Underpotential and overpotential electrocrystallization of semiconducting silver-tetracyanoquinodimethane onto gold substrates from an ionic liquid

Electrocrystallization of nanoneedles and nanorods of silver- tetracyanoquinodimethane (AgTCNQ) onto a gold substrate has been achieved from the ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF ₄), containing dissolved TCNQ and Ag⁺. In ionic liquid media, underpotential deposition (UPD) and overpotential deposition (OPD) of metallic Ag at a gold electrode occur at more positive potentials than that for reduction of TCNQ to TCNQ^-. In contrast, the reduction of TCNQ and Ag⁺ occurs at almost the same potential in MeCN. The different thermodynamics that apply in the ionic liquid environment enables controlled electrocrystallization of AgTCNQ via potential-dependent mechanisms. Nanoneedles AgTCNQ could be obtained at 0.3 V vs. Fc^0/+ (Fc = ferrocene), while nanorods could be formed at -0.2 V vs. Fc^0/+. Raman, IR and X-ray diffraction data imply that the formation of highly pure and crystalline phase of AgTCNQ on gold, and that AgTCNQ electrocrystallized under UPD or OPD conditions only differ in morphology and not in phase. The study highlights the capability of the electrocrystallization method to precisely control the morphology of nanomaterials, and also using ionic liquids as media for preparation of technologically important metal-TCNQ charge transfer complexes.