ABSTRACT
Complex study of quadrupolar azacrown dye (E,E)-5,5Ì-Bis[2-(4-(4',7',10',13',16'-pentaoxa-1 azacyclooctadecyl)phenyl)ethenyl]-2,2Ì-bipyridine 1 was performed. Electronic spectra of absorption and fluorescence in different solvents exhibit strong solvatochromism. Electrooptical absorption measurements (EOAM) were performed to determine the electric dipole moments. These measurements gave large values of dipole moments in the ground µg and Franck-Condon excited state µeFC equal to 6.8 ± 0.14C m and 39.3 ± 0.3C m, respectively. Furthermore, the results of EOAM suggest the existence two conformers in the ground state with close energies of electronic transitions. Density functional theory (DFT) calculations directly show that the shape of this molecule is not planar in the ground state and also allows the existence of two stable conformers with close energies. They appeared due to different orientations of the left and right pyridine fragments of the solute. The energies, electric dipole moments and dependences of dipole moments on the strength of applied electric field were calculated for found stable conformers of 1. DFT calculations with TD / B3LYP / 3-21G and cc-pVDZ (Time Depend) approach show that external electric field increases dramatically the dipole moments of the solute under study. The higher field intensity the larger the excited electric dipole in the range intensities from zero to â¼ 2.8·× 10 9 V/m.
ABSTRACT
Electrooptical absorption measurements (EOAM), solvatochromic dependences and quantum chemical simulations testify to large dipole moments change of two quadrupolar oligophenylenevinylenes upon transition to Franck-Condon excited state µeFC. The values of the dipole moments µg and µeFC are in the range [(4.2 - 4.9)1030] C m and (30.8 - 47.0)1030C m, respectively. The relations of dipole moments in the ground and excited states determined by EOAM correlate well with results obtained via the solvatochromic method. Calculations carried out by density functional theory (DFT) show that optimized configuration of the ground state of these molecules is not planar. The results from all methods applied unequivocally show the structural symmetry breaking in the studied compounds.
ABSTRACT
Time-resolved and steady-state spectra and kinetics of anisotropy of 1-phenylnaphthylamine (1-AN) fluorescent probe in phosphatidylcholine bilayer membranes have been examined using a nanosecond laser spectrofluorimeter. In this system we consider two kinds of inhomogeneous broadening of spectra, the first of which is due to different probe locations in membrane, while the second one is due to the statistical distribution of interaction energy within a given location. This broadening causes the red shift of the fluorescence spectrum at red-edge excitation, the specific dependences of instantaneous fluorescence and fluorescence anisotropy spectra on the wavelength of excitation. A field diagram is presented which, by describing the free energy levels of the polar fluorescent probe in membranes, makes it possible to unambiguously interpret the whole set of experimental data. It is suggested that the release of potential energy of intermolecular interactions which occurs in the process of relaxation, results in accelerated (light-induced) rotation of the probe inside the membrane.