Self-Assembly of Radially π-Extended Tetrathiafulvalene Tetramers for Visible and Near Infrared Electrochromic Nanofiber

Abstract The self-assembly and electrochromic nanofiber formation of radially π-extended tetrathiafulvalene (TTF) tetramers anchored to 1,2,4,5-tetraethynylbenzene were investigated. The tetramer with SBu-substituents underwent self-assembly in solution. Cationic species of the tetramer, obtained by chemical oxidation with Fe(ClO4)3, exhibited a marked electrochromism in the solution. Their electronic spectra revealed absorption bands corresponding to intermolecular mixed-valence aggregation based on (TTF//TTF)•+, and π-aggregation based on (TTF•+//TTF•+) due to the strong molecular association in the cationic species. Furthermore, the tetramer formed an entangled nanoscale fibrous material from CHCl3–hexane. Electrochemical oxidation of the nanofiber on an indium tin oxide electrode revealed a repeatable redox profile. The nanofiber displayed remarkable electrochromic behavior: the color of the fiber changed from purple (neutral) to brown/brownish green (dication and trication) and green (tetracation). These color changes of the nanofiber are similar to those in solution, and the electronic spectra of the oxidized nanofibers reflected the stacked TTF units in the cationic nanofibers.