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

Abstract

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 (Φ_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_// = 1.9726 and g_⊥ = 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.