Unraveling Complex Aggregate Behavior: Perylene Diimides, A Case Study

Research Seminar

2-dimensional infrared spectroscopy (2DIR) probes molecular vibrations in solution, and thus, is useful for its structural sensitivity to molecular as well as aggregate structures. However, molecular orientation, the nature of coupling, solvation, and many degrees of freedom contribute to the resulting 2DIR spectrum. The relative orientations of molecules in an aggregate effect the strength and manner of coupling between the vibrations of the individual molecules. Computational studies provide an opportunity to extract deeper understanding from experimental results by relating spectral features to well defined molecular geometries. The 2DIR spectrum of a given aggregate structure can be calculated and compared to the experimental 2DIR spectrum, to determine whether or not that given structure contributes to the 2DIR spectrum and thus infer whether that particular aggregate structure is present in solution. Some structures can be reasonably deduced by narrowing the parameter space of likely structures through chemical intuition [1], and some are determined through other experiments [2]. That happens when the number and range of possible aggregate structures is much larger? We need some way of narrowing the list of relevant structures. In these circumstances, developing an efficient method to predict the most relevant structures is highly desirable. Theory fulfills a crucial role here, using molecular dynamics and enhanced sampling techniques we can find the most probable aggregate structures, thus narrowing the possibilities substantially. Vibrational modes of these structures can be calculated and compared to experimental linear IR and 2DIR to elucidate the true nature of aggregation in solution. This talk will highlight theoretical work on perylene diimides that will help interpret interesting experimental linear IR and 2DIR results in our lab.
[1] Cyran, J. D.; Krummel, A. T. J. Chem. Phys. 2015, 142 (21), 212435.
[2] Krummel, A. T.; Zanni, M. T. J. Phys. Chem. C 2006, 110 (28), 13991

Division(s): Physical

Speaker: Max Mattson

Speaker Institution: Colorado State University

Event Date: 03-09-2017

Event Time: 4:00 PM

Event Location: Chemistry A101

Mixer Time: 3:45 PM

Mixer Location: Chemistry B101E

Host: A. Krummel