Conjugated Polymer Networks: Synthesis and Properties

Conjugated Polymer Networks: Synthesis and Properties

Bibliographic Details
Main Author: Kokil, Akshay
Language:English
Published: Case Western Reserve University School of Graduate Studies / OhioLINK 2005
Subjects:
Conjugated Polymers
Conjugated Polymer Networks
Charge Carrier Mobility
Time-of-Flight
Online Access:http://rave.ohiolink.edu/etdc/view?acc_num=case1121451946
id ndltd-OhioLink-oai-etd.ohiolink.edu-case1121451946
record_format oai_dc
collection NDLTD
language English
sources NDLTD
topic Conjugated Polymers
Conjugated Polymer Networks
Charge Carrier Mobility
Time-of-Flight
spellingShingle Conjugated Polymers
Conjugated Polymer Networks
Charge Carrier Mobility
Time-of-Flight
Kokil, Akshay
Conjugated Polymer Networks: Synthesis and Properties
author Kokil, Akshay
author_facet Kokil, Akshay
author_sort Kokil, Akshay
title Conjugated Polymer Networks: Synthesis and Properties
title_short Conjugated Polymer Networks: Synthesis and Properties
title_full Conjugated Polymer Networks: Synthesis and Properties
title_fullStr Conjugated Polymer Networks: Synthesis and Properties
title_full_unstemmed Conjugated Polymer Networks: Synthesis and Properties
title_sort conjugated polymer networks: synthesis and properties
publisher Case Western Reserve University School of Graduate Studies / OhioLINK
publishDate 2005
url http://rave.ohiolink.edu/etdc/view?acc_num=case1121451946
work_keys_str_mv AT kokilakshay conjugatedpolymernetworkssynthesisandproperties
_version_ 1719421383394459648
spelling ndltd-OhioLink-oai-etd.ohiolink.edu-case11214519462021-08-03T05:31:59Z Conjugated Polymer Networks: Synthesis and Properties Kokil, Akshay Conjugated Polymers Conjugated Polymer Networks Charge Carrier Mobility Time-of-Flight <p>The experimental research program that forms the basis of this thesis has been directed towards the design, synthesis, processing and physical characterization of well-defined conjugated polymer networks. It attempts to provide answers to the questions how such materials can be synthesized and processed and how the introduction of cross-links can be exploited for the creation of polymeric materials with optimized optic and electronic characteristics. Interestingly, this family of materials has received little attention in the past, at least as far as systematic studies of well-defined systems are concerned. This situation may be a direct consequence of the challenge to introduce conjugated cross-links into conjugated polymers and retain adequate processibility.</p> <p>We have shown that organometallic polymer networks based on linear conjugated polymers are readily accessible through ligand-exchange reactions. This approach was exemplified by exploiting the ethynyl moieties comprised in poly(p-phenylene ethynylene) (PPE) derivatives as ligand sites, which allow for complexation with selected metals and cross-linking via the resulting PPE-Metal complexes. Focusing on the dinuclear complex [Pt-(μ-Cl)Cl-PPE]<sub>2</sub> and PPE-Pt<sup>0</sup> as crosslinks, we have conducted an in-depth investigation on how the nature of the metal cross-links influences the materials characteristics, in particular the charge transport properties. We first investigated the charge carrier mobility of poly[2,5-dioctyloxy-1,4-diethynyl-phenylene-alt-2,5-bis(2'-ethylhexyloxy)-1,4-phenylene] (EHO-OPPE), as a classic representative of poly(p-phenylene ethynylene) (PPE) derivatives, which represent an important class of conjugated polymers. In what appears to be the first study ever conducted on the mobility of any PPE, we found that EHO-OPPE displays ambipolar charge transport characteristics with very high electron (1.9*10<sup>-3</sup> cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>) and hole (1.6*10<sup>-3</sup> cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>)) mobilities. Most importantly, the introduction of Pt<sup>0</sup> cross-links was found to enhance the charge carrier mobility of the investigated systems by up to an order of magnitude. Electron and hole mobilities of the order of 1.5*10<sup>-2</sup> cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>) were measured for these materials, representing the highest mobilities ever reported for disordered conjugated polymers. More importantly, the study unequivocally proves that the introduction of conjugated cross-links indeed leads to a significant improvement of the carrier mobility of conjugated polymers. Work involving [Pt-(ì-Cl)Cl-PPE]<sub>2</sub> cross-links suggests that the nature of the metallic cross-links is exceedingly important. We have shown that the Pt<sup>II</sup> centers act as traps for both electrons and holes and impede efficient charge transport. With the aim to expand the materials basis and exploit other chemical platforms for the cross-linking process, we integrated 2,2’-bipyridine (bipy) moieties into the conjugated polymer backbone. Bipy is a most versatile ligand, which can bind to a broad variety of metals. We have synthesized a library of PPEs in which the bipyridine content is systematically varied. Using a variety of transition metal complexes, we have systematically investigated the ligand-exchange reactions of these polymers. Complexation studies suggest that ligand exchange indeed leads to three-dimensional networks, which feature BipyPPE-metal-BipyPPE cross-links and display interesting optoelectronic properties. We also showed that the ligand exchange is a cooperative process, which in the presence of a competing ligand is fully reversible. Complexes with group 12 d<sup>10</sup> ions (Zn<sup>2+</sup> and Cd<sup>2+</sup>) are emissive, while other transition metals such as Cu<sup>+</sup>, Ni<sup>2+</sup> form non-radiative metal-to-ligand charge-transfer complexes with the polymers.</p> <p>In a second approach we have demonstrated that the processing issues associated with covalently cross-linked conjugated polymer networks can be readily overcome if these materials are synthesized in the form of cross-linked nanoparticles and processed as suspensions. In a series of ground-breaking experiments, we have shown that covalently cross-linked conjugated polymer particles can be produced by conducting cross-coupling reactions in aqueous emulsions instead of homogeneous solutions and using multifunctional cross-linkers. The size of the spherical polymer particles can easily be tuned over a wide range (mm to nm) by modification of the reaction conditions. The resulting materials can be processed in the form of suspension and promise interesting electronic properties.</p> 2005-07-18 English text Case Western Reserve University School of Graduate Studies / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=case1121451946 http://rave.ohiolink.edu/etdc/view?acc_num=case1121451946 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

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