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Control of Charge Transfer Using Highly Luminescent Small Molecular Donor-Acceptor Systems

고발광 단분자 도너-억셉터 시스템을 이용한 전하 이동 제어 연구

  • 박선영 (아주대학교 일반대학원)

초록/요약

The performance of organic optoelectronic materials is fundamentally governed by intermolecular interactions, specifically the precise manipulation of charge transfer (CT) states. This thesis aims to establish versatile platforms for high-sensitivity sensing and stimuli-responsive optical switching by exploiting high-efficiency thermally activated delayed fluorescence (TADF) emitters as a core framework, modulated through chemical doping and morphological engineering strategies. In the first part of this study, a "turn-on" chemosensor for ammonia gas detection was designed by controlling ground-state electron transfer. By doping a strong electron acceptor (F4-TCNQ) into a TADF donor matrix, complete fluorescence quenching was initially induced. Upon exposure to electron-donating gases such as ammonia, competitive interaction between the dopant and the analyte triggers a dedoping process, resulting in the instantaneous recovery of the suppressed TADF emission. This strategy demonstrates that high sensitivity and naked-eye detectability can be achieved on commercial substrates like filter paper without complex chemical synthesis. The second part focuses on controlling excited-state electron transfer-specifically exciplex formation-via the morphological engineering of supramolecular assemblies. By blending a TADF donor with self-assembling dicyanostilbene (DCS)-based acceptors, efficient TADF- exciplex emission was realized in the pristine amorphous films. Crucially, the application of solvent vapor annealing (SVA) as an external stimulus induced "narcissistic self-sorting" of the DCS molecules, leading to macroscopic phase separation and the formation of crystalline nanowires. This structural evolution physically decoupled the donor-acceptor interactions, extinguishing the exciplex channel and switching the emission pathway to the intrinsic aggregation-induced enhanced emission (AIEE) of the DCS aggregates. This offers a novel methodology to dynamically switch not only the emission color but also the exciton lifetime and radiative mechanism. Collectively, this work demonstrates that CT interactions in small-molecule organic systems can be multi-dimensionally controlled at both the molecular level (doping) and the component level (modulation of the acceptor species). Specifically, by tuning the chemical nature of the acceptor, we successfully realized distinct CT states, namely Integer Charge Transfer (ICT) and exciplex formation, thereby controlling the overall degree of charge transfer. The strategies presented herein provide essential design guidelines for the development of next-generation intelligent chemical sensors and secure optical memory devices.

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목차

Introduction 1
Chapter 1. Integer Charge Transfer in Highly Luminescent Emitter for Efficient Detection of Ammonia Gas 4
1.1. Experimental section 4
1.1.1. Materials and Instrumentation 4
1.1.2. Preparation of TCzTrz:F4-TCNQ Probe Solution 4
1.1.3. Selectivity Test 5
1.2. Results and Discussion 5
1.2.1. Photophysical Behavior and integer Charge Transfer of TCzTrz 5
1.2.2. Ammonia Vapor Sensing Behavior of the TCzTrz:F4-TCNQ Optical Probe 9
1.2.3. Mechanism of Ammonia-Induced PL Recovery in the TCzTrz:F4-TCNQ 12
1.2.4. Solid-State Application and Visual Detectability of ammonia sensing 15
1.3. Conclusion 17
Chapter 2. Modulation of Exciplex Emission Using Highly Luminescent and Self-Assembling Small Molecules 18
2.1. Experimental section 18
2.1.1. Materials and Instrumentation 18
2.1.2. Samples Preparation 18
2.2. Results and Discussion 18
2.2.1. Electronic and Photophysical Properties of materials 19
2.2.2. Formation and Characterization of D-A Exciplex Systems 24
2.2.3. Solvent Vapor Annealing-Induced Phase Transition and Emission Switching 27
2.3. Conclusion 31
Conclusion 32
References 35

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