A Novel N-Type Molecular Dopant With a Closed-Shell Electronic Structure Applicable to the Vacuum-Deposition Process

Rational design, synthesis, and characterization of a new efficient versatile n-type dopant with a closed-shell electronic structure are described. By employing the tetraphenyl-dipyranylidene (DP0) framework with two 7π-electron systems modified with N,N-dimethylamino groups as the strong electron-donating substituent, 2,2',6,6'-tetrakis[4-(dimethylamino)phenyl]-4,4'-dipyranylidene (DP7), a closed-shell molecule with an extremely high-lying energy level of the highest occupied molecular orbital, close to 4.0 eV below the vacuum level, is successfully developed. Thanks to its thermal stability, DP7 is applicable to vacuum deposition, which allows utilization of DP7 in bulk doping for the development of n-type organic thermoelectric materials and contact doping for reducing contact resistance in n-type organic field-effect transistors. As vacuum-deposition processable n-type dopants are very limited, DP7 stands out as a useful n-type dopant, particularly for the latter purpose.