[Comparative Studies of Alternating and Random (Statistical) Fluorene/ Dibenzothiophene-S, S-Dioxide Copolymers]

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Acknowledgement

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Abstract

The electrochemical polymerization study of a set of monomers, dibenzothiophene (DBT), benzothiophene-S,S-dioxide (BTO), and dibenzothiophene-S,S-dioxide (DBTO) was reported and novel conducting poly(dibenzothiophene-S,S-dioxide) (PDBTO) was successfully electrosynthesized in boron trifluoride diethyl etherate (BFEE) and in the binary solvent system of BFEE and trifluoroacetic acid (TFA) for the first time. The strong electron-withdrawing sulphonyl group substitution on BTO partly damaged the aromatic system of BT and significantly inhibited electrochemical polymerization. The electronic clouds of DBT and the electron spin density of its radical cation centralized dominantly on the sulfur atom, thus making it impossible to get the corresponding polymer electrochemically. Furthermore, structural characterization, molecular weight, ionization potentials and electron affinities, fluorescence properties, thermal stability, electrical conductivity, and morphology of PDBTO were minutely investigated. From FT-IR spectra and computational results, DBTO was probably polymerized through the coupling at C(3) and C(7) positions, with the same structure to electrosynthesized polyfluorenes. The substitution of sulphonyl group in the fluorene ring increases its electron affinity considerably for improving electron injection/transport. Additionally, as-formed PDBTO was found to be a typical blue -light-emitter with maximum emission at 458 nm and concurrently exhibited good electroactivity and thermal stability. The successful electrosynthesis of PDBTO should represent a unique approach to DBTO-based donor-acceptor co-oligomers/polymers, which hold promise for the design of a new generation of optoelectronic materials and are hotly researched in the field of electronic devices currently. dried under vacuum at 60 °C for 24 h before use. All solvents and reagents were used as supplied. Anhydrous N,N-dimethylformamide (DMF), tetrahydrofuran (THF), diisopropylamine, copper(I) iodide (CuI), potassium carbonate, sodium sulfate and fluoranthene were purchased from Kanto Chemicals. Dichlorobis(triphenylphosphine)palladium(II) [Pd(PPh3)2Cl2] and 4-bromobenzyl bromide were obtained from Tokyo Chemical Industry Co., Ltd. Methyl iodide, sodium hydride (NaH, 60% dispersion in oil) and triphenylphosphine (PPh3) were purchased from Nakalai Tesque.

Table of Contents

CHAPTER 1: INTRODUCTION1

History of organic electroluminescence3

Basic OLED structure and operation4

Importance of the Removal of Hindered Dibenzothiophenes8

OLEDs10

Solid-State Lighting (SSL)11

Energy Transfer14

Multilayer Devices15

Polymer Blends24

Single Polymer Devices28

Stacked Devices33

External Phosphors34

Excimer/Exciplex Emission34

Materials for Organic Semiconductor Devices35

Low Molar Mass (LMM) Materials37

Polymeric Materials (PMs)45

Liquid Crystals46

Structure Property Relationships47

Thermotropic Liquid Crystals50

Calamitic Liquid Crystals50

The Nematic (N) Phase53

The Chiral Nematic (N*) Phase55

The Smectic Phase56

The Smectic A (SmA) Phase57

The Smectic C (SmC) Phase58

Calamitic Liquid Crystals as Charge-Carrier Transport Layers59

Liquid Crystalline Polymer Networks61

Charge-Transport Parameters of Functionalized Tetracenes64

Electronic Structure of Phosphine Oxides68

Singlet and Triplet Excited States of Phosphine Oxides69

Effect of Interconnection Position70

Oxadiazole-Containing Molecules71

Electronic Structure of Oxadiazoles73

Singlet and Triplet Excited States of Oxadiazoles74

Hybrid Oxadiazole/Carbazole Compounds76

Electronic Structure of Hybrid Oxadiazole/Carbazole Compounds77

Singlet and Triplet Excited States of Hybrid Oxadiazole/Carbazole Compounds78

CHAPTER 2: EXPERIMENTAL DESIGN81

Characterization81

Light-emitting diode ...