Synthetic explorations toward the preparation of fluoroalkylated π-conjugated electron-deficient heterocyclic monomers for OSC polymer materia ;Synthesis and study of the reversible formation of carbene–fullerene adducts with remarkable solubility

Abstract

In chapter I are described our design and synthetic efforts towards the preparation of highly electron-deficient perfluoroalkylated heterocyclic monomers for potential applications as p-type polymer materials in organic solar cells (OSC). Our approach relied on a copper-catalyzed coupling reaction between perfluoroalkyl iodides, such as C6F13I and halogenated 2,1,3-benzothiadiazoles. The introduction of highly electron-withdrawing perfluoroalkyl groups serves to affect the electron density in the 2,1,3,-benzothiadiazole ring to afford a more e-poor unit. The combination of 5,6-bis/5-bis(perfluoroalkyl)-2,1,3-benzothiadia- zole units as the e-acceptors and thiophenes as e-donors would result, according to the donor-acceptor approach, in target monomers with attractive characteristics for low band gap conjugated polymer. These polymer could confer a broader solar spectrum coverage in OSC applications, increased stability, elevated resistance to degradation and enhanced hydrophobicity. Three different synthetic routes toward the target doubly perfluoroalkylated monomers featuring the Cu-catalyzed perfluoroalkyl coupling were explored. While these couplings could be perfected to reach acceptable yields, methods for the introduction of the flanking thiophene rings could not be identified. In chapter II, we present the preparation of differently 1,3-diaryl and 4,5-dialkyl substituted imidazolium salts by the coupling of formamidines with bromoketones, the latter themselves obtained by a thiazolium-catalyzed dimerization of aldehydes (benzoin condensation) followed by an Appel bromination. The resulting imidazolium salts serve as precursors (protonated salts) of N-heterocyclic carbenes (NHC) that, by virtue of their long flexible alkyl chain substituents, are extremely soluble in ordinary non-polar solvents. These solubilizing NHCs were then reacted with buckminster fullerene (C60) to form adducts that, unlike the vast majority of fullerene derivatives and the small number of known NHC-C60 adducts, show high solubility in ordinary organic solvents such as THF, CDCl3, 1,2-C6H4Cl2. With these soluble derivatives on hand, we were for the first time able to carry out solution-phase studies of the propertiesof this family of NHC-fullerene adducts. In particular, we have been able to establish that the formation of adducts must be reversible since their thermolysis in toluene solution liberates pristine C60. These studies constitute the foundation for the development of methods for the solution-phase processing of single-walled carbon nanotubes (SWCNTs) on the basis of the reversible formation of soluble covalent adducts.;본 연구의 제1장은 유지 태양전지 재료 중 하나인 전자가 결핍하고 퍼플 루오르 알킬화한 헤테로 사이클릭 단량체에 대한 설계와 합성에 관한 것이다. 전자 결핍 기능 그룹인 퍼플 루오로 알킬 그룹을(perfluoroalkyl groups) 도입한 2,1,3-benzothiadiazoles를 전자수용체로 한 것에 전자공여체인 thiophenes도 도입하여 이론적으로 낮은 밴드 갭을 가진 공액 고분자 단체를 합성하려 하였다. 응용의 안정성을 위하여 광기전력 효율이 더 좋은 태양전지 재료를 잠재력이 좋은 p형 재료로 하였다. 하지만 지금도 thiophenes의 도입은 진해중에 있다. 그러나 본 연구에서는 이미 2,1,3-benzothiadiazoles에 퍼플 루오로 알킬그룹의 도입을 성공적으로 합성하게 되였다. 제2장은 포름아미딘과 (formamidine) 브로 모 케톤 (bromoketone)의 공액반응을 통하여 여러가지 치환기를(substituent) 가진 imidazolium salts 합성에 관한 것이다. N-heterocyclic carbenes을 전구체로 한 imidazolium salts에 긴 알킬링을 도입하여 카르벤의 용해성을 증가할 수 있었다. 용해성이 좋은 N-heterocyclic carbenes과 풀러렌의 부가물은 풀러렌이 THF, CDCl3,1,2-C6H4Cl에서의 용해성 증가에 작용을 하였다. 계속하여 온도를 가했을 때 이 부가물은 원래의 C60으로 환원되는 것을 확인하였다. NHC-C60 특성에 관한 연구는 앞으로 single-walled 나노튜브의 정제에도 응용될 것이다.