proaromatic donors seems a promising approach towards the optimisation of zwitterionic NLO chromophores.

Linear and V-Shaped Nonlinear Optical Chromophores with Multiple 4H-Pyran-4-ylidene Moieties

A simple synthesis of dipolar one- and two-dimensional chromophores bearing two or three 4H-pyran-4-ylidene moieties is reported. Whereas the pyranylidene fragments acting as donors are proaromatic, the spacer one is not. In the linear derivatives, chain elongation gives rise to a sharp increase in the second order nonlinear optical responses, but some V-shaped derivatives display first hyperpolarizabilities (beta) lower than those of their linear analogues. This uncommon feature lends experimental support to previous theoretical studies on the relative contribution and sign of the beta-tensor components.

Second-order nonlinear optical properties of tetrathiafulvalene-π-(thio)barbituric acid chromophores

Abstract Donor-acceptor polyenes that combine an electron-donating tetrathiafulvalene (TTF) unit with a barbituric or thiobarbituric acid have been prepared for the first time and characterized as nonlinear optical (NLO) chromophores. The electrochemical and thermal properties of these derivatives are also reported.

Second-order nonlinear optical properties of tetrathiafulvalene-π-3-(dicyanomethylidene)indan-1-one chromophores

Novel conjugated donor-acceptor chromophores, based on the strong electron donating tetrathiafulvalene moiety and the strong electron-withdrawing 3-(dicyanomethylidene)indan-1-one acceptor, exhibit large second-order optical nonlinearities. The effect of increasing the length of the polyenic spacer on the NLO properties of the new molecules has been studied by using the electric field-induced second harmonic generation (EFISH) method.

Iminium Salts of ω-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.

Synthesis and characterization of novel NLO-phores from π-extended tetrathiafulvalene (TTF) derivatives

Abstract Donor-π-Acceptor systems containing extended TTF derivatives with quinonoid structures have been synthesized and characterized. Their properties as second order NLO chromophores have been studied by experimental (EFISH) and theoretical methods.

Synthesis and properties of push–pull chromophores for second-order nonlinear optics derived from π-extended tetrathiafulvalenes (TTFs)

Abstract Novel π-extended tetrathiafulvalene (exTTF) derivatives connected to a p -nitrophenyl electron-accepting unit through a π-conjugated oligoenic spacer ( 14a – c – 16a – c ) show good second-order optical nonlinearities. The effect of the conjugation length of the oligoenic spacer and the presence of a thiophene ring in the π-conjugated bridge ( 20a – c ) have been theoretically (PM3) and/or experimentally (EFISH technique) studied. The redox properties of the novel compounds have been investigated by cyclic voltammetry (CV) and the CV data reveal the good donor ability of the exTTF unit. Although the energy of the intramolecular charge-transfer (ICT) band displayed by these compounds and their redox potentials are fairly insensitive to the nature of the conjugated spacer linking the donor and the acceptor moieties, an increase in their second order nonlinear optical responses is observed on increasing the conjugation lengths. Compounds 20a – c bearing a thiophene ring show a remarkable thermal stability with decomposition temperatures over 400°C. A new series of D-π-A compounds ( 23a – c ) bearing a 1,3-dithiol-2-ylidene donor unit has also been synthesized and studied.

BETA -DIKETONE, PYRAZOLE AND ISOXAZOLE DERIVATIVES WITH POLAR GROUPS : LIQUID CRYSTALLINE AND NON-LINEAR OPTICAL PROPERTIES

The liquid crystalline behaviour of 1-(4-n-decyloxyphenyl)-3-(4-X-phenyl)propan-1,3-diones and their pyrazole and isoxazole derivatives has been studied by optical microscopy, DSC and X-ray techniques. The 4-substituents (X) were chosen to include a range of different polar and non-polar substituents: H, OCH3, Cl, Br and CN. A monotropic SA phase is observed for the beta-diketone derivative in which X CN and this is the first example of this phase found in a 1,3-diphenylpropan-1,3-dione derivative. The majority of the pyrazole and isoxazole compounds show SA phases. As regards the cyano-substituted compounds, X-ray diffraction studies on the mesophase show that the layer spacing is consistent with a partial bilayer SA mesophase. The first hyperpolarizabilities of the cyano-derivatives due to their push-pull structure have been measured by the EFISH method. Values for these compounds were found to be comparable to those for other conjugated CH3O-pi-CN systems.