Energy transfer processes between metal ions and a ReI polymer

ULISES N. FAGIOLI; YENY A. TOB¨®N C.; GUSTAVO T. RUIZ; M. R. FELIZ; E. WOLCAN

CEPEMA-USP, Cubatao, SP, Brasil

Congreso; IX Encuentro Latinoamericano de Fotoqu¨ªmica y Fotobiolog¨ªa; 2008

Numerous studies have been concerned with thermal and photochemical reactions of inorganic polymers in the solid-state and solution phase. Interest in their photochemical and photophysical properties is driven by their potential applications in catalysis and optical devices.1 The properties in the solution phase of the polymers I and II (see Scheme 1) were investigated in previous works.1-3 Marked differences were found between the photochemical and photophysical properties of polymers I and II and those of the related monomeric complexes, pyReI(CO)3L+ (py = pyridine; L = phen, 2,2¡ä-bpy). The main cause of these differences is the photogeneration of MLCT excited sates in concentrations that are much larger when -ReI(CO)3L+ chromophores are bound to poly-4-vinylpyridine, (vpy)600. This is the photophysical result of ReI chromophores being crowded in strands of a polymer instead of being homogeneously distributed through solutions of a pyReI(CO)3L+ complex. The recently communicated association of several hundred strands of II in nearly spherical aggregates also contributes to the crowding of chromophores in small spaces in the solution, where the interaction between excited states becomes appreciable.3 The photogeneration of MLCT excited states in close vicinity within a polymer strand makes possible the study of energy transfer processes if donor and acceptor pendants are distributed along the strand. Coordination of CuII ions to poly-4-vinylpyridine has been reported in the literature.4-8 In this presentation, we report the coordination of CuII species to {[(vpy)2-vpyRe(CO)3phen]CF3SO3}n=200.We also explore the quenching of the ReI polymer¡¯s MLCT excited state by the coordination of CuX2 (X = Cl or CF3SO3) to the free pyridines of the polymer backbone. The addition of an acetonitrile solution of CuX2 (X = Cl or CF3SO3) to an acetonitrile solution of the polymer I produces a rapid coordination of the CuII species to the uncoordinated pyridines with approximate stoichometry of [CuII]/[py] ¡Ö 0.4 and [CuII]/[py] ¡Ö 0.2 for CuCl2 y Cu(CF3SO3)2, respectively. The emission spectrum of {[(vpy)2-vpyRe(CO)3phen]CF3SO3}n=200 in deoxygenated CH3CN at room temperature exhibited an unstructured band centered at 550 nm. The quenching of the luminescence of the ReI polymer by CuCl2 and/or Cu(CF3SO3)2 was studied using steady state and time-resolved techniques under similar experimental conditions to those utilized in the investigation of the binding of CuII species to the ReI polyelectrolyte. The MLCT luminescence quenching by CuII species does not follow a Stern-Volmer kinetics. Moreover, there is a progressive shifting of the emission spectrum maximum to shorter wavelengths as the quenching proceeds.   REFERENCES [1] Wolcan, E.; Ferraudi, G. J. Phys. Chem. A  2000, 104, 9281. [2] Wolcan, E.; Feliz, M. R. Photochem. Photobiol. Sci. 2003, 2, 412. [3] Wolcan, E.; Alessandrini, J. L.; Feliz, M. R. J. Phys. Chem. B 2005, 109, 22890. [4] Tsuchida, E.; Kaneko, M.; Nishide, H. Makromol. Chem. 1973,164, 203. [5] Kirsh, Y. E.; Kovner, V. Ya.; Kokorin, A. I.; Zamaraev, K. I.;Cherniak, V. Ya.; Kabanov, V. A. Eur. Polym. J. 1974, 10, 671. [6] Agnew, H. J. Polym. Sci. 1976, 14, 2819. [7] Nishide, H.; Tsuchida, E. J. Polym. Sci. 1981, 19, 835. [8] Jeschke, G. J. Phys. Chem. B 2000, 104, 8382.