Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit.

Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction.

Decorating graphene nanosheets with electron accepting pyridyl-phthalocyanines.

We describe herein the preparation of novel exfoliated graphene-phthalocyanine nanohybrids, and the investigation of their photophysical properties. Pyridyl-phthalocyanines (Pcs) are presented as novel electron accepting building blocks of variable strengths with great potential for the exfoliation of graphite via their immobilization onto the basal plane of graphene in dimethylformamide (DMF) affording single layered and turbostratic graphene based . were fully characterized (AFM, TEM, Raman, steady-state and pump probe transient absorption spectroscopy) and were studied in terms of electron donor-acceptor interactions in the ground and excited states. In this context, electron transfer upon photoexcitation from graphene to the electron accepting Pcs with dynamics, for example, in of <1 and 330 ± 50 ps for charge separation and charge recombination, respectively, was corroborated in a series of steady-state and time-resolved spectroscopy experiments.

Electroactive carbon nanoforms: a comparative study via sequential arylation and click chemistry reactions.

The reactivity of several carbon nanoforms (CNFs), single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and graphene, has been investigated through a combination of arylation and click chemistry Cu(I)-mediated azide-alkyne cycloaddition (CuAAC) reactions. The approach is based on the incorporation of electroactive π-extended tetrathiafulvalene (exTTF) units into the triazole linkers to modulate the electronic properties of the obtained conjugates. The introduction of strain, by bending the planar graphene sheet into a 3D carbon framework, is responsible for the singular reactivity observed in carbon nanotubes. The formed nanoconjugates were fully characterized by analytical, spectroscopic, and microscopic techniques (TGA, FTIR, Raman, UV-Vis-NIR, cyclic voltammetry, TEM and XPS). In the case of SWCNT conjugates, where the functionalization degree is higher, a series of steady-state and time resolved spectroscopy experiments revealed a photoinduced electron transfer from the exTTF unit to the electron-accepting SWCNT.

Electron-donating behavior of few-layer graphene in covalent ensembles with electron-accepting phthalocyanines.

We describe herein the first example of highly exfoliated graphene covalently linked to electron accepting phthalocyanines. The functionalization of the nanocarbon surface with alkylsulfonyl phthalocyanines was attained by means of a "click" chemistry protocol. The new ensemble was fully characterized (thermogravimetric analysis, atomic force microscopy, transmission electron microscopy and Raman, as well as ground-state absorption) and was studied in terms of electron donor-acceptor interactions in the ground and in the excited state. In particular, a series of steady-state and time-resolved spectroscopy experiments demonstrated photoinduced electron transfer from the graphene to the electron-accepting phthalocyanines. This is the first example of an electron donor-acceptor nanoconjugate, that is, few-layer graphene/phthalocyanine, pinpointing the uncommon electron donating character of graphene.

Tuning the stability of graphene layers by phthalocyanine-based oPPV oligomers towards photo- and redoxactive materials.

In contrast to pristine zinc phthalocyanine (1), zinc phthalocyanine based oPPV-oligomers (2-4) of different chain lengths interact tightly and reversibly with graphite, affording stable and finely dispersed suspensions of mono- to few-layer graphene-nanographene (NG)-that are photoactive. The p-type character of the oPPV backbones and the increasing length of the oPPV backbones facilitate the overall π-π interactions with the graphene layers. In NG/2, NG/3, and NG/4 hybrids, strong electronic coupling between the individual components gives rise to charge transfer from the photoexcited zinc phthalocyanines to NG to form hundreds of picoseconds lived charge transfer states. The resulting features, namely photo- and redoxactivity, serve as incentives to construct and to test novel solar cells. Solar cells made out of NG/4 feature stable and repeatable photocurrent generation during several 'on-off' cycles of illumination with monochromatic IPCE values of around 1%.

Interfacing nanocarbons with organic and inorganic semiconductors: from nanocrystals/quantum dots to extended tetrathiafulvalenes.

There is no doubt that the outstanding optical and electronic properties that low-dimensional carbon-based nanomaterials exhibit call for their implementation into optoelectronic devices. However, to harvest the enormous potential of these nanocarbons it is essential to probe them in multifunctional electron donor-acceptor systems, placing particular attention on the interactions between electron donors/electron acceptors and nanocarbons. This feature article outlines challenges and recent breakthroughs in the area of interfacing organic and inorganic semiconductors with low-dimensional nanocarbons that range from fullerenes (0D) and carbon nanotubes (1D) to graphene (2D). In the context of organic semiconductors, we focus on aromatic macrocycles and extended tetrathiafulvalenes, and CdTe nanocrystals/quantum dots represent the inorganic semiconductors. Particular emphasis is placed on designing and probing solar energy conversion nanohybrids.

Linking photo- and redoxactive phthalocyanines covalently to graphene.

"Green" graphene: For the first time, the covalent attachment of a light-harvesting and electron-donating phthalocyanine to the basal plane of few-layer graphene is reported. Physicochemical characterizations reveal an ultrafast charge separation from the photoexcited phthalocyanine to few-layer graphene followed by a slower charge recombination.

Decorating polyelectrolyte wrapped SWNTs with CdTe quantum dots for solar energy conversion.

We report herein on the development of a synthetic route towards SWNT/polyelectrolyte/QD nanohybrids. On one hand, negatively charged thioglycolic acid capped CdTe QDs were prepared via an aqueous solution based synthesis. On the other hand, SWNTs were coated with a positively charged polyelectrolyte. By virtue of electrostatic interactions between QDs and SWNTs, SWNT/ polyelectrolyte/QD nanohybrids were realized, whose formation was corroborated by thorough spectroscopic and microscopic investigations. Of particular relevance are changes of the QD related emission - quantum yields and lifetimes - upon their integration into the nanohybrids. The latter is indicative for electronic communication between both the photo- and redoxactive constituents, namely QDs and SWNTs, whose nature is electron transfer.

Toward combining graphene and QDs: assembling CdTe QDs to exfoliated graphite and nanographene in water.

Herein, we report for the first time on a full-fledged investigation of water-soluble CdTe quantum dots (QD) that are immobilized onto exfoliated graphite (EG) and/or nanographene (NG). Particular emphasis was placed on a top-down preparation of stable aqueous dispersions-starting from natural graphite rather than graphene oxide-while preserving the intrinsic properties of graphene. To this end, we circumvented the harsh conditions commonly employed for the pre-exfoliation (i.e., Hummers method). First, a hydrophobic-hydrophobic/π-π stacking motif was tested between EG and pyrene, to which QDs are covalently attached (QD-pyrene). Second, we employed the combination of hydrophobic-hydrophobic/π-π stacking and electrostatic interactions to build up hierarchical structures composed of NG, positively charged pyrene (pyrene(+)), and negatively charged QDs. The novel nanohybrids-QD-pyrene/EG and QD/pyrene(+)/NG-were characterized with specific emphasis on electron-transfer chemistry. In fact, both assays provide kinetic and spectroscopic evidence that support electron transfer dynamics that vary, however, between EG and NG as a reflection of the different degree of graphite exfoliation.

Control over charge transfer through molecular wires by temperature and chemical structure modifications.

A series of electron donor-acceptor arrays containing π-conjugated oligofluorenes (oFL) of variable length between a zinc porphyrin (ZnP) as electron donor and fullerene (C(60)) as electron acceptor have been prepared by following a convergent synthesis. The electronic interactions between the electroactive species were determined by cyclic voltammetry, UV-visible, fluorescence, and femto/nanosecond transient absorption spectroscopy. Our studies clearly confirm that, although the C(60) units are connected to the ZnP donor through π-conjugated oFL frameworks, no significant electronic interactions prevail in the ground state. Theoretical calculations predict that a long-range electron transfer occurs primarily due to a maximized π-conjugated pathway from the donor to the acceptor. Photoexcitation of ZnP-oFL(n)-C(60) results in transient absorption maxima at 715 and 1010 nm, which are unambiguously attributed to the photolytically generated radical ion pair state, [ZnP(•+)-oFL(n)-C(60)(•-)], with lifetimes in the microsecond time regime. Temperature-dependent photophysical experiments have shown that the charge-transfer mechanism is controllable by temperature. Both charge separation and charge recombination processes give rise to a molecular wire behavior of the oFL moiety with an attenuation factor (ß) of 0.097 Å(-1). The correlation ß to the connection pattern between the ZnP donor and the oFL linker revealed that even small alterations of the linker π-electron system break the homogeneous π-conjugation pattern, leading to higher values of ß.