Fluorescence resonance energy transfer (FRET) in the Solution Phase Photophysics of -Re(CO)3L+ Pendants Bonded to Poly(4-vinylpyridine)

L. L. B. BRACCO; M. P. JULIARENA; G. T. RUIZ; M. R. FÉLIZ; G. J. FERRAUDI; E. WOLCAN

Lima, Perú

Congreso; Simposio Latinoamericano y IX Congreso Iberoamericano de Polímeros (SLAP2008); 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 were investigated in previous works.1,2,3 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+ (L = phen, 2,2¢-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-vynilpyridine, (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 We have applied ligand substitution reactions of the ReI complexes to the derivatization of polymers (III), (IV), (V), (VI) and (VII), which consist of a 4-polyvynilpyridine backbone with pendant chromophores -ReI(CO)3L1 and -ReI(CO)3L2. Morphologies of these polymers were studied using TEM. Multiple morphologies of aggregates from these ReI polymers were obtained by using different solvents. We have chosen L1 and L2 to be L1 = 5-Nitro-1,10 phenanthroline (NO2-phen) and L2 = 3,4,7,8-tetramethyl-1,10 phenanthroline (tmphen) to be able to observe FRET between the MLCTRe® tmphen and MLCTRe® NO2-phen inside the polymers. Energy transfer between  MLCTRe® tmphen and MLCTRe® NO2-phen excited states inside the polymers was evidenced by steady state and time resolved spectroscopy. Current Förster resonance energy transfer theory was successfully applied to energy transfer processes in these polymers. Luminescence quantum yields and lifetimes of polymers (V)-(VII) are discussed in terms of the current FRET theories applicable to energy transfer between acceptors and donors randomly distributed in a polymer.                               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.