@phdthesis{Hecht2021,
  author    = {Hecht, Markus},
  title     = {Liquid-Crystalline Perylene Bisimide and Diketopyrrolopyrrole Assemblies},
  doi       = {10.25972/OPUS-21698},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-216987},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {The research presented in this thesis illustrates that self-assembly of organic molecules guided by intermolecular forces is a versatile bottom-up approach towards functional materials. Through the specific design of the monomers, supramolecular architectures with distinct spatial arrangement of the individual building blocks can be realized. Particularly intriguing materials can be achieved when applying the supramolecular approach to molecules forming liquid-crystalline phases as these arrange in ordered, yet mobile structures. Therefore, they exhibit anisotropic properties on a macroscopic level. It is pivotal to precisely control the interchromophoric arrangement as functions originate in the complex structures that are formed upon self-assembly. Consequently, the aim of this thesis was the synthesis and characterization of liquid-crystalline phases with defined supramolecular arrangements as well as the investigation of the structure-property relationship. For this purpose, perylene bisimide and diketopyrrolopyrrole chromophores were used as they constitute ideal building blocks towards functional supramolecular materials due to their thermal stability, lightfastness, as well as excellent optical and electronic features desirable for the application in, e.g., organic electronics.},
  subject      = {Selbstorganisation},
  language  = {en}
}
@article{HechtLeowanawatGerlachetal.2020,
  author    = {Hecht, Markus and Leowanawat, Pawaret and Gerlach, Tabea and Stepanenko, Vladimir and Stolte, Matthias and Lehmann, Matthias and W{\"u}rthner, Frank},
  title     = {Self-Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra-Bay-Acyloxy Perylene Bisimide},
  series = {Angewandte Chemie International Edition},
  volume    = {59},
  journal   = {Angewandte Chemie International Edition},
  number    = {39},
  doi       = {10.1002/anie.202006744},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224586},
  pages     = {17084 -- 17090},
  year      = {2020},
  abstract  = {A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self-assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen-bond-directed self-assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid-crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo- or heterochiral self-assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self-sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self-assemblies proceeds by dissociation via the monomeric state.},
  language  = {en}
}
@article{ShenBialasHechtetal.2021,
  author    = {Shen, Chia-An and Bialas, David and Hecht, Markus and Stepanenko, Vladimir and Sugiyasu, Kazunori and W{\"u}rthner, Frank},
  title     = {Polymorphism in squaraine dye aggregates by self-assembly pathway differentiation: panchromatic tubular dye nanorods versus J-aggregate nanosheets},
  series = {Angewandte Chemie International Edition},
  journal   = {Angewandte Chemie International Edition},
  number    = {21},
  edition   = {60},
  doi       = {10.1002/anie.202102183},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256443},
  pages     = {11949-11958},
  year      = {2021},
  abstract  = {A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes with a phenylene spacer unit. The aggregation behavior of this bis(squaraine) was investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into two supramolecular polymorphs with entirely different packing structures and UV/Vis/NIR absorption properties. The self-assembly pathway can be controlled by the cooling rate from a heated solution of the monomers. For both polymorphs, quasi-equilibrium conditions between monomers and the respective aggregates can be established to derive thermodynamic parameters and insights into the self-assembly mechanisms. AFM measurements revealed a nanosheet structure with a height of 2 nm for the thermodynamically more stable polymorph and a tubular nanorod structure with a helical pitch of 13 nm and a diameter of 5 nm for the kinetically favored polymorph. Together with wide angle X-ray scattering measurements, packing models were derived: the thermodynamic polymorph consists of brick-work type nanosheets that exhibit red-shifted absorption bands as typical for J-aggregates, while the nanorod polymorph consists of eight supramolecular polymer strands of the bis(squaraine) intertwined to form a chimney-type tubular structure. The absorption of this aggregate covers a large spectral range from 550 to 875 nm, which cannot be rationalized by the conventional exciton theory. By applying the Essential States Model and considering intermolecular charge transfer, the aggregate spectrum was adequately reproduced, revealing that the broad absorption spectrum is due to pronounced donor-acceptor overlap within the bis(squaraine) nanorods. The latter is also responsible for the pronounced bathochromic shift observed for the nanosheet structure as a result of the slip-stacked arranged squaraine chromophores.},
  language  = {en}
}