Javier Garín

Semiconducting charge transfer complexes from [60]Fullerene-tetrathiafulvalene (C60-TTF) systems

Abstract The first CT-complexes of covalently bound [60]Fullerene-tetrathiafulvalene (TTF) systems with tetrafluorotetracyano-p-quinodimethane (TCNQF 4 ) show a semiconducting behaviour.

Evolution of linear absorption and nonlinear optical properties in v-shaped ruthenium(II)-based chromophores

In this article, we describe a series of complexes with electron-rich cis-{Ru(II)(NH(3))(4)}(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845-4859). They have been isolated as their PF(6)(-) salts and characterized by using various techniques including (1)H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities beta have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d --> pi* metal-to-ligand charge-transfer (MLCT) and pi --> pi* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant beta(0) responses as high as ca. 600 x 10(-30) esu. These pseudo-C(2v) chromophores show two substantial components of the beta tensor, beta(zzz) and beta(zyy), although the relative significance of these varies with the physical method applied. According to HRS, beta(zzz) dominates in all cases, whereas the Stark analyses indicate that beta(zyy) is dominant in the shorter chromophores, but beta(zzz) and beta(zyy) are similar for the extended species. In contrast, finite field calculations predict that beta(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand pi-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880-3891).

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.

New D-π-A-conjugated organic sensitizers based on 4H-pyran-4-ylidene donors for highly efficient dye-sensitized solar cells.

We have synthesized a series of four new promising D-π-A conjugated organic sensitizers with a proaromatic 4H-pyran-4-ylidene as a donor, a thiophene ring in the bridge, and 2-cyanoacrilic acid as acceptor. Comparison between different donor substituents and the modification of the thiophene ring resulted in molar extinction coefficients as high as 36399 M(-1) cm(-1) at 551 nm. The photovoltaic properties of the DSSCs demonstrate power conversion efficiencies as high as 5.4%.

The bis-linking of tetrathiafulvalene (TTF) to C60: Towards the control of electron transfer between π-donors and C60

The bis-linking of a tetrathiafulvalene (TTF) to C60 is carried out by [4+2] Diels-Alder cycloaddition of C60 to the 2,3-dimethylene-TTF 2, this transient diene being generated by KI-[18]crown-6 mediated dibromine reductive elimination of the 2,3-bis(bromomethyl)TTF 3. The C60-TTF target cycloadduct 1a is charaterized by spectroscopy and electrochemical study.

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.

Electronic absorption spectra of closed and open-shell tetrathiafulvalenes: the first time-dependent density-functional study

Abstract The lowest energy transitions of tetrathiafulvalene (TTF) derivatives are calculated at different levels of theory. Whereas semiempirical (CNDO/S, ZINDO) and HF methods (CIS, TD-HF) give unrealistic excitation energies, time-dependent density-functional theory (TD-DFT) calculations provide a much improved description of the electronic absorption spectra of these compounds, including the unusual behavior of some TTF-containing nonlinear optical chromophores. Moreover, the study of radical cations of TTF derivatives allows the evaluation of the performance of TD-DFT methods on sulfur-containing open-shell species for the first time.

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.