Effects of internal electric fields and electrostatic potentials on optical spectra of linear polyenes

The distribution of the nuclear and electronic charges determine a moleculeʹs chemical and physical behavior. The electric fields and electrostatic potentials that one molecule produces at another could not be effectively addressed experimentally because a sensitive probe for electrostatic effects at the atomic or molecular level was lacking. This is no longer the case. We have shown that it is possible to obtain detailed information about electric fields arising from molecular charge distributions by investigating the effects of externally applied electric fields on spectral holes burned into the absorption band of probe molecules. The experiments were carried out on the linear polyene all-trans-octatetraene (an important model system for conducting polymers like polyacetylene) in polycrystalline n-alkane matrices and resulted in surprisingly different Stark profiles for alkanes with almost identical dielectric properties. These observations are reconciled by our more detailed understanding of the microscopic structure of the chromophore sites in different alkane crystals.