Multistate/Multifunctional Systems. A Thermodynamic, Kinetic, and Photochemical Investigation of the 4′-Dimethylaminoflavylium Compound Ana Roque, ² Carlos Lodeiro, ² Fernando Pina,* ,² Mauro Maestri,* ,‡ Stephane Dumas, ‡ Paolo Passaniti, ‡ and Vincenzo Balzani ‡ Contribution from the Departamento de Quı ´mica, Centro de Quı ´mica-Fina e Biotecnologia, Faculdade de Cie ˆ ncias e Tecnologia, UniVersidade NoVa de Lisboa, Quinta da Torre, 2825-Monte de Caparica, Portugal, and Dipartimento di Chimica “G. Ciamician”, UniVersita ` di Bologna, 40126 Bologna, Italy Received September 27, 2002 ; E-mail: mmaestri@ciam.unibo.it Abstract: The 4′-dimethylaminoflavylium ion in aqueous solution undergoes an intricate network of chemical reactions controlled by pH and light excitation. It is shown that nine different forms are involved, including two species that are not present in previously investigated compounds of the flavylium family. The thermodynamic and kinetic constants of the equilibria and interconversion processes have been obtained by pH jump (included stopped-flow) experiments. The photochromic properties exhibited by the trans/cis chalcone forms have been investigated. The peculiar aspect of 4′-dimethylaminoflavylium, as compared to previously investigated compounds of the same family, is a close to planarity structure, as demonstrated by the X-ray analysis on the parent 4′-aminoflavylium compound (2.3° torsion angle between the benzopyrylium and benzene ring). The results obtained show that the flavylium cation is strongly stabilized by the electron-donor character of the dimethylamino substituent on the benzene ring. The donor-acceptor interaction makes both the protonation of the amino group and the hydration of the flavylium cation difficult, with consequences on the tautomerization and cis/trans isomerization reactions. The multistate/multifunc- tional properties of 4′-dimethylaminoflavylium have been discussed in the frame of write-lock-read- unlock-erase cycles. Introduction By using a single input on a chemical compound, one can play with two states. When more than one input is used, the number of available states increases, leading to systems capable of performing complex functions. On the application of n independent stimuli, each one related to a couple of states, 2n different states of the systems become available in principle. A number of compounds have recently been described in which different stimuli have been used to interconvert several states. 1,2 Systems which respond to a given combination of multiple stimuli open the way to complex switches (logic gates) at the molecular scale. 3 Because of the presence of a 2-phenyl-benzopyrylium core, synthetic flavylium salts, 4-9 as well as natural anthocyanins, 10,11 can be involved in intricate networks of chemical transforma- tions in aqueous solution. Such transformations follow a general pattern, schematized in Figure 1, which involves four main species: a flavylium cation AH + , a hemicetal species B2 obtained by hydration in the 2 position of the flavylium cation, ² Universidade Nova de Lisboa. ‡ Universita ` di Bologna. (1) For reviews, see: (a) Niemz, A.; Rotello, V. M. Acc. Chem. Res. 1999, 32, 44. (b) Kaifer, A. E. Acc. Chem. Res. 1999, 32, 62. (c) Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. Angew. Chem., Int. Ed. 2000, 39, 3348. (d) Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, 2001. (2) For some leading papers, see: (a) Irie, M.; Miyatake, O.; Uchida, K.; Eriguchi, T. J. Am. Chem. Soc. 1994, 116, 9894. (b) Kawai, S. H.; Gilat, S. L.; Posinet, R.; Lehn, J.-M. Chem.-Eur. J. 1995, 1, 285. (c) Speitzer, H.; Daub, J. Chem.-Eur. J. 1996, 2, 1150. (d) Plenio, H.; Aberle, C. Angew Chem., Int. Ed. 1998, 37, 1397. (e) Ji, H.-F.; Dabestani, R.; Brown, G. M. J. Am. Chem. Soc. 2000, 122, 9306. (f) Goodman, A.; Breinlinger, E.; Ober, M.; Rotello, V. M. J. Am. Chem. Soc. 2001, 123, 6213. (g) Gobbi, L.; Seiler, P.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 674. (h) Gobbi, L.; Seiler, P.; Diederich, F.; Gramlich, V.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M. HelV. Chim. Acta 2001, 84, 743. (i) Bourgel, C.; Boyd, A. S. F.; Cooke, G.; Augier de Cremiers, H.; Duclairoir, F. M. A.; Rotello, V. M. Chem. Commun. 2001, 1954. (j) Zhao, W.; Carreira, E. M. J. Am. Chem. Soc. 2002, 124, 1582. (3) (a) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV. 1997, 97, 1515. (b) Balzani, V.; Credi, A.; Venturi, M. In Supramolecular Science: Where It is and Where It is Going; Ungaro, R., Dalcanale, E., Eds.; Kluwer: Dordrecht, 1999; p 1. (c) de Silva, A. P.; Fox, D. B.; Moody, T. S. In Stimulating Concepts in Chemistry; Shibasaki, M., Stoddart, J. F., Vo ¨gtle, F., Eds.; Wiley-VCH: Weinheim, 2000; p 307. (d) Pease, A. R.; Stoddart, J. F. Struct. Bonding 2001, 99, 189. (e) de Silva, A. P.; McClenaghan, N. D.; McCoy, C. P. In Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, 2001; p 339. (f) Raymo, F. M. AdV. Mater. 2002, 14, 401. Stojanovic, M. N.; Mitchell, T. E.; Stefanovic, D. J. Am. Chem. Soc. 2002, 124, 3555 and references therein. (4) McClelland, R. A.; Gedge, S. J. Am. Chem. Soc. 1980, 102, 5838. (5) McClelland, R. A.; McGall, G. H. J. Org. Chem. 1982, 47, 3730. (6) Figueiredo, P.; Lima, J. C.; Santos, H.; Wigand, M.-C.; Brouillard, R.; Mac ¸ anita, A.; Pina, F. J. Am. Chem. Soc. 1994, 116, 1249. (7) Brouillard, J. R.; Dubois, J. E. J. Am. Chem. Soc. 1977, 99, 1359. (8) Pina, F.; Maestri, M.; Balzani, V. J. Chem. Soc., Chem. Commun. 1999, 107. (9) Maestri, M.; Pina, F.; Balzani, V. Multistate/Multifunctional Molecular- Level Systems - Photochromic Flavylium Compounds. In Molecular Switches; Feringa, L. B., Ed.; Wiley-VCH: Weinheim, 2001; p 339. (10) Brouillard, R. In The FlaVonoids, AdVances in Research; Harborne, J. B., Ed.; Chapman and Hall: London, 1988; p 525. (11) Brouillard, R. In Anthocyanins as Food Colors; Markakis, P., Ed.; Academic Press: New York, 1982; Chapter 1. Published on Web 01/01/2003 10.1021/ja0287276 CCC: $25.00 © 2003 American Chemical Society J. AM. CHEM. SOC. 2003, 125, 987-994 9 987