Self‐Organized Discotic Liquid Crystals as Novel Organic Semiconductors

Abstract

Organic semiconductors are being intensely investigated and incorporated in device applications such as thin-film transistors, light-emitting diodes, solar cells, and sensors [1,2]. Organic molecules offer the advantage of low-cost synthesis and easy manufacture of large-area thin films by solution processing for the fabrication of a new generation of low-cost, lightweight, and flexible devices that would be inaccessible by conventional methods using inorganic semiconducting materials. The efficiency of these devices is directly related to the mobility of the charges achievable in the conducting layer fabricated by solution-processing techniques such as spin-coating, casting, or printing at ambient conditions exploitable on an industrial scale [3]. A number of different molecular and structural features (chemical purity, solubility, degree of crystallinity, energy band gap, absorption, emission, charge generation, and transport, etc.) have to be combined for optimizing device performance. On the basis of morphology of the materials in the active layers, they can be broadly classified into crystalline, amorphous, and liquid crystalline semiconductors. The highest charge-carrier mobilities (>2 cm 2 V −1 s −1 ) in organic systems have been measured in organic single crystals of pentacene and rubrene [4,5]. However, it is difficult to grow single-crystalline thin films. Charge mobilities in the polycrystalline films of polymeric semiconducting materials such as oligothiophenes, poly(phenylenevinylene), poly(thiophene), and poly(fluorine) compounds have reached values exceeding that of amorphous silicon (>1.0 cm 2 V −1 s −1 ) [6,7]. Thermal sublimation in vacuum is a common method for depositing polymeric

Cyanographene and Graphene Acid: Emerging Derivatives Enabling High-Yield and Selective Functionalization of Graphene

“…34,58,59 Since ordered systems tend to exhibit greater charge-carrier mobility than disordered ones, 58,60 the ability of G-COOH to form supramolecular crystals, combined with the predicted tunability of its band gap, is another important enabling property that could be exploited in charge-transport applications. 35,58,59,61 Finally, the selective chemical functionalization of graphene acid renders it a superior platform for synthesis of a broad family of graphene derivatives compared to nonselective chemistry currently performed with graphene oxide.…”

“…These features extend the portfolio of potential derivatives and predispose this material for further applications such as in optics and theranostics . The synthesis and isolation of G-COOH from cyanographene can be considered to bridge the gap between graphene and “graphene molecules” (derivatives of large polyaromatic hydrocarbons), , because its tendency to self-organize into 3D lattices of spherulitic morphologies and supramolecular arrangements is shared with graphene molecules. ,, Since ordered systems tend to exhibit greater charge-carrier mobility than disordered ones, , the ability of G-COOH to form supramolecular crystals, combined with the predicted tunability of its band gap, is another important enabling property that could be exploited in charge-transport applications. ,,, Finally, the selective chemical functionalization of graphene acid renders it a superior platform for synthesis of a broad family of graphene derivatives compared to nonselective chemistry currently performed with graphene oxide.…”

Liquid Crystal-Gold Nanoparticle Hybrid Materials

“…The least ordered form is the discotic nematic phase which does not form columns. With different symmetry types, the columnar LC phases have variations from hexagonal (Col h ), rectangular (Col r ), to oblique (Col ob ) [22,23]. In addition, bent-core (banana-shaped) LCs with unique sterically induced packing have also gained much attention [24].…”

“…Discotic LC, based on the molecules having disc-like shapes [22,23,74], have attracted much attention in recent years owing to their inherent ability to form selforganized columnar structures, which can provide superior charge transport ability Scheme 4.6 Chemical structures of mesogenic dendron capping agents [14][15] along the column direction. They have potential uses in opto-electronic devices [22,74,75].…”

“…They have potential uses in opto-electronic devices [22,74,75]. There have been some reports but not many in discotic molecules coated GNPs so far.…”