Indenofluorene

Last updated
The five regioisomers of indenofluorenes with the linkages highlighted. Indenofluorene regiochemistry.gif
The five regioisomers of indenofluorenes with the linkages highlighted.

An indenofluorene (IF) is any of five hydrocarbons with formula C
20H
12, whose carbon skeleton is a sequence of five fused rings with 6, 5, 6, 5, and 6 carbon atoms; an arrangement that can be described as the fusion of an indene core and a fluorene core (hence the common name). [2]

Contents

The five structural isomers (regioisomers) differ in the way the rings are connected. They have unique properties, applications, and research interests.

The name "indenofluorene" is also commonly used for any derivative of those five compounds (which are then specifically called "parent" or "unsubstituted" IFs), conceptually obtained by substituting other functional groups for some hydrogen atoms, and/or by hydrogenating the methylidene bridges (thus turning them into methylene bridges). Most IF synthesis and research work is done on these derivatives

History

Despite being first synthesized in the late 19th century [3] by Dr. S. Gabriel when he synthesized the substituted indeno [1,2-a] fluorene (shown right), the lack of robust synthesis routes left this family of molecules unexplored until the mid 20th century. After Gabriel, the next major step was the synthesis of the indeno [2,1-a] fluorene in 1939 by Weizmann et al. Next major advances came from Chardonens and Ritter with the synthesis the indeno [1,2-b] fluorene and indeno [2,1-b] fluorene in 1951. [1] Continuing with their work, Chardonens and Ritter, synthesized indeno [1,2-a] fluorene in 1955. [1] The final regioisomer, the indeno [2,1-c] fluorene was synthesized in 1961 by Ginsburg and Altman. Since the fifties and sixties, when these molecules were first being synthesized and discovered, improved synthetic routes and instrumentation have allowed IFs to be explored for uses in organic electronics including organic photovoltaics, organic light emitting diodes, and organic field effect transistors. Even with these advancements, the properties of IFs have remained largely unexplored. [1] This is likely to change, however, as improvements on synthesis and expansion of IF examples continues to be an active area of research.

Structure and nomenclature

There are several conventions for naming IFs currently in use. The preferred version uses a [1,2] or [2,1] to describe if the orientation of the methylene bridges on the 5 member rings are anti ([1,2]) or syn ([2,1]). The a, b, c designation indicates connectivity. a indicates there are no carbons between the indene and the starred fluorene carbon. Similarly, b indicates one carbon and c indicates two carbons. [1]

While indenofluorenes are members of the polycyclic hydrocarbon family, they are not necessarily members of the polycyclic aromatic hydrocarbon family. For example, the fully conjugated versions, shown below, have 20π electrons making them formally anti-aromatic.

First indenofluorene scaffold synthesized by Dr. Gabriel in 1884. The molecule is a substituted version of the [1,2-a] IF scaffold. GabrielIF.gif
First indenofluorene scaffold synthesized by Dr. Gabriel in 1884. The molecule is a substituted version of the [1,2-a] IF scaffold.

Stability

Because of the instability of parent compounds, most synthesis work and research on indenofluorenes tend to focus on the dione substituted IFs, the fully conjugated IF, or the hydrogenated (methylene bridged) IFs. Even in these molecules, though, stability remains a problem so it is not uncommon to stabilize the core indenofluorene with aromatic or bulky substituents, such as mesityl or triisopropyl silyl. Similarly, the scope of indenofluorenes have been increasing over the decades to include heteroatoms, such as sulfur, [4] [5] within the ring system. Other structural expansions include addition of rings to the outer edges, off the center [6] [7] and expanding the center core. [4]

Synthesis

There is no one way to synthesize each of the regioisomers and new routes are being discovered. Presented here are some of the published ways to get to synthetically useful versions of each IF. Preference was given to the most efficient way to get to the minimally substituted IF.

[1,2-a] IF

The first [1,2-a] IF scaffold was synthesized by Chardonens and Ritter [8] in 1955. In their publication, they showed two ways to get to the dione of the [1,2-a] IF. The first utilizes an oxidative cleavege followed by a ring closure utilizing concentrated sulfuric acid. Later they developed a route in which they condensed an indenyl ketone with quinolone base. This intermediate was then reacted sodium dichromate to produce the final dione in decent yield. [1] Despite having multiple routes to the dione, the synthesis of the fully conjugated IF remained elusive until 2017. [9]

Rittersynthesis to 12a IF dione.gif

Using the synthesis presented by Chardonens and Ritter, Dressler et al. appended various R- groups at the carbonyl to produce the diol product which was then reduced using a tin chloride catalyst to get to the desired product (below). [9] The pure IF, with no substitution, was not synthesized due to instability. [9]

Dressler Fully Conjugated 1,2 a IF.gif

[1,2-b] IF

The first [1,2-b] IF, reported in 1951 by Deuschel and co-workers, used a route similar to the synthesis below. [1]

12bdione correct.gif

This route produced the diol which could be used to make various derivatives. The collapse method, like the one shown below, was reported by Eglington et al. in 1960. [1] This method successfully produces the parent IF in approximately 60% yield. [1]

Different route to the 12b scaffold - 12b 2.gif

[2,1-a] IF

The [2,1-a] IF was the second one synthesized, after Gabriel's work, and was published in 1939 by Weizmann. His route is not shown here, as better yielding methods have been developed recently. Arguably the best route to the synthesis of the [2,1-a] IF is based on the work by Thirion et al. where they perform a Diels Alder reaction with 1,4-diphenyl-1,3-butadiene and dimethyl-but-2-ynedioate to build the skeleton of the IF. The center ring is aromatized using palladium on carbon to get to the diester. Saponification is performed to get to the carboxylic acid. Continuation with their route leads to the dione, in low yield, using a hot sulfuric acid closure. [10] From the carboxylic acid, another route can be taken. If triflic acid, trifluoroacetic anhydride, and zinc bromide were added in a sealed reaction vessel to the carboxylic acid then heated, the result would be the desired dione in a 90 + percent yield [11]

Thirion completesynthesis.gif

[2,1-b] IF

21b synthesis.gif

The first account of this scaffold was disclosed in 1951 by Deuschel et al. [1] Chardonnens and Ritter, in 1955, offered the better route (shown above) in 79% yield [1]

[2,1-c] IF

The [2,1-c] IF isomer was the last to be discovered and was published in 1961 by Ginsburg and Altman with an alternate route presented by Chardonnens and Ritter. [1] [12] Shown below is the original synthesis to the [2,1-c] dione.

21c synthesis.gif

In 2012, the first example of the fully conjugated IF was disclosed by the Haley group at the University of Oregon as an unpublished work [1]

An alternate route, not shown here, was presented by Youngs et al. where they produced the [2,1-c] IF in a collapse method similar to that disclosed by Eglington for the [1,2-b] IF. [13] The yield over the two steps was reported to be 91% [13]

Properties

Properties of indenofluorenes vary significantly between each regioisomer and even within each regioisomer as substitutions change. Presented here are the general trends for each indenofluorene.

[1,2-a] IF

The properties of this regioisomer are not well known as of this point owing to the lack of synthetic routes. That said, the [1,2-a] IF is the only one that shows centrosymmetry. [1] Dressler et al. recently published a paper on the first fully conjugated [1,2 - a] IF, and within that paper, they found a first reduction potential of -0.67 V [9]

[1,2-b] IF

The [1,2-b] IF is distinguished from the other regioisomers first by having rotational symmetry. In crystal form, [1,2- b] IFs generally show one dimensional column stacking., [1] however, the stacking can be tuned based on the substitution of the molecule. For example, the addition of fluorine to the molecule resulted in face to face π- stacking. [1] [14] No matter what substitution is present, though, the molecules pack fairly closely with distances of about 3.30 Å [1]

Kamatsu et al., in their work with [1,2-b] IFs, have shown that they behave as n-type semiconductors. [1] [15] The best n-type behavior was shown in the dione of the [1,2-b] IF in which the para positions were substituted with fluorine, which was presented by Yamahita et al. to be 0.17 cm2/Vċs. [1] [14]

Cyclic voltammetry data has shown that various [1,2-b] IFs, can reversibly accept two electrons with the first reduction occurring at -0.8 V. The parent dione has a first reduction potential of -1.19 V, and halogenated versions reduce around -0.6 V. [1] The fully conjugated version, first postulated by Deuschel in the 1950s, is believed to be even better as an electron carrier when compared to the analogus fullerene. [1] This is believed to be due to a low lying LUMO, which was calculated in the Haley Group at the University of Oregon and corroborated by the Tobe group via crystal structure analysis. [1] [16] [17] Confirmation of these low lying LUMOs wis provided by a tips acetylene appended, on the methyl bridges and the center ring, fully conjugated [1,2-b] IF had a first reduction of -0.62 V. The improvement in reduction potential is linked to the fact that the addition of 2 electrons yields an aromatic molecule with increased stability. [1] However, the addition of the steric bulk required to make the molecule stable, lead to a herringbone crystal packing which is not favorable for electron mobility through the crystal. [1] [18]

[2,1-a] IF

Similar to indeno [1,2 -b] fluorenes, see above, indeno [2,1-a] fluorenes show strong biradical character. [1] [16] [7] This biradical nature is both an advantage, in that it is believed that [2,1-a] IFs will make excellent organic electron carriers, and a curse, owing to the decreased stability of the molecule. The first reduction potential of the fully conjugated mesityl substituted compound is reported to be -1.51 V. [7] Other versions of this IF regioisomer have had first reduction potentials as low as -2.48 V. [10] As such, little work with this regioisomer has been published to-date and its properties remain largely unknown.

[2,1-b] IF

Similarly to the [2,1 - a] IF, [2,1 - b] IFs show a mirror plain of symmetry and strong biradical character. [1] [7] The first reduction of the fully conjugated methyl appended [2,1 - b] IF occurs at -1.13 V and the second reduction is at -2.03 V. [7]

[2,1-c] IF

Like the other [2,1] isomers, this version also shows mirror plane symmetry, and similar to the [1,2-a] IF, there is very little know about this molecule.

Applications

Overall the applications for IFs are anticipated to be as replacement for fullerenes in organic electronic systems such as OLEDs, OFETs, and OPVCs. [1] [19] [20] However, as IFs have been sparsely studied, to this point, actual applications and integration into products have yet to be achieved. Not all of the IF regioisomers are suited to incorporation into organic electronics mostly owing to difficult synthesis and instability. However, as research progresses, advances in synthesis are sure to be made. Similarly, as molecular libraries expand, trends in stability and electron carrying ability are likely to develop.

Related Research Articles

Pyrimidine is an aromatic heterocyclic organic compound similar to pyridine. One of the three diazines, it has the nitrogen atoms at positions 1 and 3 in the ring. The other diazines are pyrazine and pyridazine. In nucleic acids, three types of nucleobases are pyrimidine derivatives: cytosine (C), thymine (T), and uracil (U).

In organic chemistry, the Diels–Alder reaction is a chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene derivative. It is the prototypical example of a pericyclic reaction with a concerted mechanism. More specifically, it is classified as a thermally-allowed [4+2] cycloaddition with Woodward–Hoffmann symbol [π4s + π2s]. It was first described by Otto Diels and Kurt Alder in 1928. For the discovery of this reaction, they were awarded the Nobel Prize in Chemistry in 1950. Through the simultaneous construction of two new carbon–carbon bonds, the Diels–Alder reaction provides a reliable way to form six-membered rings with good control over the regio- and stereochemical outcomes. Consequently, it has served as a powerful and widely applied tool for the introduction of chemical complexity in the synthesis of natural products and new materials. The underlying concept has also been applied to π-systems involving heteroatoms, such as carbonyls and imines, which furnish the corresponding heterocycles; this variant is known as the hetero-Diels–Alder reaction. The reaction has also been generalized to other ring sizes, although none of these generalizations have matched the formation of six-membered rings in terms of scope or versatility. Because of the negative values of ΔH° and ΔS° for a typical Diels–Alder reaction, the microscopic reverse of a Diels–Alder reaction becomes favorable at high temperatures, although this is of synthetic importance for only a limited range of Diels-Alder adducts, generally with some special structural features; this reverse reaction is known as the retro-Diels–Alder reaction.

Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3. Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme.

Aromaticity Phenomenon providing chemical stability in resonating hybrids of cyclic organic compounds

In chemistry, aromaticity is a property of cyclic (ring-shaped), typically planar (flat) molecular structures with pi bonds in resonance that gives increased stability compared with other geometric or connective arrangements with the same set of atoms. Aromatic rings are very stable and do not break apart easily. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have enhanced stability.

Nitro compound Organic compounds that contain one or more nitro functional groups

Nitro compounds are organic compounds that contain one or more nitro functional groups. The nitro group is one of the most common explosophores used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.

A non-Kekulé molecule is a conjugated hydrocarbon that cannot be assigned a classical Kekulé structure.

The 1,3-dipolar cycloaddition is a chemical reaction between a 1,3-dipole and a dipolarophile to form a five-membered ring. The earliest 1,3-dipolar cycloadditions were described in the late 19th century to the early 20th century, following the discovery of 1,3-dipoles. Mechanistic investigation and synthetic application were established in the 1960s, primarily through the work of Rolf Huisgen. Hence, the reaction is sometimes referred to as the Huisgen cycloaddition. 1,3-dipolar cycloaddition is an important route to the regio- and stereoselective synthesis of five-membered heterocycles and their ring-opened acyclic derivatives. The dipolarophile is typically an alkene or alkyne, but can be other pi systems. When the dipolarophile is an alkyne, aromatic rings are generally produced.

Arynes and benzynes are highly reactive species derived from an aromatic ring by removal of two substituents. Arynes are examples of didehydroarenes, although 1,3- and 1,4-didehydroarenes are also known. Arynes are examples of strained alkynes.

Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen; the term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular formula C3H3NS. The thiazole ring is notable as a component of the vitamin thiamine (B1).

Nucleophilic aromatic substitution Chemical reaction mechanism

A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution. Just as normally nucleophilic alkenes can be made to undergo conjugate substitution if they carry electron-withdrawing substituents, so normally nucleophilic aromatic rings also become electrophilic if they have the right substituents.

Squaric acid, also called quadratic acid because its four carbon atoms approximately form a square, is a diprotic organic acid with the chemical formula C4O2(OH)2.

Pentacene Chemical compound

Pentacene is a polycyclic aromatic hydrocarbon consisting of five linearly-fused benzene rings. This highly conjugated compound is an organic semiconductor. The compound generates excitons upon absorption of ultra-violet (UV) or visible light; this makes it very sensitive to oxidation. For this reason, this compound, which is a purple powder, slowly degrades upon exposure to air and light.

Covalent organic frameworks (COFs) are a class of materials that form two- or three- dimensional structures through reactions between organic precursors resulting in strong, covalent bonds to afford porous, stable, and crystalline materials. COFs emerged as a field from the overarching domain of organic materials as researchers optimized both synthetic control and precursor selection. These improvements to coordination chemistry enabled non-porous and amorphous organic materials such as organic polymers to advance into the construction of porous, crystalline materials with rigid structures that granted exceptional material stability in a wide range of solvents and conditions. Through the development of reticular chemistry, precise synthetic control was achieved and resulted in ordered, nano-porous structures with highly preferential structural orientation and properties which could be synergistically enhanced and amplified. With judicious selection of COF secondary building units (SBUs), or precursors, the final structure could be predetermined, and modified with exceptional control enabling fine-tuning of emergent properties. This level of control facilitates the COF material to be designed, synthesized, and utilized in various applications, many times with metrics on scale or surpassing that of the current state-of-the-art approaches.

Indole Organic compound with an intense fecal odor

Indole is an aromatic heterocyclic organic compound with formula C8H7N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environment and can be produced by a variety of bacteria. As an intercellular signal molecule, indole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin.

Birch reduction Organic reaction used to convert arenes to cyclohexadienes

The Birch reduction is an organic reaction that is used to convert arenes to cyclohexadienes. The reaction is named after the Australian chemist Arthur Birch and involves the organic reduction of aromatic rings in liquid ammonia with sodium, lithium, or potassium and an alcohol, such as ethanol and tert-butanol. This reaction is unlike catalytic hydrogenation, which usually reduces the aromatic ring all the way to a cyclohexane.

Polyfluorene Chemical compound

Polyfluorene is a polymer with formula (C13H8)n, consisting of fluorene units linked in a linear chain — specifically, at carbon atoms 2 and 7 in the standard fluorene numbering. It can also be described as a chain of benzene rings linked in para positions with an extra methylene bridge connecting every pair of rings.

The Buchner ring expansion is a two-step organic C-C bond forming reaction used to access 7-membered rings. The first step involves formation of a carbene from ethyl diazoacetate, which cyclopropanates an aromatic ring. The ring expansion occurs in the second step, with an electrocyclic reaction opening the cyclopropane ring to form the 7-membered ring.

Diketopyrrolopyrroles (DPPs) are organic dyes and pigments based on the heterocyclic dilactam 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, widely used in optoelectronics. DPPs were initially used as pigments in the painting industry due to their high resistance to photodegradation. More recently, DPP derivatives have been also investigated as promising fluorescent dyes for bioimaging applications, as well as components of materials for use in organic electronics.

Tellurophenes Chemical compound

Tellurophenes are the tellurium analogue of thiophenes and selenophenes.

Mizoroki-Heck vs. Reductive Heck

The Mizoroki−Heck coupling of aryl halides and alkenes to form C(sp2)–C(sp2) bonds has become a staple transformation in organic synthesis, owing to its broad functional group compatibility and varied scope. In stark contrast, the palladium-catalyzed reductive Heck reaction has received considerably less attention, despite the fact that early reports of this reaction date back almost half a century. From the perspective of retrosynthetic logic, this transformation is highly enabling because it can forge alkyl–aryl linkages from widely available alkenes, rather than from the less accessible and/or more expensive alkyl halide or organometallic C(sp3) synthons that are needed in a classical aryl/alkyl cross-coupling.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Fix, Aaron G.; Chase, Daniel T.; Haley, Michael M. (2012). Polyarenes I. Topics in Current Chemistry. Vol. 349. Springer, Berlin, Heidelberg. pp. 159–195. doi:10.1007/128_2012_376. ISBN   9783662433782. PMID   23097030.
  2. ↑ "Indenofluorene" entry at the PUBchem database. Accessed on 2020-08-28.
  3. 1 2 Gabriel, S. (1884-01-01). "Condensationsproducte aus Phtalsäureanhydrid". Berichte der Deutschen Chemischen Gesellschaft. 17 (1): 1389–1396. doi:10.1002/cber.188401701357. ISSN   1099-0682.
  4. 1 2 Frederickson, Conerd K.; Rose, Bradley D.; Haley, Michael M. (2017-04-18). "Explorations of the Indenofluorenes and Expanded Quinoidal Analogues". Accounts of Chemical Research. 50 (4): 977–987. doi:10.1021/acs.accounts.7b00004. ISSN   0001-4842. PMID   28207235.
  5. ↑ Marshall, Jonathan L.; O’Neal, Nathaniel J.; Zakharov, Lev N.; Haley, Michael M. (2016-05-06). "Synthesis and Characterization of Two Unsymmetrical Indenofluorene Analogues: Benzo[5,6]-s-indaceno[1,2-b]thiophene and Benzo[5,6]-s-indaceno[2,1-b]thiophene". The Journal of Organic Chemistry. 81 (9): 3674–3680. doi:10.1021/acs.joc.6b00340. ISSN   0022-3263. PMID   27014864.
  6. ↑ Miyoshi, Hirokazu; Nobusue, Shunpei; Shimizu, Akihiro; Hisaki, Ichiro; Miyata, Mikiji; Tobe, Yoshito (2013-11-26). "Benz[c]indeno[2,1-a]fluorene: a 2,3-naphthoquinodimethane incorporated into an indenofluorene frame". Chem. Sci. 5 (1): 163–168. doi:10.1039/c3sc52622d. ISSN   2041-6539.
  7. 1 2 3 4 5 Shimizu, Akihiro; Nobusue, Shunpei; Miyoshi, Hirokazu; Tobe, Yoshito (2014-04-17). "Indenofluorene congeners: Biradicaloids and beyond". Pure and Applied Chemistry. 86 (4): 517–528. doi: 10.1515/pac-2014-5043 . ISSN   1365-3075.
  8. ↑ Chardonnens, Louis; Ritter, René (1955-01-01). "Fluorènacènes et fluorènaphènes. Synthèses dans la série des indéno-fluorènes IV. Cis-fluorènacène (indéno-(2′,1′: 2,3)-fluorène) et trans-fluorènaphène (indéno-(1′,2′: 1,2)-fluorène)". Helvetica Chimica Acta. 38 (2): 393–396. doi:10.1002/hlca.19550380203. ISSN   1522-2675.
  9. 1 2 3 4 Dressler, Justin J.; Zhou, Zheng; Marshall, Jonathan L.; Kishi, Ryohei; Takamuku, Shota; Wei, Zheng; Spisak, Sarah N.; Nakano, Masayoshi; Petrukhina, Marina A. (2017-11-27). "Synthesis of the Unknown Indeno[1,2-a]fluorene Regioisomer: Crystallographic Characterization of Its Dianion". Angewandte Chemie International Edition. 56 (48): 15363–15367. doi: 10.1002/anie.201709282 . ISSN   1521-3773. PMID   28985444.
  10. 1 2 Thirion, Damien; Poriel, Cyril; Rault-Berthelot, Joëlle; Barrière, Frédéric; Jeannin, Olivier (2010-12-10). "(2,1-a)-Indenofluorene Derivatives: Syntheses, X-ray Structures, Optical and Electrochemical Properties". Chemistry – A European Journal. 16 (46): 13646–13658. doi:10.1002/chem.201001830. ISSN   1521-3765. PMID   21053210.
  11. ↑ Li, Shuangjiang; Aljhdli, Merfat; Thakellapalli, Haresh; Farajidizaji, Behzad; Zhang, Yu; Akhmedov, Novruz G.; Milsmann, Carsten; Popp, Brian V.; Wang, Kung K. (2017-08-04). "Synthesis and Structure of a Functionalized [9]Cycloparaphenylene Bearing Three Indeno[2,1-a]fluorene-11,12-dione-2,9-diyl Units". Organic Letters. 19 (15): 4078–4081. doi:10.1021/acs.orglett.7b01866. ISSN   1523-7060. PMID   28727459.
  12. ↑ Altman, Yanina; Ginsburg, David (1961-01-01). "293. Alicyclic studies. Part XV. Preparation and reactions of 3,3′-bi-indenyl and 2,3:2′,3′-dibenzobi(cyclohepta-2,7-dienyl)". J. Chem. Soc.: 1498–1505. doi:10.1039/jr9610001498. ISSN   0368-1769.
  13. 1 2 Youngs, Wiley J.; Djebli, Abdellah.; Tessier, Claire A. (1991-07-01). "Lithium-induced cyclization of tribenzo cyclotriynes". Organometallics. 10 (7): 2089–2090. doi:10.1021/om00053a002. ISSN   0276-7333.
  14. 1 2 Nakagawa, Tomohiro; Kumaki, Daisuke; Nishida, Jun-ichi; Tokito, Shizuo; Yamashita, Yoshiro (2008-04-01). "High Performance n-Type Field-Effect Transistors Based on Indenofluorenedione and Diindenopyrazinedione Derivatives". Chemistry of Materials. 20 (8): 2615–2617. doi:10.1021/cm800366b. ISSN   0897-4756.
  15. ↑ Miyata, Yasuo; Minari, Takeo; Nemoto, Takashi; Isoda, Seiji; Komatsu, Koichi (2007-08-01). "Synthesis of fluorinated anti-fluorenacenedione and the structural, electronic, and field-effect properties". Organic & Biomolecular Chemistry. 5 (16): 2592–2598. doi:10.1039/b706621j. ISSN   1477-0539. PMID   18019534.
  16. 1 2 Shimizu, Akihiro; Tobe, Yoshito (2011-07-18). "Indeno[2,1-a]fluorene: An Air-Stable ortho-Quinodimethane Derivative". Angewandte Chemie International Edition. 50 (30): 6906–6910. doi:10.1002/anie.201101950. ISSN   1521-3773. PMID   21678534.
  17. ↑ Rudebusch, Gabriel E.; Zafra, José L.; Jorner, Kjell; Fukuda, Kotaro; Marshall, Jonathan L.; Arrechea-Marcos, Iratxe; Espejo, Guzmán L.; Ortiz, Rocío Ponce; Gómez-García, Carlos J. (August 2016). "Diindeno-fusion of an anthracene as a design strategy for stable organic biradicals". Nature Chemistry. 8 (8): 753–759. Bibcode:2016NatCh...8..753R. doi:10.1038/nchem.2518. ISSN   1755-4349. PMID   27442280.
  18. ↑ Holmes, Daniel; Kumaraswamy, Sriram; Matzger, Adam J.; Vollhardt, K. Peter C. (1999-11-05). "On the Nature of Nonplanarity in the [N]Phenylenes". Chemistry – A European Journal. 5 (11): 3399–3412. doi:10.1002/(sici)1521-3765(19991105)5:11<3399::aid-chem3399>3.0.co;2-v. ISSN   1521-3765.
  19. ↑ Rault-Berthelot, Joëlle; Poriel, Cyril; Justaud, Frédéric; Barrière, Frédéric (2008-07-04). "Anodic oxidation of indenofluorene. Electrodeposition of electroactive poly(indenofluorene)". New Journal of Chemistry. 32 (7): 1259. doi:10.1039/b719467f. ISSN   1369-9261.
  20. ↑ Merlet, Samuel; Birau, Maria; Wang, Zhi Yuan (2002-06-01). "Synthesis and Characterization of Highly Fluorescent Indenofluorenes". Organic Letters. 4 (13): 2157–2159. doi:10.1021/ol025972l. ISSN   1523-7060. PMID   12074656.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.