Synthesis and properties of oligofluorene-thiophenes as emissive materials for organic electroluminescent devices: color-tuning from deep blue to orange

A series of oligofluorene-thiophenes end-capped with 3,6-di-tert-butylcarbazole and pyrene were designed and synthesized for application as color tunable emissive materials for organic electroluminescent devices. They were characterized by ¹H NMR, ¹³C NMR, FT-IR, UV–vis, PL spectroscopy, and mass spectrometry. Theoretical calculations revealed that the carbazole moiety attached to the end of the molecule is nearly perpendicular to oligofluorene-thiophene-pyrene plane and π-electrons in the ground state delocalize over the entire molecule. Their optical, thermal, and electrochemical properties could be tuned by varying the number of thiophene units in the molecule. All were electrochemically and thermally stable molecules. OLED devices of these materials emitted brightly in various colors from deep blue to orange. Particularly, deep blue (CIE coordinates of 0.16, 0.14) and green (CIE coordinates of 0.27, 0.61) devices showed high color quality close to the NTSC standards with high luminance efficiencies of 1.14 and 11.15 cd/A, respectively.