W E L C  O  M E

Research Topics PublicationsPast and Present Group Members 




                Electroactive
                and Fluorescent Dendrimers

Our interest in dendrimer chemistry centers on 'unsymmetrically' functionalized dendrimers. We have developed synthetic methods for the easy preparation of dendritic macromolecules possessing a single functional group (usually a fluorophore or a redox active residue) covalently attached to the focal point of a dendrimer wedge or dendron. The resulting structures are extremely interesting from the standpoint of site isolation and directional reactivity of the functional group. We have investigated extensively two series of ferrocene-containing dendrimers1 with this general structure and shown that they exhibit pronounced pH-controlled orientation effects on their heterogeneous electron transfer reactions.2 Our dendrimers constitute the first example among synthetic compounds of such orientational effects, which were traditionally confined to the field of redox proteins. We have also prepared a similar series of dansyl-containing dendrimers and investigated their photophysical properties3 in collaboration with the group of Professor Bright, at SUNY-Buffalo. The structure of our unsymmetric dendrimers allows the functional group to engage in binding interactions with suitable hosts. We are actively compiling binding data between our dendrimers as guests and a number of receptors, thus probing the effects of dendrimer size across several orders of magnitude of binding affinity. We are currently completing the synthesis and characterization of a new series of unsymmetric 4,4'-bipyridinium (viologen) dendrimers and investigating their electrochemical properties and their binding to cucurbit[7]uril, an effective host for viologens, recently identified by us.4 Viologen dendrimers appear to be particularly interesting from the standpoint of their fast electrochemical kinetic properties, as demonstrated by our group with symmetric, Fréchet-type dendrimers containing a viologen core.5

 


                

                  

                    
                    Metal
                    Nanoparticles Modified with Molecular Receptors 
                  

                


				
                  

                    
                    Syntheses
                    and Characterization of New Hosts


View an animation of pH driven orientation effects
on our dendrimer's electron transfer reactions . 
References:
1Cardona, C. M.; McCarley, T. D.; Kaifer, A. E. "Synthesis, Electrochemistry and Interactions with
b-Cyclodextrin of Dendrimers Containing a Single Ferrocene Unit Located Off-Center", J. Org. Chem. 
2000, 65, 1857-1864.

2Wang, Y.; Cardona, C. M.; Kaifer, A. E.  "Molecular Orientation Effects on the Rates of Heterogeneous
Electron Transfer of Unsymmetric Dendrimers", J. Am. Chem. Soc. 1999, 121, 9756-9757.

3Cardona, C. M.; Alvarez, J.; Kaifer, A. E.; McCarley, T. D.; Pandey, S.; Baker, G. A.; Bonzagni, N. J.;
Bright, F. V. "Dendrimers Functionalized with a Single Fluorescent Dansyl Group Attached Off-Center:
Synthesis and Photophysical Studies", J. Am. Chem. Soc. 2000, 122, 6140-6144.

4Ong, W.; Gómez-Kaifer, M.  Kaifer, A. E. "Cucurbit[7]uril: A Very Effective Host for Viologens and
Their Cation Radicals", Org. Lett. 2002, in press.

5Toba, R.; Quintela, J. M.; Peinador, C.; Román, E.; ; Kaifer, A. E. "A New Series of Dendrimers with
4,4'-Bipyridinium Cores Capable of Fast Electron Transfer Reactions", Chem. Commun. 2001, 857-858.