45078-GB10
The Physical Interaction and Energy Transfer between Single Wall Carbon Nanotubes and a Straight Chain Conjugated Polymer in Solution
In year two, my PRF Grant has allowed me to focus on current projects, which will naturally allow ideas to develop into new proposals. My successes in lab continue to attract strong students such that I can maintain a large and productive undergraduate research group. I have developed more effective ways of student management, using Gantt charts, Wikis and self-evaluation to better organize group targets and personnel. Over the last year I have more clearly defined student expectations for the communication of results, culminating in the first group publication in the Journal of Physical Chemistry, (Collison et al, 2008) with two more papers in preparation. Receipt of this grant allows me to emphasize RIT as a top-tier undergraduate research institution. My personal ambition and career goals have been raised and I currently see greater stability and positional strength within my own institute. Regarding recent students who have worked on this research, Marc O’Donnell has started medical school at NYU, Derek Skinner has used one quarter’s research experience to find employment in industry and Jessica Alexander has been successful in summer research at the Harvard Stem Cell Institute. I have five active students working on projects linked to my proposal. They learn the importance of critical thinking, reproducibility and accuracy. I provide them with the tools to be excellent scholars and effective problem solvers. I strongly encourage further education beyond their undergraduate studies and expect strong careers for them in the sciences. Our ongoing work can be broken down into three areas. This work came about after follow-up on the unusual results of a control experiment, documented in my original ACS-PRF grant proposal. We continue to investigate the interaction of R101 with analogs of SWNT so as to better understand its nanotube selectivity. Further work with this probe allows us to expand our understanding of interactions between SWNT and the solvents used to disperse them. We continue to study the interactions of MEH-PPV and CoMoCat SWNT using absorbance and fluorescence techniques. The high proportion of (6,5) nanotubes in the CoMoCat samples leads to strong tube-specific spectral features. We have been successful in observing fluorescence from the nanotubes themselves after excitation of MEH-PPV in composite dispersions, following up work by Nish et al (2008). We are optimistic that this fluorescence, shown clearly in 2D contour plots, will aid us in interpreting red-shifts seen in fluorescence quenching experiments. With results suggesting binding between MEH-PPV and SWNT in solution, we continue to work through a comprehensive set of experiments that address the impact of polymer concentration, polymer solubility and temperature on the fluorescence quenching of the fluorophore and energy transfer to the nanotubes. We must be able to qualify the purity of our nanotube sample. We continue to have projects associated with a procedure of Landi et al (2005) where we reconstruct impure samples, adding known amounts of carbonaceous impurity. We observe the effect of this impurity on the optical absorbance and/or fluorescence quenching of the sample. This work ties in directly with our R101 work. Qualification of sample purity and dispersion/debundling is critical when working with nanotubes in solvents. Any spectral data can only be interpreted fully if the actual interactions between nanotube and polymer can be separated from interactions between polymer and impurity. In summary, our work will provide strong contributions to the further understanding of interactions between SWNT and the functional groups of a wide size range of organic materials. Regarding the fluorescence quenching of conjugated polymers by these nanotubes, we look to prove our model of physical interaction and the associated quenching mechanism with a full complement of experimental data. We intend to assess the mechanism’s universal application and consider its impact upon photovoltaic efficiency in a polymer bulk heterojunction device. In truth, excited state quenching may lead to loss of performance but, on the other hand, quenching through electron transfer may demonstrate the potential of carbon nanotubes in increasing solar cell efficiencies.
