Chromophore optical transition frequency

The approach here is based on the work of Mukamel [1], to which the reader is referred for a much more complete description. Consider an optical transition between the ground and excited states of a chromophore in solution. The optical transition frequency of the ith chromophore can be written as... 

The relative strength of the hydrogen-bonding interactions may also be estimated indirectly by correlating their effect on the optical transition frequencies of the chromophore. In the Kamlet-Taft (K-T) analysis , any solvent-influenced property of the solute... 

The significance of vibrational optical activity becomes apparent when it is compared with conventional electronic optical activity in the form of optical rotatory dispersion (ORD) and circular dichroism (CD) of visible and near-ultraviolet radiation. These conventional techniques have proved most valuable in stereochemistry, but since the electronic transition frequencies of most structural units in a molecule occur in inaccessible regions of the far-ultraviolet, they are restricted to probing chromophores and their immediate intramolecular environments. On the other hand, a vibrational spectrum contains bands from most parts of a molecule, so the measurement of vibrational optical activity should provide much more information. 

Tn denotes the dephasing time of the optical transition, T the lifetime of the excited state (fluorescence hfetime) and the pure dephasing time. At low temperatures T is essentially independent on temperature while shows a strong dependence on temperature. The actual value of at a given temperature depends on the excitation of low frequency modes (phonons, librations) that couple to the electronic transition of the chromophore. In crystalline matrices at low temperatures (T <2 K) Tl approaches infinity as host phonons and local modes are essentially quenched and the linewidth is solely determined by the lifetime contribution. 

Optical spectroscopy of dilute chromophores has proven to provide a very useful probe of the structural and dynamical properties of both crystalline and amorphous solids. This is because the transition frequency for a vibronic transition of a chro-mophore is generally very sensitive to the positions of the nearby atoms, ions, or molecules of the solid. 

Here a) is the optical frequency used in the EFISH measurement, co is the frequency adopted in the electro-optic measurement, and cOq is the transition energy between the ground state and first excited state of the chromophore. 

When the chromophores (dipoles) of a polymer are oriented electrically (electric field poling) and mobility is frozen below the glass transition temperature of the polymer, these materials can be used as frequency doublers (second harmonic generation (SHG)), and materials for waveguides and electro-optical devices. ... 

Before we return to the quantitative calculation of rotational strengths in saturated ketones, one further point is worth mentioning here. So far we have emphasized the utility of the one-electron approach for symmetric chromophores. However, it should be kept in mind by the reader that from a broader point of view, a one-electron approach to optical activity is always appropriate for the calculation of rotational strengths of single electronic transitions to the same extent that the orbital approach is applicable for the calculation of frequencies and intensities of such transitions. We shall elaborate on this last statement in Section V-D. 

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