Excitation Energy Transport In Self-Assembled Molecular Nanotubes

Hidding, Jan (2018) Excitation Energy Transport In Self-Assembled Molecular Nanotubes. Master's Thesis / Essay, Nanoscience.

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Abstract

Light-harvesting complexes found in photosynthetic organisms possess extreme energy transport properties. Furthermore, these complexes rely on self-assembly to form their exceptionally ordered tubular structures. Inspired by the success of these natural photosynthetic complexes, artificially replicating these complexes holds great potential to facilitate a deeper understanding of the design principles of nature. Elucidating what is at the heart of the efficient energy transport holds great promise for potential use in next-generation solar cells. In this regard, the amphiphilic dye C8S3 is considered as a suitable model system due to its ability to self-assembly into similar highly ordered tubular structures in aqueous solution, namely double-walled nanotubes. In this work, two derivatives of C8S3 (C8S3-Cl and C8S3-Br) were investigated using spectroscopic techniques together with cryogenic transmission electron microscopy (cryo-TEM). As both dyes self-assemble into similar double-walled nanotubes, the first part of this work aimed to disrupt the energetic structure by incorporating C8S3-Br monomers into C8S3-Cl nanotubes, while retaining the homogenous morphology by mixing them together. Linear absorption spectroscopy revealed a tremendous acceleration in the agglomeration of nanotubes, termed “bundling”, induced by the C8S3-Br monomers. Stabilization of the mixtures in a sugar matrix was shown to provide a good solution to effectively freeze the bundling process and retain the structural homogeneity. Upon mixing, linear absorption spectra revealed no absorption of remaining C8S3-Br monomers even for high mixing ratios of C8S3-Br:C8S3-Cl of 1:11.4. Furthermore, cryo-TEM revealed no separate species formed by C8S3-Br for this high concentration of C8S3-Br. Lastly, a slightly inflated outer tube diameter is observed. All these observations indicate successful incorporation of C8S3-Br monomers into the C8S3-Cl nanotubes. Exciton-exciton annihilation (EEA) measurements on these mixed samples however, showed no reduced EEA due to the incorporated C8S3-Br monomers. Furthermore, no distinct spectral changes were observed in photoluminescence measurements and temperature-dependent PL spectra reveal thermally induced energy transfer between the inner and outer tube, similar to the neat C8S3-Cl nanotubes. These observations lead us to conclude, that the exciton delocalisation is retained after incorporation of C8S3-Br monomers. This suggests that the tubular structure allows for robust exciton delocalisation, i.e. exciton delocalisation which is not easily perturbed. In the second part of this work, polarisation controlled 2-dimensional electronic spectroscopy revealed energy transfer dynamics between the different walls of neat C8S3-Br nanotubes with energy transfer dynamics at a 100 fs timescale. These suggest that the multiwalled tubular structure of the natural light-harvesting complexes are key to their efficient energy transport properties.

Item Type:	Thesis (Master's Thesis / Essay)
Supervisor name:	Pchenitchnikov, M.S.
Degree programme:	Nanoscience
Thesis type:	Master's Thesis / Essay
Language:	English
Date Deposited:	30 Jul 2018
Last Modified:	30 Sep 2025 06:51
URI:	https://fse.studenttheses.ub.rug.nl/id/eprint/18134

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