New Multifunctional Bipyrimidine-Based Chromophores for NLO-Active Thin-Film Preparation.

New synthesized bipyrimidine-based chromophores presenting alkoxystyryl donor groups carrying aliphatic achiral and chiral chains in the 4 position, connected to electron-accepting 2,2-bipyrimidine cores have been synthesized. Their linear and nonlinear optical (NLO) properties were investigated as well as their mesomorphic properties by various techniques (light-transmission measurements, polarized-light optical microscopy, differential scanning calorimetry measurements and two-photon excited fluorescence). The derivatives with achiral linear carbon chains were found to exhibit liquid-crystal properties with the formation smectic phases over large temperature ranges, which were confirmed by small-angle X-ray scattering analysis via stacking models. The nonlinear optical properties in the solid state for derivatives with C14 and the citronellol chains have been studied by wide-field second-harmonic generation and multi-photon fluorescence imaging, confirming centrosymmetry for these achiral mesogens and their excellent third-order nonlinearity whereas the chiral compound exhibits non-centrosymmetric organization resulting in a strong Second Harmonic Generation at the crystal state.

Investigations of the Photothermal Properties of a Series of Molecular Gold-bis(dithiolene) Complexes Absorbing in the NIR-III Region.

The photothermal properties of a series of neutral radical gold-bis(dithiolene) complexes absorbing in the near-infrared-III window (1550-1870 nm) have been investigated. This class of complexes was found to be good photothermal agents (PTAs) in toluene under 1600 nm laser irradiation with photothermal efficiencies around 40 and 60 % depending on the nature of the dithiolene ligand. To the best of our knowledge, these complexes are the first small molecular photothermal agents to absorb so far into the near infrared. To test their applicability in water, these hydrophobic complexes have been encapsulated into nanoparticles constituted by amphiphilic block-copolymers. Stable suspensions of polymeric nanoparticles (NPs) encapsulating the gold-bis(dithiolene) complexes have been prepared which show a diameter around 100 nm. The encapsulation rate was found to be strongly dependent on the nature of the dithiolene ligands. The photothermal properties of the aqueous suspensions containing gold-bis(dithiolene) complexes were then studied under 1600 nm laser irradiation. These studies demonstrate that water has strong photothermal activity in the NIR-III region that, cannot be overcome even with the addition of gold complexes displaying good photothermal properties.

Nanoprecipitation of Biocompatible Poly(malic acid) Derivative, Its Ability to Encapsulate a Molecular Photothermal Agent and Photothermal Properties of the Resulting Nanoparticles.

Biocompatible nanoparticles (NPs) of hydrophobic poly(benzyl malate) (PMLABe) were prepared by nanoprecipitation. The influence of nanoprecipitation parameters (initial PMLABe, addition rate, organic solvent/water ratio and stirring speed) were studied to optimize the resulting formulations in terms of hydrodynamic diameter (Dh) and dispersity (PDI). PMLABe NPs with a Dh of 160 nm and a PDI of 0.11 were isolated using the optimized nanoprecipitation conditions. A hydrophobic near infra-red (NIR) photothermally active nickel-bis(dithiolene) complex (Ni8C12) was then encapsulated into PMLABe NPs using the optimized nanoprecipitation conditions. The size and encapsulation efficiency of the NPs were measured, revealing that up to 50 weight percent (wt%) of Ni8C12 complex can efficiently be encapsulated with a slight increase in Dh of the corresponding Ni8C12-loaded NPs. Moreover, we have shown that NP encapsulating Ni8C12 were stable under storage conditions (4 °C) for at least 10 days. Finally, the photothermal properties of Ni8C12-loaded NPs were evaluated and a high photothermal efficiency (62.7 ± 6.0%) waswas measured with NPs incorporating 10 wt% of the Ni8C12 complex.

Liposomes Containing Nickel-Bis(dithiolene) Complexes for Photothermal Theranostics.

New thermosensitive liposomes with a phase transition at 42 °C, containing nickel-bis(dithiolene) complexes as efficient and stable photothermal agents, have been formulated and characterized. These liposomes are highly stable and keep their contents at 37 °C for more than 30 days. On the contrary, the mild hyperthermia generated by the nickel-bis(dithiolene) complex under 940 nm NIR irradiation allows for the fine controlled release of the liposome contents, making such liposomes highly suitable for on-demand drug delivery in the human body under NIR laser irradiation. These liposomes can also be directly used, as shown here, as nanoagents for photothermal therapy. In fact, strong cell death can be generated under laser irradiation in the presence of these photothermally active nanocargos containing less than 10% w/w of metal complex. We also demonstrate, for the first time, that nickel-bis(dithiolene) complexes are good photoacoustic agents, generating easily detectable ultrasonic signals directly proportional to the concentration of complexes and the used laser power.

Stable Metallic State of a Neutral-Radical Single-Component Conductor at Ambient Pressure.

Molecular metals have been essentially obtained with tetrathiafulvalene (TTF)-based precursors, either with multicomponent ionic materials or, in a few instances, with single-component systems. In that respect, gold bis(dithiolene) complexes, in their neutral radical state, provide a prototype platform toward such single-component conductors. Herein we report the first single-component molecular metal under ambient pressure derived from such Au complexes without any TTF backbone. This complex exhibits a conductivity of 750 S·cm-1 at 300 K up to 3800 S·cm-1 at 4 K. First-principles electronic structure calculations show that the striking stability of the metallic state finds its origin in sizable internal electron transfer from the SOMO-1 to the SOMO of the complex as well as in substantial interstack and interlayer interactions.

Subtle Steric Differences Impact the Structural and Conducting Properties of Radical Gold Bis(dithiolene) Complexes.

Among single component molecular conductors, neutral radical gold dithiolene complexes [(R-thiazdt)2 Au]. derived from the N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate (R-thiazdt) ligand provide an extensive series of conducting, non-dimerized, half-filled band systems. Analogues of the known R=isopropyl (iPr) derivative were investigated here with R=NMe2 , cyclopropyl (cPr) and n-propyl (nPr), aiming at rationalizing the different solid state structures adopted by these compounds despite very closely related substituents on the heterocyclic nitrogen atom. An original crisscross organization within dimerized chains is observed with R=NMe2 , differing however from the analogous iPr derivative by a 180° rotation of the heterocyclic nitrogen substituent. On the other hand, the cyclopropyl and n-propyl substituents lead to robust, uniform, non-dimerized chains with a strongly 1 D electronic structure and a formal half-filled electronic structure. The semiconducting behaviour of these two radical complexes is characteristic of a Mott insulator, whose sensitivity to external pressure has been evaluated up to 2.5 GPa.

Single-Component Conductors: A Sturdy Electronic Structure Generated by Bulky Substituents.

While the introduction of large, bulky substituents such as tert-butyl, -SiMe3, or -Si(isopropyl)3 has been used recently to control the solid state structures and charge mobility of organic semiconductors, this crystal engineering strategy is usually avoided in molecular metals where a maximized overlap is sought. In order to investigate such steric effects in single component conductors, the ethyl group of the known [Au(Et-thiazdt)2] radical complex has been replaced by an isopropyl one to give a novel single component molecular conductor denoted [Au(iPr-thiazdt)2] (iPr-thiazdt: N-isopropyl-1,3-thiazoline-2-thione-4,5-dithiolate). It exhibits a very original stacked structure of crisscross molecules interacting laterally to give a truly three-dimensional network. This system is weakly conducting at ambient pressure (5 S·cm(-1)), and both transport and optical measurements evidence a slowly decreasing energy gap under applied pressure with a regime change around 1.5 GPa. In contrast with other conducting systems amenable to a metallic state under physical or chemical pressure, the Mott insulating state is stable here up to 4 GPa, a consequence of its peculiar electronic structure.

Interplay between Organic-Organometallic Electrophores within Bis(cyclopentadienyl)Molybdenum Dithiolene Tetrathiafulvalene Complexes.

Tetrathiafulvalenes (TTF) and bis(cyclopentadienyl) molybdenum dithiolene complexes, Cp2Mo(dithiolene) complexes, are known separately to act as good electron donor molecules. For an investigation of the interaction between both electrophores, two types of complexes were synthesized and characterized. The first type has one Cp2Mo fragment coordinated to one TTF dithiolate ligand, and the second type has one TTF bis(dithiolate) bridging two Cp2Mo fragments. Comparisons of the electrochemical properties of these complexes with those of models of each separate electrophore provide evidence for their mutual influence. All of these complexes act as very good electron donors with a first oxidation potential 430 mV lower than the tetrakis(methylthio)TTF. DFT calculations suggest that the HOMO of the neutral complex and the SOMO of the cation are delocalized across the whole TTF dithiolate ligand. The X-ray crystal structure analyses of the neutral and the mono-oxidized Cp2Mo(dithiolene)(bismethylthio)TTF complexes are consistent with the delocalized assignment of the highest occupied frontier molecular orbitals. UV-vis-NIR spectroelectrochemical investigations confirm this electronic delocalization within the TTF dithiolate ligand.

Radical or not radical: compared structures of metal (M = Ni, Au) bis-dithiolene complexes with a thiazole backbone.

A complete series of dianionic, monoanionic, and neutral dithiolene complexes formulated as [Ni(Et-thiazdt)2](n), with n = -2, -1, 0, and Et-thiazdt: N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate, is prepared using an optimized procedure described earlier for the N-Me derivatives. Electrochemical and spectroscopic properties confirm the electron-rich character of the Et-thiazdt dithiolate ligand. The three complexes are structurally characterized by single-crystal X-ray diffraction. The paramagnetic anionic complex [Ni(Et-thiazdt)2](-1), as Ph4P(+) salt, exhibits side-by-side lateral interactions leading to a Heisenberg spin chain behavior. The solid-state structure of the neutral, diamagnetic [Ni(Et-thiazdt)2](0) complex shows a face-to-face organization with a large longitudinal shift, at variance with the structure of its radical and neutral gold dithiolene analogue described earlier and formulated as [Au(Et-thiazdt)2](•). Comparison of the two structures, and those of the other few structurally characterized pairs of Ni/Au dithiolene complexes, demonstrates the important role played by overlap interactions between gold dithiolene radical species. Despite its closed-shell character, the neutral nickel complex [Ni(Et-thiazdt)2](0) exhibits a semiconducting behavior with a room-temperature conductivity σRT ≈ 0.014 S cm(-1).

Non-Linear Optical Activity of Chiral Bipyrimidine-Based Thin Films.

An original series of bipyrimidine-based chromophores featuring alkoxystyryl donor groups bearing short chiral (S)-2-methylbutyl chains in positions 4, 3,4 and 3,5, connected to electron-accepting 2,2-bipyrimidine rings, has been developed. Their linear and non-linear optical properties were studied using a variety of techniques, including one- and two-photon absorption spectroscopy, fluorescence measurements, as well as Hyper-Rayleigh scattering to determine the first hyperpolarizabilities. Their electronic and geometrical properties were rationalized by TD-DFT calculations. The thermal properties of the compounds were also investigated by a combination of polarized light optical microscopy, differential scanning calorimetry measurements and small-angle X-ray scattering experiments. The derivatives were found not to have mesomorphic properties, but to exhibit melting temperatures or cold crystallization behavior that enabled the isolation of well-organized thin films. The nonlinear optical properties of amorphous or crystalline thin films were studied by wide-field second harmonic generation and multiphoton fluorescence imaging, confirming that non-centrosymmetric crystal organization enables strong second and third harmonic generation. This new series confirms that our strategy of functionalizing 3D organic octupoles with short chiral chains to generate non-centrosymmetric organized thin films enables the development of highly second order nonlinear optical active materials without the use of corona-poling or tedious deposition techniques.

Variable magnetic interactions between S = 1/2 cation radical salts of functionalizable electron-rich dithiolene and diselenolene Cp2Mo complexes.

A series of Cp(2)Mo(dithiolene) and Cp(2)Mo(diselenolene) complexes containing N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (R-thiazdt, R = Me, Et, CH(2)CH(2)OH) and N-alkyl-1,3-thiazoline-2-thione-4,5-diselenolate ligand (R-thiazds, R = Me, Et) have been synthesized. These heteroleptic molybdenum complexes have been characterized by electrochemistry, spectroelectrochemistry, and single crystal X-ray diffraction. They act as very good electron donor complexes with a first oxidation potential 200 mV lower than in the prototypical Cp(2)Mo(dmit) complex and exhibit almost planar MoS(2)C(2) (or MoSe(2)C(2)) metallacycles. All five complexes formed charge transfer salts with a weak (TCNQ) and a strong acceptor (TCNQF(4)), affording ten different charge-transfer salts, all with 1:1 stoichiometry. Crystal structure determinations show that the S/Se substitution in the metallacycle systematically affords isostructural salts, while the Cp(2)Mo(R-thiazdt) complexes with R equals ethyl or CH(2)CH(2)OH can adopt different structures, depending on the involvement of the hydroxyl group into intra- or intermolecular hydrogen bonding interactions. Magnetic susceptibility data of the salts are correlated with their structural organization, demonstrating that a face-to-face organization of the Me-thiazdt (or Me-thiazds) ligand favors a strong antiferromagnetic interaction, while the bulkier R = Et or R = CH(2)CH(2)OH substituents can completely suppress such intermolecular interactions, with the added contribution of hydrogen bonding to the solid state organization.

Anisotropic chemical pressure effects in single-component molecular metals based on radical dithiolene and diselenolene gold complexes.

On the basis of the reported radical neutral complex [Au(Et-thiazdt)(2)] (Et-thiazdt = N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate), a series of single-component conductors derived from [Au(Et-thiazdt)(2)], also noted as [AuS(4)(═S)(2)], has been developed, by replacing the outer sulfur atoms of the thiazoline-2-thione rings by oxygen atoms and/or by replacing the coordinating sulfur atoms by selenium atoms toward the corresponding diselenolene complexes. Comparison of the X-ray crystal structures and transport properties of the four isostructural complexes, noted as [AuS(4)(═S)(2)], [AuS(4)(═O)(2)], [AuSe(4)(═S)(2)], and [AuSe(4)(═O)(2)], shows that the oxygen substitution on the outer thiazoline ring actually decreases the conductivity by a factor of 100, despite a contracted unit cell volume reflecting a positive chemical pressure effect. On the other hand, the S/Se substitution increases the conductivity by a factor of 100, and the pressure needed to transform these semiconductors into the metallic state is shifted from 13 kbar in [AuS(4)(═S)(2)] to only ≈6 kbar in [AuSe(4)(═S)(2)]. Analysis of unit cell evolutions and ab initio band structure calculations demonstrates the strongly anisotropic nature of this chemical pressure effect and provides an explanation for the observed changes in conductivity. The greater sensitivity of these neutral single-component conductors to external pressure, as compared with "classical" radical salts, is also highlighted.

Synthesis, substitution kinetics, and electrochemistry of the first tetrathiafulvalene-containing beta-diketonato complexes of rhodium(I).

The synthesis of the first rhodium(I) cyclooctadiene complexes containing tetrathiafulvalene (TTF) groups substituted on a beta-diketonato ligand in either the methine position (3 position), [Rh(cod)(H(3)CCOC{S-TTF-(MeS)(3)}COCH(3))] (3), or terminal position (1 position), [Rh(cod){(Me(3)-TTF)COCHCOCH(3)}] (4), is reported. The effect of the beta-diketonato substitution position on the kinetics of substitution of the TTF-containing beta-diketonato ligand with 1,10-phenanthroline from 3 and 4 to give [Rh(cod)(phen)](+), as well as on the electrochemical properties of 3 and 4, was investigated. Second-order substitution rate constants, k(2), in methanol were found to be almost independent of the substitution position, with 4 (k(2) = 2.09 x 10(3) dm(3) mol(-1) s(-1)) reacting only about twice as fast as 3. An appreciable solvent pathway in the substitution mechanism was only observed for 4 with k(s) = 42 s(-1). A complete mechanism for both substitution reactions is proposed. The electrochemistry of 3 and 4 in CH(2)Cl(2)/0.10 mol dm(-3) [N((n)Bu)(4)][B(C(6)F(5))(4)] showed three redox processes. Two of these were electrochemically reversible and are associated with the redox-active TTF group. For 3, TTF-based formal reduction potentials, E degrees', were observed at 0.082 and 0.659 V vs Fc/Fc(+), respectively; 4 exhibited them at -0.172 and 0.703 V vs Fc/Fc(+) at a scan rate of 100 mV s(-1). A Rh(II)/Rh(I) redox couple was observed at E degrees' = 0.89 V for 3, after both TTF oxidations were completed, and at 0.51 V for 4; this is between the two TTF redox processes. The more difficult oxidation of the Rh(I) center of 3 indicates more effective electron-withdrawing from the Rh(I) center to the first-oxidized TTF(+) group at the methine position of the beta-diketonato ligand of 3(+) than to the terminal-substituted TTF(+) group in 4(+).

Hydrogen bonding interactions in single component molecular conductors based on metal (Ni, Au) bis(dithiolene) complexes.

Introduction of hydrogen bonding (HB) interactions in single component conductors derived from nickel and gold bis(dithiolene) complexes is explored with the 2-alkylthio-1,3-thiazole-4,5-dithiolate (RS-tzdt) with R = CH2CH2OH through the preparation of the neutral [Ni(HOEtS-tzdt)2]0 (closed-shell) and [Au(HOEtS-tzdt)2]˙ (radical) complexes. At variance with many other radical gold dithiolene complexes which have a strong tendency to dimerize in the solid state, [Au(HOEtS-tzdt)2]˙ crystallizes into uniform stacks interconnected by strong O-HN HB involving the nitrogen atom of the thiazole ring. [Au(HOEtS-tzdt)2]˙ is isostructural with its neutral, closed-shell nickel analog [Ni(HOEtS-tzdt)2]0, a rare situation in this metal bis(dithiolene) chemistry. It demonstrates how the strength of the HB directing motif can control the overall structural arrangement to stabilize the same structure despite a different electron count. The nickel complex behaves as a band semiconductor with weak room temperature conductivity (1.6 × 10-5 S cm-1), while the gold complex is described as a Mott insulator with a three orders of magnitude improved conductivity (6 × 10-2 S cm-1).

A single-component molecular metal based on a thiazole dithiolate gold complex.

A single component molecular conductor has been isolated from electrocrystallization of the monoanionic gold bis(dithiolene) complex based on the N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate (Et-thiazdt) ligand. The crystal structure of the system exhibits layers built from parallel uniform one-dimensional stacks of the planar molecule. At room temperature and ambient pressure the system is semiconducting (0.33 S x cm(-1)) with a small activation energy. However, the single crystal conductivity is strongly pressure dependent reaching 1000 S x cm(-1) at 21 kbar. At 13 kbar there is a crossover between semiconducting and metallic regimes. Thus, the present system is the first well characterized single-component molecular metal without TTF dithiolate ligands. First-principles DFT calculations show that the ground state is antiferromagnetic with a very small band gap. A simulation of the effect of pressure on the electronic structure provides a rationale for the observed variations of the conductivity and gives insight on how to further stabilize the metallic state of the system.

Neutral, closed-shell nickel bis(2-alkylthio-thiazole-4,5-dithiolate) complexes as single component molecular conductors.

Neutral nickel bis(dithiolene) complexes, because of their closed-shell character, are usually considered as insulating materials, unless they are formed out of highly delocalized tetrathiafulvalenedithiolate ligands. We describe here an original series of S-alkyl substituted neutral bis(thiazole-4,5-dithiolate) nickel complexes formulated as [Ni(RS-tzdt)2] (R = Me, Et), which organize in the solid state into uniform stacks and exhibit semiconducting behavior, with room temperature conductivities comparable to those reported in the prototypical [Ni(dmit)2] and [Ni(Et-thiazdt)2] neutral complexes. These findings provide new perspectives in the current search for single component molecular conductors.

Biocompatible nanoparticles containing hydrophobic nickel-bis(dithiolene) complexes for NIR-mediated doxorubicin release and photothermal therapy.

Biocompatible nanoparticles (NPs) constituted by amphiphilic poly(ethylene glycol)-block-poly(benzyl malate), PEG-b-PMLABe, have been designed for site-specific PhotoThermal Controlled Release (PTCR) of drugs thanks to the presence of a near infra-red (NIR) photothermally active nickel-bis(dithiolene) complex in the inner core of the NPs, together with doxorubicin (Dox). A nanoprecipitation technique was used to prepare well-defined nickel-bis(dithiolene) and nickel-bis(dithiolene)/Dox loaded NPs, which were characterized by dynamic light scattering (DLS), zeta-potential measurements and Transmission Electron Microscopy (TEM). We have shown that the Dox release was effectively controlled by NIR irradiation (long or pulsed NIR laser irradiation). Cytotoxicity experiments on HeLa and MDA-MB-231 cells have shown that the incorporation of more than 10 w% of nickel-bis(dithiolene) complexes does not increase the intrinsic toxicity of the polymer nanoparticles. Finally, the viability of MDA-MB-231 cells was assessed after their incubation, for 24 hours, with empty NPs, Ni4C12 loaded NPs, Dox loaded NPs or Ni4C12/Dox loaded NPs, without or with NIR irradiation. Above all, the results have highlighted that the Ni4C12 loaded NPs after 5 min NIR laser irradiation can induce strong cell death up to 80% at 50 µg mL-1. These results demonstrate that these NPs are good candidates for photothermal therapy.

Electropolymerized highly photoconductive thin films of cyclopalladated and cycloplatinated complexes.

The complete characterization of novel electropolymerizable organometallic complexes is presented. These are newly synthesized cyclometalated complexes of general formula (PPy)M(O ∧ N)(n) (H(PPy) = 2-phenylpyridine, M = Pd(II) or Pt(II), H(O ∧ N)(n) = Schiff base). Polymeric thin films have been obtained from these complexes by electropolymerization of the triphenylamino group grafted onto the H(O ∧ N)(n) ancillary ligand. The redox behavior and the photoconductivity of both of the monomers (PPy)M(O ∧ N)(n) and the electropolymerized species have been investigated. The polymeric films of (PPy)M(O ∧ N)(n) have shown a very significant enhancement of photoconductivity when compared to their monomeric amorphous counterparts. The high stability of the obtained films strongly suggests that electropolymerization of cyclometalated complexes represents a viable deposition technique of quality thin films with improved photoconduction properties, hence opening the door to a new class of materials with suitable properties for optoelectronic applications.

Self-organization of a tetrasubstituted tetrathiafulvalene (TTF) in a silica based hybrid organic-inorganic material.

A hybrid organic inorganic nanostructured material containing a TTF core substituted by four arms exhibited a high level of both condensation at silicon (96%) and self-organization as evidenced by X-ray diffraction and an unprecedented birefringent behaviour.

Vinylmercury Hydrides: Synthesis and Spectroscopic Characterization.

The first vinylmercury hydrides, and among them the parent compound, have been prepared by a chemoselective reduction of the corresponding vinylmercury chlorides with tributylstannane in the presence of a radical inhibitor. These hydrides have been characterized on the basis of their spectral data ((1)H, (13)C, and (199)Hg NMR spectroscopy and mass spectrometry). The photoelectron spectra of the ethenylmercury hydride displays bands at 9.79, 10.13, 11.41, and 13.20 eV. On the basis of photoelectron spectra and ab initio quantum chemical calculations some (d-p)pi interaction between the vinyl pi-system and the mercury d-orbitals could be concluded. Vinylmercury hydrides have been condensed and then revaporized in vacuum at low temperature, but they exhibit a very low stability at room temperature even diluted in toluene (tau(1/2) approximately 1 min); elemental mercury and the corresponding divinylmercury were formed under these conditions.