Design of new anchored p-dopants for high power efficiency OLEDs

Conductivity doping of charge transporting layers is becoming increasingly attractive for improving power efficiency in OLEDs. However, the number of commercially available organic molecular p-dopants is limited. The electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized p-dopant. F4-TCNQ can be used as a dopant for most hole transporting materials (HTM), but it is very volatile, which makes it difficult for vacuum processing, and has a low sticking coefficient. Here we present the design of novel anchored molecular dopants based on the TCNQ core. We first review how the reduction potential of TCNQ core is affected by substitution with alkyl groups of different electronic properties. Electron donating groups have negative effect on the reduction potential of the acceptor. However, attaching electron withdrawing groups such as halogens counteracts the effect of electron donating groups. Using gas phase theoretical calculations we determined that trifluorinated TCNQ can be anchored through a σ-coupled alkyl chain to an inert molecular anchor without sacrificing the electron affinity.