Photoinduced charge separation in three-layer supramolecular nanohybrids: fullerene-porphyrin-SWCNT

Bidirectional charge-transfer behavior in carbon-based hybrid nanomaterials

In recent years there has been a growing interest in finding materials revealing bidirectional charge-transfer characteristics, that is, materials behaving as an electron donor or an acceptor in the presence of redox and photoactive addends, for optoelectronic applications. In this respect, carbon-based nanostructures, such as graphene and carbon nanotubes, have emerged as promising nanomaterials for the development of hybrid systems for bidirectional charge transfer, whose behaviour can be switched from donor-type to acceptor-type by simply changing the electroactive counterpart to which they are anchored. In this review we provide an overview of the main advances that have been made over the past few years in carbon-based hybrid architectures involving different types of carbon nanostructures and photosensitizers. In particular, carbon nanotube and graphene-based hybrid systems will be highlighted.

Hybrid materials of pyrene substituted phthalocyanines with single-walled carbon nanotubes: structure and sensing properties

Hybrid materials of single walled carbon nanotubes (SWCNT) were obtained by their non-covalent functionalization with asymmetrically polyoxyethylene substituted metal-free, copper(ii) and cobalt(ii) phthalocyanines bearing one pyrene group as a substituent.

Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices

In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G(+) peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm(-1) and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm(-1).

Photoinduced Electron Transfer Processes of Functionalized Nanocarbons; Fullerenes, Nanotubes and Graphene

To solve the energy demands for a sustainable society, it is crucial to use clean solar energy. Thus, finding methods for efficient light energy conversion is an important scientific goal. For this aim, molecular devices employing composites of nanocarbons such as fullerenes, single wall carbon nanotubes (SWCNTs), and graphene are promising. In this review, we survey light-induced electron-transfer processes of these nanocarbons hybridized with photosensitizers, which have proved to be more favorable than ordinary molecules. Fullerenes connected with suitable electron donors yield characteristic long-lived radical ion pairs, suitable for constructing artificial photosynthetic systems. For SWCNTs, a combination of photosensitizers is also crucial to achieve efficient photo-induced electron transfer processes. Furthermore, in the case of diameter-sorted semi-conductive SWCNTs, each tube can be treated as a “molecule”, thus, allowing molecular orbital calculations to probe the geometry as well as the electronic structures of the photosensitizernanotube hybrids. The two-dimensional graphene has afforded a new reaction field with a wide π-system for the attached molecules. For the confirmation of electron transfer processes, transient absorption methods in the wide wavelength regions have been used effectively. The kinetic data obtained in solution are quite useful to understand the electron transfer mechanisms, which afford useful guiding principles to construct efficient light-energy harvesting devices such as photoelectrochemical and photovoltaic solar cells.

Recent advances in photoinduced electron transfer processes of fullerene-based molecular assemblies and nanocomposites

Photosensitized electron-transfer processes of fullerenes hybridized with electron donating or other electron accepting molecules have been surveyed in this review on the basis of the recent results reported mainly from our laboratories. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, fullerenes in the ground state also act as good electron acceptors in the presence of light-absorbing electron donors such as porphyrins. With single-wall carbon nanotubes (SWCNTs), the photoexcited fullerenes act as electron acceptor. In the case of triple fullerene/porphyrin/SWCNT architectures, the photoexcited porphyrins act as electron donors toward the fullerene and SWCNT. These mechanisms are rationalized with the molecular orbital considerations performed for these huge supramolecules. For the confirmation of the electron transfer processes, transient absorption methods have been used, in addition to time-resolved fluorescence spectral measurements. The kinetic data obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells.