Synthesis, Self-Assembly and Photophysical Properties of Multichromophoric Systems

Supramolecular chemistry offers a great toolbox of non-covalent interactions to organize chromophoric and multichromophoric systems into functional aggregates of precise size and order via a bottom-up approach. These interactions can be utilized to improve the photophysical properties and processes (e.g. transport of excitation energy) of the supramolecular aggregates. This thesis deals with the synthesis, the self-assembly and the investigation of photophysical properties of novel multichromophoric systems. The first part of this thesis covers the influences of steric effects and hydrogen-bonding on the self-assembly, the stacking behavior and the optical properties of pyrene derivatives. The photophysical properties of the pyrene compounds were investigated in (i) highly diluted solutions, (ii) at increased concentrations in an intermediate self-assembly regime, and (iii) in the dry crystalline state, utilizing steady-state and time-resolved optical spectroscopy. The π stacking of the pyrene moieties into weakly coupling H aggregates ─ i.e. cofacially arranged chromophores ─ is the governing driving force initiating self-assembly in solution. In this regime, the ground state H-aggregates of the pyrene moieties give rise to excimer formation ─ i.e. an excited dimer. Hydrogen-bonding and steric effects have almost no influence on the self-assembly process, but they do determine the excimer formation rate within the supramolecular aggregates. Upon transition to the crystalline state the influence of the different intermolecular interactions becomes more striking. The excimer fluorescence vanishes with increasing order in the crystalline state, which is promoted by the formation of hydrogen-bonds and is decreased with the introduction of bulky groups. The second part of this thesis deals with the synthesis and the photophysical properties of two novel carbonyl-bridged triarylamine derivatives. The C3 symmetric chromophore was connected in 2, 6, and 10 position via amide linkers and short alkyl spacers with either naphthalimides or 4-(5-hexyl-2,2’-bithiophene)-naphthalimides. The employed universal synthetic route allows for a versatile functionalization of carbonyl-bridged triarylamines. Both multichromophoric compounds show efficient energy transfer, evidenced by steady-state and time-resolved spectroscopy. The compound bearing naphthalimides in the periphery funnels the energy from the periphery to the carbonyl-bridged triarylamine core. In the second multichromophoric compound energy transfer proceeds vice versa, from the central carbonyl-bridged triarylamine to the lateral 4-(5-hexyl-2,2’-bithiophene)-naphthalimide units. Furthermore, this compound forms transparent fluorescent gels at very low concentration while retaining the optical and energy transfer properties. The last part of this thesis is concerned with the self-assembly of the carbonyl-bridged triarylamine with 4-(5-hexyl-2,2’-bithiophene)-naphthalimide substituents which forms supramolecular nanofibers. A striking feature of these aggregates is the outstanding excitation energy transport along the fibers at room temperature. Electron and atomic force microscopy techniques revealed micrometer-long supramolecular aggregates with molecular diameter. Spectroscopic investigations of these nanofibers demonstrate that hydrogen-bonding of the amide linkers together with strong π-stacking of the carbonyl-bridged triarylamine are responsible for the uniaxial self-assembly. The threefold-symmetric nature of the hydrogen-bonds enforces a cofacial H-aggregation of the carbonyl-bridged triarylamine cores leading to a significant nearest neighbor coupling. The high level of order in combination with the coupling of the carbonyl-bridged triarylamine cores result in long-range energy transport over at least 4 µm, which corresponds to more than 10.000 molecules. This was verified for individual nanofibers using a confocal fluorescence microscope. For this supramolecular system the energy transport is most likely explained by quantum coherent effects. The self-assembly of this compound is an excellent example to demonstrate the enormous potential of supramolecular chemistry towards highly ordered non-covalently bonded architectures with remarkable properties and functionality.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2015

Author dc:creator

• Haedler, Andreas T.

Contributors dc:contributor

• Schmidt, Hans-Werner

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/2125/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:2125