Synthesis and intramolecular charge-transfer properties of new tetrathiafulvalene–σ-tetracyanoanthraquinodimethane diad (TTF–σ-TCNAQ) and triad (TTF–σ-TCNAQ–σ-TTF) molecules

Abstract

We report the use of functionalised electron acceptor tetracyanoanthraquinodimethane (TCNAQ) units in the synthesis of novel diad D–σ-A compounds 6 and 7 [D=tetrathiafulvalenyl (TTF) and ferrocenyl] and the triad TTF–σ-TCNAQ–σ-TTF assembly 8. Compounds 6–8 display a very weak, broad, low-energy intramolecular charge-transfer band in the UV–VIS spectra. Nanosecond laser flash photolysis of compound 6 did not lead to any new transient absorptions in the 300–800 nm region, suggesting that if a charge-separated species is formed upon excitation, then back electron transfer occurs very rapidly to regenerate the ground state. Cyclic voltammetry of compounds 6–8 shows that reversible oxidation processes occur for the TTF and ferrocene moieties, and a reversible two-electron reduction occurs for the TCNAQ moiety. Spectroelectrochemical studies on compound 6 have enabled the redox processes to be assigned to the sequential formation of the TTF radical cation and dication upon oxidation, and the TCNAQ dianion upon reduction. Simultaneous electrochemistry and EPR (SEEPR) experiments provide further evidence for intramolecular interaction between the TTF and TCNAQ moieties in compound 6. Quantum mechanical calculations on compound 6, performed by the AM1 method, predict that in its minimum energy conformation the TTF and TCNAQ moieties are approximately orthogonal to one another, with the TCNAQ unit folded into a butterfly conformation.

References

1. (a) J. R. Ferraro and J. M. Williams, Introduction to Synthetic Electrical Conductors, Academic Press, London, 1987; (b) K. Bechgaard, in Structure and Properties of Molecular Crystals, ed. M. Pierrot, Elsevier, Amsterdam, 1990, 235; (c) J. M. Williams, A. J. Schultz, U. Geiser, K. D. Carlson, A. M. Kini, H. H. Wang, W.-K. Kwok, M.-H. Whangbo and J. E. Schirber, Science, 1991, 252, 1501; (d) A. E. Underhill, J. Mater. Chem., 1992, 2, 1; (e) J. Mater. Chem., Special Issue on Molecular Conductors, 1995, 5, 1469.
2. Reviews: (a) J. B. Torrance, Acc. Chem. Res., 1979, 12, 70; (b) F. Wudl, Acc. Chem. Res., 1984, 17, 227; (c) M. R. Bryce and L. C. Murphy, Nature, 1984, 309, 119; (d) D. O. Cowan, in New Aspects of Organic Chemistry 1, ed. Z. Yoshida, T. Shiba and Y. Oshino, VCH, New York, 1989, 177.
3. J. Ferraris, D. O. Cowan, V. Walatka and J. H. Perlstein, J. Am. Chem. Soc., 1973, 95, 498.
4. (a) For the first dimeric TTF derivative see: M. L. Kaplan, R. C. Haddon and F. Wudl, J. Chem. Soc., Chem. Commun., 1977, 388; (b) Review: M. Adam and K. Müllen, Adv. Mater., 1994, 6, 439; (c) A. Dolbecq, K. Boubekeur, P. Batail, E. Canadell, P. Auban-Senzier, C. Coulon, K. Lerstrup and K. Bechgaard, J. Mater. Chem., 1995, 5, 1707; (d) J. Y. Becker, J. Bernstein, A. Ellern, H. Gershtenman and V. Khodorkovsky, J. Mater. Chem., 1995, 5, 1557.
5. (a) T. Mitsuhashi, M. Goto, K. Honda, Y. Maruyama, T. Sugawara, T. Inabe and T. Watanabe, J. Chem. Soc., Chem. Commun., 1987, 810; (b) T. Mitsuhashi, M. Goto, K. Honda, Y. Maruyama, T. Inabe, T. Sugawara and T. Watanabe, Bull. Chem. Soc. Jpn., 1988, 261; (c) M. González, P. de Miguel, N. Martín, J. L. Segura, C. Seoane, E. Ortí, R. Viruela and P. M. Viruela, Adv. Mater., 1994, 6, 765 and references therein.
6. (a) J. Y. Becker, J. Bernstein, S. Bittner, N. Levi and S. S. Shaik, J. Am. Chem. Soc., 1983, 105, 4468; (b) J. Y. Becker, J. Bernstein, S. Bittner, N. Levi, S. S. Shaik and N. Zer-Zion, J. Org. Chem., 1988, 53, 1689; (c) V. Khodorkovsky and J. Y. Becker, in Organic Conductors: Fundamentals and Applications, ed. J. P. Farges, Marcel Dekker, New York, 1994, ch. 3, 75.
7. (a) M. P. Le Paillard and A. Robert, Bull. Soc. Chim. Fr., 1992, 129, 205; (b) A. Robert and D. Lorcy, Molecular Engineering for Advanced Materials, ed. J. Becher and K. Schaumburg, NATO ASI Series C, vol. 456, Kluwer Academic Publishers, Dordrecht, 1994, 251; (c) N. Martín and C. Seoane, in Handbook of Organic Conductive Molecules and Polymers, vol. 1, ed. H. S. Nalwa, Wiley, Chichester, 1997, ch. 1; (d) Review: N. Martín, J. L. Segura and C. Seoane, J. Mater. Chem., 1997, 7, 1661.
8. K. B. Simonsen, K. Zong, R. D. Rogers, M. P. Cava and J. Becher, J. Org. Chem., 1997, 62, 679.
9. There have been many attempts to synthesise compounds which could test the proposal (A. Aviram and M. A. Ratner, Chem. Phys. Lett., 1974, 29, 277) that a molecule of the type D σ-A (with an excited state D⁺σ-A^–) could be a unidirectional molecular rectifier. For examples see: (a) G. J. Ashwell, J. R. Sambles, A. S. Martin, W. G. Parker and M. Szablewski, J. Chem. Soc., Chem. Commun., 1990, 1374; (b) A. S. Martin, J. R. Sambles and G. J. Ashwell, Phys. Rev. Lett., 1993, 70, 218 and references therein.
10. C. A. Panetta, J. Baghdadchi and R. M. Metzger, Mol. Cryst. Liq. Cryst., 1984, 107, 103.
11. S. Frenzel and K. Müllen, Synth. Met., 1996, 80, 175.
12. (a) A. M. Kini, D. O. Cowan, F. Gerson and R. Möckel, J. Am. Chem. Soc., 1985, 107, 556; (b) A. Aumüller and S. Hünig, Liebigs Ann. Chem., 1984, 618; (c) B. S. Ong and B. Keoshkerian, J. Org. Chem., 1984, 49, 5002; (d) E. Torres, C. A. Panetta and R. M. Metzger, J. Org. Chem., 1987, 52, 2944.
13. (a) U. Schubert, S. Hünig and A. Aumüller, Liebigs Ann. Chem., 1985, 1216; (b) N. E. Heimer and D. L. Mattern, J. Am. Chem. Soc., 1993, 115, 2217; (c) E. Ortí, R. Viruela and P. M. Viruela, J. Mater. Chem., 1995, 5, 1697.
14. (a) N. Martín and M. Hanack, J. Chem. Soc., Chem. Commun., 1988, 1522; (b) K. Maruyama, H. Imahori, K. Nakagawa and T. Tanaka, Bull. Chem. Soc. Jpn., 1989, 62, 1626.
15. (a) L. R. Melby, R. J. Harder, W. R. Hertler, W. Mahler, R. E. Benson and W. E. Mochel, J. Am. Chem. Soc., 1962, 84, 3374; (b) J. R. Anderson and O. Jorgensen, J. Chem. Soc., Perkin Trans. 1, 1979, 3095.
16. Similarly well-defined anodic and cathodic redox behaviour of the fused-ring 6,11-bis(dicyanomethylene)-12-methylbenzo[b] phenoxazine donor acceptor system has been reported recently: B. IIIescas, N. Martín, J. L. Segura, C. Seoane, E. Ortí, P. Viruela and R. Viruela, J. Mater. Chem., 1995, 5, 1563.
17. (a) D. C. Green, J. Org. Chem., 1979, 44, 1476; (b) A. S. Batsanov, M. R. Bryce, J. N. Heaton, A. J. Moore, P. J. Skabara, J. A. K. Howard, E. Ortí, P. M. Viruela and R. Viruela, J. Mater. Chem., 1995, 5, 1689.
18. L. M. Goldenberg, P. J. Skabara, M. R. Bryce and M. C. Petty, J. Electroanal. Chem., 1996, 408, 173.
19. (a) S. Hünig, G. Kiesslich, H. Quast and D. Scheutzow, Liebigs Ann. Chem., 1973, 310; (b) J. B. Torrance, B. A. Scott, B. Welber, F. B. Kaufman and P. E. Seiden, Phys. Rev. B, 1979, 19, 730.
20. J. S. Chappel, A. N. Bloch, W. A. Bryden, M. Maxfield, T. O. Poehler and D. O. Cowan, J. Am. Chem. Soc., 1981, 103, 2442.
21. Y. Yamashita, T. Suzuki and T. Mukai, J. Chem. Soc., Chem. Commun., 1987, 1184.
22. A. Niemz, J. Imbriglio and V. Rotello, J. Am. Chem. Soc., 1997, 119, 887.
23. (a) Cf M. R. Bryce, G. Cooke, A. S. Dhindsa, D. Lorcy, A. J. Moore, M. C. Petty, M. B. Hursthouse and A. I. Karaulov, J. Chem. Soc., Chem. Commun., 1990, 816; (b) For an improved synthesis of TTF-CO₂H see: J. Garín, J. Orduna, S. Uriel, A. J. Moore, M. R. Bryce, S. Wegener, D. S. Yufit and J. A. K. Howard, Synthesis, 1994, 489; (c) TTF was synthesised as reported: A. J. Moore and M. R. Bryce, Synthesis, 1997, 407.
24. A. M. Abeysekera, J. Grimshaw and S. D. Perera, J. Chem. Soc., Perkin Trans. 2, 1990, 1797.