Streamlined synthesis, optoelectronic and photovoltaic characterization of large, monodisperse n-type oligomers via highly efficient direct arylation

术语非富勒烯受体（nfa）用于n型有机材料，这些材料越来越多地用于有机光伏（opv）。nfa包括单分散、小分子和分散共轭聚合物。nfa使高效光伏设备的功率转换效率大大提高了10- 15%。然而，目前尚不清楚这两种材料类别之间的主要结构差异（分散性和链长度）如何促成这一重大改进。单分散的n型低聚物弥补了这两种电子受体材料之间的差距。由于对不同长度的离散n型低聚物的探索迄今为止受到合成途径和繁琐的合成途径的限制，它们在OPV器件中的应用仍未得到探索。在这个提议中，我们将合成和表征离散的，单分散的不同链长的n型低聚物。利用对2,6-二溴二亚胺（NDI）和2,2´-双噻吩（T2）直接芳基化缩聚的机理的深入了解，我们将以最少的合成步骤制备几种低聚物（NDIT2），直到三腈（n= 33）。为了制备克级低聚物，我们的目标是无色谱纯化方案。这些低聚物是基础光学、热学和结构研究的独特材料。最后，将它们与分散的聚合物类似物PNDIT2进行比较，以揭示分散性和链长对原始材料和二元全聚合物共混物性能的影响。

The term non-fullerene acceptors (NFAs) is used for n-type organic materials that find increasing use for organic photovoltaics (OPVs). NFAs include both monodisperse, small molecules and disperse conjugated polymers. NFAs have enabled highly efficient photovoltaic devices with strongly improved power conversion efficiencies of 10-15 %. Yet, it is unclear how the major structural differences between these two material classes, dispersity and chain length, contribute to this major improvement. Monodisperse n-type oligomers bridge the gap between these two types of electron acceptor materials. As the exploration of discrete n-type oligomers of varying length has thus far been limited by synthetic access and tedious synthesis pathways, their utility for OPV devices remains unexplored as well. In this proposal, we will synthesize and characterize discrete, monodisperse n-type oligomers of varying chain length. Using mechanistic insight into the direct arylation polycondensation of 2,6-dibromonaphthalene diimide (NDI) and 2,2´-bithiophene (T2) obtained within the last funding period, we will prepare several oligomers (NDIT2)n up to the tritriacontamer (n= 33) with a minimal number of synthetic steps. To make oligomers on gram scale, we aim at chromatography-free purification protocols. These oligomers are unique materials for fundamental optical, thermal and structural investigations. Finally, they will be compared against their disperse, polymeric analog PNDIT2 in order to reveal the effect of dispersity and chain length on properties of both pristine materials as well as of binary all-polymer blends.