Rational design of quinoline-based D-A system to accomplish a switching from binary to ternary memory devices

Abstract

Quinoline-based small organic molecules containing anthracene and phenanthrene in a donor-acceptor (D-A) system have been designed and synthesized. The photophysical and electrochemical properties convey a better charge transfer possibility for the compounds with an ethylene bond between the D-A system than those without the ethylene bond. Through a red shift in the absorption spectra, the smaller band gap of the compounds (2.69–2.73 eV). Therefore, the memory behavior of the compounds also changed from binary to ternary, availing a better charge storage density in the systems. Even though all the compounds exhibited a non-volatile WORM memory performance with charge transfer and trapping as the major phenomenon behind the charge transport in the systems, the mechanism of compounds with the ethylene bridge between the D-A system differs due to the molecular orientation of the compounds. These compounds initially undergo a molecular ordering leading to a better channel for the charge transfer in the film, which takes the devices from OFF to ON1 state, followed by the charge transfer and trapping leading to an ON2 state. This guided the ternary WORM memory behavior of the compounds with a threshold voltage as low as - 0.8 V and an on/off current ratio of 104. The devices tend to show significant stability over 100 reading cycles and 4000 s under the constant stress of 0.5 V, making these devices perfect candidates for multilevel storage memory.