Leuco Crystal Violet as a Dopant for n-Doping of Organic Thin Films of Fullerene C₆₀

Abstract

The triphenylmethane dye crystal violet (CV) and its leuco base, leucocrystal violet (LCV), are investigated as dopants for n-type doping of fullerene C60. Conductivities up to 8 × 10-3 S/cm at 30 °C are achieved when C60 is doped with CV. Mass spectroscopy and optical spectroscopy (UV/VIS/NIR absorption and Fourier transform infrared transmission) confirm that the leuco base LCV is formed during sublimation of the cationic CV dye. When the commercially available LCV was directly used as a dopant in C60, a maximum conductivity of 1.3 × 10-2 S/cm was obtained at 30 °C. We found that in both cases, the leuco base became reoxidized to the cationic form by electron transfer to electron-accepting matrixes, leading to the doping effect. The donor properties of LCV in a charge-transfer complex with 7,7,8,8-tetracyanoquinodimethane (TCNQ) were confirmed by UV/VIS/NIR absorption and Fourier transform infrared (FTIR) spectroscopy. C60 anions were observed in the FTIR or NIR absorption spectra of the mixed films of C60 and LCV. Photoinduced charge transfer between LCV and C60 provides free electrons, which increase the n-type conductivity. The electron transfer becomes irreversible by hydride abstraction.