Selectively Fluorinated BTBT Derivatives Combining Pronounced Luminescence with Bipolar or Electron Transport

Abstract

Thiophene–phenylene co-oligomers are promising for organic optoelectronic applications owing to the combination of bright luminescence with efficient charge transport. Among them, various derivatives of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) show particularly high hole mobilities in their single crystals and thin films. However, the BTBT derivatives rarely show electron transport. Moreover, bipolar transport in them, which is favorable for optoelectronic applications, has not been reported to date. In this study, we present two novel derivatives of diphenyl-substituted BTBT: with fully and selectively fluorinated phenyls. The former shows electron transport, whereas the latter supports bipolar transport. Optoelectronic devices based on these BTBT derivatives, in particular on the one with selectively fluorinated phenyls, show an electroluminescence and photoelectric effect. A combined experimental and theoretical approach is applied to reveal and explain the changes in optical properties, molecular packing, and charge-carrier mobility induced by selective or full fluorination of phenyls. We anticipate that the suggested materials and the established relationships between the molecular structure and properties of the BTBT derivatives will facilitate the development of organic optoelectronics.