Abstract
Three diazafluorene derivatives triphenylamine (TPA)(PDAF)n (n = 1, 2, 3) serving as small molecular elements are designed and synthesized via concentrated sulfuric acid mediated Friedel–Crafts reaction. With highly nonplanar topological configuration, TPA(PDAF)3 shows weaker intermolecular interaction in the solid states and thus exhibits single nanomolecular behavior, which is crucial for charge stored and retained in an organic field‐effect transistor (OFET) memory device. Furthermore, diazafluorene derivatives possess a completely separate highest occupied molecular orbital/lowest unoccupied molecular orbital, which offers ideal hole and electron trapping sites. As charge storage elements, triphenylamine groups provide the hole trapping sites, while diazafluorene units provide the electron trapping sites and act as a hole blocking group to restrain the leakage of stored holes trapped in triphenylamine. The pentacene‐based OFET memory device with solution‐processing TPA(PDAF)3 shows a good hole‐trapping ability, high hole trapping density (4.55 × 1012 cm−2), fast trapping speed (<20 ms), a large memory window (89 V), and a tunable ambipolar memory behavior. The optimized device shows a large ON/OFF current ratio (2.85 × 107), good charge retention (>104 s), and reliable endurance properties. This study suggests that diazafluorene based donor–acceptor small molecular elements have great promise for high‐performance OFET memory.
Highlights
Nonvolatile organic field-effect transistor concentrated sulfuric acid mediated Friedel–Crafts reaction
Triphenylamine groups provide the hole trapping sites, while diazafluorene units provide the electron trapping sites and act as a hole blocking group to restrain the leakage of stored metal-oxide semiconductor circuits.[1]
TPA(PDAF)3 may exhibit single nanomolecular behavior with weaker intermolecular interaction, which is critical for charge storage and retention as charge storage layers in OFET memory devices
Summary
The single crystals of compounds 3 and 6 were unambiguously characterized by X-ray crystallographic analysis, as shown in Figure S1 (Supporting Information). The single crystal of TPA(PDAF) revealed a 3D topology shape, consisting a core unit of TPA and three open-arms of 4,5-diazafluorene moieties. Owing to the large steric hindrance of diazafluorene moieties connecting to TPA, TPA(PDAF) displayed the asymmetric conformation in three directions with open-armed at angles of 122°, 113°, and 125°. Compared with the angle values of the single crystals of TPA (Figure S1, Supporting Information), TPA(PDAF) displayed a larger distortion derived from the steric hindrance. The DSC curves indicate that three diazafluorene derivatives show no glass phase transition and melting point by heating to 195 °C (Figure S2, Supporting Information). These high Td values suggested the good thermal stability of TPA(PDAF)n for the application as charge storage layers in OFET memory devices
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