Biomass-Derived Degradable Poly(azomethine)s for Flexible Bistable Photonic Transistor Memories

We report on the synthesis and photonic memory applications of poly(azomethine)s (PAMs) synthesized from the condensation reaction of biomass-derived diamine, (3R,6S)-hexahydrofuro[3,2-b]furan-3,6-diyl bis(4-aminobenzoate) (ISBA) with photoactive 9,9-di-n-octylfluorene-2,7-dicarboxaldehyde (FLDA) and biomass-based 2,5-furandicarboxaldehyde (FCA). All the prepared PAMs exhibited a higher thermal stability (Tg: 118–123 °C) and lower band gaps (Eg: 2.83–2.86 eV) compared with polymer P4 (Tg: 102 °C, Eg: 3.11 eV) without the imine linkage due to chain rigidity and structural coplanarity. The organic field effect transistor (OFET) memories using P1–P4 as the electrets showed a memory window of 17–25 V and a memory ratio of up to 2.1 × 104 with photowriting-electrical-erasing characteristics. The discrepancy in the energy level between the transporting layer and chargeable electret enabled the negative photoinduced excitons stored in the electret. On the other hand, the increased ratio of the furan in the prepared PAM resulted in a higher highest occupied molecular orbital level, resulting in a larger memory window of 25 V. The imine linkages along the polymer backbone endowed a higher lowest unoccupied molecular orbital level and provided a charge stabilizer to consolidate the trapped charges, which was superior to the polymer without the imine linkage. We further demonstrated flexible memory using biomass-based polymers as the substrate and the electret, and the memory characteristics were retained even after 1000 cycles of bending under a 5 mm bending radius. By virtue of the degradable imine and ester linkages in the polymer chain, the PAM degraded into ISB biosegments under acidic conditions after 1 week. This result suggested that the prepared photoresponsive polyazomentines have the potential to be used for green electronics.