Phosphine oxides and sulfides were found
to be interesting organic/inorganic n-semiconductors with high triplet energies.
The ability of the phosphine-oxides and other organic diphosphine oxide
compounds to combine high triplet energy with low operating voltage devices is
attributed to the inductive effect of the P=O moieties, and subsequent energy
lowering of the LUMO resulting in enhancement of both electron injection and
transport in the device. Thus, they could be used as hosts for blue-light
emitting phosphorescent dopants (see CrystEngComm 2011, 13, 5423-5427.; DOI: 10.1039/C1CE05388D, also WO/2008/005609 International Application No.:
PCT/US2007/066591). During our work on various dibenzophospholes, we noticed the
propensity of these compounds to form pi-stacks in the solid state, which may
like in the case of pentacene (triplet energy 0.86 eV) and similar compounds
lead to electrical conductivity. However, unlike in pentacene, the
dibenzophosphole derivatives still maintain high triplet energies (~2.8 eV).
Examples of dibromo-dibenzophosphole oxides, sulfides, selenides are electron-transporting semiconductors showing their propensity to form various stacks and columns, a feature of importance for OLEDs and/or single-crystal field-effect transistors.
We have synthesized a number of triphenyl phosphine or arsine oxides, sulfides, selenides and grew crystals in vacuum (solvent free) to elucidate the solid state structures to be able to measure the charge mobilities. Also, we have synthesized a number of dibenzophosphole and arsole derivatives and their corresponding oxides, sulfides, selenides. We are growing crystals and preparing organic films doped with these materials to measure the corresponding triplet lifetimes (decay rates). This capability to accelerate the triplet decay is further augmented by optional substituents. Several of these derivatives show potential for acting as high triplet energy n-type semiconductors.