DOI: 10.1002/chem.201001417 Sexithiophene Encapsulated in a Single-Walled Carbon Nanotube: An In Situ Raman Spectroelectrochemical Study of a Peapod Structure Martin Kalbµc ˇ,* [a, b] Ladislav Kavan, [a] Sandeep Gorantla, [c] Thomas Gemming, [c] and Lothar Dunsch [b] Introduction Oligothiophenes as organic semiconductors [1, 2] are good can- didates for applications in electronics and devices such as or- ganic field effect transistors [3] or solar cells. [4] Among oligo- thiophenes, a-sexithiophene (6T) is particularly attractive due to its high hole mobility in the solid state. [5] It has been shown recently that the morphology of 6T in- fluences the performance of devices dramatically. [6] Howev- er, it is very difficult to control the morphology in macro- scopic crystals. The assembly of crystals inside single-walled carbon nanotubes (SWCNTs) presents a challenge for this control, because unusual crystal structures of many inorgan- ic materials can be grown in this way. [7] The diameter of SWCNTs is typically in the range of 1–2 nm. This is compa- rable to the size of small organic molecules, which can therefore be confined in the interior of SWCNTs. However, for applications in electronics it is also very important to un- derstand the electronic exchange between 6T and SWCNT in the peapod structures, 6T@SWCNT. In situ spectroelectrochemistry is the method of choice for studying carbon nanostructures, [8–13] because characteri- zation of the electronic structure of these materials both in the neutral and charged states is possible upon electrochem- ical doping. We have shown recently that the electronic structure of SWCNT is very sensitive to doping, resulting in significant changes in their Raman spectra. [14] These changes are reversible and reproducible for a selected SWCNT sample. [15, 16] Hence, SWCNTs can also be used as in situ probes for studies of hybrid materials like SWCNT/polymer composites [17, 18] and/or to monitor the electronic structure of species encapsulated inside SWCNTs. [19, 20] The SWCNTs are stable in a relatively wide potential window. Thus, the inter- action of many hybrid materials based on SWCNT in a charged state can be evaluated by this probe. Abstract: The interaction of single- walled carbon nanotubes (SWCNTs) and a-sexithiophene (6T) was studied by Raman spectroscopy and by in situ Raman spectroelectrochemistry. The encapsulation of 6T in SWCNT and its interaction causes a bleaching of its photoluminescence, and also small shifts of its Raman bands. The Raman features of the SWCNT with embedded 6T (6T-peapods) change in both inten- sity and frequency compared to those of pristine SWCNT, which is a conse- quence of a change of the resonant condition. Electrochemical doping demonstrated that the electrode poten- tial applied to the SWCNT wall causes changes in the embedded 6T. The ef- fects of electrochemical charging on the Raman features of pristine SWCNT and 6T@SWCNT were com- pared. It is shown that the interaction of SWCNT with 6T also changes the electronic structure of SWCNT in its charged state. This change of electronic structure is demonstrated both for semiACHTUNGTRENNUNGconducting and metallic tubes. Keywords: doping · electrochemis- try · nanotubes · Raman spectrosco- py · sexithiophene [a] Dr. M. Kalbµc ˇ, Prof. L. Kavan J. Heyrovsky ´ Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic Dolejs ˇkova 3, 18223 Prague 8 (Czech Republic) Fax: (+ 420) 2-8658-2307 E-mail: kalbac@jh-inst.cas.cz [b] Dr. M. Kalbµc ˇ, Prof. Dr. L. Dunsch Center of Spectroelectrochemsitry Department of Electrochemistry and Conducting Polymers Leibniz-Institute of Solid State and Materials Research (IFW Dresden) Helmholtzstr. 20, 01069 Dresden (Germany) [c] S. Gorantla, Dr. T. Gemming Institute of Complex Materials Leibniz-Institute of Solid State and Materials Research (IFW Dresden) Helmholtzstr. 20, 01069 Dresden (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001417. Chem. Eur. J. 2010, 16, 11753 – 11759 # 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 11753 FULL PAPER