Direct C–H arylation for various Ar-cored diketopyrrolopyrrole containing small molecules in solution-processed field-effect transistors

Abstract

Direct (hetero) C–H arylation is an advantageous tool for the synthesis of diketopyrrolopyrrole (DPP) derivatives, because of fewer synthetic steps, better atom economy and being environmentally friendly. Herein, four diketopyrrolopyrrole containing linear structured D–A–π–A–D small molecules Ar(DPPT₂)₂ are facilely synthesized in high yields of 73–82% through C–H direct arylation, where Ar (from electron-donating 1,4-phenyl, 1,4-naphthyl or 9,10-anthryl to electron-accepting 2,5-pyridyl) is functionalized as the core π-bridge structure, DPP as the arm and bithiophene as end-groups. The dihedral angles between the central aryl rings and DPPT₂ arms for the optimized geometries of Ph(DPPT₂)₂, NA(DPPT₂)₂ and AN(DPPT₂)₂ gradually increases from 20.3, 44.7 to 93.1°, respectively, which is 18.7° for the pyridyl cored Py(DPPT₂)₂. It is found that the optoelectronic properties can be elaborately tuned by variation of the central aryl bridge. Moreover, the coplanarity of the molecules as well as the electronic properties of central Ar units significantly affect the charge transport properties. Ph(DPPT₂)₂ possessing the best conjugated backbone planarity exhibits the highest hole mobility of 0.12 cm² V⁻¹ s⁻¹ among the three Ar(DPPT₂)₂ compounds based on the electron-donating phenyl, naphthyl and anthryl cores, while the electron-withdrawing pyridyl core Py(DPPT₂)₂ shows a poor hole mobility of 6.47 × 10⁻⁴ cm² V⁻¹ s⁻¹ despite of it having the most planar structure.