Isoindigo, a Versatile Electron-Deficient Unit For High-Performance Organic Electronics

Abstract

Isoindigo (iI) has proven successful as an electron-accepting building block for the preparation of electroactive materials for organic electronics. Its high yielding and scalable synthesis has enabled the rapid development of a large number of molecular and polymeric iI-based materials with remarkable physical properties. This perspective provides an overview of the fundamental properties of isoindigo and summarizes the progress in the development of new materials for varied electronic applications during the last 3 years, focusing in particular on organic photovoltaics (OPVs) and organic field effect transistors (OFETs). The fundamental electronic properties of isoindigo are discussed in the context of the substitution pattern effect (5,5′ vs 6,6′) on the frontier orbitals energies and optical properties. The development of molecular systems in the 6,6′-iI configuration for OPVs is examined with an emphasis on molecular design for improved electronic properties thanks to fine-tuning of the active layer morphology via crystallization control. Numerous copolymers of iI have been reported, with both electron-rich and electron-poor comonomers. The homopolymer of isoindigo displays electron-accepting and electrochromic properties and serves as a polymeric surrogate for fullerenes in all-polymer solar cells. The copolymers’ absorption profiles span the entire visible spectrum into the near-infrared, up to 900 nm. Bulk-heterojunction solar cells based on iI copolymers have reached up to 6.3% efficiency. While the effect of processing additives and cell architecture are important, the unique electronic properties of iI polymers also provide useful insight on energetic losses within blends with fullerenes. Selected copolymers also perform highly in air-stable field effect transistors, with p-type mobilities exceeding 3 cm2/(V s). New concepts concerning the effect of backbone curvature and side-chain branching or polarity have been investigated using iI copolymers. Additionally, some all-acceptor copolymers display n-type mobility. As the design of iI materials evolves, structural modifications of the iI core emerge, targeting ambipolar charge transport and enhanced backbone planarity. Overall, isoindigo provides the field of organic electronics with impressive performance as well as a valuable platform for structure–property relationship investigation.

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

“…[1][2][3][4][5][6][7] Such progress coupled with the high compatibility of solution-processable organic semiconductors with plastic or metal foil substrates makes them ideal candidates for cost-effective, mechanically flexible electronic devices for various applications, such as printed radio frequency identification tags for item-level tagging, drivers for flexible displays, wearable electronics, distributed sensors, and integrated, nonvolatile memory devices. [8][9][10][11][12][13][14][15][16][17][18][19][20] [21][22][23][24][25] Such remarkable p-channel mobilities, obtained in devices with fairly promising shelf-life and operational stabilities, have been demonstrated with conjugated polymers based on new building units, such as diketopyrrolopyrrole, [24,26,27] isoindigo, [28,29] and indacenodithiophene. [30] Similar efforts have been devoted to improving n-channel polymer semiconductors, with the performances of n-type devices still lagging behind their p-channel counterparts.…”

Synthesis of Small Band Gap Poly[Bis-EDOT-Isoindigo] via Direct Arylation and Oxidative Electropolymerization, and Its Optoelectronic Properties

“…Thus, the direct arylation using PdCl 2 offered a simple purification process: only evaporation to remove excess EDOT is enough to obtain pure BEDOTID. Figure 1 1 H NMR spectrum of BEDOTID. The protons of the isoindigo (c and f ) and EDOT (a and b) units could be assigned.…”

“…1 The highly electron-deficient isoindigo unit endows these high performance semiconductors with intriguing optoelectronic properties. In addition to these well-known applications, these isoindigo-based donor-acceptor O-conjugated copolymers provide stable nonvolatile memory devices.…”

Synthesis of N,N′-dialkyl-6,6′-dibromoisoindigo Derivatives by Continuous Flow

“…Isoindigo was already synthesized in 1988, but it took over two decades before it was recognized as a versatile component of OPV materials [32][33][34]. The isoindigo core contains two fused lactam rings, inducing a strong electron-deficient character and, therefore, rendering it attractive as an acceptor component in push-pull type organic semiconductors.…”