The effect of different binding sites on the optical and electronic properties of tetraphenylethylene-substituted thiophene isomers

Abstract

Thiophene has attracted tremendous attention in the field of optoelectronics. Here, a series of isomers containing TPE and thiophene are designed and synthesized by Suzuki coupling reactions. TPE groups were attached to the thiophene core at the 2,5-positions (M1), 3,4-positions (M2), 2,3-positions (M3) and 2,4-positions (M4), to endow the resultant molecules with not only various geometries but also high solid-state efficiencies. All the isomers are thermally stable and show good solubility in common organic solvents. They all emit weakly in solution but become strong emitters when fabricated into solid films. Isomer M1 has a more planar space arrangement and exhibits a relatively narrower optical bandgap with respect to the other three isomers. Non-doped OLEDs using the four isomers as light-emitting layers are constructed. M1 gives excellent device performance with a maximum luminance of 65 210 cd m⁻², a maximum current efficiency of 11.21 cd A⁻¹ and a maximum EQE of 4.49%.