The Design Of Photo-/electric- Modulated Smart Organic Memory Materials And Photo-electronic Properties

Diarylethenes photochromic materials exhibit molecular structural changes at specific-wavelength lights. In this paper, seven photochromic molecules, BCMThCE₁- 7, have been designed and synthesized, and they are characterized by NMR, MS, UV-visible absorption spectroscopy and Cyclic Voltammetry. These compounds show different colors under the irradiation of UV light（λ = 200-400 nm）, with a new absorption peak emerged at the longer-wavelength region. Accordingly, their frontier orbital energy levels also change in various degrees. Further upon the irradiation of visible light（λ > 400 nm）, the color, absorption spectra, and the frontier molecular orbital（FMO） levels of these compounds can be restored near to its original state.To better integrate the characteristics of photochromophores into organic field-effect transistors（OFETs）, the FMO levels were carefully compared with those of the commonly used OFET semiconductors. Thus, and finally choose copper phthalocyanine was chozed as the active semidonctor material and the photochromophore BCMThCE₅ as the doping materials to fabricate OFETs. Optical modulation of the devices were firstly investigated. Under UV irradiation, the device performance parameters decay slowly; the maximum current（|IDS|max）, the current on-off ratio（|IDS|on/off） and mobility（μ） decreases and the threshold voltage（Vth） shift in negative direction. Further irradiated with visible light, the OFET performance parameters gradually restored near to the initial state. Meanwhile, we found that the degree of deivce performance changes depends on the exposure time, which is possibly attributed to the relative concentrations of the open-ring isomer o-BCMThCE₅ and the closed-ring isomer c-BCMThCE₅ in the hybrid film. Secondly, the electrical modulation of the device was further explored. When with the same operation time, he change degrees of the device performance depend on the operating voltage. Therefore, multiple stable current levels can be achived by either electrical or light modulation, which indicates great potentials in organic multi-level storage. Finally, two simple logic gates（NOR and OR） were designed, with combination of the two modulation methods,to switch between a high-impedance state（HRS） and a low resistance state（LRS）.To further expand applications of these photochromophores, we also fabricate a crossbar organic diode memory device（ITO/BCMThCE₅/Al） by utilizing BCMThCE₅ molecules as the active layer. It was found that the memory behaviors of these devices, switching between Flash and the WORM-type memory, depend not only on the molecular isomerization, but also on the width of the electrodes.