Pyridinium Rods, Stars and Dendrimers
Stars are born …… or prepared by synthesis. Shown below is the growth of three-branched viologen stars. They consist of up to 12 bipyridinium subunits, and one star branch has a length of 6 nm. Their broad-band redox activity is due to overlaid benzyl- and phenylviologen reduction waves, as rationalized by calculations.
The stars were poymerized by electrochemical generation of three peripheral radicals on the star branches. The star substructure was identified within the polymer by STM.
Veronica-Alina Constantin, Dirk Bongard and Lorenz Walder*, Triple-Branched Viologen Stars: Synthesis and Polymerization by Peripheral Benzyl Coupling , Eur. J. Org. Chem. , 2012, pp 913–921.
Hi, I’m Kathiresan,
I have done host guest chemistry on polycationic dendrimers with organic anions.
I have found prominent changes in the NMR of the dendrimers when I added 3, 9, and 21 guest molecules. Such a series of “magic numbers” is interprteted as filling of the dendrimer shell-by-shell from the centre towards the periphery, because:
Three antrachinone disulfonate guest molecules encounter a generation one 18-fold cationic trimethylen pyridinium dendrimer host. The molecular dynamics simulation predicts complexation of the guest molecules in the innermost host shell.This surprising phenomenon was observed experimentally by K. Murugavel using 1HNMR titration techniques.
Murugavel Kathiresan and Lorenz Walder*, Trimethylenedipyridinium Dendrimers: Synthesis and Sequential Complexation of Anthraquinone Disulfonate in Molecular Shells, Macromolecules, 2010, 43, pp 9248–9256.
Murugavel Kathiresan and Lorenz Walder*, Shell-by-Shell Inside-Out Complexation of Organic Anions in Flexible and Rigid Pyridinium Dendrimers , Macromolecules, 2011, 44, pp 8563–8574.