Electrochemical Crystallization of Organic Molecular Conductors: Electrode Surface Conditions for Crystal Growth

An electrochemical cell designed to allow in situ observation of crystal growth of organic conductors was fabricated, and the initial growth process of a partially oxidized salt of bis(ethylenedithio)tetrathiafulvalene (ET) was investigated for different current values. The shape, number, and size of the single crystals grown on the electrode depended on the current. However, our results suggested that the presence of trap sites on the electrode surfaces, which promote crystal nucleation, is more important for crystal growth, since flawless surfaces prepared by melting the electrode gave no crystals. The flawless electrode modified with an alkanethiol self-assembled monolayer (SAM) did not give crystals, while with a terminal carboxylate SAM, it yielded quality crystals over the entire surface, indicating that, when modified by anionic species, the electrode surfaces promote clustering of the oxidized ET radical cations and succeed in nucleating crystal growth of the partially oxidized salt.