Tetrathiafulvalene Hetero Radical Cation Dimerization in a Redox-Active [2]Catenane

• Published in: Journal of the American Chemical Society Vol. 134; no. 46; pp. 19136 - 19145
• Main Authors: Wang, Cheng, Dyar, Scott M, Cao, Dennis, Fahrenbach, Albert C, Horwitz, Noah, Colvin, Michael T, Carmieli, Raanan, Stern, Charlotte L, Dey, Sanjeev K, Wasielewski, Michael R, Stoddart, J. Fraser
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.11.2012
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja307577t

The electronic properties of tetrathiafulvalene (TTF) can be tuned by attaching electron-donating or electron-withdrawing substituents. An electron-rich macrocyclic polyether containing two TTF units of different constitutions, namely 4,4′-bis(hydroxymethyl)tetrathiafulvalene (OTTFO) and 4,4′-bisthiotetrathiafulvalene (STTFS), has been synthesized. On two-electron oxidation, a hetero radical dimer is formed between OTTFO•+ and STTFS•+. The redox behavior of the macrocyclic polyether has been investigated by electrochemical techniques and UV–vis and electron paramagnetic resonance (EPR) spectroscopies. The [2]catenane in which the macrocyclic polyether is mechanically interlocked with the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring has also been prepared using template-directed protocols. In the case of the [2]catenane, the formation of the TTF hetero radical dimer is prevented sterically by the CBPQT4+ ring. After a one-electron oxidation, a 70:30 ratio of OTTFO•+ to STTFS•+ is present at equilibrium, and, as a result, two translational isomers of the [2]catenane associated with these electronically different isomeric states transpire. EPR titration spectroscopy and simulations reveal that the radical states of the two constitutionally different TTF units in the [2]catenane still experience long-range electronic intramolecular coupling interactions, despite the presence of the CBPQT4+ ring, when one or both of them are oxidized to the radical cationic state. These findings in the case of both the free macrocyclic polyether and the [2]catenane have led to a deeper fundamental understanding of the mechanism of radical cation dimer formation between constitutionally different TTF units.