Tunable Memory Performances of Hyperbranched Polyimides Functionalized with Metal-Porphyrins

With the rapid advancement of information technology, the need to achieve ultra-high-density data storage has become a pressing necessity. This study synthesized three hyperbranched polyimides (HBPI-TAPP, HBPI-(Zn)TAPP, and HBPI-(Cu)TAPP) by polymerizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP), which features a cavity for metal ion coordination, with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), to systematically investigate the effect of metal ion species on storage performance. According to the results, memory devices based on HBPI-(Zn)TAPP exhibit volatile SRAM (static random-access memory) characteristics, whereas devices employing HBPI-TAPP and HBPI-(Cu)TAPP demonstrate non-volatile WORM (write-once, read-many) characteristics. Molecular simulations based on density functional theory (DFT) reveal that the storage behaviors of these polymers are governed by a charge-transfer mechanism, wherein electrons transfer from the porphyrin donor segment to the 6FDA acceptor segment, forming charge-transfer complexes that are not easily dissociated. The larger dipole moments of HBPI-TAPP and HBPI-(Cu)TAPP render the complexes difficult to dissociate, resulting in WORM-type memory behavior. In contrast, HBPI-(Zn)TAPP has the lowest threshold voltage, with a stronger electron binding that hinders the dissociation of the charge transfer complex, thereby enabling SRAM-type memory behavior.