Applications
7,7,8,8-tetracyanoquinodimethane (TCNQ), 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 crystallisation 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.
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.
Tetracyanoquinodimethane (TCNQ) is also found to act as a p-type doping agent of graphene films due to its powerful electron-accepting capacity.
Description
7,7,8,8-tetracyanoquinodimethane (TCNQ), 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 crystallisation 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].
Chemical Properties
orange to green crystalline powder
History
The first report on the electrical conductivity in an organic solid appeared in 1954, namely, a perylene—bromine complex with a room-temperature conductivity of 0.1 S cm?1. In 1960, the organic acceptor Tetracyanoquinodimethane (TCNQ; 7,7,8,8-Tetracyanoquinodimethane) was synthesized, as well as a great number of its conducting charge-transfer complexes and radical ion salts. In the 1970s, the organic donor TTF led to the first organic metal TTF-TCNQ. Its room-temperature conductivity (500 S cm?1) increases with a decrease in the temperature to the value of 6000 S cm?1 at 60 K, where a metal-insulator transition occurs[1].
Uses
7,7,8,8-Tetracyanoquinodimethane is an electron-acceptor molecule used to form charge-transfer superconductors. It is an effective catalyst used for the ?-chlorination of carboxylic acids using chlorosulfonic acid; the presence of TCNQ suppresses competing free-radical chlorination.
Definition
ChEBI: A quinodimethane that is p-quinodimethane in which the methylidene hydrogens are replaced by cyano groups.
General Description
7,7,8,8-Tetracyanoquinodimethane (TNCQ) is a strong electron acceptor as it has four cyano groups and π-conjugation bonds that form charge transferring chains and ion radical salts which are mainly used as p-dopants for the fabrication of a variety of semiconductor applications.
References
[1] Tahar Abbaz. “Synthesis and electrochemical proprieties of novel unsymmetrical bis-tetrathiafulvalenes and electrical conductivity of their charge transfer complexes with tetracyanoquinodimethane (TCNQ).” International Journal of Molecular Sciences 13 7 (2012): 7872–7885.
