Fluorene, pyrene, and thiophene-based donor-acceptor asymmetric small molecules for solution-processable memory performance

摘要

In this paper, two new asymmetric donor-bridge-acceptor molecules (PFTCH and PFTCE) containing the same electron donor (pyrene group) and bridge (fluorene group) but different terminal electron acceptors (cyanoacetic acid for PFTCH and ethyl cyanoacetate for PFTCE) have been synthesized and characterized by NMR, HR-MS etc. Their photophysical properties including Uv-vis absorption and emission spectra were studied. They were further used as the memory active materials and the ITO/PFTCH or PFTCE/Al sandwich memory devices were prepared, in which the organic films were obtained by solution process. The I-V measurements display satisfactory memory performance; they have a low threshold voltage, high ON/OFF ratio (10(6)) and a low current value (10(-4) A) at the ON state. Although the electron-withdrawing ability of the cyanoacetic acid group is stronger than that of the ethyl cyanoacetate group, the two memory devices (ITO/PFTCH/Al or Au and ITO/PFTCE/Al or Au) display different memory behaviors (volatile DRAM for ITO/PFTCH/Al or Au devices and nonvolatile WORM for ITO/PFTCE/Al or Au devices). The mechanism is speculated and the different memory behaviors can be tentatively attributed to the different migration processes of the charge carriers under the influence of an electric field. This can offer a new idea for the molecular design of materials with volatile memory.