S NH 2 Au S H N Au O O S H N Au O O H N NH 2 S H N Au O O H N H N O O 5 i ii i ii –40 –30 –20 –10 0 10 20 Current density / μA cm –2 i = 5 i = 4 i = 3 i = 3 i = 4 i = 5 i = 2 i = 2 i = 1 i = 1 –0.2 0.0 0.2 0.4 E / V vs. SSCE –50 –40 –30 –20 –10 0 10 20 Current density / μA cm –2 i = 5 i = 4 i = 3 i = 3 i = 4 i = 5 i = 2 i = 2 i = 1 i = 1 i = 0 (a) (b) Polyaminoquinone self-assembled films on electrodes: synthesis of all-organic molecular wires by solution phase epitaxy Jukka Lukkari,* Kari Kleemola, Minna Meretoja and Jouko Kankare Department of Chemistry, University of Turku, FIN-20014 Turku, Finland Redox active molecular wires consisting of successive benzoquinone and diamino moieties are formed on a gold surface using repetitive self-assembly and solution epitaxy. Quinones constitute an interesting group of electroactive compounds which take part in several biologically important oxidation–reduction processes. The electrochemistry of qui- nones has been extensively studied and their complex redox mechanisms considered in detail. 1a,2 The reactivity of quinones towards nitrogen addition is also well known. 1b The reaction of 1,4-benzoquinone with an amine is kinetically facile and proceeds, in the presence of an oxidant, via successive addition of amines predominantly at the 2,5-positions. Nitrogen addition lowers the redox potential of quinone and, therefore, unreacted benzoquinone can serve as an oxidant in the process. Several aliphatic diaminoquinones have been prepared and their spectral and electrochemical properties studied. 3,4 Berlin and co-workers have employed 1,4-amino addition, using aromatic diamines, to prepare aminoquinone polymers. 1c These polymers are obtained as dark powders, which are insoluble in most solvents, rendering their purification and study difficult. They were, however, found to possess semi- conducting properties, which makes them interesting candidates for molecular wires and other devices in molecular electronics. 5 In order to avoid problems in the synthesis and purification of aminoquinone oligomers we have utilised repetitive self- assembly onto a solid substrate in order to grow aminoquinone molecular wires by solution epitaxy. The process involves successive immobilisation of quinones and diamines on a suitable primed electrode surface (Scheme 1), as originally suggested by Katz and Schmidt. 6 We have chosen p-mercaptoaniline for surface priming because it has been shown to form well ordered monolayers on Au(111). 7 The sequential formation of polyaminoquinone on the surface of a polycrystalline gold electrode was followed by cyclic voltammetry (Fig. 1).† The gold electrode primed with the monolayer of p-mercaptoaniline exhibits no electroactivity in the potential range studied. After the immobilisation of the Scheme 1 Reagents and conditions: i, benzoquinone (0.5 m), MeCN– phosphate buffer (pH 7.2) (1 : 1), 3 h; ii, 1,3-diaminopropane in EtOH (30% v/v), 40 min Fig. 1 Cyclic voltammograms of (a) quinone terminated Au–SPhNH– (Q–A) i –Q, and (b) amino terminated Au–SPhNH–(Q–A) i electrodes in 0.5 m HClO 4 at 100 mV s 21 . Dotted curve is Au–SPhNH 2 electrode. Chem. Commun., 1997 1099 Published on 01 January 1997. Downloaded on 28/10/2014 04:30:41. View Article Online / Journal Homepage / Table of Contents for this issue