Studying the vibrational energy transfer pathways and dynamics in molecules is important for different areas of chemical research, with the range of potential applications in nanotechnology, organic chemistry and biochemistry. Two transport regimes, ballistic and diffusive, are recognized for the transport in molecules; while the latter is typically slow the former can be fast and efficient. The diffusive transport regime was observed in numerous compounds, whereas there are only a few cases where the ballistic transport has been suggested in molecules. The subject of this dissertation is to identify the factors influencing the ballistic transport, including the molecular chain organization, thermodynamic conditions and end-group functionalities. The research involves several types of oligomeric chains, such as polyethyleneglycol, perfluoroalkane, and alkane chains. The experiments were performed using the relaxation-assisted two-dimensional infrared spectroscopy method, which permits measuring the energy transport time between two vibrating groups. The transport via all three chain types was found to occur with a constant speed, although different speeds were found in different chain types. The fastest speed of 14.4 Å/ps was found in linear alkanes, the slowest, 3.9 Å/ps, in perfluoroalkanes. The difference in the transport speed was attributed to involvement of different chain optical bands. The temperature dependence of the transport speed and efficiency in perfluoroalkanes demonstrated that the ballistic transport, dominating at low temperatures, is switched to the diffusive transport at elevated temperatures; the observation was supported by the theoretical modeling. The energy transport in several compounds lacking periodic structure was found to occur with an effective speed of 1.2-1.4 Å/ps, which approximately matches the speed of passing one bond-length per mean lifetime of the excited vibrational mode (1 ps). This speed was found to be 3-10 fold smaller than the transport speed via oligomeric chains. Moreover both regimes, diffusive and ballistic, were distinguished within the same compound: the transport was ballistic via the chain and diffusive within the bulky end group. The two transport times were found additive, confirming the ballistic nature of the through-chain transport. This study develops a detailed picture of energy transport in molecules and provides new opportunities for designing molecular and nanoscale materials with tailored energy transport properties, potentially useful for making novel elements for molecular electronics. / 1 / Natalia I. Rubtcova
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_45949 |
| Date | January 2015 |
| Contributors | Rubtcova, Natalia I. (author), Rubtsov, Igor (Thesis advisor), School of Science & Engineering Chemistry (Degree granting institution) |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | electronic |
| Rights | No embargo |
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