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1.
Chemistry ; 24(46): 11954-11960, 2018 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-29603481

RESUMO

Salophens and Salens are Schiff bases generated through the condensation of two equivalents of salicylaldehyde with either 1,2-phenylenediamines or aliphatic diamines, respectively. Both ligands have been extensively exploited as key building blocks in coordination chemistry and catalysis. In particular, their metal complexes have been widely used for various catalytical transformations with high yield and selectivity. Through the modification of the phenol unit it is possible to tune the steric hindrance and electronic properties of Salophen and Salen. The introduction of long aliphatic chains in salicylaldehydes can be used to promote their self-assembly into ordered supramolecular structures on solid surfaces. Herein, we report a novel method towards the facile synthesis of robust and air-stable [Al(Salophen)] derivatives capable of undergoing spontaneous self-assembly at the graphite/solution interface forming highly-ordered nanopatterns. The new synthetic approach relies on the use of [MeAlIII (Salophen)] as a building unit to introduce, via a simple acid/base reaction with functionalized acidic phenol derivatives, selected frameworks integrating multiple functions for efficient surface decoration. STM imaging at the solid/liquid interface made it possible to monitor the formation of ordered supramolecular structures. In addition, the redox properties of the Salophen derivatives functionalized with ferrocene units in solution and on surface were unraveled by cyclic voltammetry. The use of a five-coordinate aluminum alkyl Salophen precursor enables the tailoring of new Salophen molecules capable of undergoing controlled self-assembly on HOPG, and thereby it can be exploited to introduce multiple functionalities with subnanometer precision at surfaces, ultimately forming ordered functional patterns.

2.
Phys Chem Chem Phys ; 18(22): 15025-38, 2016 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-27194584

RESUMO

The synthesis of two A2B2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc(ii) () and {5,15-bis-(carbazol-3-yl-ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc(ii) (), is reported. Their photophysical properties were studied by steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a large bathochromic shift of all the absorption bands, a notable increase in the absorption coefficient of the Q(0,0) band, and higher fluorescence quantum yield compared to porphyrin , with two unsubstituted meso positions. Cyclic voltammetry and digital simulation show that electrogenerated radical ions of are more stable than those of . The lack of substituents at the meso positions of leads to dimerization reactions of the radical cation. Despite this, the annihilation reaction of and produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical experiments demonstrate that the electroreduction of leads to a strong absorption band that might quench the ECL.

3.
ACS Nano ; 7(1): 811-7, 2013 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-23244166

RESUMO

The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp(2) carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidation-reduction methods, allowing a definite control of the surface properties.


Assuntos
Materiais Biomiméticos/química , Grafite/química , Grafite/efeitos da radiação , Nanoestruturas/química , Fotossíntese , Complexo de Proteína do Fotossistema II/química , Folhas de Planta/química , Materiais Biomiméticos/efeitos da radiação , Luz , Teste de Materiais , Nanoestruturas/efeitos da radiação , Nanoestruturas/ultraestrutura , Propriedades de Superfície
4.
Nanoscale ; 4(3): 813-23, 2012 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-22159165

RESUMO

Quantum-dot Cellular Automata (QCA) exploit quantum confinement, tunneling and electrostatic interaction for transistorless digital computing. Implementation at the molecular scale requires carefully tailored units which must obey several structural and functional constraints, ranging from the capability to confine charge efficiently on different 'quantum-dot centers'-in order to sharply encode the Boolean states-up to the possibility of having their state blanked out upon application of an external signal. In addition, the molecular units must preserve their geometry in the solid state, to interact electrostatically in a controlled way. Here, we present a novel class of organometallic molecules, 6-3,6-bis(1-ethylferrocen)-9H-carbazol-9-yl-6-hexan-1-thiols, which are engineered to satisfy all such crucial requirements at once, as confirmed by electrochemistry and scanning tunneling microscopy measurements, and first principles density functional calculations.

5.
ACS Nano ; 5(12): 9892-7, 2011 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-22092255

RESUMO

We present a resonance Raman study of electrochemical charge transfer doping on polyelectrolyte single-walled carbon nanotubes (SWNTs) in solution. Changes in the intensity of the radial breathing modes of well-identified SWNTs are measured as a function of the electrochemical potential. The intensity is maximum when the nanotubes are neutral. Unexpectedly, the Raman signal decreases as soon as charges are transferred to the nanotubes, leading to intensity profiles that are triangular for metallic and trapezoidal for semiconducting nanotubes. A key result is that the width in energy of the plateaus for the semiconducting nanotubes is roughly equal to the optical gap (rather than the free carrier gap). While these experiments can be used to estimate the energy levels of individual nanotubes, strong dynamical screening appears to dominate in individual SWNT polyelectrolytes so that only screened energy levels are being probed.


Assuntos
Cristalização/métodos , Galvanoplastia/métodos , Nanotubos de Carbono/química , Nanotubos de Carbono/ultraestrutura , Análise Espectral Raman/métodos , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
7.
Chem Commun (Camb) ; 47(19): 5470-2, 2011 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-21483919

RESUMO

Thermodynamics drive the spontaneous dissolution of a graphite intercalation compound (GIC) KC(8) in NMP to form stable solutions. Reduction potential of graphene is measured at +22 mV vs. SCE. Single layer graphene flakes (ca. 1 µm(2)) have been unambiguously identified by electron diffraction.

8.
Nat Chem ; 2(10): 826-31, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20861897

RESUMO

Water is the renewable, bulk chemical that nature uses to enable carbohydrate production from carbon dioxide. The dream goal of energy research is to transpose this incredibly efficient process and make an artificial device whereby the catalytic splitting of water is finalized to give a continuous production of oxygen and hydrogen. Success in this task would guarantee the generation of hydrogen as a carbon-free fuel to satisfy our energy demands at no environmental cost. Here we show that very efficient and stable nanostructured, oxygen-evolving anodes are obtained by the assembly of an oxygen-evolving polyoxometalate cluster (a totally inorganic ruthenium catalyst) with a conducting bed of multiwalled carbon nanotubes. Our bioinspired electrode addresses the one major challenge of artificial photosynthesis, namely efficient water oxidation, which brings us closer to being able to power the planet with carbon-free fuels.


Assuntos
Nanotubos de Carbono , Água/química , Catálise , Eletroquímica , Análise Espectral Raman
9.
Chem Commun (Camb) ; (40): 4867-74, 2008 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-18931725

RESUMO

Since their very first days, electron transfer has always played a special role in carbon nanotubes' life. In view of their structural and electronic uniqueness, carbon nanotubes have been proposed either as bulk electrode materials for sensing and biosensing in advanced electrochemical devices, or as molecular-sized electrodes for very fast electrode kinetics investigations. Alternatively, electron transfer has been used to probe the electronic properties of carbon nanotubes by either direct voltammetric inspection or coupling with spectroscopic techniques, ultimately allowing, in the case of true solutions of individual uncut single-walled carbon nanotubes (SWNTs), to single-out their redox potentials as a function of diameter. For their redox properties, as emerged from these studies, SWNTs represent unique building blocks for the construction of photofunctional nanosystems to be used in efficient light energy conversion devices.

10.
J Am Chem Soc ; 130(23): 7393-9, 2008 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-18479091

RESUMO

Bandgap fluorescence spectroscopy of aqueous, micelle-like suspensions of SWNTs has given access to the electronic energies of individual semiconducting SWNTs, while substantially lower is the success achieved in the determination of the redox properties of SWNTs as individual entities. Here we report an extensive voltammetric and vis-NIR spectroelectrochemical investigation of true solutions of unfunctionalized SWNTs and determine the standard electrochemical potentials of reduction and oxidation as a function of the tube diameter of a large number of semiconducting SWNTs. We also establish the Fermi energy and the exciton binding energy for individual tubes in solution. The linear correlation found between the potentials and the optical transition energies is quantified in two simple equations that allow one to calculate the redox potentials of SWNTs that are insufficiently abundant or absent in the samples.


Assuntos
Nanotubos de Carbono/química , Eletroquímica/métodos , Oxirredução , Soluções , Espectroscopia de Luz Próxima ao Infravermelho , Termodinâmica
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