Svetlana V Kilina (North Dakota State University Fargo), Dmitri S Kilin (University of South Dakota) and Andrei Kryjevski (North Dakota State University Fargo) are supported in an award co-funded by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program, the Office of the Experimental Program to Stimulate Competitive Research (EPSCoR) and the Chemical Theory, Models and Computational Methods (CTMC) program. The project is to use computational techniques to investigate carbon nanotubes (CNTs), which are small tubes with carbon connected together. Series of carbon-carbon bonds may spiral around the axis of the tube, and different spiraling rates indicate different types of CNTs. The tubes can be decorated with attachments of small organic molecules or polymers (functionalization), and the choices of which attachments and where can be customized so as to design, for example, what light comes out and how intense it is when an outside light shines on a CNT. Another goal being pursued is to use computations to optimize the molecular decoration for each type of CNT so that chemical processes may be used to separate sticky bundles of CNTs with different rates of spiral, which is the usual way CNTs are produced. Having them separated is ideal for carrying out experiments on CNTs, since experiments can then provide much more discriminating information. The computations for the decorated or functionalized CNTs use both quantum and classical mechanics to interpret and predict properties relevant to experiments. This research aims to facilitate control over the processes of solar energy capture and conversion in functionalized CNTs at the fundamental level, and, thus, will be relevant to chemistry, materials science and engineering.
Functionalization of CNTs by small organic surfactants and conjugated polymers can improve chemical control of their optoelectronic and transport properties as well as offer promise in separation techniques for obtaining CNT samples with similar chiralities. The objective of this research is a systematic theoretical investigation of morphology, electronic structure, and excited state dynamics of CNTs functionalized by different types of conjugated oligomers and polymers. Using computational modeling, the investigators are working to understand fundamental physical processes occurring at organic-inorganic interfaces and governing the operation of CNT-based optoelectronic and photovoltaic devices such as exciton relaxation and recombination, charge transfer, and creation of several excitons from one absorbed photon (carrier multiplication). Density functional theory (DFT) and time dependent DFT (TDDFT) are being used for computing accurate electronic structure and optical response of polymer-CNT hybrids. Furthermore, quantum-classical non-adiabatic dynamics methods are being used to model phonon-mediated dynamics including charge and energy transfer in these systems. A novel approach to the calculation of quantum efficiency, the number of excitons generated by a photon, based on DFT augmented by the many body perturbation theory technique of quantum field theory is being applied to functionalized CNTs. Calculations of a variety of spectroscopic observables permit direct comparison and validation with ultrafast laser spectroscopic data (by other lasboratories) probing the fundamental electronic dynamics in functionalized CNTs. Just as importantly, these calculations provide explicit interpretations and predictions of the key phenomena occurring in the experimental measurements.
