Georgia Pagona

Carbon nanotubes: materials for medicinal chemistry and biotechnological applications.

Carbon nanotubes are considered as molecular wires exhibiting novel properties for diverse applications including medicinal and biotechnological purposes. Surface chemistry on carbon nanotubes results on their solubilization in organic solvents and/or aqueous/physiological media. Herein, we will present how interfacing such novel carbon-based nanomaterials with biological systems may lead to new applications in diagnostics, vaccine and drug delivery. Recent developments in this rapidly growing field will be presented thus suggesting exciting opportunities for the utilization of carbon nanotubes as useful tools for biotechnological applications. Emphasis will be placed in the integration of biomaterials with carbon nanotubes, which enables the use of such hybrid systems as biosensor devices, immunosensors and DNA-sensors.

COMPOSITION AND INSECT ATTRACTING ACTIVITY OF THE ESSENTIAL OIL OF Rosmarinus officinalis

The essential oil and a number of extracts of Rosmarinus officinalisL. in solvents of increasing polarity were isolated, and their components identified and tested as pest control agents. Ethanol and acetone extracts attract grape berry moth Lobesia botrana. However, none of the extracts had a significant effect on western flower thrips Frankliniella occidentalis, which is attracted by 1,8-cineole, a major essential oil component.

Properties, applications and functionalisation of carbon nanohorns

Functionalisation of carbon nanohorns (CNHs), by covalent bonding or non-covalent supramolecular interacting organic moieties, overcomes insolubility problems and enhances manipulation and processibility. The present review paper summarises our recent accomplishments in the field of chemical modification of CNHs together with various critical and important aspects related to their synthesis, morphology, properties and applications. Moreover, the design and preparation of some novel hybrid materials consisting of CNHs and electron donors will be presented.

Nanocrystalline/microcrystalline materials based on lead-halide units

The preparation, photoluminescence (PL) spectra and related properties of particulate (nanocrystalline/microcrystalline) materials based on Pb(BrxCl1−x)3, Pb(BrxI1−x)3, and Pb(ClxI1−x)3 (x = 0–1) units, in several macroscopic forms, are reported. The materials in the form of suspensions in toluene or in toluene containing polymethyl methacrylate (PMMA) were obtained from the corresponding n-layer materials (or their precursors), mainly, by a titration-like method. This is the injection of solutions of the corresponding compounds with the Pbn(BrxCl1−x)3n+1, Pbn(BrxI1−x)3n+1, and Pbn(ClxI1−x)3n+1 (n > 2) units, respectively, into neat toluene or toluene–PMMA, with parallel observation of the PL-spectra. With this method, the mass of the lead-halide materials is controlled and the position of the low frequency PL band could be tuned in a wide spectral range, i.e., from ca. 400 to ca. 700 nm. From the suspensions in toluene the corresponding materials in the form of precipitates (powders) were obtained by centrifugation and decantation. From suspensions in toluene–PMMA, the corresponding materials in the form of composite thin films (of PMMA-matrix) were obtained by drop-casting, deep-coating and/or spin-coating techniques. So, blue, green, yellow and red narrow PL-band (of 20–35 nm) emitters (in forms of suspensions, powders and films) were obtained and their PL and optical absorption spectra were investigated further. The PL-intensity varies as in the case of CsPbBr3 particles in a CsBr matrix. Also, some similarities with the spectra of metal chalcogenide quantum dots were found. They were suggested as candidate materials for several optical and optoelectronic applications.

Solvent-free microwave-assisted Bingel reaction in carbon nanohorns

In this paper we exploit the benefits of microwave-assisted functionalization of carbon nanohorns (CNHs). Using Bingel reaction conditions we have successfully incorporated malonyl moieties in CNHs. The resulting hybrid materials were characterized by diverse and complementary analytical techniques, including Raman, UV-Vis and photoluminescence spectroscopy, transmission electron microscopy, thermogravimetric analysis, while electrochemistry was employed to determine possible variations in the energy levels when photoactive units were grafted onto the skeleton of CNHs.

Azafullerenes encapsulated within single-walled carbon nanotubes.

Methods of insertion of azafullerenes in single-walled carbon nanotubes (SWNTs) at different temperatures were investigated, while the effects of the conditions applied on the structure of azafullerene-based peapods, namely, C59N@SWNTs, were explored. Morphological characteristics of C59N@SWNTs were assessed and evaluated by means of high-resolution transmission electron microscopy (HR-TEM). Pathways and chemical reactions that occur upon encapsulation of C59N within SWNTs were evaluated. Monomeric azafullerenyl radical C59N. as inserted into SWNTs at high temperature, from purified (C59N)2 in the gas phase, can undergo a variety of different transformations forming dimers, oligomers or existing in its monomeric form inside SWNTs due to the stabilization effect by nanotube side walls. However, under milder conditions, that is, at lower temperature, bisazafullerene (C59N)2 can be inserted into SWNTs in its pristine dimeric form.

Photoinduced electron-transfer processes of carbon nanohorns with covalently linked pyrene chromophores: charge-separation and electron-migration systems

Carbon nanohorns (CNHs) have been covalently functionalized with pyrene chromophores forming dispersible nanohybrids in CH2Cl2. Their photo-physical properties have been investigated by complementary steady-state and time-resolved absorption and fluorescence spectroscopies as well as electrochemistry. Upon photo-excitation of CNH–pyrene nanohybrids, in the presence of hexyl-viologen dication (HV2+) and a hole trap, the HV˙+ was accumulated in the polar organic solvent. This observation suggests that photoinduced charge-separation takes place, producing CNH˙−–pyrene˙+, which was further confirmed by observing pyrene˙+ in the nanosecond time-scale transient absorption spectra. From CNH˙−, an electron is migrated to HV2+ and a hole shifts from pyrene˙+ to the hole trap, which suppresses the back electron transfer resulting in the persistence of HV˙+.

The impact of thienothiophene isomeric structures on the optoelectronic properties and photovoltaic performance in quinoxaline based donor–acceptor copolymers

The influence of the monomers isomeric structure on the optical, electrochemical, charge transporting properties and photovoltaic performance of donor–acceptor (D–A) conjugated polymers has been demonstrated for the first time by studying two D–A copolymers consisting of bis(3-octyloxy)phenyl)quinoxaline as the electron deficient unit and the two isomeric structures of thienothiophene (thieno[3,2-b]thiophene and thieno[2,3-b]thiophene) as the electron rich units. The drastic effect of incorporating two different isomeric structures on the polymer backbone of these copolymers, manifests in changes observed in their optical, electrochemical and charge transporting properties. In contrast, the overall photovoltaic performance of the copolymers is similar, but distinct differences in the device photocurrents occur. These differences were attributed to morphology variations rather than the balanced mobility ratio. For further developments in the field, the isomeric structures of different functional monomers should be considered in the designing of new materials with even superior performance.

A New Approach for the Photosynthetic Antenna–Reaction Center Complex with a Model Organized Around an s‐Triazine Linker

Two new artificial mimics of the photosynthetic antenna-reaction center complex have been designed and synthesized (BDP-H2 P-C60 and BDP-ZnP-C60). The resulting electron-donor/acceptor conjugates contain a porphyrin (either in its free-base form (H2P) or as Zn-metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C60-X-NH2 (X=spacer). In both cases, the three different components were connected by s-triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star-type arrangement of the three photo- and redox-active components around the central s-triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy- and electron-transfer properties of the resulting electron-donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP-H2P-C60 and BDP-ZnP-C60 with those of BDP-H2P, BDP-ZnP and BDP-C60, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H2P or ZnP. This is then followed by an electron transfer to C60, yielding the formation of the singlet charge-separated states, namely BDP-H2(·+) -C60(·-) and BDP-ZnP(·+)-C60(·-). As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis.

Donor–acceptor graphene-based hybrid materials facilitating photo-induced electron-transfer reactions

Summary Graphene research and in particular the topic of chemical functionalization of graphene has exploded in the last decade. The main aim is to increase the solubility and thereby enhance the processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. To this end, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets that are soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. However, it was obvious that the high-defect framework of graphene oxide cannot be readily utilized in applications that are governed by charge-transfer processes, for example, in solar cells. Alternatively, exfoliated graphene has been applied toward the realization of some donor–acceptor hybrid materials with photo- and/or electro-active components. The main body of research regarding obtaining donor–acceptor hybrid materials based on graphene to facilitate charge-transfer phenomena, which is reviewed here, concerns the incorporation of porphyrins and phthalocyanines onto graphene sheets. Through illustrative schemes, the preparation and most importantly the photophysical properties of such graphene-based ensembles will be described. Important parameters, such as the generation of the charge-separated state upon photoexcitation of the organic electron donor, the lifetimes of the charge-separation and charge-recombination as well as the incident-photon-to-current efficiency value for some donor–acceptor graphene-based hybrids, will be discussed.