Fluorene-Based Conjugated Polymers: Theoretical Analysis, Synthesis, Characterization, Morphology, and Device Application

茀系共軛高分子近來由於其在發光二極體、薄膜電晶體、與光伏打電池的廣泛應用而備受矚目。如何調控茀系共軛高分子之光電特性與形態決定其在上述應用的價值。本論文藉由理論與實驗探討一系列茀系施體-受體共聚高分子之光電性質與受體結構及其含量之關係。並針對茀系硬桿-柔軟嵌段共聚高分子刷之表面結構與其光物理特性對選擇性溶劑之反應進行理論與實驗探討。 本文的第一個部分（第二章）針對茀系交替施體-受體共聚高分子與其組成分子之幾何結構與電子特性藉由density function theory進行理論分析。以理論分析探討電子特性與分子扭轉角度、施體-受體間鍵長、單雙鍵鍵長改變量、與分子間電荷轉移的關連性。茀系交替施體-受體共聚高分子與其組成分子之幾何結構受到受體結構之影響甚鉅，特別是受體在主鏈上之共軛環數。決定茀系交替施體-受體共聚高分子與其組成分子之電子特性的主要因素為：受體強度、主鏈之平面性、與分子間電荷轉移程度。由理論分析之結果可知茀系交替施體-受體共聚高分子之電子特性可藉由其幾何結構與受體強度進行調控。 本文的第二個部分乃進行茀系施體-受體共聚高分子之合成、性質鑑定、並將其應用於發光二極體之製備。在第三章中，吾人合成一系列新穎茀系施體-受體共聚高分子，包括茀-受體交替共聚高分子、茀-受體雜聚高分子、含三種發光單元之茀系雜聚高分子。性質鑑定結果顯示受體之強度及其含量影響高分子之電子與光電特性甚鉅。影響此系列茀系施體-受體共聚高分子之發光性質的主要因素有：能量轉移、分子間電荷轉移、或高原子量元素所引起的螢光抑制。以此系列茀系施體-受體共聚高分子為發光層所製備之發光二極體的發光顏色可涵蓋整個可見光範圍，包括藍綠紅與白光。在第四章中，吾人探討由茀-受體雜聚高分子所組成之一系列高分子混摻的螢光與電致發光特性。針對高分子混摻的組成高分子結構與其含量對其能量轉移與量子效率之影響進行仔細的研究。並藉由精準之高分子混摻組成比例控制達成不完整的能量轉移，此時由各成分的適量發光混成出高效率之白光。 本文的第三部分（第五章）為建立一個以分散粒子動力學為基礎之理論模式來模擬硬桿-柔軟嵌段共聚高分子刷之表面結構。針對溶劑極性、嵌段比例、與高分子刷表面密度對高分子刷表面結構之影響進行有系統的研究。而為了驗證此理論模式之準確性，吾人合成一具有多功能性之雙親硬桿-柔軟嵌段共聚高分子，並將其製備為高分子刷。藉由模擬出之表面結構與實驗所得原子力顯微鏡影像之比較可證實本理論模式之準確性。Polyfluorenes (PFs) have been widely studied recently due to their potential applications in light-emitting diodes, thin-film transistors, and photovoltaic cells. Manipulation of their electronic structures and morphology of polyfluorenes play key roles for the above applications. In this thesis, both theoretical and experimental investigations were conducted on various fluorene-acceptor copolymers to investigate the effects of acceptor strength on their electronic and optoelectronic properties. Variation on the surface structures and photophysical prperties of fluorene-based rod-coil block copolymer brushes with selective solvents were investigated theoretically and experimentally. In the first part of this thesis (Chapter 2), the theoretical geometries and electronic properties of fluorene-based alternating donor-acceptor conjugated copolymers and their model compounds were studied by the density function theory (DFT) at the B3LYP level with 6-31G or 6-31G** basis set. The torsional angle, bridge bond length, bond length alternation, and intramolecular charge transfer were simulated and correlated with the electronic properties, i.e. HOMO, LUMO level, and band gap. It was found that the geometries of fluorene-based donor-acceptor alternating copolymers and their model compounds are significantly affected by the structure of acceptors, particularly the ring size on the backbone. The electronic properties of the polymers and their model compounds are well correlated with the acceptor strength, coplanarity of the backbone, and intramolecular charge transfer. The theoretical study suggests that the electronic properties of alternating fluorene-acceptor conjugated copolymers could be tuned by the geometries or acceptor strength. In the second part of this thesis, fluorene-based donor-acceptor copolymers was synthesized and utilized as the emissive layer of light-emitting diodes. In Chapter 3, a series of novel light-emitting copolymers consisted of 9,9-dihexylfluorene (F) and different acceptor segments, including quinoxaline (Q), 2,1,3-benzothiadiazole (BT) and thieno[3,4-b]-pyrazine (TP), were synthesized by the palladium-catalyzed Suzuki coupling reaction. Three fluorene-acceptor alternating copolymers (PFQ, PFBT, PFTP), six F-TP (PFTP0.5~PFTP35) random copolymers, four random copolymers with three emitting units (PFQTPs and PFBTTPs) were investigated and compared with the parent polyfluorene (PF). The experimental results suggest that the acceptor strength or content significantly affect the electronic and optoelectronic properties. The luminescence characteristics based on the prepared polymers depend on the Förster energy transfer or the intramolecular charge transfer, or heavy-atom fluorescence quenching. The tuning of the electronic and optoelectronic properties could be achieved by incorporating various acceptors or content into the polyfluorenes. The emissive color of these LEDs covers the entire visible region, including red, green, blue, and white. In Chapter 4, the photoluminescence and electroluminescence characteristics of a series of polymer blends based on fluorene-acceptor alternating copolymers were investigated. The dependences of energy transfer and quantum efficiency on the chemical structure of component and on the composition of polymer blend were rationalized. Precise control of the composition of polymer blends resulted in incomplete Förster energy transfer from donor to acceptors. Emission from all the components simultaneously resulted in efficient white emission. In the third part of this thesis, a theoretical model based on dissipative particle dynamics was established to simulate the surface structure of rod-coil block copolymer brushes. The effects of different solvent polarities, block ratios, and grafting densities of brushes on the surface structures were investigated. For the justification of our theoretical model, a novel multifunctional amphiphilic rod-coil block copolymer of the type of PF-b-PPEGMA-b-PPOPS was synthesized by ATRP and the functional rod-coil polymer brush was successfully prepared using reactivity of the silanol-carrying PPOPS block. The comparison between simulated surface structures and AFM images shows highly similar surface structures indicating the feasibility of this theoretical model.Abstract i 摘要 iv Content vi Table Captions xii Figure Captions xiii Chapter 1 Introduction 1 1-1 Introduction to Conjugated Polymers 1 1-2 Conjugated polyfluorenes 5 1-2-1 Synthesis of Polyfluorenes 6 1-2-1-1 Yamamoto coupling 6 1-2-1-2 Suzuki coupling 7 1-2-2 Solid-State Ordering and Morphology 9 1-2-3 Photophysical properties 10 1-2-3-1 Morphology-related optical properties 11 1-2-3-2 Degradation-related optical properties 13 1-2-4 Electroluminescence 18 1-3 Chemical Modification of Polyfluorenes 20 1-3-1 Fluorene-based Donor-Acceptor Copolymers 20 1-3-1-1 Light-Emitting Diodes (LEDs) 21 1-3-1-2 Organic Thin-Film Transistors (OTFTs) 22 1-3-1-3 Polymer Solar Cells 22 1-3-2 Fluorene-based Rod-Coil Block Copolymers 27 1-4 Research Objectives 29 References 31 Chapter 2 Electronic Structure and Properties of Alternating Fluorene- Acceptor Conjugated Copolymers and Their Model Compounds 38 2-1 Introduction 38 2-2 Theoretical Analysis 41 2-2-1 Methodology 41 2-2-2 Geometrical Parameters and Electronic Properties Analyzed 41 2-3 Results and Discussion 43 2-3-1 Justification of the Theoretical Analysis 43 2-3-2 Optimized Geometries and Electronic Properties of Model Compounds 43 2-3-3 Optimized Geometries and Electronic Properties of Fluorene-Acceptor Copolymers 51 2-4 Conclusions 59 References 60 Chapter 3 Synthesis and Characterization of New Fluorene-Acceptor Alternating and Random Copolymers for Light-Emitting Applications 62 3-1 Introduction 62 3-2 Experimental 66 3-2-1 Materials 66 3-2-2 General Procedure of Polymerization 66 3-2-3 Characterization 72 3-2-4 Device Fabrication and Testing 73 3-3 Results and Discussion 75 3-3-1 Structure Characterization of Fluorene-based Donor-Acceptor Copolymers 75 3-3-2 Thermal Properties 78 3-3-3 Optical Absorption and Electrochemical Characteristics 79 3-3-4 Photoluminescence Properties 85 3-3-5 Electroluminescence (EL) characteristics 92 3-4 Conclusions 101 References 103 Chapter 4 PF-Based Polymer Blends: Characteristics of Energy Transfer and Their Applications in Light-Emitting Diodes 106 4-1 Introduction 106 4-2 Experimental 109 4-2-1 Materials 109 4-2-2 Preparation of PF-Based Blends and Thin Films 109 4-2-3 Characterization 109 4-2-4 Device Fabrication and Testing 109 4-3 Results and Discussion 111 4-3-1 Miscibility of PF-Based Polymer Blends 111 4-3-2 Photophysics of PF-Based Binary Blends 112 4-3-3 Photophysics of PF-Based Ternary Blends 116 4-3-4 Electroluminescence of PF-Based Binary Blends 119 4-3-5 Electroluminescence of PF-Based Ternary Blends 126 4-4 Conclusions 131 References 133 Chapter 5 Theoretical Analysis and Experimental Investigation on the Surface Structures of Fluorene-Based Rod-Coil Block Copolymer Brushes 135 5-1 Introduction 135 5-2 Theoretical Analysis 140 5-2-1 The Basic Dissipative Particle Dynamics (DPD) Simulation Method 140 5-2-2 Rod-Coil Block Copolymer Brushes 141 5-2-3 Parameters 142 5-3 Experimental 143 5-3-1 Materials 143 5-3-2 Synthesis 143 5-3-3 Self-Assembly of Triblock Copolymers on Oxidized Surfaces 146 5-3-4 Characterization 146 5-4 Results and Discussion 147 5-4-1 Simulated Surface Structures of Rod-Coil Block Copolymer Brushes 147 5-4-2 PF-b-PPEGMA-b-PPOPS Rod-Coil Block Copolymer Brushes 153 5-5 Conclusions 163 References 164 Chapter 6 Conclusion and Future Work 167 Appendix Morphology Transformation and Photophysical Proeprties of poly[2,7- (9,9-di-n-hexylfluorene)]-block-poly(acrylic acid) (PF-b- PAA) Rod-Coil Copolymers in Solution 170 A-1 Introduction 170 A-2 Experimental 173 A-2-1 Materials 173 A-2-2 Synthesis 173 A-2-3 Preparation of PF-b-PAA Aggregate in Solution 174 A-2-4 Characterization 175 A-3 Results and Discussion 181 A-3-1 Self-Assembly of PF-b-PAA 181 A-3-2 Photophysical Properties 187 A-4 Conclusions 189 References 190 Publication Lists 19