Synthesis and photoelectrical properties of carbon nanotube–dendritic porphyrin light harvesting molecule systems L. Valentini a, ⁎ , M. Trentini b , F. Mengoni a , J. Alongi b , I. Armentano a , L. Ricco b , A. Mariani c , J.M. Kenny a a Department of Civil and Environmental Engineering, University of Perugia and INSTM NIPLAB Centre, Loc. Pentima Bassa, 05100 Terni, Italy b Department of Chemistry and Industrial Chemistry, University of Genova and INSTM NIPLAB Centre, Via Dodecaneso 31, 16146 Genova, Italy c Department of Chemistry, University of Sassari and INSTM Local Unit, Via Vienna 2, 07100 Sassari, Italy Received 25 July 2006; received in revised form 15 November 2006; accepted 30 November 2006 Available online 11 January 2007 Abstract Supramolecular structures consisting of dendritic porphyrins and single-walled carbon nanotubes (SWNTs) have been prepared and characterized as an efficient donor/acceptor system. Non-covalent interactions enable the pair system to produce suitable electron transfer through a process occurring from the dendritic porphyrin core to the graphenic wall of carbon nanotubes. The role of structure/architecture of our dendritic molecules on SWNT photoelectrical behaviour has been also investigated. © 2006 Elsevier B.V. All rights reserved. Keywords: Light harvesting molecules; Dendritic porphyrins; Nanotubes; Electrical properties characterization 1. Introduction Recently, functionalization of carbon nanotubes through surface modification has attracted relevant interest [1–4]. Functionalization strategies involving reactions of organic or polymeric molecules onto carbon nanotubes have been primarily focused on dispersion or dissolution properties. In particular, non-covalent interactions of porphyrins with single- walled carbon nanotubes (SWNTs) have been used for the dispersion and also for the separation of semiconducting and metallic tubes [5–9]. A donor/acceptor system consisting of an anionically-functionalized porphyrin and a cationically-functio- nalized pyrene stacked on SWNTs has been shown to exhibit electron transfer properties [10]. Non-covalent modifications involving dyes have used polymers, such as poly-m-phenylenevinylene [11] and dendri- meric polyamidoamine (PAMAM®) [12,13], and molecules with an extended π-system, such as poly(aryleneethynylene) [14], anthracene [15], phthalocyanine [16] and porphyrin [17]. The use of organic dyes, as porphyrins, enables the use of photovoltaic devices for visible light applications [18,19] and photoresponsive devices [20]. Porphyrin assemblies are of great relevance as models for the study of energy and electron transfer as light harvesting antennae in the photosynthetic re- action centre [21]. More recently, incorporation of antenna molecules, such as dendritic porphyrins, that are able to absorb light and channel it to a reaction core interacting with the extended π electrons of carbon nanotubes would constitute an ideal supramolecular nano-assembly for potential photovoltaic applications [22,23]. In the present paper, we have explored the possibility of combining SWNTs with two dendritic porphyrins characterized by a different structure/architecture, with the aim of evaluating the influence of the latter parameters on the photoelectrical answer of SWNTs non-covalently interacting with the porphyr- ins. The highly aromatic structure of porphyrins ensures the high level of π-bonds needed to interact non-covalently with carbon nanotubes. The different architecture and rigidity of the two porphyrin structures allow to differentiate the extent of interactions between the porphyrin and carbon nanotube. The first structure used as light harvesting antenna molecule is 1,3,5-phenylene-based dendritic porphyrin, having a pyrrole Diamond & Related Materials 16 (2007) 658 – 663 www.elsevier.com/locate/diamond ⁎ Corresponding author. E-mail address: mic@unipg.it (L. Valentini). 0925-9635/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2006.11.097