7,7,8,8-tetracyanoquinodimethane (TCNQ), CAS number 1518-16-7, with a LUMO at 4.5 eV, is known for the charge-transfer salts formed by its radical anion TCNQ in photovoltaic, light-emitting diodes, and organic field-effect transistor devices. TCNQ and its derivatives have been used as dopants, leading to an increase in hole mobility or to the lowering of injection barriers. One classic example of such is the treatment of tetrathiafulvene (TTF), an electron donor with TCNQ. TFF and TCNQ form an ion pair, the TTF-TCNQ complex. This process of doping leads to the crystallization of the ion pair into a one-dimensionally stacked polymer. This polymer consists of segregated stacks of cations and anions of the donors and the acceptors, respectively. The complex crystal is an organic semiconductor that exhibits metallic electric conductivity [1, 2].
It also has been shown that TCNQ can effectively modify Cu or Ag surfaces. The formation of Cu-TCNQ and Ag-TCNQ enhances the work function of such electrodes and reduces the hole injection barrier dramatically. Furthermore, it improves electrode/organic layer contact, hence the reduction of contact resistances [3].
Tetracyanoquinodimethane (TCNQ) is also found to act as a p-type doping agent of graphene films due to its powerful electron-accepting capacity [4].