Title

Novel electroactive and fluorescent dendrimers

Date of Award

1999

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

The encapsulating effect of a polyamido dendritic matrix based on one of Nekome's building blocks at the focal site was investigated. Departing from Behera's amine, the basic building block, the second and third generation dendrons were prepared combining divergent-convergent methodologies. These dendrons had tert-butyl esters at their branch ends. In turn, an electrophore (ferrocene) or a fluorophore (dansyl and pyrene) was attached to the focal point of the dendrons giving rise to a three-generation dendritic family. Subsequent hydrolysis of the esters produced dendritic families soluble in water, thus allowing the study of the electrochemical properties of the ferrocene dendrimers both in organic and aqueous media and the monitoring of the photophysical properties of the fluorescent dendrimers in phosphate buffered solutions at pH 7.0.The redox behavior of the focally located probe was monitored with cyclic voltarmmetry (CV) with typical size electrodes (0.5 and 0.75-mm diameter, glassy carbon) and an ultramicroelectrode (4-mum radius, Pt). The kinetic parameters for the heterogeneous electron transfer process and the diffusion coefficients were obtained from digital simulated voltammograms (Digi Sim 2.1) that best fitted those acquired experimentally with the typical size electrodes and from the ultramicroelectrode current-potential data treated with the Milkin-Bard method. These studies revealed that the heterogeneous electron transfer process is thermodynamically favored in an organic solvent, CH2Cl2, as the size of the dendritic polymer increases.Our molecules contain an electrochemical or fluorescent probe within the dendritic matrix in a non-symmetrical environment. The cascading polymer thus encapsulates the core in an uneven manner allowing it to interact with other species in an aqueous solution. Therefore, the progressive isolation of the probe, as dendritic layers were added on, was detected by host-guest interactions between the focally positioned ferrocene or dansyl unit, the guest, and beta-cyclodextrin beta-CD the host. Such interactions were monitored with CV in a tris buffered solution (pH 7.0. 0.1 M NaCl) and fluorescence spectroscopy in a phosphate buffered medium (pH 7.0, mu = 0.1) at 25°C, respectively. The observed decrease in binding constant, K, as the dendritic size increases suggested that the focal site is self-encapsulated by the branched polymer interfering with the accessibility of the probe to the beta-CD cavity. In fact, the fluorescence properties of the dendrimers containing a dansyl or a pyrene probe at the focal center corroborate this ensuing isolation. Not only does the polarity of the microenvironment around the fluorophore change with increasing generation, but quenching experiments with Nal revealed how inaccessible the focal site becomes by the third generation. (Abstract shortened by UMI.)

Keywords

Chemistry, Organic; Chemistry, Physical

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9961255