Charge-transfer states and white emission in organic light-emitting diodes: a theoretical investigation

Efficient white light emission has been recently reported in an electroluminescent device where the active material is a complex made of N,N′-bis(α-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and a boron–fluorine derivative of 1,6-bis(2-hydroxy-5-methylphenyl)pyridine ((mdppy)BF). Here, we investigate theoretically the intermolecular charge transfer in the materials. The interfacial layer is modeled on the basis of a simple dimer structure, for which the lowest excited states are described in the framework of a correlated quantum-chemical semiempirical technique. From the analysis of the calculated excited-state wavefunctions, we find that the lowest excited state possesses significant contributions from charge-transfer excitations from the donor (NPB) to the acceptor ((mdppy)BF). The influence of intermolecular distance and medium polarization are also explored.