Triphenylamine/Tetraphenylethylene Substituted 4-Thieno[3,2-b]thiophen-3-ylbenzonitriles: Synthesis, Photophysical-Electronic Properties, and Applications

Five novel fluorescent materials, TT-TPA, TT-TPE, TPA-TT-TPA, TPE-TT-TPE, and TPA-TT-TPE, containing a strongly electron-donating triphenylamine (TPA) and a bulky tetraphenylethylene (TPE), linked through a thienothiophene, 4-thieno[3,2-b]thiophen-3-ylbenzonitrile, and possessing a strongly electron-withdrawing nitrile moiety, were systematically designed, synthesized, and their optical and electrochemical properties were compared. The structure of the main skeleton, 4-thieno[3,2-b]thiophen-3-ylbenzonitrile (TT-CN), along with the structure of its precursor, the monoketone 4-(2-bromoacetyl)benzonitrile, were clarified by single-crystal X-ray diffraction. Information on their conformation and optical and electronic properties was obtained by density functional theory (DFT), which revealed that they are suitable compounds for OLED applications. They exhibited mega Stokes shifts between 113 and 177 nm, except for TT-TPE and TT-CN, and showed positive solvatochromic behavior from blue to orange with increasing solvent polarity and dual emission both at solid-state and in solution. Their solid-state quantum yields were recorded to be between 9 and 58%, and their solution quantum yields were determined to be close to 100%. As the compounds had suitable solid-state quantum yields, their OLEDs were fabricated, which had performances with a maximum luminance of around 2800 cd m^–2, a maximum current efficiency of 4.70 cd A^–1 and displayed emission colors from blue to green and yellowish green.