Electrogenerated Chemiluminescence from Derivatives of Aluminum Quinolate and Quinacridones: Cross-Reactions with Triarylamines Lead to Singlet Emission through Triplet−Triplet Annihilation Pathways

Abstract

Solution electrogenerated chemiluminescence (ECL) was evaluated for molecules of interest for organic light-emitting diodes (OLEDs), using high-frequency voltage pulses at a microelectrode. Radical cations of different energies were electrogenerated from a series of triarylamine hole-transport materials (x-TPD), in the presence of radical anions of a high electron affinity sulfonamide derivative of tris(8-hydroxyquinoline)aluminum (Al(qs)3), or a bis(isoamyl) derivative of quinacridone (DIQA). The resultant emission was from the excited singlet states 1Al(qs)3* or 1DIQA*, the same excited state produced in OLEDs based on these molecules. In solution, the majority of the reaction pairs had insufficient energy to populate 1Al(qs)3* or 1DIQA* directly, but could form the triplet states 3Al(qs)3* or 3DIQA*. The reaction order and the temporal response of the emission were consistent with subsequent formation of the excited singlet states via triplet−triplet annihilation (TTA). For reactions with a low excess ...