Optical and electronic properties of fluorene‐based copolymers and their sensory applications

A series of novel, fluorene‐based conjugated copolymers, poly[(9,9‐bis{propenyl}‐9H‐fluorene)‐co‐(9,9‐dihexyl‐9H‐fluorene)] ( P1 ), poly[(9,9‐bis{carboxymethylsulfonyl‐propyl}fluorenyl‐2,7‐diyl)‐co‐(9,9‐dihexyl‐9H‐fluorene)] ( P2 ) and poly[(9,9‐dihexylfluorene)‐co‐alt‐(9,9‐bis‐(6‐azidohexyl)fluorene)] ( P3 ), are synthesized by Suzuki coupling reactions and their electrochemical properties, in the form of films, are investigated using cyclic voltammetry. The results reveal that the polymer films exhibit electrochromic properties with a pseudo‐reversible redox behavior; transparent in the neutral state and dark violet in the oxidized state. Among the three polymers, P2 possesses the shortest response time and the highest coloration efficiency value. These polymers emit blue light with a band gap value of around 2.9 eV and have high fluorescent quantum yields. Their metal ion sensory abilities are also investigated by titrating them with a number of different transition metal ions; all of these polymers exhibit a higher selectivity toward Fe³⁺ ions than the other ions tested with Stern–Volmer constants of 4.41 × 10⁶M^?1, 3.28 × 10⁷M^?1, 1.25 × 10⁶M^?1, and 6.56 × 10⁶M^?1 for P1 , P2 , water soluble version of P2 ( P2S ) and P3 , respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and properties of new fluorene‐based polyquinoxalines with an ether linkage in the main chain for light‐emitting diodes

A new series of fluorene‐based polyquinoxalines with an ether linkage in the main chain were prepared by the polycondensation reaction between a tetraketone monomer and 3,3′,4,4′‐tetraaminodiphenyl ether. The polycondensation was usually carried out in m‐cresol. The resulting polymers ( P1 – P3 ) [ P1 = poly(quinoxaline‐co‐9,9‐dihexyl‐2,7‐dimethyl‐9H‐fluorene) P2 = poly(quioxaline‐co‐9,9‐dihexyl‐9‐pentyl‐2,7‐di‐p‐tolyl‐9H‐fluorene) P3 = poly(quioxaline‐co‐9,9‐bis‐(4‐methoxy‐phenyl)‐2,7‐dimethyl‐9H‐fluorene)] showed good solubility in common organic solvents and high thermal stability with only a 5% weight loss up to 440 °C. P1 and P2 had very high glass‐transition temperatures of 212 and 223 °C, respectively, whereas P3 did not show any phase‐transition temperature in repeated scans up to 300 °C. All the polymers in photoluminescence showed blue emissions in the range of 432–465 nm, both in chloroform solutions and in thin films. Light‐emitting diode devices of the configuration indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polymer:poly(N‐vinylcarbazole) blend (2:8)/LiF/Al were fabricated with P1 or P2 and emitted blue light with electroluminescence peak wavelengths of 434 and 448 nm, respectively. The maximum brightness and the external quantum efficiency of P1 were 0.56 μW/cm² at 29 V and 0.056%, whereas P2 showed 0.50 μW/cm² at 34 V and a relatively low value of 0.015%, respectively. Cyclic voltammetry studies revealed that these polymers possessed low‐lying ionization potential energy levels ranging from ?5.49 to ?5.86 eV and low‐lying electron affinity energy levels ranging from ?2.65 to ?2.88 eV. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1189–1198, 2006     

Design and synthesis of 9,9‐dioctyl‐9H‐fluorene based electrochromic polymers

Two novel heterocycle‐fluorene‐heterocycle monomers, 2,2′‐(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)dithiophene (Th‐F‐Th) and 5,5′‐(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxine) (EDOT‐F‐EDOT), were synthesized via Stille coupling reaction and electropolymerized to form corresponding polymers P(Th‐F‐Th) and P(EDOT‐F‐EDOT). Furthermore, the optoelectronic properties of the obtained monomers and polymers were explored using cyclic voltammetry (CV), UV–vis, and emission spectra and in situ spectroelectrochemical techniques. The band gap values of monomers calculated by DFT were 3.75 eV for EDOT‐F‐EDOT and 4.03 eV for Th‐F‐Th, while that of P(EDOT‐F‐EDOT) and P(Th‐F‐Th) were brought down to 1.70 and 2.10 eV, respectively. Both polymers exhibited excellent redox activity and electrochromic performance. P(EDOT‐F‐EDOT) exhibited a maximum optical contrast of 25.8% at 500 nm in visible region with a response time of 1.2 s. In addition, the coloration efficiency of P(EDOT‐F‐EDOT) was calculated to be 220 cm² C^?1. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 325–334     

螺二芴富勒烯吡咯烷衍生物的合成及电化学和光限幅性能

设计合成了3种新颖的螺二芴键联富勒烯(C₆₀/C₇₀)吡咯烷衍生物, 其结构通过IR, ¹H NMR, ¹³C NMR和MALDI-TOF进行确证, 其电化学性质用循环伏安法进行研究. 结果表明, C₇₀衍生物6的还原电位较C₆₀衍生物7分别向负电势移动0.1, 0.12和0.01 V. 同时, 使用纳秒和飞秒激光分别研究了化合物6, 7和8的光限幅性能, 其光限幅阈值分别为15.3, 23.3和13.7 J/cm², 表明材料具有优异的光限幅性能.     

Incorporation of different conjugated linkers into low band gap polymers based on 5,6‐Bis(octyloxy)‐2,1,3 benzooxadiazole for tuning optoelectronic properties

Four new 2,1,3‐benzooxadiazole‐based donor–acceptor conjugated polymers, namely poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSC), poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFC), poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSFL), and poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFFL), were synthesized via Stille polycondensation reaction. All polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. Their structures were verified by ¹H‐NMR and the molecular weights were determined by gel permeation chromatography (GPC). The polymer films exhibited broad absorption bands. Among all polymers, photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PSBSC:PC₇₁BM(1:3, w/w)/LiF/Al revealed an open‐circuit voltage of 0.62 V, a short circuit current of 7.63 mA cm^?2 and a power conversion efficiency of 1.89%. This work demonstrates a good example for tuning absorption range, energy level, and photovoltaic properties of the polymers with different spacers and donor units can offer a simple and effective method to improve the efficiency of PSCs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2459–2467     

Synthesis of fusible and soluble conducting polyfluorene derivatives and their characteristics

Conducting polyfluorene derivatives with alkyl chains—poly(9-alkylfluorene)s and poly-(9,9-dialkylfluorene)s—have been synthesized by chemical polymerization utilizing FeCl₃ as an oxidizing agent. The polymers obtained are found to be soluble in conventional organic solvents such as chloroform and have been characterized by ¹H- and ¹³C-NMR. The results indicate that the fluorene moeities are mainly linked in the 2,7′-fashion to yield the straight chain polymer. The degree of polymerization is estimated (by gel permeation chromatography) to be of the order of 10. The polymers are found to be fusible and the thermal properties of the polymers have been characterized by differential scanning calorimetry. The glass transition temperature is found to decrease with an increase of the alkyl chain length. © 1993 John Wiley & Sons, Inc.     

Preparation and properties of polybenzimidazoles containing cardo groups

Several polybenzimidazoles containing cardo groups were prepared: A cardodicarboxylic acid, 9,9-bis(4-carboxyphenyl)fluorene, and two cardotetramines, 9,9-bis(3,4-diaminophenyl)fluorene and 9,9-bis(3,4-diaminophenyl)10-anthrone. The cardodicarboxylic acid was condensed with aromatic tetramines and the cardotetramines were condensed with aromatic dicarboxylic acids. Prior to polymer synthesis two model compounds, 9,9-bis[4,(2-benzimidazolyl)phenyl]fluorene and 2,2′-diphenyl-5,5′-(9,9-fluorenediyl)-bibenzimidazole were prepared and characterized by spectral methods. The polymers were obtained in 60–70% yield and showed reduced viscosity in the range of 0.7–1.1 dL/g. They were soluble in dimethyl formamide (DMF) and chlorinated solvents like tetrachlorethane. The thermal stabilities of these cardopolymers were superior to noncardopoly-benzimidazoles.     

Synthesis, optical, electrochemical, and thermal properties of α,α′-bis(9,9-bis-n-hexylfluorenyl)-substituted oligothiophenes

A series of new α,α′-bis(9,9-bis-n-hexylfluorenyl)-substituted oligothiophenes with 2-, 4-, and 6-thiophene rings have been synthesized via a nickel-catalyzed reductive dimerization and their optical, electrochemical, and thermal properties investigated. The fluorene substituents have shown electronic interactions with the oligothiophene chains, enhanced the solubility of these materials and stabilized the radical cation and dication by blocking the reactive α-positions of the thiophene moieties. The absorption, fluorescence, electrochemical, and thermal properties of these materials can be tuned by varying the conjugation length of the oligothiophene segment.     

Incorporation of fluorene‐based emitting polymers into silica

Novel polyfluorene copolymers with pendant hydroxyl groups, poly[2,7‐(9,9‐dihexylfluorene)‐2,7‐(9,9‐bis(6‐hydroxyhexyl)fluorene)‐co‐2,7‐(9,9‐dihexylfluorene)‐1,4‐phenylene] (PFP‐OH) and poly[2,7‐(9,9‐dihexylfluorene)‐2,7‐(9,9‐bis(6‐hydroxyhexyl)fluorene)‐co‐2,7‐(9,9‐dihexylfluorene)‐4,7‐(2,1,3‐benzothiadiazole)] (PFBT‐OH) were prepared. Acid‐catalyzed polycondensations of tetraethoxysilane were carried out in the presence of these polymers to obtain homogeneous hybrids. Photoluminescence spectra of these hybrids suggested the polymers were immobilized in silica matrix retaining their π‐conjugated structures. Further, hybrids of coat film were prepared utilizing perhydropolysilazane as a silica precursor. Their optical properties were examined. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Random poly(fluorenylene‐vinylene)s containing 3,7‐Dibenzothiophene‐5,5‐dioxide units: Synthesis,photophysical, and electroluminescence properties

The synthesis of new random poly(arylene‐vinylene)s containing the electron withdrawing 3,7‐dibenzothiophene‐5,5‐dioxide unit was achieved by the Suzuki–Heck cascade polymerization reaction. The properties of poly[9,9‐bis(2‐ethylhexyl)‐2,7‐fluorenylene‐vinylene‐co‐3,7‐dibenzothiophene‐5,5‐dioxide‐vinylene] (50/50 mol/mol, P1 ) and poly[1,4‐bis(2‐ethylhexyloxy)‐2,5‐phenylene‐vinylene‐co‐3,7‐dibenzothiophene‐5,5‐dioxide‐vinylene] (50/50 mol/mol, P2 ) were compared with those of terpolymers obtained by combining the fluorene, dibenzothiophene, and 1,4‐bis(2‐ethylexyloxy)benzene in 20/40/40 ( P3 ), 50/25/25 ( P4 ), and 80/10/10 ( P5 ) molar ratios. The polymers were characterized by ¹H NMR and IR, whereas their thermal properties were investigated by TGA and DSC. Polymers P1–5 are blue–green emitters in solution (λ_em between 481 and 521 nm) whereas a profound red shift observed in the solid state is emission (λ_em from 578 to 608 nm) that can be attributed both to the charge transfer stabilization exerted by the polar medium and to intermolecular interactions occurring in the solid state. Cyclic voltammetry permitted the evaluation of the ionization potentials and also revealed a quasi‐reversible behavior in the reduction scans for the polymers ( P1–4 ) containing the higher amounts of 3,7‐dibenzothiophene‐5,5‐dioxide units. Electroluminescent devices with both ITO/PEDOT‐PSS/ P1–5 /Ca/Al (Type I) and ITO/PEDOT‐PSS/ P1–5 /Alq₃/Ca/Al (Type II) configuration were fabricated showing a yellow to yellow–green emission. In the case of P4 , a luminance of 1835 cd/m² and an efficiency of 0.25 cd/A at 14 V were obtained for the Type II devices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2093–2104, 2009     

New poly(amide-lmide)s syntheses. XV. Preparation and properties of poly(amide-imide)s derived from 9, 9-bis[4-(4-aminophenoxy) phenyl]fluorene and various bis(trimellitimide)s

Fifteen bis(phenoxy) fluorene-containing poly(amide-imide)s III were synthesized by the direct polycondensation of 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAPPF) with var-ious aromatic bis(trimellitimide)s II in N-methyl-2-pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. Poly(amide-imide)s III having inherent vis-cosities up to 1.45 dL/g were obtained in quantitative yields. Most of the resulting polymers showed an amorphous nature and were readily soluble in polar solvents such as NMP and N,N-dimethylacetamide. All the soluble poly(amide-imide)s afforded transparent, flexible, and tough films. The glass transition temperatures of these polymers were in the range of 263–315°C and the 10% weight loss temperatures were above 510°C in nitrogen. Some properties of poly(amide-imide)s III were compared with those of the corresponding isomeric poly(amide-imide)s III ′ prepared from 9,9-[4-(4-trimellitimidophenoxy)phenyl]fluorene and various aromatic diamines. © 1995 John Wiley & Sons, Inc.     

Synthesis and photo- and electroluminescent properties of copolyfluorenes with nile red fragments in side chains

New copolyfluorenes containing units of 4,7-dibromo-2,1,3-benzothiadiazole (green luminophore) and 3,6- or 2,7-dibromocarbazole derivatives with side-chain fragments of green (4-pyrrolidinyl-1,8-naphthalimide) and red (Nile red) luminophores and additional carbazole or diphenyloxadiazole groups are synthesized via the Suzuki copolycondensation reaction. The structure of the polymers is modified via insertion of triphenylamine, aryloxadiazole, and quinoxaline units in the backbone of copolyfluorenes and via introduction of triphenylamine, fluorene, and benzene terminal groups. The molecular-weight characteristics of the polycondensation products and the specific features of the transfer of polyfluorene emission energy to the indicated luminophores in solutions and films are studied. Coating the emissive copolyfluorene layer with electron-conducting and hole-blocking layers of poly[9,9-bis(6′-diethoxyphosphorylhexyl)fluorene] makes it possible to increase the brightness of light-emitting diodes (to 2380–3900 cd/m²) and their current and luminance efficiencies.     

Synthesis and light emitting properties of polyacetylenes having pendent fluorene groups

Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA1 ), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) ( PFA2 ), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA3 ), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA4 ), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA5 ) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers ( M1–M5), using WCl₆, MoCl_5, and TaCl₅ as catalysts and n‐Bu₄Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m² at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m² at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006     

Enantioselective synthesis of (R) and (S)-[9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol: a furo-fused BINOL derivative

The enantioselective synthesis of [9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol, a modified BINOL, was achieved using an inexpensive route. Both enantiomers of [9,9′]bi[naphtho(2,1-b)furanyl]-8,8′-diol were obtained with satisfactory stereoselectivities by employing two optical antipodes of phenylethylamine as chiral influence in a Cu(II)Cl₂ catalyzed oxidative coupling step.     

Donor–acceptor semiconducting polymers based on pyromellitic diimide

Three donor–acceptor copolymers P1 , P2 , and P3 with N,N′‐dodecylpyromellitic diimide as the electron‐acceptor unit with three diethynyl‐substituted donor monomers: 1,4‐diethynyl‐2,5‐bis(octyloxy)benzene, 2,7‐diethynyl‐9,9‐dioctyl‐9H‐fluorene, and 3,3′‐didodecyl‐5,5′‐diethynyl‐2,2′‐bithiophene have been synthesized by Sonogashira crosscoupling polymerization. The synthesized polymers showed deep highest occupied molecular orbital energy levels and larger band gaps (>2.5 eV). Polymers P1 , P2 , and P3 underwent fluorescence quenching with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM), indicating the intermolecular photo‐induced charge transfer between the donor polymers and the PCBM acceptor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1617–1622     

Synthesis and properties of highly refractive polyimides derived from fluorene‐bridged sulfur‐containing dianhydrides and diamines

Highly refractive and transparent polyimides (PIs) based on fluorene‐bridged and sulfur‐containing monomers have been developed. An aromatic dianhydride, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), was polymerized with several fluorene‐containing diamines, including commercially available 9,9′‐bis(p‐aminophenyl)fluorene (APF), 9,9′‐bis[4‐(p‐aminophenoxy)phenyl]fluorene (OAPF), and newly synthesized 9,9′‐bis[4‐(p‐aminophenyl)sulfanylphenyl]fluorene (ASPF) to afford series A PIs. Meanwhile, series B PIs were obtained from a new dianhydride, 4,4′‐[(9H‐fluorene‐9‐ylidene)bis(p‐phenylsulfanyl)]diphthalic anhydride (FPSP) and two aromatic diamines, ASPF and 4,4′‐thiobis[(p‐phenylenesulfanyl)aniline] (3SDA) via a two‐step polycondensation procedure. The PIs exhibit good thermal stabilities, such as relatively high glass transition temperatures in the range of 220–270 °C and high initial thermal decomposition temperatures (T_10%) exceeding 490 °C. The 9,9′‐disubstituted fluorene moieties endow the PI films with good optical transparency. The optical transmittances of the PI films at 450 nm are all higher than 80% for the thickness of about 10 μm. Furthermore, the highly aromatic fluorene moiety and flexible thioether linkages in the molecular chains of the PIs provide them with high refractive indices of 1.6951–1.7258 and small birefringence of 0.0056–0.0070. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1510–1520, 2008     

Synthesis,Photophysics, and Electroluminescence of Poly(dibenzofluorene)s

Summary: A series of soluble poly(dibenzofluorene) derivatives that contain dibenzo[a,g]fluorene, dibenzo[a,i]fluorene, and dibenzo[c,g]fluorene repeat units in the main chain have been synthesized, characterized, and explored as emissive materials in polymer light emitting diodes (PLEDs). These polymers possess higher glass transition temperatures (108–133 °C) than that of poly(2,7‐(9,9‐dialkyl)fluorene) (PFO). The photophysical and electrochemical properties of these polymers are affected by the steric hindrance effect. These polymers emit blue light in dilute solution (378–400 nm) and in the solid state (426–447 nm). As emissive materials in PLEDs, blue electroluminescence with a brightness of up to 3 130 cd · m⁻² is obtained from single‐layer diodes of P₂ with aluminum/barium in air.

The photophysical and electrochemical properties of these polymers are affected by the size effect.     

Rhodium(i)-catalyzed polymerization of fluorenylacetylenes

The synthesis and characterization of poly(monofluorenylacetylenes) obtained by polymerization of 2-ethynyl-9,9-bis[(S)-3,7-dimethyl-octyl]fluorene and 2-ethynyl-9,9-bis[(S)-2-methylbutyl]fluorene are described. The effect of the structure of the alkyl chain at the C(9) position of fluorene on the properties of the materials was studied by differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction analysis, UV/Vis spectroscopy, photoluminescence, and circular dichroism. Polymerization of chiral 2-ethynylterfluorene functionalized with (S)-2-methylbutylalkyl chains was studied. The resulting polymer exhibits high thermal stability; its emission spectrum occurs in the violet-blue region and shows no significant red shift on passing from a solution to the solid state.Based on the report presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1962–1967, September, 2004.     

Synthesis and properties of photoluminescent polymers bearing electron‐facilitating oxadiazole derivative side groups

Poly(p‐divinylene phenylene) derivatives bearing fluorene and carbazole units in the main chain and 5‐phenyl‐1,3,4‐oxadiazole moieties as side groups were prepared by the polycondensation of a newly synthesized monomer, [2‐(5′‐phenyl‐1′,3′,4′‐oxadiazole‐2′‐yl)‐1,4‐xylylene]bis(triphenyl phosphonium bromide) (OXAD), with 9,9‐dibutylfluorene‐2,2′‐dicarbaldehyde (DBFDA) and 9‐(2‐ethylhexyl)carbazole‐3,6‐dicarbaldehyde (EHCDA), which gave DBFDA–OXAD and EHCDA–OXAD. Analogues of these polymers without the side groups were also synthesized by the reaction of 1,4‐xylene bis(triphenyl phosphonium bromide) (PXYL) with the dicarbaldehydes, which gave DBFDA–PXYL and EHCDA–PXYL. All the synthesized polymers are soluble in organic solvents, giving films of good quality. The polymers are stable beyond 375 °C. They emit blue and blue‐green light, and their quantum yields are 38–79% in solution and 1–24% in film, depending on the fluorene and carbazole units as well as the side groups. In particular, the OXAD‐based polymers contain hole‐facilitating backbones and electron‐facilitating side groups, perhaps allowing these polymers to transport both holes and electrons. Overall, the synthesized polymers are potential candidates for the fabrication of light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1173–1183, 2002     

Cascade radical cyclizations of benzannulated enyne-allenes. Unusual cleavage of a benzene ring leading to twisted 1,1'-dialkyl-9,9'-bifluorenylidenes and spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorenes

Treatment of the benzannulated enediynyl propargylic alcohol 16 (isomer ratio = 2:1) with thionyl chloride induced a sequence of reactions leading to the twisted 1,1'-dipropyl-9,9'-bifluorenylidene 17, the polycyclic compounds 18 and 19, and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 (trans/cis = 5:1). The transformation from 16 to the unexpected 17 presumably involved an initial formation of the benzannulated enyne-allene 21 followed by a C(2)-C(6) cyclization reaction and an intramolecular radical-radical coupling reaction, giving rise to the formal Diels-Alder adduct 23. Repeat of this sequence then furnished 24. Cleavage of the bond connecting the two carbons having the propyl substituent afforded 25. A subsequent rotation of the carbon-carbon bond joining the two central five-membered rings then gave the trans isomer 26. Oxidation of 26, presumably by oxygen, followed by hydrolysis then produced 17. Interestingly, the pathway leading to 17 involved an unusual cleavage of a benzene ring. The X-ray crystal structure of 17 reveals that it has a twist angle of 45.2 degrees for the carbon-carbon double bond connecting the two bifluorenylidene fragments. The spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 apparently was produced via two intramolecular [2 + 2] cycloaddition reactions of the benzannulated enyne-allene moieties, generated in situ from the benzannulated enediynyl propargylic alcohols. The twisted 1,1'-dimethyl-9,9'-bifluorenylidene 33 and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 39 (trans/cis = 3:1) were likewise produced from 32 and 38, respectively.