Molecular conformation-dependent memory effects in non-conjugated polymers with pendant carbazole moieties

Abstract

Single-layer devices of the structure indium-tin-oxide/polymer/aluminum were fabricated from two non-conjugated polymers with pendant carbazole groups in different spacer units. The device based on poly(2-(N-carbazolyl)ethyl methacrylate) (PMCz) exhibited non-volatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 106, while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 103. In the absence of a spacer unit between the pendant carbazole group and the main chain, regioregular poly(N-vinylcarbazole) (PVK) exhibited only one conductivity state (ON state). The formation of carbazole excimers resulting from conformation-induced conductance switching under an electric field was revealed in situ by fluorescence spectroscopy. The electrical behavior of the polymer in a device was found to be dictated by the chemical structure and steric effect of the spacer unit between the pendant carbazole group and the main chain. © 2008 Materials Research Society.