On the electronic structure of barrelene-based rigid organic donor-acceptor systems. A comparison of INDO/S-CI calculations with absorption and fluorescence emission spectra

We investigate at the INDO/S-CI level the electronic structure of a series of barrelene-based organic donor-acceptor molecules exhibiting photo-induced charge separation even in nonpolar solution. Results for excitation energies, oscillator strengths, and excited state dipole moments are compared to static UV absorption and fluorescence emission spectra. Satisfactory agreement is obtained for transition energies and excited state dipole moments if the induced part of the dipole moment of the donor-acceptor molecules in solution is properly taken into account. A particular focus lies on the conditions that foster the occurrence of low-lying charge-transfer states.