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Regioregular poly(3-hexylthiophene) containing one diaminopyrimidine side group per ten repeat units (P3HT-co-P3(ODAP)HT) can form molecular composites with 1-(6-mercaptohexyl)thymine capped CdSe nanocrystals (CdSe(MHT)) via hydrogen bonds directed molecular recognition. Here we report complementary spectroscopic, electrochemical and spectroelectrochemical investigations of both the functionalized poly(thiophene) and its composite with the nanocrystals, the latter being fabricated using the layer-by-layer (LbL) deposition technique. UV-Vis-NIR and Raman spectroelectrochemical investigations unequivocally show that the onset of the first anodic peak in the cyclic voltammogram of the copolymer can be attributed to the oxidation of the pi-conjugated backbone in the polymer chains. For this reason, it is possible to determine the width and the position of its band gap (corresponding to the pi-pi* transition) by UV-Vis spectroscopy combined with cyclic voltammetry. These studies show that the polymer exhibits a slightly larger band gap with the HOMO level insignificantly lower in energy (by 0.03 eV) as compared to the case of regioregular poly(3-hexylthiophene) of comparable degree of polymerization. Hydrogen bond interactions of the polymer with CdSe(MHT) in the molecular composite result in a hypsochromic shift of the band corresponding to the pi-pi* transition from 504 nm to 488 nm. This can be taken as a spectroscopic manifestation of the conformational changes induced by shortening of the conjugation length. The observed spectral modifications are consistent with electrochemically determined lowering of the polymer HOMO level (from -4.91 eV in the pure polymer to -4.99 eV in the composite). Cyclic voltammetry studies supported by spectroelectrochemistry also show that the redox stability of CdSe(MHT) in the molecular composite with P3HT-co-P3(ODAP)HT is lower than that determined for stearate-capped nanocrystals. Their irreversible oxidation starts at E = +0.7 V vs. Ag/0.1 M Ag(+)i.e. at potentials by ca. 0.3 V lower than the oxidation of stearate stabilized CdSe nanocrystals of the same size. We show that-despite these modifications-the alignment of the HOMO and LUMO levels of the composite components remains appropriate for its use in hybrid solar cells, which is demonstrated by the photovoltaic effect observed for the LbL-processed composite sandwiched between two electrodes.

Vibrational properties of composites based on single-walled carbon nanotubes (SWNTs) and conducting polymers of the type polyaniline (PANI) and poly (3,4-ethylene dioxythiophene) (PEDOT) are reported. For PANI-functionalized SWNTs, the intensity increase of the Raman band at 178 cm -1 , associated with radial breathing modes of SWNTs bundles, indicates an additional roping of nanotubes due to the presence of the polymer. The interaction of this composite with NH 4 OH solution involves an internal redox reaction between PANI and SWNTs. Thus, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. The functionalization of SWNT side walls with PEDOT is invoked as well. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report on a new procedure to analyze individual single walled carbon nanotube (SWNT), based on an improved use of a confocally selective nanovolume Raman set-up coupled to a refined signal treatment. This technique permits to further improve the resolution in both vertical and lateral dimensions. To acquire spectrally selected SWNT, we registered the spatial distribution of the emitted photons in x,y and z vectors with unprecedented accuracy and were able to resolve details in the specimen with near-field resolution in 3D. The SWNTs are localized with an accuracy better than 17 run in the lateral x,y and better than 2nm in the z direction. In this letter we report what we believe to be the first evidence of selective nanovolume Raman spectroscopy of carbon nanotubes. [Copyright &y& Elsevier]

In this experiment, we report on a new procedure to analyze nanoparticles, like individual single-walled carbon nanotubes (SWNT), based on an improved use of a confocally selective nanovolume Raman spectroscopy set-up coupled to a refined signal treatment. This concept is based on actually available imaging microspectrometry systems for working in the near-field domain combined with a stigmatic solid immersion lens. The combination of different techniques with modified and configured equipment entitles us to expand the functionality toward a three-dimensional mapping of Raman and photoluminescence intensity with a possible discrimination in polarization as well as photoluminescence decay time constant mapping. This technique permits to further improve the resolution in both the vertical and lateral dimensions. To acquire a spectrally selected SWNT, we registered the spatial distribution of the emitted photons in x, y, z vectors with an unprecedented accuracy and were able to resolve details in the specimen with a near-field resolution. In this experiment, we report what we believe to be the first evidence of selective nanovolume Raman spectroscopy of individual nanoparticles. [ABSTRACT FROM AUTHOR]

We present a systematic Raman study over a range of excitation energies of arc discharge single-walled carbon nanotubes (SWCNTs) covalently functionalized according to two processes, esterification and reductive alkylation. The SWCNTs are characterized by resonance Raman spectroscopy at each step of the functionalization process, showing changes in radial breathing mode frequencies and transition energies for both semiconducting and metallic tubes. Particular attention is given to a family of tubes clearly identified in the Kataura plot for which we continuously tune the excitation energy from 704 to 752 nm. This allows us to quantify the energy shift occurring in the spacing of the van Hove singularities. We demonstrate that, independently of the functionalization technique, the type of chain covalently bound to the tubes plays an important role, notably when oxygen atoms lie close to the tubes, inducing a larger shift in transition energy as compared to that of other carbonaceous chains. The study shows the complexity of interpreting Raman data and suggests many interpretations in the literature may need to be revisited. [ABSTRACT FROM AUTHOR]