Excited state orientational dynamics

Now, let us consider a system where an achiral molecule (A) and a chiral molecule (C) have a fixed mutual orientation. An electronic transition of the achiral molecule from the ground state z(0> to the excited state Aa, higher in energy by E0a, has a zero-order (non-perturbed) electric dipole moment po0 and an orthogonal magnetic dipole moment ma0. These moments are increased in the molecular pair (A -C) by first-order dynamic coupling as ... 

In order to understand the dynamics of the solvent fluctuation, many experimental as well as theoretical efforts have been made intensively in the last decade. One of the most convenient methods to observe solvent reorganization relaxation processes within the excited state molecule is time resolved fluorescence spectroscopy. By using time resolved techniques a time dependent fluorescence peak shift, so ( ed dynamic Stokes shift, has been detected in nanosecond picosecond >, and femtosecond time regions. Another method to observe solvent relaxation processes is time resolved absorption spectroscopy. This method is suitable for the observation of the ground state recovery of the solvent orientational distribution surrounding a solute molecule. 

The Bi contain information on the collision dynamics, in particular on the alignment and orientation of the excited states. 

Thus, knowledge of the transition moment direction of a phenol band could help in interpreting the fluorescence spectrum of a tyrosine chromophore in a protein in terms of orientation and dynamics. The absorption spectrnm of the first excited state of phenol was observed around 275 nm with a fluorescence peak aronnd 298 nm in water. The tyrosine absorption was reported at 277 nm and the finorescence near 303 nm. Fluorescent efficiency is about 0.21 for both molecules. The fluorescent shift of phenol between protic and aprotic solvents is small, compared to indole, a model for tryptophan-based protein, due to the larger gap between its first and second excited states, which resnlts in negligible coupling . ... 

The SHG intensity from interfaces is determined by the second-order nonlinear susceptibility and the Fresnel coefficients. The SHG spectra of the probe pulses change depending on the transient electronic population and the orientation of the chromophores through these physical quantities. Hohlfeld and coworkers have studied hot electron dynamics in thin metal films by this technique [21]. From the transient response of the SHG intensity, electronic temperature decay due to the electron-phonon coupling in the metal substrate is extracted. Eisenthal and coworkers have studied ultrafast excited state dynamics of dye molecules at liquid interfaces [22]. Particularly, the isomerization dynamics of an organic dye at the interfaces was found to become significantly slower than in the bulk. 

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