Carbon quantum dots/block copolymer ensembles for metal-ion sensing and bioimaging.

Fluorescent carbon quantum dots (CQDs) rich in amine moieties that can be easily protonated under acidic conditions were electrostatically interacted with diblock copolymer poly[sodium(carboxylate sulfamate) isoprene]-b-poly(ethylene oxide) (CSS-IEO-3) possessing negatively charged sulfamate and carboxylate species on the CSS part of the diblock copolymer. The so-formed CQDs/CSS-IEO-3 material was found to be stable in a neutral and high salinity environment, which is critical when aiming for biological applications. Moreover, the photoluminescence of CQDs within CQDs/CSS-IEO-3, with emission at 420 nm upon excitation at 320 nm, was unaffected by pH and salinity changes, denoting the absence of significant aggregation phenomena and highlighting the potential of CQDs/CSS-IEO-3 for bioimaging. The photoluminescence of CQDs/CSS-IEO-3 was employed to develop a selective and sensitive method for the facile detection of Fe3+, in the presence of other metal salts, with a detection limit of 8.37 µM. Furthermore, integration of bovine serum albumin (BSA) furnished the three-component CQDs/CSS-IEO-3·BSA nanoensemble, without causing cytotoxicity when subjected to RKO human colon adenocarcinoma cell line. Evidently, confocal fluorescence microscopy allowed the imaging of CQDs/CSS-IEO-3·BSA within living cells, and illustrated its application potential for bioimaging and drug delivery.

Photoinduced charge separation in an oligophenylenevinylene-based Hamilton-type receptor supramolecularly associating two C60-barbiturate guests.

The supramolecular association of an oligophenylene-vinylene (OPV)-based Hamilton-type receptor 1 with C60-barbiturate 2, via six hydrogen bonds per OPV terminal, forming C60/OPV/C60 complex 3 is presented. The particular host-guest motif expressed in 3 ensures strong interactions between the discrete components of the complex based on the multiple hydrogen bonding interactions as conveyed by an association constant greater than 10(5) M(-1). Furthermore, femto- and nano-second transient absorption studies disclose photoinduced charge separation from (1)OPV* to C60 within 9.4 ps. The observed ultrafast charge separation phenomena in the C60/OPV/C60 complex open up wide avenues toward the efficient construction of new materials for optoelectronic and solar cell applications.

Single-Step Functionalization and Exfoliation of Graphene with Polymers under Mild Conditions.

The simultaneous polymer functionalization and exfoliation of graphene sheets by using mild bath sonication and heat treatment at low temperature is described. In particular, free-radical polymerization of three different vinyl monomers takes place in the presence of graphite flakes. The polymerization procedure leads to the exfoliation of graphene sheets and at the same time the growing polymer chains are attached onto the graphene lattice, which gives solubility and stability to the final graphene-based hybrid material. The polymer-functionalized graphene sheets possess fewer defects as compared with previously reported polymer-functionalized graphene. The success of the covalent functionalization and exfoliation of graphene was confirmed by using a variety of complementary spectroscopic, thermal, and microscopy techniques, including Raman, IR and UV/Vis spectroscopy, thermogravimetric analysis, and transmission electron microscopy.

Oligothiophene/graphene supramolecular ensembles managing light induced processes: preparation, characterization, and femtosecond transient absorption studies leading to charge-separation.

Advances in organic synthetic chemistry combined with the exceptional electronic properties of carbon allotropes, particularly graphene, is the basis used to design and fabricate novel electron donor-acceptor ensembles with desired properties for technological applications. Thiophene-based materials, which are mainly thiophene-containing polymers, are known for their notable electronic properties. In this frame moving from polymer to oligomer forms, new fundamental information would help for a better understanding of their electrochemical and photophysical properties. Furthermore, a successful combination of their electronic properties with those of graphene is a challenging goal. In this study, two oligothiophene compounds, which consist of three and nine thiophene-rings and are abbreviated 3T and 9T, respectively, were synthesized and noncovalently associated with liquid phase exfoliated few-layered graphene sheets (abbreviated eG), thus forming donor-acceptor 3T/eG and 9T/eG nanoensembes. Markedly, intra-ensemble electronic interactions between the two components in the ground and excited states were evaluated with the aid of UV-Vis and photoluminescence spectroscopy. Furthermore, redox assays revealed the one-electron oxidation of 3T accompanied by one-electron reduction due to eG in 3T/eG, whereas there were two reversible one-electron oxidations of 9T accompanied by one-electron reduction of eG9T/eG. The electrochemical band gap for the 3T/eG and 9T/eG ensembles were calculated and verified, in which the negative free-energy change for the charge-separated state of 3T/eG and 9T/eGvia the singlet excited state of 3T and 9T, respectively, were thermodynamically favorable. Finally, the results of transient pump-probe spectroscopy studies at the femtosecond time scale were supportive of charge transfer type interactions in the 3T/eG and 9T/eG ensembles. The estimated rates for intra-ensemble charge separation were found to be 9.52 × 10(9) s(-1) and 2.2 × 10(11) s(-1), respectively, for 3T/eG and 9T/eG in THF, which reveal moderate to ultrafast photoinduced events in the oligothiophene/graphene supramolecular ensembles.

Functionalized multi-walled carbon nanotubes in an aldol reaction.

The covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde was evaluated for the first time, showing to proceed almost quantitatively in aqueous media. Furthermore, several amino-modified MWCNTs were prepared and examined in the particular aldol reaction. These new hybrid materials exhibited an enhanced catalytic activity in water, contrasting with the pristine MWCNTs as well as the parent organic molecule, which failed to catalyze the reaction efficiently. Furthermore, the modified MWCNTs proved to catalyze the aldol reaction even after three repetitive cycles. Overall, a green approach for the aldol reaction is presented, where water can be employed as the solvent and modified MWCNTs can be used as catalysts, which can be successfully recovered and reused, while their catalytic activity is retained.

Photocatalytic applications with CdS • block copolymer/exfoliated graphene nanoensembles: hydrogen generation and degradation of Rhodamine B.

Amphiphilic block copolymer poly(isoprene-b-acrylic acid) (PI-b-PAA) was used to stabilize exfoliated graphene in water, allowing the immobilization of semiconductor CdS nanoparticles forming CdS â€¢ PI-b-PAA/graphene. Characterization using high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy proved the success of the preparation method and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS â€¢ PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS â€¢ PI-b-PAA/graphene, in the presence of ammonium formate as a quencher for the photogenerated holes, resulted in the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (>80 ± 4% at 20 min; 100% at 24 min), much faster and more efficient compared to when reference CdS â€¢ PI-b-PAA was used as the photocatalyst (<30 ± 3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS â€¢ PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS â€¢ PI-b-PAA/graphene was rationalized in terms of effective separation of holes and electrons, contrary to reference CdS â€¢ PI-b-PAA, in which rapid recombination of the hole-electron pair is inevitable due to the absence of exfoliated graphene as a suitable electron acceptor.

Photocatalytic application of nanosized CdS immobilized onto functionalized MWCNTs.

Nanosized semiconductor CdS immobilized onto modified multi-walled carbon nanotubes (MWCNTs) carrying poly(amidoamine) dendron units were visualized by HR-TEM. Evidently, spherical CdS nanoparticles 3-5 nm in diameter were identified. Moreover, EDX spectroscopy gave additional spectroscopic proof of the presence of CdS in the CdS-MWCNTs hybrid material. The photocatalytic activity of CdS-MWCNTs toward the decomposition of rhodamine B (RhB) was examined by monitoring spectral changes in the characteristic absorption band of RhB centred at 554 nm. The latter absorption band of RhB was found to continuously depress during visible light irradiation in the presence of CdS-MWCNTs, with faster kinetic rates as compared with the case when only reference CdS was present. The current result was rationalized in terms of efficient photoinduced electron-transfer from CdS to MWCNTs within the intrahybrid CdS-MWCNTs. In this frame, the suggested mechanism for the high and fast photocatalytic decomposition of RhB supports the accumulation of electrons in MWCNTs, which then react with molecular oxygen, thus reducing it to superoxide radical anion O2˙(-) responsible for the generation of the highly reactive species of HO˙ and HOO˙. The latter together with the holes generated in photoexcited CdS were responsible for the decomposition of RhB. Finally, the photocatalyst CdS-MWCNTs was recovered and efficiently reused for four consecutive catalytic cycles, thus highlighting its wider applicability in removing organic pollutants from water.

Linear and nonlinear optical properties of [60]fullerene derivatives.

Using a wide variety of quantum-chemical methods we have analyzed in detail the linear and non-linear optical properties of [60]fullerene-chromophore dyads of different electron-donor character. The dyads are composed of [60]fullerene covalently linked with 2,1,3-benzothiadiazole and carbazole derivatives. Linear scaling calculations of molecular (hyper)polarizabilities were performed using wave function theory as well as density functional theory (DFT). Within the former approach, we used both semiempirical (PM3) and ab initio (Hartree-Fock and second-order Møller-Plesset perturbation theory) methods. Within the latter approach only the recently proposed long-range (LRC) schemes successfully avoid a large overshoot in the value obtained for the first hyperpolarizability (ß). Calculations on model fullerene derivatives establish a connection between this overshoot and the electron-donating capability of the substituent. Substitution of 2,1,3-benzothiadiazole by the triphenylamine group significantly increases the electronic first and second hyperpolarizabilities as well as the two-photon absorption cross section. For [60]fullerene-chromophore dyads we have, additionally, observed that the double harmonic vibrational contribution to the static beta is much larger than its electronic counterpart. The same is true for the dc-Pockels ß as compared to the static electronic value, although the vibrational term is reduced in magnitude; for the intensity-dependent refractive index the vibrational and electronic terms are comparable. A nuclear relaxation treatment of vibrational anharmonicity for a model fulleropyrrolidine molecule yields a first-order contribution that is substantially more important than the double harmonic term for the static ß.

Resonant processes and Coulomb interactions in (C59N)2.

We have determined the on-site molecular Coulomb interaction energy U of a (C59N)2 bulk film and find values ranging from 1.10+/-0.10 eV for the highest occupied molecular orbital to 1.35+/-0.10 eV for the deeper lying orbitals, comparable to values found in C60. The on-site Coulomb interaction between a carbon core hole and valence electrons, Uc, is, however, substantially lower than in C60 at 1.35+/-0.07 eV. Resonant photoemission (RESPES) results show a weakened participator decay channel, especially around the N 1s threshold, where resonance of the highest occupied molecular orbital shoulder is absent. Near-edge x-ray absorption fine structure and constant initial state measurements, taken in parallel with the RESPES data, indicate, however, that matrix element effects cannot be ruled out.

Element-specific probe of the magnetic and electronic properties of Dy incar-fullerenes.

The magnetic and electronic properties of a single atom and a pair of Dy atoms encapsulated inside fullerene carbon cages have been examined using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) as well as resonant photoelectron spectroscopy (RESPES) across the Dy M(4,5)-edge. The comparison of the measured XAS spectra with multiplet calculations indicates that the encaged Dy has a 4f( 9) configuration. The presence of Dy 5d spectral weight in the valence band is not detected by RESPES, indicating that Dy is in a formally trivalent state. The evolution of the encaged Dy orbital and spin moments of the 4f orbitals as a function of the applied magnetic field and temperature has been obtained from XMCD measurements. At 6.9 T and 4 K, both the orbital and the spin magnetic moments of the encaged Dy 4f electrons are dramatically smaller than those expected for the free Dy(3+) at saturation.

Multipole induced splitting of metal-cage vibrations in crystalline endohedral D2d-M2@C84 dimetallofullerenes.

Metal-carbon cage vibrations of crystalline endohedral D2d-M2@C84 (M=Sc,Y,Dy) dimetallofullerenes were analyzed by temperature dependent Raman scattering and a dynamical force field model. Three groups of metal-carbon cage modes were found at energies of 35-200 cm(-1) and assigned to metal-cage stretching and deformation vibrations. They exhibit a textbook example for the splitting of molecular vibrations in a crystal field. Induced dipole-dipole and quadrupole-quadrupole interactions account quantitatively for the observed mode splitting. Based on the metal-cage vibrational structure it is demonstrated that D2d-Y2@C84 dimetallofullerene retains a monoclinic crystal structure up to 550 K and undergoes a transition from a disordered to an ordered orientational state at a temperature of approximately 150 K.

Photooxidation of olefins sensitized by bisazafullerene (C(59)N)(2) and hydroazafullerene C(59)HN: product analysis, emission of singlet oxygen, and transient absorption spectroscopy.

The photooxidation reactions of olefins sensitized by the excited triplet states of bisazafullerene (C(59)N)(2) and hydroazafullerene C(59)HN have been studied. Oxidation yields were compared with those of pristine C(60). The singlet oxygen yields are also determined directly from the emission intensities, which are in good agreement with the oxidation yields. The triplet states of (C(59)N)(2) and C(59)HN have been identified by the time-resolved spectroscopic method by observing the triplet-triplet absorption spectra, which decay in the presence of oxygen. It has been proven that (C(59)N)(2) and C(59)HN have the ability to sensitize the reactions via singlet oxygen in about half of the efficiency of that of pristine C(60). For both azafullerenes, the triplet lifetimes are shorter than that of pristine C(60), which may be related to the nitrogen atom embedded in the C(60) moiety.

Cis- and trans-N-benzyl-octahydrobenzo[g]quinolines. Adrenergic and dopaminergic activity studies.

In vitro assays on a series of cis- and trans-octahydrobenzo[g]quinolines indicated an unusual trend of affinities at the dopaminergic receptors and alpha adrenoceptors. The trans N-benzyl analogues exhibited affinity at the alpha2 as well as the D1-like receptors whereas their N-unsubstituted congeners showed a distinct preference for the alpha2 adrenoceptor. Enhanced activity for the alpha2 receptors was also exhibited by the cis N-benzylated isomers. These observations are interpreted by theoretical calculations.

Fullerenes in medicinal chemistry and their biological applications.

The isolation and preparation ten years ago of the fullerenes in bulk quantities, sparked off a truly remarkable interdisciplinary research activity, encompassing diverse fields of chemistry, physics, materials science and medicinal chemistry. Pharmaceutical and biological studies have revealed that fullerene-based compounds exhibit various types of biological activity either in vitro or in vivo and are discussed in this review.

Organic chemistry with heterofullerenes: photosensitized oxygenation of alkenes

Heterofullerenes C(59)HN and (C(59)N)(2) sensitize the reaction of olefins with molecular oxygen under photolytic conditions. 2-Methyl-2-butene and alpha-terpinene undergo ene and Diels-Alder photooxygenation reactions, respectively, even in the presence of minute amounts of azafullerenes to produce the corresponding peroxides.

N-(Iodopropenyl)-octahydrobenzo[f]- and -[g]quinolines: synthesis and adrenergic and dopaminergic activity studies.

A series of N-(iodopropenyl)-octahydrobenzo[f]- and -[g]quinolines was synthesized and assayed in vitro for their dopaminergic and alpha-adrenergic activity. Structure-activity relationship (SAR) analysis revealed that the tested benzoquinolines exhibited activity at the D1 rather than the D2 receptor sites in contrast to the D2 receptor subfamily activity reported for their aminotetralin congeners. N-Iodopropenyl substitution was apparently a decisive factor for D1 activity independent of ring substitution pattern. Considering the structural factors influencing alpha-adrenergic activity, in a general trend, N-iodopropenyl analogues were alpha1-active, with the ring-hydroxylated congeners exhibiting the highest affinity. Affinity to the alpha2 receptor was even higher with no detectable trend of SAR. However, a combination of the linear arrangement of the [g]-ring system, combined with the ring hydroxyl and the N-iodopropenyl substitution in compound 5c, resulted in a significant enhancement of alpha2 activity in this series as demonstrated by an IC50 value of 0.5 nM. A new synthetic approach to the [g]benzoquinoline system is also described.