5CB 를 전구체로 한 탄소나노점의 합성과 광발광 제어를 통한 적용 : UV-Vis 셔터 및 UV 센서 = Synthesis of Carbon Nanodots Using 5CB as a Precursor and Their Applications via Photoluminescence Control: UV? Vis Shutter, UV Sensor, and Emerging Photonic Applications

다국어 초록 (Multilingual Abstract)

Carbon nanodots (CNDs) are a class of green, photostable, luminescent nanomaterials with significant potential for optoelectronic applications.[1–9] However, their practical implementation is hampered by limited synthetic scalability, incompatibility with functional soft material matrices, and the lack of controlled photoluminescence anisotropy. This dissertation addresses these fundamental challenges and demonstrates that anisotropic CNDs are viable electro-optical components for liquid-crystal-based photonic structures. Anisometric CNDs were synthesized through microwave-assisted carbonization of a calamitic nematic liquid-crystal precursor (5CB), yielding
nanoparticles that preserve the intrinsic shape anisotropy of their molecular template while exhibiting broad ultraviolet absorption, blue
photoluminescence, and exceptional dispersibility without requiring postsynthetic surface functionalization. The structural anisotropy and preferential π-domain orientation of these CNDs enable polarized visible emission when integrated into nematic host matrices, where their uniaxial alignment is governed by the host liquid-crystal director field. To realize multifunctional photonic materials, anisometric CNDs were incorporated within polymer network liquid crystals (PNLC), producing hybrid films with dual lightresponsive
functionality. These systems demonstrate electrically switchable light modulation between transparent (transmittance ≈ 93.1% and scattering
(transmittance ≈ 13.3%) states with ultrafast response kinetics (≈7.6 ms turnon,≈5.4 ms turn-off) alongside adjustable photoluminescence under ultraviolet excitation. Notably, the CNDs facilitate polymer network formation during photopolymerization, enabling efficient light scattering at ultralow polymer concentrations, a capability absent in CND-free controls. The synergistic alignment of CNDs with the nematic director produces linearly polarized photoluminescence with an emission dichroic ratio of ≈1.63, establishing direct structure-function relationships wherein particle anisotropy governs macroscopic photonic response. This work establishes a design paradigm for soft photonic materials through anisometric nanocarbon integration in liquid-crystal-templated architectures, enabling dualresponsive,
polarized, electrically switchable systems applicable to smart windows, adaptive optical shutters, ultraviolet-protection coatings, and
polarization-based security devices while providing fundamental insights into nanocarbon-enabled photoluminescence phenomena.

목차 (Table of Contents)

• CHAPTER 1. INTRODUCTION 1
• 1.1 Background and fundamentals of light-modulating materials 1
• 1.1.1 Evolution of the optical modulation system 1
• 1.1.2 Requirements for next-generation smart photonic devices 1
• 1.2 Liquid crystal and electro-optic switching platforms 2
• 1.2.1 Liquid crystals: structure, alignment, and optical anisotropy 2
• 1.2.2 PDLC (Polymer Dispersed Liquid Crystal) / PNLC (Polymer Network Liquid Crystal): formation and scattering mechanisms 14
• 1.2.3 Limitations of conventional PDLC/PNLC systems, especially in the UV regime 19
• 1.3 Carbon nanodots (CNDs) as luminescent nanomaterials 21
• 1.3.1 Structure, optical behavior, and photoluminescent mechanisms of CNDs 21
• 1.3.2 Synthesis approaches, tunability, and scalability challenges 22
• 1.3.3 Limitations of conventional CNDs for LC-Based photonic applications 22
• 1.4 Hybrid liquid crystal nanomaterial photonic systems 24
• 1.4.1 Interaction mechanisms in nanomaterial hybrids. 24
• 1.4.2 Limitations of existing LC-nanomaterial architectures. 25
• 1.5 Knowledge gap and challenges 27
• 1.6 Motivation 29
• CHAPTER 2. SYNTHESIS OF LC-BASED ANISOMETRIC CND AND ITS CHARACTERIZATIONS 33
• 2.1 Material details.. 33
• 2.2 Introduction 35
• 2.3 Synthesis and Characterizations of CNDs in 5CB 35
• 2.3.1 Detailed description of microwave-assisted synthesis of CNDs using 5CB as precursor.. 35
• 2.3.2 Extraction and purification of CNDs from 5CB matrix. 42
• 2.3.3 Structural and chemical characterization of CNDs. 45
• 2.3.3.1 HRTEM analysis of CND morphology and size distribution 45
• 2.3.3.2 XPS and FTIR studies of surface chemistry and functional groups 47
• 2.3.4 Optical characterization: UV-vis absorption and photoluminescence spectra 53
• CHAPTER 3. POLARIZED EMISSION PROPERTIES OF CNDs 67
• 3.1 Introduction 68
• 3.2 Planar-aligned CNDmliquid crystal cells fabrication details 68
• 3.3 Polarized Emission Properties of CNDs. 71
• CHAPTER 4. ELECTRIC FIELD SWITCHING OF CNDs 78
• 4.1 Introduction 78
• 4.2 Electric Field Induced Switching and Corresponding Modulation of the Emission Properties of CNDs. 78
• CHAPTER 5. POLYMER NETWORK FORMATION AND OPTICAL MODULATION IN PNLC CELLS 84
• 5.1 Introduction 84
• 5.2 Polymer Network Formation 84
• CHAPTER 6. SPECTRAL AND OPTICAL PROPERTIES OF THE CND24-BASED UVVISIBLE SHUTTER AND UV SENSOR 99
• 6.1 Introduction 99
• 6.2 Spectral and optical properties of the CND24-based UVvisible shutter and UV sensor. 99
• 6.3 Mechanism of Optical Switching in PNLC Cells 110
• CHAPTER 7. CONCLUSION AND FUTURE PROSPECTS 127
• REFERENCES 132
• LIST OF PUBLICATIONS. 149
• 국 문 초 록 150