Handbook of Inorganic Chemistry Research

EZEQUIEL WOLCAN; MARIO. R. FÉLIZ

Photophysical and Photochemical Properties of Inorganic Polymers Containing Re(CO)3L+ Pendants

Nova Science Publishers

Lugar: Nueva York; Año: 2010; p. 1 - 52

In this chapter, we describe the synthesis, photophysical and photochemical properties of inorganic polymers containing-Re(CO)3L+ pendants with general formula [(vpy)2-vpyRe(CO)3 L+]n~200 (vpy = vinylpyridine, L=a–diimine). Marked differences were found between the photochemical and photophysical properties of the polymers and those of the related monomeric complexes, pyRe(CO)3L+ (py = pyridine). The main cause of these differences is the photogeneration of the metal-to-ligand charge transfer (MLCT) excited sates in concentrations that are much larger when -Re(CO)3L+ chromophores are bound to (vpy)n~600. This is the photophysical result of Re(I) chromophores being crowded in strands of a polymer instead of being homogeneously distributed through solutions of a pyRe(CO)3L+ complex. The photochemical and photophysical properties of polymers {[(vpy)2-vpyRe(CO)3L]CF3SO3}n~200 and the related monomers CF3SO3[pyRe(CO)3L] (L = phen and bpy) were investigated in solution phase. The yield of formation and the kinetics of decay of the MLCT excited state were found to be dependent on medium and laser power. MLCT excited states in the polymers undergo a more efficient annihilation and/or secondary photolysis than in the monomers. Solvent and temperature effects on the polymers photophysical properties are rationalized in terms of the transition between rigid rod and coil structures of the Re(I)-polymers. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies on acetonitrile solutions of the polymer {[(vpy)2-vpyRe(CO)3(bpy)]CF3SO3}n~200 demonstrated that the Re(I) polymer molecules aggregate to form spherical nanodomains of radius R ~ 156 nm. Coordination of Cu(II) species to the Re(I) polymer causes a decrease in the nanodomain radius and a distortion from the spherical shape as well as a quenching of the MLCT excited state by energy transfer processes that are more efficient than those in the quenching of the monomer CF3SO3[pyRe(CO)3(bpy)] luminescence by Cu(II). Energy transfer between MLCT(Re®tmphen) and MLCT(Re®NO2-phen) excited states inside mixed polymers like {[(vpy)2-vpyRe(CO)3(tmphen)+]}n{[(vpy)2-vpyRe(CO)3(NO2-phen)+]}m 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. The photochemical and photophysical properties of the polymers [(vpy-CH3+)2-vpyRe(CO)3(phen)]n~200 have been investigated in solution phase and compared to those of a related polymer, [(vpy)2-vpyRe(CO)3(phen)]n~200, and monomer, pyRe(CO)3(phen)+. Irradiations at 350 nm induce intrastrand charge separation in the peralkylated polymer, a process that stands in contrast with the energy migration observed with [(vpy)2-vpyRe(CO)3(phen)]n~200. Electronically excited -vpyRe(CO)3(phen)+ chromophores and charge separated intermediates react with neutral species, e.g., 2,2´,2´´-nitrilotriethanol (TEOA), and anionic electron donors, e.g., SO32- and I-. The anionic electron donors react more efficiently with the MLCT excited state of these polyelectrolytes than with the excited MLCT state of pyRe(CO)3(phen)+