Well-defined triphenylamine-containing polymers as hole-transporting layers in solution-processable organic light-emitting diodes via living anionic polymerization

In this study, we conducted anionic polymerization of N-[1,1 '-biphenyl]-4-yl- N-(4 '-ethenyl[1,1 '-biphenyl]-4-yl)- 9,9-dimethyl-9 H-fluoren-2-amine ( A ) incorporating a triphenylamine group as a hole-transporting unit using sec- butyllithium and potassium naphthalenide as initiators in tetrahydrofuran at-30 degrees C for 10 min. The resultant poly( A )s exhibited controlled molecular weights ( M n = 20.9-126.3 kg/mol) and narrow molecular weight distributions ( M w / M n <= 1.12). The living nature of the propagating chain end of poly( A ) was confirmed by postpolymerization. Additionally, block copolymerization of A with styrene (St) and 2-vinylpyridine (2VP) was performed to assess its relative reactivity. Copolymerization resulted in the precise synthesis of well-defined block copolymers with poly( A ) segments. Thermal properties of poly( A ) were investigated using thermogravimetric analysis and differential scanning calorimetry. Notably, the thermal annealing of poly( A ) film at 230 degrees C for 10 min made it insoluble in toluene, indicating its solvent resistance. Thus, poly( A ) was used as the holetransporting layer (HTL) in solution-processable organic light-emitting diodes (OLEDs). A comparative analysis against a reference device containing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) revealed an enhancement in the performance of the OLED comprising thermally annealed poly( A ) as the HTL. These results strongly suggest that poly( A ) is a promising HTL material for solution-processable OLEDs.