Investigation of sequence-property correlations in precisely defined synthetic macromolecules

Yu, Hao

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https://hdl.handle.net/2142/114079 Copy

Description

Title

Investigation of sequence-property correlations in precisely defined synthetic macromolecules

Author(s)

Yu, Hao

Issue Date

2021-11-24

Director of Research (if dissertation) or Advisor (if thesis)

Moore, Jeffrey S

Doctoral Committee Chair(s)

Schroeder, Charles M

Committee Member(s)

• Diao, Ying
• Guironnet, Damien S

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Sequence-defined polymer
• Sequence-controlled polymer
• precision polymer

Abstract

A major challenge in synthetic macromolecules lies in understanding how primary monomer sequence affects the properties of polymeric materials. The challenges are twofold. The first difficulty lies in the efficient and scalable production of non-biological oligomers and polymers with discrete chain lengths and sequences. In addition to the synthetic challenges, developing new molecular-scale characterization methods is desired to probe the intrinsic structure-property relations. In my Ph.D. research, the synthesis of precisely defined materials is pursued in parallel with single molecule conductance experiments and molecular modeling. To achieve these goals, I work closely with students in the Schroeder lab who develop single-molecule methods. Together, we correlate properties within precisely defined sequences and investigate the molecular origins of the sequence-dependent properties. The main goal of my Ph.D. research is to gain a fundamental understanding of how primary monomer sequence determines the properties in precisely defined synthetic macromolecules. Studies in chapter 2 show that charge transport properties in single molecule junctions critically depends on the primary monomer sequence of conjugated oligomers. In particular, our work correlates properties within precisely defined sequences in a ‘monomer-by-monomer’ fashion, thereby revealing the subtle but important role of molecular structures including steric hinderance and directionality of heteroatoms in determining charge transport properties. In chapter 3, we show that the single-molecule conductance decreases exponentially as the length of the backbone increases in a series of conjugated oligomers containing alternating donor-acceptor sequence. Importantly, the alternating sequence had a smaller conductance decay constant compared to the homo-oligomers oligothiophene and oligophenylene. In chapter 4, we find that the charge transport in oxazole-terminated molecules is critically determined by the heteroatom substitution position of the oxazole anchor in addition to the aryl substitution pattern of the π-conjugated core. Additionally, I have further continued this theme in a new direction investigating the intermolecular charge transport in discrete pyridinium dimers using a supramolecular self-assembly approach (chapter 5). In addition to investigating charge transport properties, I also study the structural characteristics of sequence-controlled periodic polymers (chapter 6). The long-term goal of this project is to transition the proposed deconstruct-reconstruct strategy into a platform that will enable developing synthetic polymer with structural and functional complexity approaching proteins. Expanding the strategy used in this work can further provide new insights on the rules used by biology. Overall, my dissertation research directly address the fundamental question regarding sequence-property correlations in synthetic materials. From a broad perspective, the knowledge gained in this work will open new avenues to tune the structure and property of next-generation organic materials.

Graduation Semester

2021-12

Type of Resource

Thesis

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http://hdl.handle.net/2142/114079

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© 2021 by Hao Yu. All rights reserved.

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