Self-assembly of nanostructured polymetallaynes I. Fratoddi a, * , C. Gohlke b , C. Cametti c , M. Diociaiuti d , M.V. Russo a a Department of Chemistry, University of Rome ‘‘Sapienza’’, P.le A. Moro 5, 00185 Rome, Italy b Department of Biomedical Engineering, University of California, Irvine, USA c Department of Physics, University of Rome ‘‘Sapienza’’, P.le A. Moro 5, 00185 Rome, Italy and INFM-CRS-SOFT, Unita ` di Roma1, Italy d Department of Technology and Health, Istituto Superiore di Sanita `, Viale Regina Margherita 299, 00161 Rome, Italy article info Article history: Received 21 January 2008 Received in revised form 7 May 2008 Accepted 11 May 2008 Available online 21 May 2008 Keywords: Polymetallaynes Nanostructured polymers Nanofibers abstract Organometallic conjugated polymers containing transition metal centers in the main chain (poly- metallynes), with general formula –[M–(PBu 3 ) 2 –C^C–X–C^C–] n – with M ¼ Pt(II) and Pd(II), X ¼ organic conjugated spacer, namely poly[1,1 0 -bis(ethynyl)-4,4 0 -biphenyl-(bis-tributylphosphine)Pd(II)] (Pd-DEBP), poly[1,1 0 -bis(ethynyl)-4,4 0 -biphenyl-(bis-tributylphosphine)Pt(II)] (Pt-DEBP) and poly-[1,4- bis(ethynyl)-2,5-dihexadecyloxybenzene-bis(triphenylphosphine)platinum(II)] (Pt-BOB) were synthe- sized and fully characterized. The polymeric compounds were cast deposited onto glass substrates and their morphologies studied by means of SEM (Scanning Electron Microscopy) and EF-TEM (Energy Fil- tered-Transmission Electron Microscopy). The formation of nanostructured fibrils with diameters in the range 100–300 nm was revealed by SEM. EF-TEM images showed that the fibers are made of hollow nanotubes, randomly oriented, with external diameter of about 6–7 nm. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction One-dimensional nano-sized polymeric materials, prepared by chemical or physical methods, have been investigated extensively [1–3] and their main features related to the properties of both the organic and the inorganic materials are reviewed [4]. Conducting polymeric nano-structures such as polyaniline, polypyrrole and polythiophene have been obtained by several strategies, including template synthesis, interfacial polymerization, self-assembly and stepwise electrochemical deposition [5]. Among these materials, conjugated polymers containing metal centers represent a class that possesses interesting optical and electronic properties. Organometallic polymers with high content of ethynyl bridging p-conjugated organic spacers in rigid-rod structure (polymetallaynes) have been synthesized and character- ized [6]. Other molecular structures could be built by changing the configuration of the precursor complex. For example, self-assem- bled metallomacrocycles are reported with a variety of symmetric shapes, i.e. triangles, squares, and hexagons [7]. These shapes usually develop when cis-blocked square-planar Pt(II) and Pd(II) complexes are used. These materials allow modeling their physical properties fol- lowing a building block approach, i.e. changing the transition metal center, the geometry around the metal, the organic spacer, the distance and the angles between metal centers [8]. It is expected that they may form molecular architectures at nanometric scale with relevant implications for technological applications such as molecular sensing, optoelectronics or catalysis [9]. In fact, the construction of precise shaped and sized macromolecules is strictly correlated to peculiar properties and efficiency in different appli- cations [10]. The production of nano/microscaled fibers of polymeric mate- rials is important because of their potentials in many fields of sci- ence and technology, such as tissue engineering, optoelectronics and drug delivery [11]. Two main techniques, electrospinning and porous templates, are reported for obtaining nano-tubular structures, for example bio-nanowebs and mesoporous carbon nanowires. The linear conjugated molecular structure of our poly- metallaynes is expected to allow production of photo or electro- active nanostrucures with an intimate control of the reactive properties. In this context, the production of nano-sized fibrils by simple self-assembly, as in the case of amphiphilic polymers [12] and polyelectrolytes [13], could be groundbreaking. In this paper we report on polymetallaynes prepared at a nanoscale size, forming unforeseen hollow tubes with a diameter of a few nanometers and up to microns long. The synthesis of these linear rigid-rod-like structures is based on the coupling of trans metal dihalides with conjugated dialkynes, yielding polymers with partially delocalized p electrons, which result from the interaction of the metal d orbitals with p * orbitals of the alkyne [14]. * Corresponding author. Tel.: þ390649913182; fax: þ3906490324. E-mail address: ilaria.fratoddi@uniroma1.it (I. Fratoddi). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2008.05.022 Polymer 49 (2008) 3211–3216