Charged Frenkel biexcitons in organic molecular crystals

It is known that the energy of the lowest electronic transition in the neut ral molecules of anthracene, tetracene, and other polyacenes is blue-shifte d in comparison with the corresponding transition energy in univalent molec ular ions. This effect in a molecular crystal may be responsible for the at traction between a molecular (Frenkel) exciton and a charge carrier. Due to this attraction, a bound state of Frenkel exciton and free charge (charged Frenkel exciton) may be formed [5]. As we demonstrate below, the same mech anism can be responsible for the formation of a charged biexciton (bound st ate of two Frenkel excitons and a charge carrier). A one-dimensional lattic e model is used which corresponds to J aggregates and is also a good approx imation for quasi-one-dimensional crystals. Calculations are performed for molecular crystals like tetracene, where the exciton band at low temperatur e is much narrower than the band of the charge carrier. (C) 2001 MAIK "Nauk a/Interperiodica".