Polymerization Mechanism of Di(benzylidene)tetrathiapentalenes into Linearly Extended TTF Polymers Philippe Hapiot, 1a Fouad Salhi, 1b Bernadette Divisia-Blohorn, 1c and Harald Mu 1 ller* ,1b Laboratoire d’Electrochimie Mole ´ culaire de l’UniVersite ´ Denis Diderot-Paris 7, UMR 7591 (UniVersite ´ /CNRS), 2 place Jussieu, Case Courrier 7107, 75251 Paris Cedex 05, France, European Synchrotron Radiation Facility (ESRF), B.P. 220, 38043 Grenoble Cedex 09, France, and Laboratoire d’Electrochimie Mole ´ culaire et Structures des Interfaces, UMR 5819 (CEA/CNRS/UniVersite ´ Grenoble 1), De ´ partement de Recherche Fondamentale sur la Matie ` re Condense ´ e, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 09, France ReceiVed: April 14, 1999; In Final Form: October 6, 1999 The mechanism of the oxidative polymerization of di(benzylidene)tetrathiapentalenes (R-DBTTP; where R ) H, OCH 3 , CF 3 ) into linearly extended TTF polymers has been investigated by cyclic voltammetry at low and high scan rates. The polymerization involves as a first step the formation of the monomer radical cations which undergo rapidly a radical dimerization reaction. The dimerization rate constants were found to be in the range of 2k dim ) 4 × 10 6 to 10 7 L mol -1 s -1 . The dimerization products slowly deprotonate to give the corresponding vinylogous tetrathiafulvalene (TTF) derivatives (k H ) 0.02-10 s -1 ). Polymerization only occurs, if the TTF intermediates are oxidized to the radical trication, a behavior which sharply contrasts the known electropolymerization mechanism of pyrrole or thiophene. Introduction The π-electron donor tetrathiafulvalene (TTF) and its deriva- tives are the key building blocks in the rapidly evolving field of molecular conductors. Owing to the exciting solid-state properties of their radical cation salts, such as high electrical conductivity or even superconductivity, TTF and its derivatives have been the focus of general interest for more than 2 decades. 2,3 The potential technological applications of these materials have spurred numerous attempts to incorporate TTF radical salts into polymeric backbones to combine their electrical conductivity with the enhanced processability of macromolecular structures. To date, the polymeric TTF derivatives described in the literature have been prepared from functionalized TTF monomers and consist of essentially independent TTF moieties attached to a polymeric backbone or of segregated TTF units linked through suitable spacer groups. 4 Recently, the synthesis of a series of bis-substituted tetrathia- pentalenes has been reported with the objective of employing these compounds as precursors for the preparation of linearly extended TTF oligo- and polymer derivatives by oxidative radical coupling. 5 Linear fusion of TTF units could offer a promising approach to stabilize metallic conductivity in oligo- and polymeric TTF derivatives. 6 The synthetic strategy takes advantage of the fact that the oxidation of TTF leads generally to stable radical cations, whereas the radical cation of hypothetic, iso-π-electronic 1,3,4,6- tetrathiapentalene (TTP) is expected to be highly reactive 7 (cf. Chart 1). Very recently, the one step preparation of the first linearly annelated TTF polymer (poly-1, see Chart 1) starting from a TTP precursor could be realized successfully. 8 A detailed understanding of the individual reaction steps involved in the oligo- and polymerization of TTP is not only of considerable interest for the accurate control of the polym- erization conditions but also of fundamental importance as a preparative coupling reaction involving C-C bond formation. 9 We present hereafter a detailed study of the oxidative oligo- and polymerization mechanism of para-disubstituted 2,5-di(R- benzylidene)-1,3,4,6-tetrathiapentalenes (R-DBTTP; R ) H, OCH 3 , CF 3 ; 1-3) by classical as well as ultrafast cyclic voltammetry. In the text and Charts 1 and 2, a simplified notation will be used. The monomer will be referred to as HAH, the corresponding dimer as HAAH. For simplicity, the structural formulas shown in the charts are based on the trans (E) conformation of R-DBTTP. Experimental Section Chemicals. CH 2 Cl 2 was of spectroscopy grade and used as received (Merck). The supporting electrolyte n-NBu 4 PF 6 as well * Corresponding author. Phone: 33-47688-2484. Fax: 33-47688-2542. E-mail: mueller@esrf.fr. CHART 1: General Formula of the Radical Cations of Tetrathiafulvalene (TTF) and Tetrathiapentalene (TTP) (Top) and of the Neutral Polymer Poly-1 (Bottom) 11221 J. Phys. Chem. A 1999, 103, 11221-11226 10.1021/jp991217m CCC: $18.00 © 1999 American Chemical Society Published on Web 11/18/1999