Extended Tetrathiafulvalenes: Intramolecular Interactions Within 2,2'-Biphenyl-Bridged Fluorene-Dithiafulvenes

Tetrathiafulvalene (TTF) is a well-known redox-active molecule that undergoes two reversible one-electron oxidations to afford stable cationic species. Its redox and optical properties, as well as molecular geometry and self-association behavior, can be systematically tuned through incorporation of a π-conjugated framework between the two dithiole rings. Herein, we report the synthesis of novel extended TTF scaffolds in which two fluorene-dithiafulvene units are rigidly connected via a 2,2'-biphenyl spacer. Crystallographic, computational, and ¹H nuclear magnetic resonance (NMR) spectroscopic studies show that the neutral scaffolds take a conformation allowing for intramolecular associations between the two fluorene-dithiafulvene units. Electrochemical studies further reveal intramolecular stabilization of radical cations owing to mixed valence dimer formation, supported by a strong near-infrared absorption.