Synthesis and Characterization of Dithieno[3,2-b:2',3'-d]thiophene Derivatives for Organic Thin Film Transistors

Abstract

In chapter 1, In this study, we report a series of dithieno[3,2-b:2’,3’-d]thiophene (DTT)-based small molecules featuring five different end-capping substituents: 2-octyl-6-(5-(phenylethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene (compound 1), triisopropyl((5-(6-octyldithieno[3,2-b:2',3'-d]thiophen-2-yl)thiophen-2-yl)ethynyl)silane (compound 2), 2-octyl-6-(5-(thiophen-2-ylethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene (compound 3), 2-octyl-6-(5-((5-octylthiophen-2-yl)ethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene (compound 4), and 2-(5-((5-(2-ethylhexyl)thiophen-2-yl)ethynyl)thiophen-2-yl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (compound 5). To enhance solubility, a one-sided linear octyl chain was introduced on the DTT core, while extended π-conjugation was achieved through the incorporation of additional thiophene rings and acetylenic linkages to promote effective charge transport. The thermal, optical, and electrochemical properties of the synthesized compounds were characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV-visible absorption spectroscopy (UV-vis), and cyclic voltammetry (CV). Solution-sheared thin films were further analyzed via atomic force microscopy (AFM) and X-ray diffraction (XRD) to investigate surface morphology and molecular ordering. All compounds employed as organic semiconductors for organic field-effect transistors (OFETs) exhibited p-type semiconducting behavior. Notably, compound 3, which features a thienyl end group without additional alkyl substituents, demonstrated the best performance under ambient conditions, achieving a hole mobility of 0.034 cm2 V-1 s-1 and an current on/off ratio exceeding 106. These results highlight the critical role of side-chain engineering in enhancing molecular packing and thin-film crystallinity, thereby improving OFET performance.|In chapter 2, This research focuses on the design and synthesis of three new Dithieno[3,2-b:2',3'-d]thiophene derivatives were designed and synthesized: 2-([2,2'-bithiophen]-5-ylethynyl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (compound 6), 2-octyl-6-((5'-octyl-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (compound 7), and 2-((5'-(2-ethylhexyl)-[2,2'-bithiophen]-5-yl)ethynyl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (compound 8). These compounds were used as active layers in organic thin-film transistors (OTFTs). The electrical properties of the compounds were evaluated, showing mobility values of 0.031 cm2 V-1 s-1 for compound 6, 0.099 cm2 V-1 s-1 for compound 7, and 0.000045 cm2 V-1 s-1 for compound 8. Compound 7 exhibited the highest mobility 0.099 cm² V⁻¹ s⁻¹ and the best on/off current ratio of 2.97 × 107.|In chapter 3, In this study, innovative DTT derivatives were synthesized for potential application in organic thin-film transistors (OTFTs). The synthetic route involved Stille and Sonogashira coupling reactions, yielding target compounds modified with various alkyl side chains. The successful incorporation of these alkyl groups was confirmed by NMR spectroscopy, which aimed to improve solubility and optimize molecular packing. Among the synthesized compounds, 2,6-bis((5'-octyl-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (compound 9) exhibited the highest hole mobility (0.013 cm² V⁻¹ s⁻¹), attributed to its superior crystallinity and favorable molecular alignment. In contrast, 2,6-bis((5'-(2-ethylhexyl)-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (compound 10), bearing a bulkier side chain, showed reduced mobility (0.0028 cm² V⁻¹ s⁻¹) due to disrupted π–π stacking. These findings highlight the critical role of side-chain engineering in tuning charge transport properties and provide valuable insight for the future design of high-performance organic semiconducting materials.|Chapter 1, 본 연구에서는 dithieno[3,2-b:2’,3’-d]thiophene(DTT) 기반의 소분자 화합물 시리즈를 보고하며, 서로 다른 말단 치환기를 갖는 다섯 가지 유도체를 설계하였다. 이들은 각각 2-octyl-6-(5-(phenylethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene (화합물 1), triisopropyl((5-(6-octyldithieno[3,2-b:2',3'-d]thiophen-2-yl)thiophen-2-yl)ethynyl)silane (화합물 2), 2-octyl-6-(5-(thiophen-2-ylethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene(화합물 3), 2-octyl-6-(5-((5-octylthiophen-2-yl)ethynyl)thiophen-2-yl)dithieno[3,2-b:2',3'-d]thiophene (화합물 4), 그리고 2-(5-((5-(2-ethylhexyl)thiophen-2-yl)ethynyl)thiophen-2-yl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (화합물 5)으로 구성된다. 용해도 향상을 위해 DTT 코어의 한쪽에 선형 옥틸 사슬을 도입하였고, 전하 이동성을 높이기 위해 추가적인 티오펜 고리와 아세틸렌 결합을 통해 π-공액계를 확장하였다. 합성된 화합물들의 열적, 광학적, 전기화학적 특성은 열중량분석(TGA), 시차주사열량법(DSC), 자외선-가시광선 흡수 분광법(UV-vis), 순환 전압전류법(CV)을 통해 분석하였다. 또한 용액-전단(solution-shearing) 방식으로 제작된 박막에 대해 원자힘현미경(AFM)과 X선 회절분석(XRD)을 사용하여 표면 형태와 분자 배열 특성을 조사하였다. 모든 화합물은 유기 박막 트랜지스터(OFET)에 적용되었으며 p-형 반도체 특성을 나타냈다. 특히 말단에 추가적인 알킬 치환기가 없는 티오펜 유도체 구조를 갖는 화합물은 상온 대기 조건에서도 가장 우수한 성능을 보여주었으며, 홀 이동도는 0.034 cm² V⁻¹ s⁻¹, 온/오프 전류비는 10⁶ 이상을 기록하였다. 이러한 결과는 측쇄 설계를 통해 분자 간 조밀한 배열과 박막 내 결정성을 향상시킴으로써 OFET 성능을 효과적으로 향상시킬 수 있음을 보여준다.|Chapter 2, 이 연구는 세 가지 새로운 Dithieno[3,2-b:2',3'-d]thiophene 유도체의 설계 및 합성에 중점을 두고 있다: 2-([2,2'-bithiophen]-5-ylethynyl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (화합물 6), 2-octyl-6-((5'-octyl-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (화합물 7), 2-((5'-(2-ethylhexyl)-[2,2'-bithiophen]-5-yl)ethynyl)-6-octyldithieno[3,2-b:2',3'-d]thiophene (화합물 8). 이 화합물들은 유기 박막 트랜지스터(OTFT)의 활성층으로 사용되었다. 화합물들의 전기적 특성은 평가되었으며, 화합물 6은 0.031 cm² V⁻¹ s⁻¹, 화합물 7은 0.099 cm² V⁻¹ s⁻¹, 화합물 8은 0.000045 cm² V⁻¹ s⁻¹의 이동도를 나타내었다. 화합물 7은 가장 높은 이동도 0.099 cm² V⁻¹ s⁻¹ 와 최고의 온/오프 전류 비율 2.97 × 107을 보였다.|Chapter 3, 본 연구에서는 유기 박막 트랜지스터(OTFT)에서 사용될 수 있는 혁신적인 DTT 유도체들이 합성되었다. 합성 과정은 Stille 결합과 Sonogashira 결합을 포함하며, 다양한 알킬 그룹 수정이 이루어진 목표 화합물들을 생성했다. NMR 분광법을 통해 이러한 알킬 그룹의 성공적인 도입이 확인되었으며, 이는 용해도와 분자 배열 최적화를 목표로 했다. 이 중 2,6-bis((5'-octyl-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (화합물 9)는 결정성이 우수하고 분자 정렬이 양호하여 가장 높은 이동도(0.013 cm² V⁻¹ s⁻¹)를 나타냈다. 반면, 부피가 큰 측쇄를 가진 2,6-bis((5'-(2-ethylhexyl)-[2,2'-bithiophen]-5-yl)ethynyl)dithieno[3,2-b:2',3'-d]thiophene (화합물 10)은 π–π 적층이 저해되어 이동도(0.0028 cm² V⁻¹ s⁻¹)가 감소하였다. 이러한 결과는 유기 반도체에서 측쇄 구조 제어가 전하 수송 특성에 중요한 영향을 미친다는 점을 보여주며, 향후 유기 반도체 소재 설계에 유용한 통찰을 제공한다.