title: Tetrathiafulvalene hetero radical cation dimerization in a redox-active [2]catenane.
abstract: 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) (CBPQT(4+)) 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 CBPQT(4+) 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 CBPQT(4+) 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.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.forename: Scott M
authors.initials: SM
authors.lastname: Dyar
authors.forename: Dennis
authors.initials: D
authors.lastname: Cao
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.forename: Noah
authors.initials: N
authors.lastname: Horwitz
authors.forename: Michael T
authors.initials: MT
authors.lastname: Colvin
authors.forename: Raanan
authors.initials: R
authors.lastname: Carmieli
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Stern
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Dey
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart