Synthesis and optical and electrochemical memory properties of fluorene–triphenylamine alternating copolymer†
A highly soluble fluorene–triphenylamine conjugated alternating copolymer (PF–TPA) was designed and synthesized under Suzuki coupling reaction conditions in this work. The structure of the copolymer was characterized by Fourier transform infrared (FT-IR) spectroscopy, and hydrogen and carbon nuclear magnetic resonance (1H-NMR, 13C-NMR). The copolymer showed excellent thermal stability, and an onset decomposition temperature up to 443 °C. The optical and electrochemical properties of PF–TPA were investigated by using ultraviolet visible (UV-vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, transient photocurrent responses and cyclic voltammetry (CV). The main absorption peak of PF–TPA appeared at λmax = 382 nm in the thin film and exhibits strong photoluminescence with maximum emission peaks centered at 464 nm in chloroform. The simulation results of the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and energy band gap are −5.04, −2.22 and 2.82 eV, respectively. A non-volatile rewritable flash memory device based on the active layer of PF–TPA was fabricated with the sandwich structure ITO/PF–TPA (102 nm)/Al. The memory device exhibits good electrical bistable resistive switching behavior, with low threshold voltage (VSET ∼ −1.2 V and VRESET ∼ 3.2 V), high ON/OFF current ratio in excess of 103, high stability in retention time up to 104 s and a number of read cycles up to 300 under a read voltage of 2 V in both ON and OFF states. The conductivity mechanism of the ITO/PF–TPA/Al device is discussed. The as-fabricated device exhibited good data retention characteristics, stability and reliability.