Effects of electrostatic fields and potentials on the electronic energies of conjugated organic molecules

Spectroscopic experiments that study the effect of an externally applied electric field on transition energies provide a wealth of information if carried out under high-resolution conditions. We present experimental data for octatetraene incorporated into two alkane hosts, n-hexane and n-heptane, where persistent holes burned into the lowest lying electronic singlet transition serve as precise transition frequency markers. To access the information contained in these data, we use molecular mechanics simulations to arrive at microscopic models for the guest-host geometries and calculate the internal and polarization potentials of the structures. A general model describing how molecular electronic energy levels are affected by an arbitrary distribution of electrostatic fields and potentials over the size of a probe molecule is presented and applied to a simple pi-electron model that accurately reproduces the electronic energies of linear polyenes. On this basis, the hole profiles are calculated and compared to the experimental results, leading to a microscopic picture of the guest-host structures and molecular electrostatic fields.