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Abstract:

We report the observation of an ultrafast (∼ 430 fs) charge transfer process at the interface between a single-walled carbon nanotube (SWNT) wrapped by a semi-conducting polymer, poly(3-hexylthiophene) (P3HT), creating free polarons on both materials. The addition of excess P3HT as a surrounding network allows these free polarons to be long-lived at room temperature. Our results suggest that SWNT-P3HT blends incorporating only 1% fractions of SWNTs can achieve a charge separation efficiency comparable to a conventional 60:40 P3HT-fullerene blend, provided small-diameter tubes are embedded in an excess P3HT matrix. © 2011 Materials Research Society.

Abstract:

We report on the noncovalent binding of conjugated porphyrin oligomers to small diameter single-walled carbon nanotubes (SWNTs) and highlight two remarkable observations. First, the binding of the oligomers to SWNTs is so strong that it induces mechanical strain on the nanotubes in solution. The magnitudes of the strains are comparable to those found in solid-state studies. Comparable strains are not observed in any other SWNT-supramolecular complexes. Second, large decreases in polymer band gap with increasing length of the oligomer lead to the formation of a type-II heterojunction between long chain oligomers and small-diameter nanotubes. This is demonstrated by the observation of enhanced red-shifts for the nanotube interband transitions. These complexes offer considerable promise for photovoltaic devices. © 2011 American Chemical Society.

Abstract:

(Figure Presented) Like the tentacles of an octopus: Porphyrin oligomers bind strongly to single-walled carbon nanotubes, and debundle multitube aggregates. The strength of this interaction increases sharply with the number of porphyrin units in the oligomer, and the affinity is greatest for chiral (7,5) and (8,6) tubes. Quantitative information on these noncovalent recognition processes was obtained from UV/Vis/NIR absorption (see picture) and fluorescence titrations. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA.

Abstract:

We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are individually embedded in the P3HT matrix.

Abstract:

The position and intensity of the Ï€ plasmon absorbance of a series of single-walled and multi-walled carbon nanotubes has been systematically investigated for the first time using ultraviolet-visible (UV-vis) absorption spectroscopy. All nanotube samples obey the Lambert-Beer law and exhibit similar extinction coefficients (∼50 mL/mg cm) regardless of their structure or method of preparation. The absolute wavelength (energy) of the Ï€ plasmon absorbance has been shown to vary with nanotube diameter as EÏ€ = 4.80 + 0.70/(dNT)². This empirical relationship when correlated with nanotube pyramidalisation angle can be used to estimate the energy range for the Ï€ plasmon in a single sheet of graphene to be 4.8-4.9 eV. © 2010 Elsevier B.V. All rights reserved.