Self-assembled aggregates of synthetic organic dyes exhibit unique linear and non-linear optical properties as well as effective excitation energy transport. Thus, they are of fundamental interest as models for understanding the photophysical processes occurring in natural light harvesting complexes, and as systems to study the nature and dynamics of excited states in molecular assemblies of low dimensionality. Potential applications in optoelectronics, energy transport, and artificial light harvesting make them attractive from the practical perspective. I will discuss the challenges faced by theoretical modelling of the excitonic phenomena in self-assembled organic materials, using as an example two systems that we recently studied. The first one are nanotubes formed by TPPS4 porphyrin molecules ([1-3], see figure (b)). This novel material mimics the structure of photosynthetic antenna system of green sulphur bacteria (the chlorosomes) and exhibits long-range energy transport. The second system I will discuss are the dimers of the pseudoisocyanine (PIC) dye, formed at the initial stage of the aggregation process [4] see figure (a). The first difficulty encountered by theory is posed be the lack of the atomic-scale information about the aggregate structure, as the experimental methods are not yet precise enough to image the stacking of the molecules within the aggregate, or to reveal the initial stages of the self-aggregation process. I will discuss two approaches of overcoming this problem: phonomenological modelling and molecular dynamics simulations. References: [1] S.M. Vlaming, R. Augulis, M.C.A. Stuart, J. Knoester, and P.H.M. van Loosdrecht, J. Phys. Chem. B 113, 2273 (2009). [2] A. Stradomska and J. Knoester, J. Chem. Phys. 133, 094701 (2010). [3] Y. Wan, A. Stradomska, S. Fong, Z. Guo, R.D. Schaller, G.P. Wiederrecht, J. Knoester, and L. Huang, J. Phys. Chem. C 43, 24854 (2014). [4] F. Haverkort, A. Stradomska, J. Knoester, J. Phys. Chem. B 118, 8877 (2014).

From dimers to self-assembled molecular nanotubes: Challenges for theory

251st National Meeting (2016)

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