Synthesis of new ethynylbipyridine-linked mono- and bis-tetrathiafulvalenes: electrochemical, spectroscopic, and Ru(II)-binding studies Christine Goze a , Shi-Xia Liu a, * , Claudia Leiggener b , Lionel Sanguinet c , Eric Levillain c , Andreas Hauser b , Silvio Decurtins a a Departement fu ¨r Chemie und Biochemie, Universita ¨t Bern, Freiestrasse 3, CH-3012 Bern, Switzerland b De ´partement de chimie physique, Universite ´ de Gene `ve, 30 quai Ernest-Ansermet, CH-1211 Gene `ve 4, Switzerland c Chimie, Inge ´nierie Mole ´culaire et Mate ´riaux d’Angers (CIMMA) CNRS, UMR 6200, Universite ´ d’Angers, 2 bd Lavoisier, 49045 Angers Cedex, France Received 11 October 2007; received in revised form 2 November 2007; accepted 16 November 2007 Available online 22 November 2007 Abstract Two new ethynylbipyridine-linked mono- and bis-tetrathiafulvalene (TTF) derivatives, together with a Ru(II) complex, were synthesized using Sonogashira coupling reactions and characterized by UV/vis spectroscopy and cyclic voltammetry. They display a clear electrochemically amphoteric behavior consisting of two reversible single-electron oxidation waves (typical for TTF derivatives) and one reversible single-electron reduction wave (bpy) and act as donoreacceptor (DeA) systems. Furthermore, for the Ru(II) complex, a quite intense fluorescence originating from the 3 MLCT state is observed. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Tetrathiafulvalene; Ruthenium(II) complex; Photophysical properties; Cyclic voltammetry; Donoreacceptor systems 1. Introduction Tetrathiafulvalene (TTF) and its derivatives are well-known as p electron-donor materials in the field of organic conduc- tors. 1 As a result of progress in synthetic TTF chemistry, TTFs have been incorporated into a number of macrocyclic, molecular, and supramolecular systems in order to create multifunctional materials with desired structures, stability, and physical properties. 1e3 Therefore, considerable efforts are currently devoted to the modification of the TTF core with substituents such as pyridine-type heterocycles, 4 acetyl- acetonates, 5 and phosphines, 6 all of which are well tailored for a chelating coordination function toward various transition metal ions. On the other hand, TTFs are frequently used as donor units in donoreacceptor (DeA) ensembles, which are of considerable research interest due to their potential applica- tions in sensors, optoelectronics, and molecular devices. 3,7 DepeA systems have gained increasing attention as the p-conjugated spacer may optimize the communication between the D and A units. 3,8 Furthermore, an acetylenic spacer can of- fer an excellent control of the distance between the D and A centers because of its linearity and rigidity, and concomitantly provide a synthetic handle for further elaboration of sophisti- cated molecular structures. 9 To gain insight into such intramo- lecular electronic interactions, such DeA systems containing TTFs and triple bond linkages have been studied recently. 10 For ex- ample, Martı ´n et al. have demonstrated that through a specific exchange of C]C for C^C the long-range photo-induced electron transfer in DeA conjugates can be considerably alter- ed. 10a Moreover, the p-conjugation is disrupted by a neutral TTF unit in TTFeOXD (OXD¼2,5-diphenyl-1,3,4-oxadi- azole) hybrids. 10b * Corresponding author. Tel.: þ41 31 6314296; fax: þ41 31 6313995. E-mail address: liu@iac.unibe.ch (S.-X. Liu). 0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2007.11.056 Available online at www.sciencedirect.com Tetrahedron 64 (2008) 1345e1350 www.elsevier.com/locate/tet