Experimental and computational investigations of heterofluorene oligomers

• Author / Creator

  Coumont, Leah Shawn

• In response to an increasing global need for inexpensive, energy efficient electronics, the field of organic semiconductors has experienced tremendous growth over the last 3 decades. In addition to their low cost, and interesting electronic and optical properties, organic semiconductors offer the additional benfits of being composed largely of earth-abundant elements, having electronic properties that are easily tailored through structural modifications, and can be solution processed to form flexible films. In particular, the heterofluorene structure has become a popular structural motif in organic semiconductors as a result of their straightforward preparation, and excellent electronic properties which have made them popular materials for devices ranging from transistors to solar cells. In this thesis, I present the results of original research on the subject of heterofluorene oligomers based on two structural motifs: i) macrocyclic carbazole tetramers, and ii) linear trimers of group 14-bridged spirobifluorenes. The early chapters of this thesis outline the preparation of a family of shape persistent macrocycles based on a carbazole monomer unit through the coupling of 3,6-dibromocarbazole and a series of N-alkylated derivatives with bis-(1,5-cyclooctadiene)Nickel(0) (i.e., Ni(COD)2). The macrocycles produced using this methodology were then used as building-blocks for the preparation of soft carbon nano and micromaterials through polarity induced self-assembly in acetone/water and THF/water co-solvent mixtures. The impact of the assembly process on the optical properties of the tetramers was also studied, and revealed that the alkyl-free derivative underwent aggregation-induced emission enhancement. The substitution of the tetramers with larger N-alkyl substituents disrupted the aggregation process leading to this favourable behaviour, but allowed the preparation of a range of morphologies from twisted nanofibers through microrods, ribbons and paddlewheels, the nature of which depended on the length and steric bulk of the N-alkyl substituent. The latter work in this thesis presents the results of a theoretical investigation into a series of linear trimers based on a spirobifluorene monomer unit in which the identity of the spiro-bridging atom is varied from C, Si, Ge and Sn. The potential for spiro-conjugation based charge transfer was calculated at three levels of theory, and suggested that the carbon and silicon analogues are most appropriate for spiroconjugation-based off-chain charge transfer in these trimers. The use of long-range corrected functionals dramatically decreased the charge transfer contributions to the singlet excited states of the trimers, and increased the estimated band gaps to values that were more comparable to experimental results obtained using the carbon-bridged trimer.

• Subjects / Keywords

  • Carbazole
  • Macrocycle
  • Heterofluorene

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R34J0BC0P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.