Face-to-Face Dimeric Tetrathiafulvalenes and Their Cation Radical and Dication Species as Models of Mixed Valence and π-Dimer States

Abstract

Abstract Intramolecular interactions of face-to-face tetrathiafulvalenes (TTFs) in 1,8-bis(tetrathiafulvalenyl)naphthalene frameworks were investigated in neutral and cationic states. From X-ray analysis and NMR spectroscopy on neutral 1,8-bis(tetrathiafulvalenyl)naphthalenes, which exist as a mixture of syn- and anti-isomers in solution, there is steric repulsion between TTF moieties. However, analysis of the cyclic voltammogram (CV) revealed that a strong attractive interaction was present in the cation radical state. Electronic spectra of the cation radical state showed the presence of a mixed-valence (MV) state with a strong charge resonance feature. ESR spectra of the 1,8-bis(tetrathiafulvalenyl)naphthalene cation radical showed a typical signal of an MV state. Furthermore, a π-dimer, which exhibits pronounced Davydov splitting in the electronic spectra, was formed in the dication state. The observed absorption bands in the electronic spectra were characterized by using quantum chemical calculations of the cation radical and dication species. NMR spectra of both the π-dimer and tetracation species show either a deshielding effect due to cationic charge or a shielding effect due to diamagnetic ring currents. To our knowledge, this is the first reported example of a 1H NMR spectrum of TTF π-dimer.