Optical switching of carrier transport in polymeric transistors with photochromic spiropyran molecules

We demonstrate the optical switching of transistor properties by adopting the photoisomerization of spiropyran (SP) molecules dispersed in a poly(triarylamine) (PTAA) channel layer. The drain current (I_DS) was reduced by ultra-violet (UV) light irradiation, while visible (VIS) light irradiation restored the I_DS to its original value. The UV and VIS light irradiation brought about the photoisomerization reactions of SP, i.e., an ionic polarized open-ring isomer was induced by UV and a less polarized closed-ring isomer was induced by VIS. To clarify the mechanism of the photoisomerization-induced optical switching, we evaluated the variations in transistor properties, namely I_DS, carrier mobility and threshold voltage, when subjected to UV and VIS light irradiation. We found that the ionic polarized open-ring SP isomer worked as a carrier scattering site that effectively suppressed carrier transport in the polymer channel.