Functionalized π-Conjugated Organic Materials for Phototherapy, Colorimetric Sensing, and Photovoltaic Applications

다국어 초록 (Multilingual Abstract)

Since the discovery and development of conductive polymers in the 1970s, which led to the 2000 Nobel Prize in Chemistry awarded to Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa, the science and technology of π-conjugated molecules and polymers have rapidly advanced. Significant efforts have been devoted to developing applications in organic light- emitting diodes (OLEDs), organic field-effect transistors (OFETs), photovoltaic cells (OPVCs), dye-sensitized solar cells (DSSCs), sensors, and bioimaging, resulting in substantial growth of the field. The π-conjugated system is generally defined, in a Lewis structure, as an alternation of formal single and double (or triple) bonds along a chain of carbon atoms (or heteroatoms), which contains delocalized electrons. The carbon atoms in such conjugated systems are sp2- hybridized and form three σ-bonds with neighboring atoms, whereas the remaining p-orbitals (perpendicular to the sp2 backbone) participate in the formation of delocalized π-bonds through continuous p-orbital overlap. This extended delocalization results in smaller electronic energy gaps than those of σ-bonded compounds, Eg(π) < Eg(σ), leading to low-energy electronic excitations and optical absorption extending into the visible-to-near-infrared region. Additionally, the electronic and optical properties of π-conjugated compounds can not only be predicted to a good extent but also be systematically tuned by introducing substituents onto the π-conjugated framework. In π-conjugated single-molecule systems, the molecular structures are typically based on a donor–π–acceptor (D–π–A) structure, in which a π-bridge is end-capped by electron-donating and electron-accepting groups. Such D–π–A arrangements facilitate efficient intramolecular charge transfer (ICT) between the donor and acceptor moieties and generate a xviii dipolar push–pull system, thereby enhancing the molecular polarizability and enabling the tuning of the electronic energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) through substantial π-electron delocalization.
In Chapter I, several fluorophore-based photothermal agents and photosensitizers for phototherapy were developed owing to their promising phototherapeutic properties. In Chapter I-A, the coumarin-based photothermal agents (ICou and ICouR) were synthesized, incorporating a dicyanomethylidene-substituted indan derivative. The introduction of the indan derivative induced a red-shift in the absorption wavelength and enhanced the photothermal properties. Furthermore, ICouR, which contains a CF3 rotor, exhibited not only remarkable photothermal performance, achieving a photothermal conversion efficiency (PCE) of 54.2%, but also excellent photostability.
In Chapter I-B, the pyromellitic diimide-based photothermal agent (PI-DA) was synthesized by incorporating dimethylamine groups as rotatable electron-donating units. In aqueous solution, PI-DA formed J-aggregates and exhibited aggregation-induced emission (AIE) behavior. In addition, the photothermal performance of PI-DA was evaluated under 690 nm laser irradiation, achieving a PCE of 33.4% through non-radiative decay via a twisted intramolecular charge transfer (TICT) state.
In Chapter I-C, the 1,8-naphthalimide-based photosensitizer (RL) was synthesized, which contains a prodrug moiety that can be activated by either of the two cancer-associated stimuli, GSH and H2O2. The photosensitizing ability of RL was achieved through the substitution of oxygen with sulfur, resulting in remarkable singlet oxygen (1O2) generation as well as a red- shift in the absorption wavelength. Under both oxidative and reductive stress, the release of camptothecin (CPT) was observed. The significant 1O2 generation and redox-responsive drug release demonstrate the potential of RL for dual photodynamic/chemo therapy.
In Chapter Ⅱ, a polydiacetylene (PDA) based sensor, which is one of the conjugated polymers, was developed as a colorimetric sensing platform owing to its unique optical and electronic properties. An organic-reaction-based PDA sensor for cyanide detection (PDA-BMN) was synthesized by incorporating a cyanide-reactive head group onto the PDA backbone. In the presence of cyanide, PDA-BMN exhibited a distinct color transition from the blue to the orange phase, achieving a limit of detection of 0.55 μM. To facilitate on-site monitoring, PDA-BMN was integrated into a lateral flow assay (LFA) platform. The PDA-coated LFA strip also displayed a clear colorimetric response, and its sensitivity was further improved by applying mechanical pressing to the strip, reducing the limit of detection from 233.5 μM to 173.4 μM.
In Chapter Ⅲ, a poly(acrylic acid) (PAA) template-assisted method was developed to prepare uniform and small MgO nanoparticles (NPs). DSSCs, one of the representative applications of π-conjugated systems, employ π-conjugated dyes as sensitizers. When fabricating DSSC devices, the introduction of a MgO interlayer composed of small and uniform NPs prepared by the PAA template-assisted method resulted in enhanced photovoltaic performance. This improvement is attributed to the high light transmittance resulting from a highly uniform particle size distribution, as well as the wide band gap of MgO.

국문 초록 (Abstract)

1970년대 전도성 폴리아세틸렌(플라스틱)의 발견과 발전은 Alan J. Heeger, Alan G. MacDiarmid, Hideki Shirakawa에게 2000년 노벨화학상을 수여하는 계기가 되었으며, 이를 기반으로 π-공액 분자 및 고분자에 대한 과학과 기술은 빠르게 진보해 왔다. 이러한 π-공액 시스템은 유기 발광 다이오드(OLEDs), 유기 전계 효과 트랜지스터(OFETs), 유기 태양전지(OPVCs), 염료감응 태양전지(DSSCs), 센서 및 바이오이미징을 포함한 다양한 분야에서 핵심 응용이 가능해지며 연구가 활발히 진행되고 있다. 일반적으로 π-공액 시스템은 루이스 구조 관점에서 단일–이중(또는 삼중) 결합이 교대로 배열된 구조로 정의되며, sp2 혼성화된 탄소가 σ-결합을 형성하고 수직 방향의 p- 오비탈이 연속적인 중첩을 통해 π-전자 비편재화가 일어난다. 이러한 광범위한 비편재화는 σ-결합 화합물보다 작은 전자 에너지 갭(Eg(π) < Eg(σ))을 유도하여 가시광선–근적외선 영역까지 확장되는 낮은 에너지의 전자전이를 가능하게 한다. 또한 π-공액 화합물의 전자·광학적 특성은 구조 내 치환기 도입을 통해 예측 및 조절이 가능하다. 단분자 π-공액 시스템에서는 일반적으로 전자공여체–π– 전자수용체(D–π–A) 구조가 사용되며, 이는 분자 내 전하 이동(ICT)을 촉진하고 쌍극자 push–pull 시스템을 형성하여 높은 분극성과 HOMO–LUMO 에너지 갭 조절을 가능하게 한다.
제 Ⅰ장에서, 우수한 광치료 성능을 가지는 형광체 기반 광열제 및 광감작제를 개발하였다. 제 Ⅰ- A장에서, 쿠마린 (coumarin) 기반 광열제(ICou, ICouR)를 합성하였으며, 다이사이아노메틸리덴 치환 인단 유도체의 도입을 통해 흡수 파장의 적색 이동과 향상된 광열 특성을 확인하였다. 또한 CF3 회전자(rotor)를 포함한 ICouR은 54.2%의 광열 전환 효율과 함께 우수한 광안정성을 나타냈다.
제Ⅰ-B장에서, 파이로멜리틱 다이미드 (pyromellitic diimide) 기반 광열제(PI-DA)를 합성하였으며, 다이메틸아민기 도입을 통해 회전 가능한 전자공여 단위를 부여하였다. PI-DA는 수용액에서 J-응집체를 형성하며 AIE(aggregation-induced emission) 특성을 보였다. 또한, PI-DA의 광열 성능은 690 nm 레이저 조사 하에서 평가되었으며, 비틀린 분자 내 전하 이동(TICT) 상태를 통한 비방사성 붕괴를 통해 33.4%의 광열 변환 효율(PCE)을 달성하였다.
제 Ⅰ-C장에서, 1,8-나프탈이미드 (1,8-naphthalimide) 기반 감광제(RL)를 설계하여 합성하였으며, 이는 암 미세환경의 산화 환원 환경(GSH 및 H2O2)에 의해 활성화될 수 있는 전구약물 링커를 포함한다. 산소를 황으로 치환함으로써 RL의 광감작 능력이 향상되어 우수한 단일항 산소 생성과 흡수 파장의 적색 이동을 유도하였으며, 환원 및 산화 스트레스 조건에서 camptothecin (CPT) 방출이 확인되었다. 이러한 반응성 약물 방출과 우수한 활성산소 생성은 RL의 광역학–화학 이중 치료(PDT/chemo dual therapy) 가능성을 보여준다.
제 Ⅱ 장에서는 공액 고분자의 일종인 폴리다이아세틸렌(PDA)을 기반으로 독특한 광학·전자적 특성을 활용한 컬러리메트릭 센서를 개발하였다. 시안화물 반응성 리셉터를 PDA 백본에 도입하여 PDA-BMN 센서를 합성하였으며, 시안화물이 존재할 때 청색에서 오렌지색으로의 뚜렷한 색 변화와 0.55 μM의 낮은 검출한계를 확인하였다. 현장 분석을 용이하게 하기 위해 PDA-BMN을 lateral flow assay (LFA) 플랫폼에 적용하였으며, 압착 처리된 LFA 스트립은 233.5 μM에서 173.4 μM로 감소한 검출한계와 선명한 색 변화 응답을 보였다.
제 Ⅲ 장에서는 poly(acrylic acid) 기반 템플릿 보조 합성법을 통해 크기가 작고 균일한 MgO 나노입자를 제조하였다. DSSC는 대표적인 π-공액 시스템 응용 분야로서 π-공액 염료를 감응제로 활용한다. 본 연구에서는 균일한 MgO 나노입자로 구성된 MgO 중간층을 DSSC 광전극에 도입하였으며, 이는 매우 균일한 입자 크기 분포로 인한 높은 광 투과율과 MgO의 넓은 밴드갭으로 인해 DSSC의 광전 성능 향상으로 이어졌다.

목차 (Table of Contents)

• Chapter I. Functional D–π–A systems for phototherapy 1
• I.1. Introduction 2
• I.2. References 6
• Chapter I-A. Coumarin based NIR photothermal agents for photothermal therapy 8
• I-A-1. Introduction 8
• I-A-2. Results and Discussion 10
• I-A-3. Conclusion 14
• I-A-4. Experimental Section 15
• I-A-5. References 18
• Chapter I-B. Pyromellitic diimide based NIR photothermal agent for photothermal therapy 19
• I-B-1. Introduction 19
• I-B-2. Results and Discussion 20
• I-B-3. Conclusion 26
• I-B-4. Experimental Section 26
• I-B-5. References 29
• Chapter I-C. 1,8-naphthalimide based photosensitizer for photodynamic/ chemo dual therapy 31
• I-C-1. Introduction 31
• I-C-2. Results and Discussion 35
• I-C-3. Conclusion 37
• I-C-4. Experimental Section 39
• I-C-5. References 43
• Chapter Ⅱ. π-Conjugated polydiacetylene based colorimetric sensor for cyanide detection 45
• Ⅱ-1. Introduction 46
• Ⅱ-2. Results and Discussion 51
• Ⅱ-3. Conclusion 69
• Ⅱ-4. Experimental Section 69
• Ⅱ-5. References 73
• Chapter Ⅲ. Preparation of MgO nanoparticles for MgO interlayer to improve photovoltaic performance of dye sensitized solar cells 76
• Ⅲ-1. Introduction 77
• Ⅲ-2. Results and Discussion 80
• Ⅲ-3. Conclusion 96
• Ⅲ-4. Experimental Section 96
• Ⅲ-5. References 101
• Appendix 102
• Chapter I-A. Appendix 103
• Chapter I-B. Appendix 115
• Chapter I-C. Appendix 121
• Chapter Ⅱ. Appendix 135
• Chapter Ⅲ. Appendix 145