Fluorescence amplification of unsaturated oxazolones using palladium: photophysical and computational studies

Weakly fluorescent (Z)-4-arylidene-5-(4H)-oxazolones (1), ΦPL < 0.1%, containing a variety of conjugated aromatic fragments and/or charged arylidene moieties, have been orthopalladated by reaction with Pd(OAc)2. The resulting dinuclear complexes (2) have the oxazolone ligands bonded as a C^N-chelate, restricting intramolecular motions involving the oxazolone. From 2, a variety of mononuclear derivatives, such as [Pd(C^N-oxazolone)(O2CCF3)(py)] (3), [Pd(C^N-oxazolone)(py)2](ClO4) (4), [Pd(C^N-oxazolone)(Cl)(py)] (5), and [Pd(C^N-oxazolone)(X)(NHC)] (6, 7), have been prepared and fully characterized. Most of complexes 3–6 are strongly fluorescent in solution in the range of wavelengths from green to yellow, with values of ΦPL up to 28% (4h), which are among the highest values of quantum yield ever reported for organometallic Pd complexes with bidentate ligands. This means that the introduction of the Pd in the oxazolone scaffold produces in some cases an amplification of the fluorescence of several orders of magnitude from the free ligand 1 to complexes 3–6. Systematic variations of the substituents of the oxazolones and the ancillary ligands show that the wavelength of emission is tuned by the nature of the oxazolone, while the quantum yield is deeply influenced by the change of ligands. TD-DFT studies of complexes 3–6 show a direct correlation between the participation of the Pd orbitals in the HOMO and the loss of emission through non-radiative pathways. This model allows the understanding of the amplification of the fluorescence and the future rational design of new organopalladium systems with improved properties

Cycloaurated phosphinothioic amide complex as a precursor of gold(I) nanoparticles: Efficient catalysts for A3 synthesis of propargylamines under solvent-free conditions

A C,S-cycloaurated complex based on an ortho-substituted phosphinothioic amide framework has been synthesized in high yield through tin(IV)-Au(III) transmetalation from the corresponding chlorodimethylstannyl derivative. The latter was prepared in a two-step process involving directed ortho lithiation/quenching with MeSnCl followed by Me/Cl exchange. The tin(IV) and gold(III) complexes have been characterized in solution and in the solid state. In both complexes, the phosphinothioic amide moiety acts as a C-C-P-S pincer ligand with formation of five-membered-ring metalacycles. The use of the gold(III) complex in the amine-aldehyde-alkyne (A) three-component coupling synthesis of propargylamines showed that the compound is transformed into the Sonogashira-type o-alkynylphosphinothioic amide with generation of Au(I) nanoparticles with an average size of around 7 nm. These nanoparticles proved to be excellent catalysts in A coupling processes, providing propargylamines in high yields under solvent-free conditions with loadings as low as 0.1 mol % and without the use of additives.We thank the MINECO and FEDER program for financial support (projects CTQ2011-27705 and CTQ2014-57157-P). E.B.S. thanks the MICINN for a Ph.D. fellowship. E.P.U. thanks the Gobierno de Aragon-FEDER (Spain, group E97) for financial support.Peer Reviewe

Novel gas sensors based on carbon nanotube networks

6 figures, 2 tables.-- Work presented at the 4th World Congress on biomimetics, artificial muscles and nano-bio, 6 - 9 November 2007, Torre Pacheco, Spain.Novel resistive gas sensors based on single-walled carbon nanotube (SWNT) networks as the active sensing element nave been investigated for gas detection. SWNTs networks were fabricated by airbrushing on alumina substrates. As-produced- and Pd-decorated SWNT materials were used as sensitive layers for the detection of NO2 and H2, respectively. The studied sensors provided good response to NO2 and H2 as well as excellent selectivities to interfering gases.This work has been supported by MEC (Spain, projects TEC2004-05098-C02-01/MIC and TEC2004-05098-C02-02/MIC, and Programa I3 2006 8 0I 060), and the European Regional Development Fund (ERDF)

Novel materials for optoelectronic devices: Conjugated polymer nanoparticle-graphene oxide charge-transfer complexes

Resumen del trabajo presentado al Nano Application Workshop, celebrado en Munich (Alemania) del 19 al 21 de septiembre de 2018.Conjugated polymers (CPs) constitute the base of organic thin film optoelectronic devices, such as organic photovoltaic solar cells (OSCs) and organic light emitting devices (OLEDs). Deposited onto large areas of any shape they critically contribute to the development of self-powered, smart and ubiquitous communication platforms. Operational performance and fabrication from 'green' solutions compatible with large-area coating or printing technologies are key requirements for their commercial implementation. Applying self-assembly strategies, CPs can be prepared in the form of water dispersible nanoparticles being of actual interest for achieving improved device performance. In this work we present novel pathways for the design of improved organic thin film optoelectronic devices by marrying nanoparticles of CPs (CPNPs) with 2D sheets of graphene oxide (GO). Using poly(3-hexylthiophene) (P3HT) as benchmark CP, we demonstrate the game-changing role of GO in tuning the excitonic aggregate behavior of P3HTNPs and the efficient formation P3HTNPs-GO charge-transfer complexes. Thin films thereof reveal improved separation of photo-generated charge carriers. Integration into a photoelectrochemical device shows significantly improved photoactivity. Moreover, the thin films reveal unique molecular switching behavior. The possibility to overcome external performance limitations and to employ 'green' processing technologies offers exciting possibilities for further progress in the field of organic thin film optoelectronic devices.EU Horizon 2020 Marie Sklodowska-Curie grant 642742 ("Enabling Excellence"), Spanish Ministry MINEICO (ENE2016-79282-C5-1-R), Government of Aragón (Recognized Group DGA-T03-17R).Peer Reviewe

Novel Cyclopalladated Imino-thiophenes: Synthesis and Reactivity Toward Alkynes and Carbon Monoxide

ortho-palladated complexes based on thiophene and benzothiophene ligands 1a and 1b have been synthesized by direct C–H activation under mild conditions. These species were fully characterized, including single-crystal X-ray diffraction analysis. The reactions of these novel complexes with internal alkynes afforded a variety of thieno[3,2-c]pyridinium salts substituted at the 6- and 7-positions. The thiophene-based complex 2a also reacts with carbon monoxide, in the presence of different alcohols, forming the corresponding esters by tandem alkoxycarbonylations. This latter reaction can be exploited for the unexpected, but straightforward, formation of the monomeric bis-cyclometallated complexes 6a and 6b from 2a or 2b, whose syntheses do not require the employment of transmetallating agents. The structures of these monomeric palladacycles were also fully elucidated by means of X-ray diffraction studies.Funding by the Ministerio de Ciencia e Innovación (MICINN) (Spain, Project CTQ2008-01784) and Gobierno de Aragón (Spain, group E97 and Project PI071/09) is gratefully acknowledged. L.C. thanks Consejo Superior de Investigaciones Científicas (Spain) for a Juan de la Cierva contract.Peer Reviewe

Regioselective CH Bond Activation on Stabilized Nitrogen Ylides Promoted by Pd(II) Complexes: Scope and Limitations

The orthopalladation of N-ylides [HxCyN–CHC(O)Ar] (HxCyN = pyridine, benzylamine, imidazole, aniline, and phenylpyridine; Ar = aryl) has been studied. The incorporation of the Pd atom to these substrates is regioselective, since the orthopalladation is produced, in most of the cases, only at the aryl ring of the benzoyl group with concomitant C-bonding of the N-ylide. The X-ray structure of one representative example is reported. Factors governing the observed orientation are discussed, because this regioselectivity is worthy of note, considering the deactivating nature of the carbonyl group. Two exceptions to the general trend have been observed. The first one is the double metalation of the ylide [PhMe2NCHC(O)Ph], which incorporates one Pd at each Ph. The second one is the palladation of the phenylpyridine derivative, which occurs at the pyridinic 2-phenyl ring and produces a six-membered palladacycle.Funding by the Ministerio de Ciencia e Innovacion (MICINN) (Spain, Project CTQ2008-01784) and Gobierno de Aragon (Grupo E97) is gratefully acknowledged. L.C. thanks Consejo Superior de Investigaciones Cientificas and MICINN for a Juan de la Cierva contract.Peer reviewe