Sosorev Andrey Yu, Trukhanov Vasiliy A, Maslennikov Dmitry R, Borshchev Oleg V, Polyakov Roman A, Skorotetcky Maxim S, Surin Nikolay M, Kazantsev Maxim S, Dominskiy Dmitry I, Tafeenko Viktor A, Ponomarenko Sergey A, Paraschuk Dmitry Yu
Faculty of Physics and International Laser Center , Lomonosov Moscow State University , Leninskie Gory 1/62 , Moscow 119991 , Russia.
Institute of Spectroscopy , Russian Academy of Sciences , Fizicheskaya 5, Troitsk , Moscow 108840 , Russia.
ACS Appl Mater Interfaces. 2020 Feb 26;12(8):9507-9519. doi: 10.1021/acsami.9b20295. Epub 2020 Feb 14.
Organic optoelectronics requires materials combining bright luminescence and efficient ambipolar charge transport. Thiophene-phenylene co-oligomers (TPCOs) are promising highly emissive materials with decent charge-carrier mobility; however, they typically show poor electron injection in devices, which is usually assigned to high energies of their lowest unoccupied molecular orbitals (LUMOs). A widely used approach to lower the frontier orbitals energy levels of a conjugated molecule is its fluorination. In this study, we synthesized three new fluorinated derivatives of one of the most popular TPCOs, 2,2'-(1,4-phenylene)bis[5-phenylthiophene] (PTPTP) and studied them by cyclic voltammetry, absorption, photoluminescence, and Raman spectroscopies. The obtained data reveal a positive effect of fluorination on the optoelectronic properties of PTPTP: LUMO levels are finely tuned, and photoluminescence quantum yield and absorbance are increased. We then grew crystals from fluorinated PTPTPs, resolved their structures, and showed that fluorination dramatically affects the packing motif and facilitates π-stacking. Finally, we fabricated thin-film organic field-effect transistors (OFETs) and demonstrated a strong impact of fluorination on charge injection/transport for both types of charge carriers, namely, electrons and holes. Specifically, balanced ambipolar charge transport and electroluminescence were observed only in the OFET active channel based on the partially fluorinated PTPTP. The obtained results can be extended to other families of conjugated oligomers and highlight the efficiency of fluorination for rational design of organic semiconductors for optoelectronic devices.
有机光电子学需要兼具明亮发光和高效双极性电荷传输的材料。噻吩 - 亚苯基共聚物（TPCOs）是一类很有前景的高发射材料，具有不错的电荷载流子迁移率；然而，它们在器件中通常表现出较差的电子注入能力，这通常归因于其最低未占据分子轨道（LUMO）的高能级。一种广泛用于降低共轭分子前沿轨道能级的方法是对其进行氟化。在本研究中，我们合成了最常用的TPCO之一2,2'-（1,4 - 亚苯基）双[5 - 苯基噻吩]（PTPTP）的三种新型氟化衍生物，并通过循环伏安法、吸收光谱、光致发光光谱和拉曼光谱对它们进行了研究。所获得的数据揭示了氟化对PTPTP光电性能的积极影响：LUMO能级得到精细调节，光致发光量子产率和吸光度均有所提高。然后我们从氟化的PTPTP中生长出晶体，解析了它们的结构，并表明氟化显著影响堆积模式并促进π堆积。最后，我们制备了薄膜有机场效应晶体管（OFET），并证明了氟化对两种电荷载流子（即电子和空穴）的电荷注入/传输都有强烈影响。具体而言，仅在基于部分氟化PTPTP的OFET有源沟道中观察到了平衡的双极性电荷传输和电致发光。所获得的结果可以推广到其他共轭低聚物家族，并突出了氟化在合理设计用于光电器件的有机半导体方面的有效性。
