Photophysics and Stability of Multichromophoric Polyelectrolytes

University Of Rochester, Rochester NY

Investigators

Abstract

Nontechnical description: The research team studies a class of water-soluble polymers that are capable of light emission. The materials are being studied in collaboration with chemists who are developing them for biomedical imaging of tumors, and for applications to detection of proteins and DNA sequences of medical interest. These polymers organize into geometries that are determined by factors such as salt and acid concentrations in the water. Those geometries strongly influence both the color and brightness of the light emitted from the polymers. The project employs microscopy of single polymer strands to investigate how the polymer conformation and solution conditions affect the intensity and stability of the emitted light. Participation in the research provides training for graduate students in optics and polymer science, as well as interactions with international collaborators working on problems with medical significance. Since the materials under study are non-toxic, the research team is using them to develop hands-on activities as part of a summer course at the University of Rochester for gifted students, and for exhibitions for the general public at the Rochester Museum and Science Center. Technical description: The research team is testing models of how energy transfer in multi-chromophore ensembles comprising fluorescent conjugated polyelectrolytes controls their degradation, fluorescence intensity, and spectrum. In particular, the group is investigating the circumstances under which chromophore aggregation leads to fluorescence quenching and fluctuations in the emission intensity and spectrum. The hypothesis that intense fluorescence arises from bleaching of nearly non-emissive chromophores is being tested using superresolution imaging combined with simultaneous spectroscopy. A complementary approach to measure the absorption of single chains using photothermal detection is being developed to test the "dark matter" hypothesis for fluorescence quenching in these materials. The researchers are studying the spectroscopy and fluorescence dynamics for these conjugated polyelectrolyte chains in different salt and pH environments, as well as when adsorbed on hydrophilic and hydrophobic surfaces. The team is developing computational models of energy transfer for guiding the design of polymer morphology, to improve fluorescence efficiency and stability for imaging applications.