A solution-processable polymer-grafted graphene oxide derivative for nonvolatile rewritable memory

A new conjugated polymer, poly{[9,9-di(triphenylamine) fluorene]-[9,9-dihexylfluorene]-[4,4'-(9H-fluorene-9,9-diyl) dibenzenamine]}(PTHF), was synthesized by the Suzuki coupling reaction and used to react with the graphene oxide (GO) containing surface-bonded acyl chloride moieties to give a solution-processable GO-PTHF. Covalent attachment of PTHF onto GO resulted in the partial fluorescence quenching of the parent polymer, suggesting energy and/or electron transfer between the excited singlet states of the PTHF moiety and the GO moiety. The absolute photoluminescence (PL) quantum yields (Phi(PL)) of the samples were changed from 0.59 for PTHF to 0.31 for GO-PTHF. A light-induced electron paramagnetic resonance (LEPR) technique was employed to study the photoinduced spins in the conjugated GO-PTHF. Upon irradiation with a 432 nm laser, both the polaron signals of the polymer chain at g = 2.1132, 2.0665 and 2.0197, and the signals of radical anions on GO at g(parallel to) = 1.9726 and g(perpendicular to) = 1.9747 were kept unchanged, while the signal at g = 2.0002 almost completely disappeared due to a typical photoinduced selective quenching of the triplet state or a photoinduced spin polarization transfer process acting with a radical-triplet pair mechanism. A memory device based on GO-PTHF, in which the GO-PTHF film was sandwiched between the indium-tin oxide and Al electrodes, can be switched to the ON state under a negative electrical sweep, and can also be reset to the initial OFF state by a reverse (positive) electrical sweep.