Polyfluorene-Based Push-Pull Type Functional Materials for Write-Once-Read-Many-Times Memory Devices

A highly soluble polyfluorene-based copolymer containing electron-rich triphenylamine (TPA) and electron-poor 9,9-bis(3,4-bis(3,4-dicyanophenoxy)phenyl side chains in the C-9 position of the fluorene unit was synthesized under Yamamoto conditions. By applying 306 nm as excitation wavelength, the resultant polymer exhibits strong photoluminescence with maximum emission peaks centered at 413 and 433(sh) nm in chloroform. The calculated highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy bandgap, ionization potential, and electron affinity are -5.66, -3.44, 2.22, 5.92, and 3.70 eV, respectively. The as-fabricated polymer film exhibited typical stable write-once-read-many-times (WORM) memory characteristics, which are desirable for ultralow-cost permanent storage of digital images. The currents in both ON and OFF states did not show any degradation, suggesting good device stability. The ON/OFF current ratio observed in the sweep I-Vcharacteristics at +1.0 V is 6.1 x 10(3). The conduction mechanism through ITO/polymer/Al device is discussed.