ELECTROABSORPTION STUDY OF EXCITED-STATES IN HYDROGEN-BONDING SOLIDS - EPINDOLIDIONE AND LINEAR TRANS-QUINACRIDONE

Electroabsorption (EA) spectra within the first absorption band of vacuum-evaporated films of epindolidione (EPI) and linear trans-quinacridone (QAC) have been studied in search of the hydrogen-bonding effect on electronic excited states. Whereas the EPI EA spectra are determined by well-localized molecular excitons, the EA spectra of QAC can be rationalized only by the involvement of the low-energy.charge-transfer (CT) excitons. The lowest CT state is found to appear within the first dominant absorption transition at 2.22 +/- 0.02 eV. Near resonance between an intramolecular (Frenkel type) excitation and nearest-neighbour CT states is suggested to underlie the strong absorption and electroabsorption features in this spectral range. The EA effect is ascribed to the electric-field-induced mixing of the hybridized Frenkel/symmetric CT excitons with antisymmetric CT states. Intermolecular hydrogen bonding of the N-H ... 0 type is suggested to play an important role in creation of the CT states in QAC.