Sterically-Hindered Derivatives of Pentacene: Synthesis, Properties, and Stability

• Author / Creator

  Rezghi Rami, Parisa

• Polycyclic aromatic hydrocarbons (PAHs), or more specifically pentacene derivatives, are promising candidates for solar energy conversion. Pentacenes can undergo π-stacking in solution and, consequently, can be poorly soluble. Furthermore, the pentacene moiety can react with oxygen, and it can participate in cycloaddition reactions with either itself or C60 used as an acceptor in a solar cell. This thesis focuses on the synthesis and characterization of monomeric and dimeric pentacenes with a focus to provide kinetic stability through substitution. All pentacene derivatives are characterized by 1H NMR, 13C NMR, IR, as well as mass spectroscopy. UV-vis spectroscopy, CV, DSC, and X-ray crystallography experiments have been used to study the effect of different substituents on photostability, electronic properties, thermal stability, and solid-state packing.
  Chapter 1 of this thesis gives a short introduction into the synthesis of symmetrical and unsymmetrical functionalized pentacene derivatives and their application in solar cells.
  Chapter 2 discusses the synthesis of sterically-hindered pentacene derivatives through substitution in 6- and 13-positions and the effects of the supertrityl substituent (tris(3,5-di-tertbutylphenyl)methyl) on solubility, photostability, and thermal stability of symmetrical and unsymmetrical derivatives. The other functional groups that were used for substitutions are triisopropylsilyl-, trimethylsilyl-, triisobutylsilyl-, and phenylacetylene. The photostability of all derivatives has been studied via UV-vis in different solutions which are held in the presence of light and/or oxygen, as well as in the absence of light and/or oxygen. Interestingly, the compound bearing two bulky supertrityl groups was not the most photostable derivative in solution, whereas it showed the greatest thermal stability in the liquid phase. The electrochemical and optical HOMO-LUMO gap calculated by CV and UV-vis data were in good agreement.
  Chapter 3 focuses on the synthesis of two dimeric pentacene derivatives tethered by a m-phenylene spacer through connections at the 13-position of the pentacene scaffold via the Sonogashira cross-coupling reaction. Photo- and thermal stability comparisons of dimeric derivatives were not accomplished since one of the pentacene dimers was not sufficiently pure to give reliable results. In collaboration with the Torres group in Spain, SubPc-pentacene conjugates have been synthesized in order to explore intramolecular Förster resonance energy transfer (iFRET), and intramolecular singlet fission (iSF) is explored with the Guldi group in Germany.
  Chapter 4 gives a brief conclusion and an outlook for the field of sterically-hindered pentacene monomers and dimers.
  Chapter 5 gives the experimental details of all compounds discussed in the research work as well as the NMR spectra of all synthesized compounds and DSC scans of the final pentacene derivatives.

• Subjects / Keywords

  • singlet fission
  • kinetic stability
  • synthesis
  • substituted Pentacene
  • photo-oxidation

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-a81t-sv68

• License

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