Date of Award
12-1-2023
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
College/School/Department
Department of Chemistry
Dissertation/Thesis Chair
Marina A Petrukhina
Committee Members
Evgeny Dikarev, Jeremy I Feldblyum, Michael T Yeung
Subject Categories
Chemistry
Abstract
Molecular nanocarbons, which can be considered as fragments of fullerenes, carbon nanotubes, or graphene have invigorated the rapid development of carbon chemistry at the nanoscale in recent decades. Not only do molecular nanocarbons possess extraordinary chemical and physical properties, but they also exhibit such unique features as controllable and scalable molecular compositions, atomically uniform precision, and good stability. The advance of nanocarbon chemistry give rise to unique applications such as electron transfer, semiconductors, superconductors, and lithium-ion batteries. However, an in-depth understanding of controlled doping, charge transfer effects, and structure–property correlations has been limited in nanocarbon chemistry due to the lack of phase-pure single-crystalline materials. In this work, we focused on the chemical reduction studies of several classes of topologically unique molecular nanocarbons and investigated the structural consequences of their multi-electron acquisition processes. Specifically, we explored the chemical reduction of pentacene (C22H14) with all the Group 1 metals and examined the structural response of its π-system to a two-electron addition and alkali metal binding. Complementary use of NMR spectroscopy and comprehensive computational studies allowed us to evaluate the electronic structure, aromaticity changes and metal binding preferences of the doubly-reduced pentacene. In addition, the first stepwise chemical reduction of a highly twisted polyarene, twistacene (C74H46), was accomplished with lithium and cesium metals to afford several reduced products in different charged states isolated as the corresponding alkali metal salts. Interestingly, upon two-electron acquisition the twistacene core undergoes a double dehydrogenative annulation (C74H422–), thus expanding the aromatic core by inclusion of two new aromatic rings and significantly changing the geometry of the molecular skeleton. However, no further annulation was observed upon reduction to the tetraanion (C74H424–), despite the availability of two more cyclization sites. Notably, these stepwise reduced products represent the first crystallographically characterized examples of a negatively charged twistacene, which allowed an analysis of the consequences of the gradual charge build-up on the twistacene core transformation. Moreover, the chemical reduction behavior of a paraphenylene, namely p-quinquephenyl (C30H22), was investigated with alkali metals ranging from lithium to rubidium. As a result, four new doubly-reduced p-quinquephenyl anions were isolated with Group 1 countercations and crystallographically characterized. Analysis of the doubly-reduced products in conjunction with NMR spectroscopy and computational studies revealed a notable asymmetric quinoidal distortion and significant aromaticity reduction. Furthermore, the chemical reduction of a conformationally fluxional naphthyl-based macrocycle with ether bridges (C44H28O2) resulted in multiple C−O bond cleavages, a Z/E isomerization, and hydrogenation. As a result, a new chain-like dianion (C22H162−) was isolated in the form of potassium salts and fully characterized by joint X-ray crystallographic structure determination, NMR and UV-Vis spectroscopy, followed by a computational elucidation of the electronic structure. While the studied macrocycle did not afford stable chemically reduced species under the conditions used, we were able to isolate the main decomposition product in the single-crystalline form and revealed sufficient instability of this macrocyclic system towards reduction. In summary, we revealed the chemical reduction properties of several topologically unique molecular nanocarbons. The reduced products were isolated in single-crystalline form and fully characterized using X-ray diffraction and spectroscopic methods. The consequences of multi-electron addition to these topologically different classes of polyarenes were methodically investigated for the first time. The metal binding preferences, stability, and reactivity of the products, as well as the solid-state packing trends were analyzed and reported. These findings should provide better understanding of the redox behavior of planar, twisted and macrocyclic polyaromatic compounds, facilitating their use in energy storage and charge transfer applications.
Recommended Citation
Pennachio, Matthew John, "Planar, Twisted, And Macrocyclic Polyarenes: Structures, Reduction Limits, And Reactivity" (2023). Legacy Theses & Dissertations (2009 - 2024). 3217.
https://scholarsarchive.library.albany.edu/legacy-etd/3217
