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

Spectroscopic experiments that study the effect of an externally applied el ectric field on transition energies provide a wealth of information if carr ied out under high-resolution conditions. We present experimental data for octatetraene incorporated into two alkane hosts, n-hexane and n-heptane, wh ere persistent holes burned into the lowest lying electronic singlet transi tion serve as precise transition frequency markers. To access the informati on contained in these data, we use molecular mechanics simulations to arriv e at microscopic models for the guest-host geometries and calculate the int ernal and polarization potentials of the structures. A general model descri bing how molecular electronic energy levels are affected by an arbitrary di stribution of electrostatic fields and potentials over the size of a probe molecule is presented and applied to a simple pi-electron model that accura tely 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.