Vibrational spectra of ternary charge transfer complexes of pyrene

Pyrene, a condensed hydrocarbon forms ternary CTCs with chloranil – I2, DDQ – I2, TCNQ – I2 and TCNE – I2 combinations. The FTIR spectra of these ternary complexes have been studied. They show forbidden direct transitions in three ternary complexes except TCNQ complex in which it is allowed direct transition. Only chloranil and DDQ complexes show band gap at 0.1125 eV (EP/2). However, actual absorption show exciton bands in these excitonic semiconductors. There is a possibility of electron-exciton interaction in these ternary complexes of pyrene, which can be called exciplexes.