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2 Bulletin of the Polish Academy of Sciences. Chemistry

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Hydrogen bonded complexes of coumarin 153

Królicki R., Jarzęba W., Soroushian B., Lampre I., Mostafavi M.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 4

435-449

Detailed studies of the hydrogen-bonded complexes of coumarin 153 (C153) have been carried out. It has been shown that nonlinear shifts of the steady-state absorption and fluorescence spectra taken in toluene-methanol solvent mixtures are caused by the formation of hydrogen bonded complexes between C153 and methanol, while preferential solvation plays a minor role only. IR measurements confirmed the ability of C153 to form hydrogen-bonded complexes with methanol and phenol. The stoichiometry of the formed complexes and relevant equilibrium constants have been estimated. Femtosecond solvation dynamics measurements of C153 in the toluene-methanol mixture (xMeOH = 0.2) showed that the average solvation time is higher than that in the pure solvents indicating slower relaxation of methanol in the mixture. The slow component of solvation dynamics (ok 20ps) can be attributed to translational diffusion of methanol to the first solvation shell of C153 and to the relatively slow reorientational motion of methanol involved in formation of hydrogen bond with the excited C153.

Ultrafast electron transfer in tetracyanoethylene-benzene charge transfer complex

Jarzęba W., Tokarczyk B., Murata S., Tachiya M.

Bulletin of the Polish Academy of Sciences. Chemistry

1999

Vol. 47, No. 4

347-360

Ultrafast pump-probe transient absorption spectroscopy has been applied to study return electron transfer in the tetracyanoethylene- benzene electron donor-acceptor complex in several polar and non-polar solvents. Ultrafast excitation of the charge transfer band of the complex yields an excited Franck-Condon state, which relaxes to form a contact ion pair. The decay time of the ion pair is, in most cases, longer than the solvation time and is observed on a time scale from 2 picoseconds to 1 ns, depending on the solvent. Using the empirical solvent polarity scale ^vG153 and a conventional non-adiabatic theory of electron transfer, absolute rate constants for the non-radiative return electron transfer can be predicted in different solvents.