4,5‐Diazafluorene‐Based Donor–Acceptor Small Molecules as Charge Trapping Elements for Tunable Nonvolatile Organic Transistor Memory

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.

Tunable Synaptic Plasticity in Crystallized Conjugated Polymer Nanowire Artificial Synapses

“…Organic materials have tunable properties by easy modification of chemical and physical structures . In addition, it is compatible with the solution process that enables facile and scalable fabrication.…”

Organic semiconductors based on complex diarylfluorenes via Friedel-Crafts protocols of fluorenols

“…在电场诱导作用下, 苯基芴位阻基团发生 构象变化. 该变化会阻止PVK上的咔唑单元π-π堆积, [44] . TPA(PDAF) 3 筑分子建筑与分子窗格的重要基元, 探索其跨尺度合 成以及有机智能的纳米分子集成平台将成为重要的研 究方向 [73] .…”

Application of organic field-effect transistors in memory

“…47 Subsequently, the application of electrets in OFET memory has developed rapidly. [48][49][50] Charges trapped in polymer electrets can be generated by the following mechanisms: (i) charges trapped by structural defects and impurity centers; (ii) orientation of dipoles (in polar materials); and (iii) build-up of charges near heterogeneities such as grain boundaries (in polycrystalline materials) and amorphous-crystalline interfaces (in semicrystalline polymers). 51 In 2008, Kim and co-workers systematically studied the characteristics of various polymer electrets, 51 and concluded that only non-polar and hydrophobic polymers could be used as effective dielectrics, acting like floating gates in floating gate memories.…”