@phdthesis{Selby2022,
  author    = {Selby, Joshua},
  title     = {Design and Chiroptical Properties of Chirally Substituted Indolenine Squaraine Mono-, Oligo-, and Polymers},
  doi       = {10.25972/OPUS-28206},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-282067},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {A series of monomeric chirally substituted indolenine squaraine monomers were successfully synthesized and utilized for the construction of various oligo- and polymers, in order to study their chiroptical properties in terms of exciton chirality. The quaternary carbon atom at the 3-position of the indolenine subunit, as well as the alkyl side chain attached to the indolenine nitrogen were selected as the most suitable site for chiral functionalization. For the C(3)-chiral derivatives, two synthetic routes depending on the desired substitution at the stereogenic center were established. The chiral side chains were prepared via Evans asymmetric alkylation where the resulting branching point at the 2 position constituted the chiral center. While the chiral substitution only had minor effects on the linear optical properties and geometric structure of the chromophore, all compounds exhibited a distinct and measurable CD signal that correlated with the distance of the chiral center to the central chromophore. Polymers bearing chiral side chains exhibited a solvent- and temperature-dependent helix-coil equilibrium, which was influenced by the type of side chain used. CD spectroscopy revealed the helical conformation to possess a preferred twist sense, and temperature-dependent measurements showed the degree of homohelicity to be nearly complete in certain cases. Furthermore, a CPL signal was able to be obtained for the helical conformer of one polymer. Various (co)oligo- and polymers comprising the C(3)-chiral monomers only displayed a solvent-independent J-type absorption behavior and thus did not form helical conformations in solution. CD spectroscopy revealed a solvent-dependent adoption of quasi-enantiomeric conformers, which was elucidated by quantum chemical TDDFT calculations.},
  subject      = {Squaraine},
  language  = {en}
}