Carlos Romero-Nieto

Low dimensional nanocarbons – chemistry and energy/electron transfer reactions

This Minireview sheds light onto the electronic communication between, on one hand, low dimensional nanocarbons – single and multiwalled 1D carbon nanotubes and 2D graphene – and, on the other hand, a variety of electroactive species en-route to novel electron donor–acceptor conjugates and hybrids in relation to their covalent and non-covalent chemistry, respectively. A common denominator to any of the highlighted conjugates/hybrids is charge transport across different scales, that is, from individual molecular conjugates/hybrids to morphologically controlled devices.

Tetrathiafulvalene-Based Nanotweezers—Noncovalent Binding of Carbon Nanotubes in Aqueous Media with Charge Transfer Implications

Electron donor-acceptor hybrids based on single wall carbon nanotubes (SWCNT) are one of the most promising functional structures that are currently developed in the emerging areas of energy conversion schemes and molecular electronics. As a suitable electron donor, π-extended tetrathiafulvalene (exTTF) stands out owing to its recognition of SWCNT through π-π stacking and electron donor-acceptor interactions. Herein, we explore the shape and electronic complementarity between different types of carbon nanotubes (CNT) and a tweezers-shaped molecule endowed with two exTTFs in water. The efficient electronic communication between semiconducting SWCNT/multiwall carbon nanotubes (MWCNT), on one hand, and the water-soluble exTTF nanotweezers 8, on the other hand, has been demonstrated in the ground and excited state by using steady-state as well as time-resolved spectroscopies, which were further complemented by microscopy. Importantly, appreciable electronic communication results in the electronic ground state having a shift of electron density, that is, from exTTFs to CNT, and in the electronic excited state having a full separation of electron density, that is oxidized exTTF and reduced CNT. Lifetimes in the range of several hundred picoseconds, which were observed for the corresponding electron transfer products upon light irradiation, tend to be appreciably longer in MWCNT/8 than in SWCNT/8.

Integrating Water‐Soluble Graphene into Porphyrin Nanohybrids

Scheme 1. Schematic representation of a graphene sheet to which positively charged pyrene 1 is immobilized and the electrostatic interaction of NG/1 with negatively charged porphyrin 2. An overwhelming interest rests on graphene, the rising star in the field of nanotechnology.[1] Its extraordinary properties[2] render it a promising material for electronics,[3] material sciences,[4] and photoconversion systems.[5] The high electron mobility of graphene at room temperature calls for its implementation into transparent conducting electrodes.[6] In accordance with recent results doping is, however, crucial to harvest the full potential of graphene.[7] Solution processed graphene layers essentially have to be stabilized by means of surface active molecules prior to their transfer to solid substrates.[8] Usually graphene oxide[9] is used, which, however, requires chemical reduction or annihilation under high temperature[10] or UV-light assisted[11] conditions to afford either reduced graphene oxide also known as chemically converted graphene.[12] Notably, the overall reaction conditions (i.e., oxidation and reduction) are rather harsh and oxygen residues remain within the reduced graphene oxide structure.[13] In other words, irreversible damages of the conjugated π-system of graphene stay behind, which exert appreciable changes to the electronic properties such as conductivity.[14] A viable alternative to the aforementioned comprises the covalent[15] and/ or the non-covalent[16] functionalization of just graphite using reaction protocols similar to those developed in the context of the chemistry of fullerenes and/or of carbon nanotubes.[17] As a matter of fact, non-covalent functionalization of graphene as conducted by ultrasonicating graphite in presence of building blocks assists in the exfoliation to graphene,[18] on one hand, and ensures the stability of the resulting dispersions, on the other hand. Recently, we reported on the exfoliation of graphite and the concomitant non-covalent functionalization of graphene by a chromophoric electron donor. Beneficial was its use as a spectroscopic marker for probing electron transfer processes in solution.[19] A major concern related with this approach is the stability of the chromophores during the ultrasound treatment. Therefore, we report here on a novel non-invasive functionalization approach, namely tuning/altering the intrinsic features of photochemically “transparent” graphene, by integrating water-soluble porphyrins. The integration by means of electrostatic interactions necessitates an anchoring group, which is provided by a positively charged water-soluble pyrene

Charge transfer interactions in self-assembled single walled carbon nanotubes/Dawson–Wells polyoxometalate hybrids

We demonstrate the success in self-assembling pyrene-modified Dawson–Wells-type polyoxometalates (POMs) with single walled carbon nanotubes (SWCNTs) by means of π–π interactions. In this context, the immobilization of POMs onto SWCNTs is corroborated by aberration-corrected high-resolution electron microscopy, thermogravimetric analysis, and Raman spectroscopy. From steady-state and time-resolved photophysical techniques we derived evidence for mutual interactions between SWCNTs and POMs in the excited states. The latter are the inception to a charge transfer from the SWCNTs to the POMs. Our results corroborate the suitability of POM–SWCNTs assemblies for photoactive molecular devices.

Self‐Ordering Electron Donor–Acceptor Nanohybrids Based on Single‐Walled Carbon Nanotubes Across Different Scales

When dealing with SWCNTs, limited control over theirgrowth and homogeneous production imposes, however,major drawbacks for emerging areas of nanotechnology.Equally problematic is their rather poor solubility in commonorganic solvents. Large spaghetti-like bundles, that originatefrom attractive interactions such as p–p stacking and Londondispersion forces, are the cause of insolubility.

Stable Electron Donor–Acceptor Nanohybrids by Interfacing n‐Type TCAQ with p‐Type Single‐Walled Carbon Nanotubes

Financial support from MINECO of Spain (CTQ2011-24652, PIB2010JP-00196, 2010C-07-25200, and Consolider- Ingenio CSD2007-00010), FUNMOLS (FP7-212942-1), CAM (MADRISOLAR-2 S2009/PPQ-1533), DFG (GU 517/16-1), and DFG (Excellence Cluster – Engineering of Advanced Materials) is greatly appreciated.

Cyclopentadienylruthenium π Complexes of Subphthalocyanines: A “Drop‐Pin” Approach To Modifying the Electronic Features of Aromatic Macrocycles

Facing facts: Coordination of Cp*Ru (Cp*=C(5)Me(5)) to the concave and convex π surfaces of subphthalocyanines constitutes a new approach to the functionalization of subazaporphyrins. While the convex face shows higher reactivity, coordination to the concave side produces a stronger diatropic influence on the Cp* ligand and a greater perturbation of the macrocyclic π-electronic features.

Towards enhancing light harvesting-subphthalocyanines as electron acceptors.

One carbon atom is too many. Two subphthalocyanine-extended TTF electron donor-acceptor conjugates were synthesized and characterized. Their photophysical properties prompt the remarkable impact that one extra carbon between the two constitutents exerts on photoinduced processes, that is, charge recombination dynamics in the normal versus inverted region.

Controlling the crystalline three-dimensional order in bulk materials by single-wall carbon nanotubes

The construction of ordered single-wall carbon nanotube soft-materials at the nanoscale is currently an important challenge in science. Here we use single-wall carbon nanotubes as a tool to gain control over the crystalline ordering of three-dimensional bulk materials composed of suitably functionalized molecular building blocks. We prepare p-type nanofibres from tripeptide and pentapeptide-containing small molecules, which are covalently connected to both carboxylic and electron-donating 9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene termini. Adding small amounts of single-wall carbon nanotubes to the so-prepared p-nanofibres together with the externally controlled self assembly by charge screening by means of Ca(2+) results in new and stable single-wall carbon nanotube-based supramolecular gels featuring remarkably long-range internal order.

Host-Guest Complexation of (60)Fullerenes and Porphyrins Enabled by "Click Chemistry"

Herein the synthesis, characterization, and organization of a first-generation dendritic fulleropyrrolidine bearing two pending porphyrins are reported. Both the dendron and the fullerene derivatives were synthesized by Cu(I) -catalyzed alkyne-azide cycloaddition (CuAAC). The electron-donor-acceptor conjugate possesses a shape that allows the formation of supramolecular complexes by encapsulation of C60 within the jaws of the two porphyrins of another molecule. The interactions between the two photoactive units (i.e., C60 and Zn-porphyrin) were confirmed by cyclic voltammetry as well as by steady-state and time-resolved spectroscopy. For example, a shift of about 85 mV was found for the first reduction of C60 in the electron-donor-acceptor conjugate compared with the parent molecules, which indicates that C60 is included in the jaws of the porphyrin. The fulleropyrrolidine compound exhibits a rich polymorphism, which was corroborated by AFM and SEM. In particular, it was found to form supramolecular fibrils when deposited on substrates. The morphology of the fibrils suggests that they are formed by several rows of fullerene-porphyrin complexes.