. (2017) High operational and environmental stability of high-mobility conjugated polymer fieldeffect transistors achieved through the use of molecular additives. Nature Materials, 16 (3 Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. challenge is now to achieve the required device uniformity for large-area 46 applications, such as displays. With conjugated polymers that show high field-effect 47

Herein we report the synthesis and characterization of a series of 6,12-diarylindeno[1,2-b]fluorenes (IFs). Functionalization with electron donor and acceptor groups influences the ability of the IF scaffold to undergo two-electron oxidation and reduction to yield the corresponding 18- and 22-π-electron species, respectively. A single crystal of the pentafluorophenyl-substituted IF can serve as an active layer in an organic field-effect transistor (OFET). The important finding is that the single-crystal OFET yields an ambipolar device that is able to transport holes and electrons.

Highly conjugated hydrocarbons have attracted interest for use as active materials in electronic devices such as organic field effect transistors (OFET) and organic photovoltaics (OPV). In this Account, we review our progress in synthesizing and studying a new class of small molecules for potential use as organic semiconductors. The idea originated from prior research on octadehydrodibenz[12]annulene, as the system can undergo double transannular cyclization to yield the indeno[1,2-b]fluorene skeleton. Subsequent functionalization afforded the first stable, well-characterized indeno[1,2-b]fluorene derivatives, albeit in minute quantities (tens of milligrams). The preparation of these formally antiaromatic compounds has since been optimized: the new synthetic routes utilize inexpensive starting materials, involve robust and high-yielding transformations, and are amenable to considerably larger scale reaction. We have since researched the chemical space of indeno[1,2-b]fluorenes and related quinoidal structures by substitution with a number of functional groups and by permutation of the indenofluorene scaffold. These modifications have allowed us to explore fundamental concepts such as biradical character and antiaromaticity, important considerations when tuning electronic properties to yield functional organic materials. Altering the outer rings by exchange of carbocycles for heterocycles or by inclusion of additional rings as part of the fully conjugated skeleton is one strategy we have examined. Fusing these different aryl groups to s-indacene revealed a dependence of the antiaromaticity of the indacene core upon the outer group. Computational analysis of a series of indeno[1,2-b]fluorene derivatives uncovered an array of different levels of antiaromaticity in the core of the indeno[1,2-b]fluorene derivatives, with one of the benzothiophene derivatives calculated to be as antiaromatic as the parent s-indacene itself. Conversely, we have prepared compounds with expanded cores, starting with the naphthalene-based fluoreno[4,3-c]fluorene, which was produced through a similar route as the indeno[1,2-b]fluorene, using a dione as the key intermediate. Similar to indeno[1,2-b]fluorene, fluoreno[4,3-c]fluorene showed a closed shell ground state, with no evidence of open shell character even upon heating to 170 °C. Increasing the size of the quinoidal core to three rings afforded a diindeno[b,i]anthracene (DIAn) derivative, a compound with a much more complex electronic picture. To produce DIAn, a new synthetic route was devised involving a Friedel-Crafts alkylation to form the five-membered ring and a DDQ oxidation to produce the final compound. DIAn displayed NMR signals that were broadened at room temperature and disappeared when heated, indicative of a molecule with significant biradical character. Extensive computational and experimental investigation verified the controllable expression of its biradical character, with DIAn best described with a ground state that lies between a closed shell compound and a open-shel...

No abstract

Polycyclic hydrocarbons that possess extended p conjugation are of significant interest because of their potential use in optical and electronic devices such as light emitting devices, field-effect transistors, and photovoltaics.[1] While a majority of studies have focused on acenes such as pentacene and its derivatives (e.g., 1; Scheme 1), [2] these systems are susceptible to oxidative and photolytic degradation; [3] thus, there is a need for alternative, acene-like molecules. One avenue in this search has explored compounds containing five-membered rings, rather than the more traditional six-membered rings. Prime examples of such molecules are dibenzopentalene (2) and derivatives thereof, wherein the groups of Saito, Kawase, and Tilley have recently described improved methods for their construction. [4] Another attractive topology is the indeno[1,2-b]fluorene (IF) skeleton (e.g., 3), an acene analogue in which the B and D rings each contain one fewer carbon atom, thus making the 20-p-electron molecule formally antiaromatic. While the pentacyclic IF framework is common in the literature, nearly all examples bear substituents on the 6-and 12-positions, thus resulting in either cross-conjugation (e.g., ketones, exocyclic olefins) [5] or disrupted conjugation (e.g., disubstitution, spirofusion). [6] Of the four fully conjugated IFs known prior to 2011, three are rapidly oxidized by trace amounts of oxygen [7] and the other is poorly characterized.[8]Very recently we reported the synthesis of tetraalkynylated indeno[1,2-b]fluorenes (e.g., 4).[9] The compounds exhibited similar UV/Vis absorption profiles and slightly larger HOMO/LUMO energy gaps compared to those of 1 while maintaining potentially superior solution stabilities; however, the packing of 4 in the solid state resembled an expanded herringbone pattern, a motif often found in unsubstituted acenes. Since the steric bulk of the four interdigitated (triisopropylsilyl)ethynyl groups was the most likely cause for inhibiting a desirable "brick and mortar" p stacking, we sought to examine additional IF derivatives.[10]As a guide for experimental studies, we performed DFT calculations (B3LYP/6-311 + G** [11] using Gaussian 09) [12] on substituted IFs to determine the effect ethynylogation of 3 has on the HOMO (À5.53 eV) and LUMO (À3.03 eV) energy levels, and the energy gap (2.50 eV) of the IF core (Scheme 2, Table 1). Inclusion of the four ethynyl units in 5 significantly lowers the LUMO by approximately 0.5 eV while the HOMO remains unchanged, thus affording a gap energy of 1.97 eV. Inclusion of only two acetylenes at positions 5 and 11 (e.g., 6) slightly lowers the HOMO yet significantly raises the LUMO compared to 5, thus affording a net gap increase of 0.41 eV. If the two alkynes are located at positions 6 and 12, as in 7, the HOMO (À5.51 eV) is on par with that of 5 (À5.53 eV) and the LUMO is elevated slightly (À3.46 eV versus À3.56 eV), thus increasing the gap by only 0.08 eV. Similar to acenes, [2] these results illustrate that judicious positioning of the...

A new class of fully conjugated indenofluorenes has been synthesized and confirmed by solid-state structure analysis. These indeno[2,1-c]fluorene molecules, containing an antiaromatic as-indacene core (in red), possess high electron affinities and show a broad absorption that reaches into the near-IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons. Their electronic properties make this class of compounds attractive for applications in organic electronic devices.

We report on the formation of charge-transfer (CT) excitons and their effect on photocurrent dynamics in composites with a fluorinated anthradithiophene (ADT-TES-F) donor (D) and acceptors (A) with (i) various LUMO energy offsets with respect to that of the donor (ΔLUMO) and (ii) several different side groups that modify spatial D/A separation at the D/A interface. Exciplexes and nonemissive CT excitons were formed in composites with ΔLUMO <0.6 and >0.6 eV, respectively. A competition between fast charge carrier photogeneration and CT exciton formation was observed, with outcomes depending on the applied electric field (E) and on the D/A separation. At low E fields, CT formation was dominant, and up to a factor of 2 increase in charge photogeneration efficiency due to CT exciton dissociation was observed in composites with large spatial D/A separation compared with that in pristine D films. At high E fields, fast charge carrier photogeneration was dominant in all composites, and no improvement in charge photogeneration efficiency with respect to that in pristine D films was observed. Dramatic changes in charge recombination dynamics were observed depending on the spatial D/A separation. These contributed to a factor of 5−10 improvement in continuous-wave photocurrents in composites with large spatial D/A separation as compared with those in pristine D films.

The electron deficiency and trans-planar conformation of bithiazole is potentially beneficial for the electrontransport performance of organic semiconductors. However, the incorporation of bithiazole into polymers through a facile synthetic strategy remains a challenge. Herein, 2,2′-bithiazole was synthesized in one step and copolymerized with dithienyldiketopyrrolopyrrole to afford poly(dithienyldiketopyrrolopyrrole-bithiazole), PDBTz. PDBTz exhibited electron mobility reaching 0.3 cm 2 V −1 s −1 in organic field-effect transistor (OFET) configuration; this contrasts with a recently discussed isoelectronic conjugated polymer comprising an electron-rich bithiophene and dithienyldiketopyrrolopyrrole, which displays merely hole-transport characteristics. This inversion of charge-carrier transport characteristics confirms the significant potential for bithiazole in the development of electron-transport semiconducting materials. Branched 5-decylheptacyl side chains were incorporated into PDBTz to enhance polymer solubility, particularly in nonhalogenated, more environmentally compatible solvents. PDBTz cast from a range of nonhalogenated solvents exhibited film morphologies and field-effect electron mobility similar to those cast from halogenated solvents.