Nickel (II) tetraphenylporphyrin modified surfaces via electrografting of an aryldiazonium salt Andrew J. Gross a , Christophe Bucher b , Liliane Coche-Guerente b , Pierre Labbé b , Alison J. Downard a, ⁎, Jean-Claude Moutet b, ⁎⁎ a MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand b Université Joseph Fourier Grenoble 1, Département de Chimie Moléculaire, UMR CNRS-5250, ICMG, FR CNRS-2607, BP 53, 38041 Grenoble, Cedex 9, France abstract article info Article history: Received 1 August 2011 Received in revised form 16 August 2011 Accepted 22 August 2011 Available online 28 August 2011 Keywords: Metal complex TPP Film PPF Electrografting Diazonium salt We have prepared and isolated the monodiazonium salt of nickel (II) tetraphenylporphyrin and grafted the corresponding complex to glassy carbon, pyrolysed photoresist film, gold and indium tin oxide surfaces via reduction of the diazonium moiety. Characterisations of the films by voltammetry, UV–vis spectroscopy and atomic force microscopy depth profiling confirm that the metallated porphyrin is intact in the film and is stably attached to the surface with well-behaved, but highly solvent-dependent electrochemistry. Under the grafting conditions used, the films appear to have close to monolayer thickness with the porphyrin macrocycles oriented predominantly upright on the surface. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Electrochemically assisted surface modification from aryldiazo- nium salt solutions is a well-known approach for controlled deposi- tion of nanoscale thin films [1,2]. To date, aryldiazonium salts have been used extensively to graft organic species [1], metal complexes and organometallic species [3–5] at a wide range of electrode sur- faces, for potential applications in electrocatalysis, molecular elec- tronics, corrosion protection and sensor fabrication [2]. The use of aryldiazonium salts for surface modification arises from the high sta- bility of the surface attachment (e.g. a covalent attachment between the surface and the modifier), the ability to controllably deposit mono- and multilayer films, and the wide substrate compatibility. Thin films of porphyrin derivatives are attractive due to their opti- cal, photoluminescent and electric properties, which have resulted in numerous applications in optical devices, chemical sensors and elec- trocatalysis. The importance of nickel-porphyrin modified electrodes was demonstrated by Malinski and Taha who developed a microsen- sor for detection of nitric oxide release from single-cells [6]. More re- cently, nickel-porphyrin modified electrodes have been used for electrocatalytic oxidation of substrates including methanol [7,8], eth- anol [8], phenols [9], formaldehyde [10] and hydrazine [8]. Despite the advantages of electrografting from diazonium salt solutions as a method for thin film formation, there are no reports on the electro- grafting of porphyrin molecules from their corresponding aryldiazo- nium salts. Guo et al. modified single-walled carbon nanotubes via a thermal reaction with in-situ generated free-base porphyrin diazoni- um compounds and characterised the materials using spectroscopy and microscopy [11,12]. Similarly, Lu et al. exploited the spontaneous reaction of in-situ generated diazonium compounds at H-passivated silicon (100) to graft porphyrin films [13]. Only brief electrochemical characterisation of the surfaces was reported. We describe here the electrografting of nickel tetraphenylpor- phyrin groups at carbon, indium tin oxide (ITO) and gold surfaces by the reduction of the corresponding diazonium salt. The films are characterised by electrochemistry, spectroscopy and atomic force mi- croscopy (AFM). 2. Experimental 5-(p-aminophenyl)-10,15,20-triphenylporphyrin (TPP A H 2 ) was synthesised as reported [14]. Nickel (II) was incorporated in the macrocycle using DMF as the solvent and nickel (II) acetate as the metal source, yielding 5-(p-aminophenyl)-10,15,20-triphenylpor- phyrinatonickel (II) (TPP A Ni) [15,16]. The porphyrin–diazonium salt, (TPP D )Ni (Fig. 1a), was synthesised in the dark under an argon atmo- sphere, using freshly purified nitrosium tetrafluoroborate (NOBF 4 ) as the diazotising agent [17,18]. (TPP A )Ni (5.82 × 10 -5 mol) was Electrochemistry Communications 13 (2011) 1236–1239 ⁎ Corresponding author. Tel.: +64 3 364 2501; fax: +64 3 364 2110. ⁎⁎ Corresponding author. Tel.: + 33 476514481; fax: + 33 76514267. E-mail addresses: alison.downard@canterbury.ac.nz (A.J. Downard), jean-claude.moutet@ujf-grenoble.fr (J.-C. Moutet). 1388-2481/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2011.08.035 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom