RESUMO
In the present work, new rhenium(i) polypyridyl compounds, fac-[Re(L)(CO)3(cbz2phen)](+/0) where cbz2phen = 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline and L = Cl(-), pyridine (py) or 2-aminomethylpyridine (ampy) were synthesized and characterized by (1)H NMR, UV-Vis and IR spectroscopy combined with theoretical calculations using time-dependent density functional theory (TD-DFT). Their photophysical properties were investigated by steady state and time-resolved emission spectroscopy. These compounds show a strong and broad absorption band around 350-500 nm that, also by TD-DFT, corresponds to the carbazol â phenanthroline intraligand charge transfer transition, (1)ILCTcbz2phen, with some contribution of the Re(i) â phenanthroline metal-to-ligand charge transfer transition, (1)MLCTReâcbz2phen. In contrast to typical Re(i) polypyridyl complexes, cbz2phen-based Re(i) compounds exhibit two emission maxima in CH3CN solution and relatively low emission quantum yields, 10(-3)-10(-2). Solution phase time-resolved photoluminescence and excited state quenching experiments provided meaningful information on the presence of multiple emitter states after light excitation, which were identified as an (1)ILCTcbz2phen excited state deactivation at higher energies and a long-lived phosphorescence attributed to the (3)MLCTReâcbz2phen excited state. When embedded into a PMMA matrix, the radiative decay from the singlet state is inhibited and the contribution of both (3)MLCT and (3)ILCTcbz2phen to the luminescence is observed. The photophysics of these Re(i) compounds reported herein provide new insights into the understanding of substitutional groups on the polypyridyl ligands that are relevant to practical and fundamental development of photo-induced molecular devices.
RESUMO
Two special dynamical transitions of universal character have recently been observed in macromolecules (lysozyme, myoglobin, bacteriorhodopsin, DNA and RNA) at T* ~100-150 K and T(D) ~180-220 K. The underlying mechanisms governing these transitions have been the subject of debate. In the present work, a survey is reported on the temperature dependence of structural, vibrational and thermodynamical properties of a nearly anhydrous amino acid (orthorhombic polymorph of the amino acid l-cysteine at a hydration level of 3.5%). The temperature dependence of x-ray powder diffraction patterns, Raman spectra and specific heat revealed these two transitions at T* = 70 K and T(D) = 230 K for this sample. The data were analyzed considering amino acid-amino acid, amino acid-water, water-water phonon-phonon interactions and molecular rotor activation. Our results indicated that the two referred temperatures define the triggering of very simple and particular events that govern all the interactions of the biomolecular: activation of CH(2) rigid rotors (T < T* ), phonon-phonon interactions between specific amino acid and water dimer vibrational modes (T* < T < T(D)), and water rotational barriers surpassing (T > T(D)).