Fluorination as a tool for controlling properties, molecular order and functionality of polythiophene derivatives
File(s)
Author(s)
Boufflet, Pierre
Type
Thesis
Abstract
In this work, we explore the uses of fluorination in the context of π-conjugated polymers. Using extensively studied model systems such as poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(3- alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), we are able to probe the influence of thiophene fluorination on the electronic structure and thin-film morphology, two defining aspects of organic semiconductor performance in electronic devices such as organic field effect transistors (OFET). Experimental data obtained from Ultraviolet photoelectron, UV-Visible and Raman spectroscopy along with differential scanning calorimetry, atomic force microscopy and X-ray diffraction suggest that fluorination leads to a stabilisation of the frontier molecular orbital levels and increased backbone planarity. The latter manifest itself as an enhanced propensity to aggregate and much higher melting point. Hole carrier mobilities in OFET devices are considerably enhanced in the backbone-fluorinated polymers, an observation attributed to the increased planarity of the polymer backbone. Computational calculations also predict an increased backbone rigidity and a strong preference for the coplanar arrangement of fluorinated thiophene rings. The origins of such planarisation are thought to be intramolecular in nature, likely from sulfur-fluorine inter-ring interactions as evidenced by S-F short contacts observed in the single crystal X-ray structure of a bithiophene monomer precursor.
By synthesising well-defined diblock and alternating copolymers, backbone fluorination is then explored as a potential tool to control phase separation and dielectric constants, two key factors involved in the context of organic photovoltaic (OPV) devices.
The utility of fluorine atoms as a good leaving-group in nucleophilic aromatic displacements on electron-poor aromatic systems is then used to produce a P3HT derivative end-capped with pentafluorobenzene. This polymer can then be reacted with good nucleophiles in mild conditions. As a proof of concept, three functional moieties are tethered to the P3HT derivative in this manner, opening the door towards sensing applications and hybrid organic/inorganic semiconductor interface engineering.
By synthesising well-defined diblock and alternating copolymers, backbone fluorination is then explored as a potential tool to control phase separation and dielectric constants, two key factors involved in the context of organic photovoltaic (OPV) devices.
The utility of fluorine atoms as a good leaving-group in nucleophilic aromatic displacements on electron-poor aromatic systems is then used to produce a P3HT derivative end-capped with pentafluorobenzene. This polymer can then be reacted with good nucleophiles in mild conditions. As a proof of concept, three functional moieties are tethered to the P3HT derivative in this manner, opening the door towards sensing applications and hybrid organic/inorganic semiconductor interface engineering.
Version
Open Access
Date Issued
2016-04
Date Awarded
2016-06
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Heeney, Martin
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/K503733/1
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)