Radically enhanced molecular recognition.
The tendency for viologen radical cations to dimerize has been harnessed to establish a recognition motif based on their ability to form extremely strong inclusion complexes with cyclobis(paraquat-p-phenylene) in its diradical dicationic redox state. This previously unreported complex involving three bipyridinium cation radicals increases the versatility of host-guest chemistry, extending its practice beyond the traditional reliance on neutral and charged guests and hosts. In particular, transporting the concept of radical dimerization into the field of mechanically interlocked molecules introduces a higher level of control within molecular switches and machines. Herein, we report that bistable and tristable [2]rotaxanes can be switched by altering electrochemical potentials. In a tristable [2]rotaxane composed of a cyclobis(paraquat-p-phenylene) ring and a dumbbell with tetrathiafulvalene, dioxynaphthalene and bipyridinium recognition sites, the position of the ring can be switched. On oxidation, it moves from the tetrathiafulvalene to the dioxynaphthalene, and on reduction, to the bipyridinium radical cation, provided the ring is also reduced simultaneously to the diradical dication.
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Ali
A
Trabolsi
Niveen
N
Khashab
Albert C
AC
Fahrenbach
Douglas C
DC
Friedman
Michael T
MT
Colvin
Karla K
KK
Cotí
Diego
D
Benítez
Ekaterina
E
Tkatchouk
John-Carl
JC
Olsen
Matthew E
ME
Belowich
Raanan
R
Carmielli
Hussam A
HA
Khatib
William A
WA
Goddard
Michael R
MR
Wasielewski
J Fraser
JF
Stoddart
D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry*; D010084:Oxidation-Reduction; D011726:Pyridinium Compounds / Q000737:chemistry; D011789:Quantum Theory; D043862:Rotaxanes / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014755:Viologens / Q000737:chemistry
D005609:Free Radicals; D011726:Pyridinium Compounds; D043862:Rotaxanes; D014755:Viologens