Advanced opto-electronics materials by fullerene and acetylene scaffolding

Functional π-systems with unusual opto-electronic properties are intensively investigated from both fundamental research and technological application viewpoints. This article reports on novel π-conjugated systems obtained by acetylenic and fullerene scaffolding. Linearly conjugated acetylenic nanorods, consisting of monodisperse poly(triacetylene) (PTA) oligomers and extending up to 18 nm length, were prepared to investigate the limits of effective conjugation and to explore at which length a monodisperse oligomer reaches the properties of an infinite polydisperse polymer. With the cyanoethynylethenes (CEEs), a powerful new class of electron acceptors is introduced that undergo intense intramolecular charge-transfer (CT) interactions with appended donors. Macrocyclic scaffolds with unusual opto-electronic properties are perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes bearing peripheral dialkylanilino donor groups. Extended porphyrin-fullerene conjugates are investigated for their novel photophysical and efficient multicharge storage properties. Self-assembly of fullerenes and porphyrins, governed by weak interactions between the two components, leads to unprecedented nanopatterned surfaces that are investigated by scanning tunneling microscopy (STM

Conjugation and optoelectronic properties of acetylenic scaffolds and charge-transfer chromophores

Our group started a research program in acetylene chemistry in 1987; since then, an intense research effort led to a fascinating journey into acetylenic scaffolding, aimed at exploring conjugative and optoelectronic properties of acetylenic chromophores. This journey included the generation of a unique molecular construction kit for acetylenic scaffolding, consisting of (E)-1,2-diethynylethenes [DEEs, (E)-hex-3-ene-1,5-diynes], tetraethynylethenes (TEEs, 3,4-diethynylhex-3-ene-1,5-diynes), chiral 1,3-diethynylallenes (DEAs, hepta-3,4-diene-1,6-diynes), 1,4-di and 1,1,4,4-tetraethynylbutatrienes, chiral trialkynylmethanes, and 1,1,2,2-tetraethynylethanes. These building modules were subsequently applied to the synthesis of carbon-rich architectures extending into one, two, and three dimensions. They include multinanometer-long monodisperse oligomers as models for infinite acetylenic polymers, molecular switches, perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes, and an octamethoxy-substituted expanded cubane with a central C56 core. Donor-substituted cyanoethynylethenes (CEEs) and 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) were introduced as new push-pull chromophores featuring intense intramolecular charge-transfer (CT) interactions. Dendritic multivalent CT chromophores were constructed using atom-economic, "click"-like reactions, and these systems were shown to behave as "molecular batteries", featuring exceptional electron uptake and storage capacity. The research finally led to the development of an unprecedented cascade reaction for the preparation of dendritic and oligomeric donor-acceptor (D-A) molecules. New [AB]-type oligomers become accessible in domino reactions involving repetitive sequences of [2+2] cycloadditions of tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) to polyynes, followed by retro-electrocyclization

Supramolecular Fullerene Materials

With its unique physical and chemical properties, buckminsterfullerene C60 is becoming an attractive functional component for incorporation into three-dimensional molecular assemblies and supramolecular arrays with potential applications as advanced materials. In this article, we discuss the self-organization of C60 derivatives into ordered fullerene thin films using Langmuir techniques. Subsequently, it is shown how metal ion complexation at a crown ether site in tight proximity to the fullerene surface perturbs the electronic structure of the carbon sphere. Covalently modified fullerenes are used for the construction of interlocked molecules, such as rotaxanes and catenanes, with fascinating topologies. Finally, the formation of a C60-containing tetracationic cyclophane by PtII-directed self-assembly of two di(pyridyl)methanofullerene moieties is presented. These recent advances have become possible only through the development of a new synthetic methodology, which provides controlled, regioselective access to multiply functionalized fullerene derivatives

Nonplanar Push–Pull Chromophores for Opto-Electronic Applications

Donor-substituted cyanoethynylethenes (CEEs) are planar push–pull chromophores featuring intense intramolecular charge-transfer (CT) interactions and high third-order optical nonlinearities. Their thermal stability allows for the formation of crystalline thin films by vapor-phase deposition. On the other hand, high-quality amorphous thin films are preferred for opto-electronic applications and such films can be prepared using nonplanar push–pull chromophores with a less pronounced propensity to crystallize. By taking advantage of a versatile, atom-economic 'click-chemistry'-type transformation, involving a formal [2 + 2] cycloaddition of tetracyanoethene (TCNE) to electron-rich alkynes, followed by cycloreversion, stable donor-substituted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) are obtained in high yield and large quantities. These nonplanar push–pull chromophores also feature intense intramolecular CT and, in many cases, high third-order optical nonlinearities. Some of these compounds form high-optical-quality amorphous thin films by vapor-phase deposition, and first applications in next-generation opto-electronic devices have already been demonstrated. Chiral derivatives display high helical twisting power and are efficient dopants to translate molecular into macroscopic chirality, by switching nematic into cholesteric liquid crystalline phases

Cadaver dogs and the deathly hallows—a survey and literature review on selection and training procedure

Human remains detection dogs (HRDDs) are powerful police assets to locate a corpse. However, the methods used to select and train them are as diverse as the number of countries with such a canine brigade. First, a survey sent to human remains searching brigades (Ncountries = 10; NBrigades = 16; NHandlers = 50; Nquestions = 9), to collect their working habits confirmed the lack of optimized selection and training procedures. Second, a literature review was performed in order to outline the strengths and shortcomings of HRDDs training. A comparison between the scientific knowledge and the common practices used by HRDDs brigade was then conducted focusing on HRDDs selection and training procedures. We highlighted that HRDD handlers select their dogs by focusing on behavioral traits while neglecting anatomical features, which have been shown to be important. Most HRDD handlers reported to use a reward-based training, which is in accordance with training literature for dogs. Training aids should be representative of the odor target to allow a dog to reach optimal performances. The survey highlighted the wide diversity of homemade training aids, and the need to optimize their composition. In the present document, key research topics to improve HRDD works are also provided.Peer reviewe

The Non-Mevalonate Pathway to Isoprenoid Biosynthesis:A Potential Source of New Drug Targets

Isoprenoids are an essential class of natural products with a myriad of biological functions. All isoprenoids are assembled using two common five-carbon precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) that are biosynthesized via two completely independent routes: the mevalonate and the non-mevalonate pathway. While the former is used by humans, the latter is employed exclusively by a number of important pathogens such as the malarial Plasmodium falciparum parasite or the tuberculosis-causing Mycobacterium tuberculosis bacterium. Hence, the constituent enzymes are potentially very interesting drug targets in the ongoing fight against diseases, whose treatment has been complicated by the emergence of multi-drug resistance. After a short description of the biosynthetic pathway, an overview will be given on the known inhibitors of the individual enzymes

Design and synthesis of Aviram-Ratner-type dyads and rectification studies in Langmuir-Blodgett (LB) films

The design and synthesis of Aviram–Ratner-type molecular rectifiers, featuring an anilino-substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ-spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X-ray analysis. The photophysical properties of the TTF-BCO-exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.This work was supported by the ERC Advanced grant no.246637 (“OPTELOMAC”) and the Swiss National Science Foundation (SNF). A.D.F.acknowledges the NSF-IRFP (USA) for a postdoctoral fellowship. S.M. and P.C. are grateful for financial assistance from Ministerio de Ciencia e Innovación from Spainin the framework of grants CTQ2012-33198 and CTQ2013-50187-EXP.Peer Reviewe

Self-assembly and two-dimensional spontaneous resolution of cyano-functionalized [7]helicenes on Cu111

Birds of a feather flock together: STM and DFT studies provide the first example of spontaneous chiral resolution of a helicene on a surface. Racemic 6,13-dicyano[7]helicene forms fully segregated domains of pure enantiomers (2D conglomerate) on Cu(111). The propensity of the system to optimize intermolecular CN⋅⋅⋅HC(Ar) hydrogen bonding and CN⋅⋅⋅CN dipolar interactions translates into chiral recognition with preferential assembly of homochiral molecules