Block Co-oligomers for Organic Electronics and Optoelectronics: Synthesis, Photophysics, Electroluminescence, and Field-Effect Charge Transport of Oligothiophene-b-oligoquinoline-b-oligothiophene Triblock Co-oligomers

New oligothiophene-b-oligoquinoline-b-oligothiophene triblock co-oligomers, 6,6′-bis(5-methylthiophenyl-2-yl)-4-phenylquinoline (B1TPQ), 6,6′-bis(2,2′-bithiophenyl-5-yl)-4-phenylquinoline (B2TPQ), and 6,6′-bis(2,2′,5′,2′′-terthiophenyl-5-yl)-4-phenylquinoline (B3TPQ), were synthesized, characterized, and found to be efficient blue, green, and yellow emitters in organic light-emitting diodes (OLEDs). The triblock co-oligomers have high fluorescence quantum yields in solution (61−91%), and positive solvatochromism was observed in B2TPQ and B3TPQ. Optical band gaps of evaporated thin films were 2.72 eV (B1TPQ), 2.53 eV (B2TPQ), and 2.27 eV (B3TPQ), indicating strong electronic delocalization over the three blocks of the co-oligomers. Cyclic voltammetry showed reversible reduction in the three triblock co-oligomers from which nearly identical LUMO energies (2.71−2.76 eV) were obtained, implying strong localization of the LUMO on the oligoquinoline middle block. Similarly estimated, the HOMO energy varied from 5.57 eV in B1TPQ to 5.12 eV in B3TPQ and showed strong delocalization of the HOMO across the three blocks of the co-oligomers. Thin films of the co-oligomers showed field-effect charge transport with a hole mobility that varied from 0.7 × 10−5 cm2/(V s) in B2TPQ to 4.3 × 10−5 cm2/(V s) in B3TPQ. Bright blue OLEDs based on B1TPQ gave a high luminance (4620 cd/m2) with a high efficiency (5.6 cd/A, 4.3% EQE). Green OLEDs based on B2TPQ combined high brightness (6535 cd/m2) with high luminous efficiency (6.5 cd/A). These results provide useful insights for the design and optimization of multicomponent organic/polymer semiconductors for high-performance electronics and optoelectronics.