Dr. Chris Collison
Assistant Professor, Department of Chemistry

• Electron transfer from excited states of a conjugated polymer, MEH-PPV
• Investigation of molecular fluorophore uptake by conjugated polymer nanoparticles.
• Fluorescence quenching of proteins as a tool to determine conformational changes and substrate binding.
  
  

Electron transfer from excited states of a conjugated polymer, MEH-PPV
One goal in our lab is to improve the fundamental understanding of interactions between conducting polymers and carbon nanotubes, two important components of organic photovoltaic devices. Carbon nanotubes will quench the fluorescence of our polymer, MEH-PPV, but the quenching mechanism is unclear. By testing for quenching of MEH-PPV through an electron transfer mechanism to a known electron acceptor, we can better interpret data obtained by quenching polymer fluorescence with carbon nanotubes.

Investigation of molecular fluorophore uptake by conjugated polymer nanoparticles.
The aim of this work is to better understand the driving forces for molecular doping of a hydrophobic conjugated polymer. Conjugated polymer nanoparticles may act as models for the study of molecular transport through a medium and for targeted drug delivery systems. Doped conjugated polymer nanoparticles may also have significant potential for sensitive fluorescence-based assays.
By varying the hydrophobicity and/or functional groups of certain laser dye molecules, we intend to study the relative amounts of fluorophore that are incorporated within polymer nanoparticles versus those molecules that merely interact with the nanoparticle surface or stay independently in solution. We intend to follow the uptake of fluorophore using spectroscopy.

Fluorescence quenching of proteins as a tool to determine conformational changes and substrate binding.
Fluorescence quenching has been used as a tool to determine position of the tryptophan residue within tertiary structures of proteins. Changes in fluorescence quenching behavior also indicates the change in the conformation of enzymes as they perform functions upon their target substrates. Preliminary data must be collected to assess the viability of using fluorescence to monitor binding and/or conformational changes in a Protein of interest to faculty in RIT’s chemistry department.

Current Projects

Organic photovoltaic devices promise low-cost, flexible options for future renewable energy that will reduce reliance on oil. My vision is to increase the efficiency of organic solar cells using single wall carbon nanotubes while maintaining low-cost manufacturing advantages, leading to their widespread acceptance.

The immediate goal is to improve the fundamental understanding of interactions between conducting polymers and carbon nanotubes, two important components of organic photovoltaic devices.

The current projects can be broken down into the following areas.

• Debundling of single wall nanotubes in solution and the effect of surfactants.
• Assignment of spectral features to intrinsic carbon nanotube properties.
• Reproducibility of carbon nanotube dispersion in solution.
• Fluorescence quenching of carbon nanotubes in solution and thin film.
• Atomic Force Microscopy of nanotube-polymer nanoparticle composites
• Quantitative polymer-nanotube interaction studies with centrifugation techniques.
  

We will assess the physical and electronic interactions of carbon nanotubes, conjugated polymers, molecules, solvents, etc using UV-Vis absorption and visible fluorescence spectroscopy. The current projects can be broken down into the following areas:

• Investigating solubility of fluorophores
• Investigating physical interactions/solubility of fluorophores when a third system or phase is added to the system of study.
• Assignment of spectral features.
• Fluorescence quenching using Stern-Volmer methodology
  

The role of the student will be to develop familiarity and, later, expertise on UV-Vis and Fluorescence spectroscopy equipment through routine use. Samples will be made up reproducibly by the student and then studied using this equipment. Sample generation will likely take as much time as the subsequent instrumental analysis. Error analysis will be important based on limitations from each analytical instrument used in a given experiment. Training will be provided on the instrumentation along with the theory behind it. Training will also be provided on the techniques required to make up polymer composites in solution.
Six hour blocks of time may be important when running certain time sensitive measurements, however many experiments may be completed in an afternoon or morning. Interpretation of data will be encouraged but will carry fewer time constraints than the actual measurements themselves.

Students should be interested in analytical instrumentation, quantitative analysis and molecules that glow! Students will be encouraged to think critically about their results. Students will otherwise be trained on instrumentation and will be taught about the long term goals of using polymer-nanotube composites in organic photovoltaic devices, use of polymers in drug delivery systems or of using fluorescence to understand more about the structure and function of proteins.