Matsidik Rukiya, Komber Hartmut, Brinkmann Martin, Schellhammer Karl Sebastian, Ortmann Frank, Sommer Michael
Institut für Chemie, TU Chemnitz, Professur Polymerchemie, Straße der Nationen 62, 09111 Chemnitz, Germany.
Forschungszentrum MAIN, TU Chemnitz, Rosenbergstraße 6, 09126 Chemnitz, Germany.
J Am Chem Soc. 2023 Apr 6. doi: 10.1021/jacs.3c00058.
Efficient organic electronic devices are fabricated from both small molecules and disperse polymers, but materials with characteristics in between remain largely unexplored. Here, we present a gram-scale synthesis for a series of discrete n-type oligomers comprising alternating naphthalene diimide (NDI) and bithiophene (T2). Using C-H activation, discrete oligomers of type T2-(NDI-T2) ( ≤ 7) and persistence lengths up to ∼10 nm are made. The absence of protection/deprotection reactions and the mechanistic nature of Pd-catalyzed C-H activation allow one to produce symmetrically terminated species almost exclusively, which is key to the fast preparation, high yields, and the general success of the reaction pathway. The reaction scope includes different thiophene-based monomers, end-capping to yield NDI-(T2-NDI) ( ≤ 8), and branching at T2 units by nonselective C-H activation under certain conditions. We show how the optical, electronic, thermal, and structural properties depend on oligomer length along with a comparison to the disperse, polymeric analogue PNDIT2. From theory and experiments, we find that the molecular energy levels are not affected by chain length resulting from the strong donor-acceptor system. Absorption maxima saturate for = 4 in vacuum and for = 8 in solution. Linear oligomers T2-(NDI-T2) are highly crystalline with large melting enthalpies up to 33 J/g; NDI-terminated oligomers show reduced crystallinity, stronger supercooling, and more phase transitions. Branched oligomers and those with bulky thiophene comonomers are amorphous. Large oligomers exhibit similar packing characteristics compared to PNDIT2, making these oligomers ideal models to study length-structure-function relationships at constant energy levels.
高效的有机电子器件由小分子和分散聚合物制成，但兼具两者特性的材料在很大程度上仍未得到探索。在此，我们展示了一种克级规模的合成方法，用于制备一系列由交替的萘二亚胺（NDI）和联噻吩（T2）组成的离散n型低聚物。利用C-H活化，制备出了T2-(NDI-T2)（≤7）型的离散低聚物，其持久长度可达约10 nm。无需保护/脱保护反应以及Pd催化C-H活化的机理特性使得几乎只能生成对称端基的物种，这对于反应途径的快速制备、高收率以及总体成功至关重要。反应范围包括不同的基于噻吩的单体，封端可得到NDI-(T2-NDI)（≤8），并且在某些条件下通过非选择性C-H活化在T2单元处实现支化。我们展示了光学、电子、热学和结构性质如何取决于低聚物长度，并与分散的聚合物类似物PNDIT2进行了比较。从理论和实验中，我们发现由于强供体-受体体系，分子能级不受链长影响。在真空中，n = 4时吸收最大值达到饱和；在溶液中，n = 8时吸收最大值达到饱和。线性低聚物T2-(NDI-T2)具有高度结晶性，熔化焓高达33 J/g；以NDI为端基的低聚物结晶度降低，过冷度更强，且有更多相变。支化低聚物以及带有庞大噻吩共聚单体的低聚物是非晶态的。与PNDIT2相比，大型低聚物表现出相似的堆积特征，这使得这些低聚物成为在恒定能级下研究长度-结构-功能关系的理想模型。
