Simple and Efficient Method for Obtaining Fluorene and Spirobifluorene Bromide Derivatives

A mild, simple, and efficient synthetic procedure for the preparation of 2-monobromo-, 2,7-dibromo-, and 2,2′,7,7′-tetrabromo-substituted spirobifluorene derivatives and their key intermediates, 2-monobromo- and 2,7-dibromo-substituted fluorene compounds, has been developed. The oxidative bromination of fluorene and spirobifluorene was achieved using NaBr/H₂O₂ as the bromine source. High conversion of the starting materials was achieved together with good selectivities under optimized reaction conditions.     

Synthesis and mesomorphic properties of four ring,rod-like fluorene derivatives – the influence of the lateral substitution on mesomorphic properties of 2,7-bis(4-alkylphenyl)-fluorenes

ABSTRACT

This work presents new rod-like compounds being fluorene derivatives linked with other parts of the core at 2 and 7 positions – its synthesis and properties. The fluorene moiety is located in the central position of the four rings molecular core. The chain system in most cases was symmetrical and limited to pentyl or hexyl chains. To study the influence of the lateral substituents on mesomorphic properties two types of substituents have been incorporated, centrally located various short alkyl groups at fluorene’s 9,9 positions and outer core fluorosubstitutions located at side phenyl rings. All synthesised compounds exhibit liquid crystalline properties, where for laterally non-substituted and fluorosubstituted derivatives the dominant phases are smectics, while the nematics phases (nematic and chiral nematic – observed mostly on cooling cycle) occurs for compounds having alkyl substituents at 9,9 positions of fluorene. The synthetic methodology and mesomorphic properties of title compounds will be presented in detail as well as photophysical properties such as UV-visible absorption spectra and fluorescence spectra.     

New synthetic approaches to polycyclic aromatic hydrocarbons and their carcinogenic oxidized metabolites: derivatives of benzo[s]picene, benzo[rst]pentaphene, and dibenzo[b,def]chrysene

A new synthetic approach to polycyclic aromatic compounds is described that entails in the key steps double Suzuki coupling of PAH bisboronic acid derivatives with o-bromoaryl aldehydes to furnish aryl dialdehydes that are converted to larger polycyclic aromatic ring systems by either (a) conversion to diolefins by Wittig reaction followed by photocyclization or (b) reductive cyclization with triflic acid and 1,3-propanediol. This synthetic method provides convenient access to as many as three different polycyclic aromatic ring systems from a single Suzuki coupled intermediate. It was utilized to synthesize substituted derivatives of benzo[s]picene, benzo[rst]pentaphene, dibenzo[b,def]chrysene, and 13,14-dihydro-benz[g]indeno[2,1-a]fluorene, as well as the putative carcinogenic bisdihydrodiol metabolites of benzo[s]picene, benzo[rst]pentaphene, and dibenzo[b,def]chrysene.     

芴类化合物的研究新进展

芴及其衍生物是一类重要的具有刚性平面联苯结构的化合物,分子内含有较大的共轭体系,这种特殊的刚性稠环结构使芴类化合物表现出许多独特的光电性能及生物活性,在光电材料、医药等多领域具有潜在的广泛应用.更为重要的是芴类化合物易于进行结构修饰,在芴环上可方便地引入各种功能基,芴类衍生物的合成及其开拓芴类化合物潜在的新用途,成为近些年来十分活跃的研究领域,且发展迅速.结合自己的工作,参考国内外文献,全面综述了芴类化合物在有机电致发光材料、双光子吸收材料、光致变色材料、太阳能电池材料和生物医药等领域的研究与开发新进展,并对其发展趋势作了展望.     

Impact of electron acceptor on three-photon absorption cross-section of the fluorene derivatives

Small three-photon absorption (3PA) cross-section values of present nonlinear organic molecules limit their practical applications. Although electron donors and electron acceptors have a great effect on 3PA cross-section, little is known about how the strength and situation of electron acceptors influence the 3PA cross-section value of a compound. The present work reports 3PA effects of two fluorene derivatives with symmetric D-π-π(A)-π-D archetype, which are named as 2,7-bis(4-methoxyphenylacetylene)-9-fluorenone (FATT) and 2,7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene (TSATL). Large 3PA cross-section and ideal 3PA-induced optical limiting effects have been found in the two fluorene derivatives. The two molecules both have a different electron acceptor on the fluorene core, by which the 3PA cross-section value for FATT is enhanced by nearly 3-fold compared with that for TSATL. The mechanism of this significant enhancement in 3PA cross-section has been investigated by density functional theory (DFT) and configuration interaction singles (CIS) method with use of 6-311+G basis set in combination with conductor polarizable continuum model (CPCM). The theoretical results show that increase of electronegative character of the electron acceptor on the core is responsible for the increase of 3PA cross-section values of the two molecules.     

Synthesis and oxidative polymerization of dialkyl fluorene-9,9-dicarboxylates

Novel long-chain dialkyl fluorene-9,9-dicarboxylates were synthesized by treating fluorene with lithium diisopropylamide followed by alkyl chloroformates. The fluorene derivatives were readily electro-oxidized to form electroactive films on the surface of a glassy carbon electrode. From the viewpoint of suitable potential window (from −2.5 to 1.5 V vs Ag/Ag⁺), cyclic voltammograms of the films indicated the electroactive properties of the fluorene derivatives that make them good candidates for electrochemical capacitor materials.     

Synthesis of fused polycycles from propargylic compounds with terminal alkynes via a palladium-catalyzed tandem C-H activation/biscyclization process

Various benzo[b]fluorene and fluorene derivatives have been prepared from propargylic compounds with terminal alkynes through a novel palladium-catalyzed tandem biscyclization reaction. This reaction involved a sequence of carboannulation, coupling, C-H activation and C-C bond formation process. A plausible mechanism has been proposed that was consistent with the deuterium-labeling experiment.     

2,3-Disubstituted Fluorene Scaffold for Efficient Green Phosphorescent Organic Light-Emitting Diodes

Fluorene is a classic three-membered polycyclic aromatic hydrocarbon, and it has been widely used in optoelectronic devices. Here we explore a simple and efficient strategy for the derivatization at the 2- and 3- positions in fluorene unit. By introducing different types of substituents, we design two pairs of 2,3-disubstituted fluorene isomers and use them as host materials for phosphorescent organic light-emitting diodes (PHOLEDs). The green PHOLEDs hosted by these fluorene derivatives realize high external quantum efficiencies (EQE) over 20 % with low efficiency roll-off. Particularly, the devices hosted by 2TRz3TPA and 2TPA3TRz achieve nearly 24 % EQE and 104 lm W⁻¹ power efficiency. These results clearly demonstrate that the 2,3-disubstituted fluorene platforms are potentially useful for constructing host materials.     

Photoluminescent color tuning in fluorene derivative/copolymer composite films based on H-bonds

Reversible addition-fragmentation chain transfer (RAFT) polymerization is used to synthesize diblock and random copolymers of poly[(2-trifluoroethyl methacrylate)-co-(methacrylic acid)]. Copolymer films doped with fluorene derivatives comprised of pyridine groups exhibit reversible photoluminescent (PL) color tuning by adjusting the location of fluorene derivatives in H-bonds or non-H-bonds environments. The composite films exhibit green and blue photoluminescence with and without effective H-bonding between the pyridine ring in the fluorene derivative and the carboxylic acid side group, respectively. At elevated temperatures, the H-bonded structure dissociates and the fluorene derivative migrates to the hydrophobic block in the diblock polymer, and they do not form H-bonds upon cooling. However, re-formation of H-bonds also occurs upon cooling random copolymers. Moreover, adjusting the annealing temperature and the solvent annealing reversibly tunes the PL color in the diblock copolymer composite films.     

Kerr-effect in solutions and molecular polarity of liquid crystalline fluorenes

As part of a broader study of liquid crystal polymers with side groups containing fluorene moieties, more information was required about the properties of fluorene derivatives. With this aim in mind, the solution Kerr-effects for five fluorene-based mesogens have been measured and used in conjunction with other results to determine the polarizability anisotropies and dipole moments.     

The synthesis of blue emitting 3-Amino-1-hetarylfluorenes and their unprecedented alkylated derivatives

Novel 3-Amino-1-hetarylfluorene derivatives have medicinal uses and challenging transformation in organic synthesis have been synthesized via decyanation process. Surprisingly, the alkylated compounds derived from 3-Amino-1-hetarylfluorenes were obtained via further nucleophilic substitution to the 9-C and 3-N positions of the fluorene ring because of the harsh reaction condition employed. The synthesized compounds were characterized by spectroscopic techniques as well as X-ray single crystal diffraction analysis. This new family of blue emitting fluorene derivatives have low to moderate quantum yields (the largest value of Φ_F = 0.52 for compound 15).     

Synthesis,Design and Electrochemical Properties of Langmuir–Blodgett (LB) Films Built of Bis(Pyrrolyl)Fluorene

The synthesis, characterization, electropolymerization, electrical and sensing properties of LB films of mono‐ and dihexadecyl‐bis(pyrrolyl)fluorene derivatives are reported. Different responses to different gases at various concentrations obtained for mono‐ and disubstituted derivatives of bis(pyrrolyl)fluorene make these materials a very good candidates for elements of gas sensing devices of the different type of an “artificial nose” or a neuronic network.     

Study of the substituent groups effect on the room-temperature phosphorescent emission of fluorene derivatives in solution

We present here the first study of the effect of substituent groups and the chemical structure of fluorene derivatives on phosphorescent emission. A group of fluorene derivatives have been studied with a new methodology of room-temperature phosphorescence emission called heavy atom induced room-temperature phosphorescence (HAI-RTP). This methodology makes use of RTP emission directly from the compound in fluid solution, without a protective medium but only with the presence of high concentrations of heavy atom perturbers and an oxygen scavenger. These experimental conditions permit sufficient interaction between the perturbers and the phosphors to produce effective population of the triplet states of the latter and, consequently, intense phosphorescent emission. Good deoxygenation conditions are obtained using sodium sulfite as the oxygen scavenger. We show here that it is possible that many fluorene derivatives can exhibit RTP emission in aqueous solutions in the absence of a protective medium. Phosphorescence spectral characteristics of these compounds (excitation and emission wavelengths and lifetime) and the optimization of the chemical variables involved in the phosphorescence phenomenon are reported. Under optimal experimental conditions, calibration graphs and detection and quantification limits in the ng ml⁻¹ level have been established.     

6,12-二乙炔基茚并[1,2-b]芴系列衍生物的非线性光学性质

采用密度泛函理论(DFT) CAM-B3LYP方法对6,12-二乙炔基茚并[1,2-b]芴系列衍生物的极化率(α_s)和第二超极化率(γ_s)进行研究. 结果表明, 此类分子具有较大的γ_s值. 用乙炔基硅烷基和氧原子取代茚并[1,2-b]芴分子6,12位的氢原子后, 分子的几何构型发生改变, 进而影响其非线性光学(NLO)性质. 连接乙炔基硅烷基的分子α_s值和γ_s值均增大, 而连接氧原子的分子α_s值和γ_s值均减小. 茚并[1,2-b]芴环2,8位取代基R(R=H, F, CH₃)的不同, 对分子的γ_s值也有一定的影响, R为CH₃时分子的α_s值和γ_s值均较大. 由含时密度泛函理论(TD-DFT)方法计算的吸收光谱分析可知, 与茚并[1,2-b]芴系列分子相比, 引入乙炔基硅烷基的分子共轭性增强, 最大吸收波长红移; 引入氧原子的分子几何结构扭曲, 共轭性降低, 最大吸收波长蓝移.     

Star-like fluorene based polyamines: non-conjugated building blocks for light-harvesting materials

We report herein a series of novel tetramines (2-6) built using the fluorene core. The design features a diamine conjugated by a fluorene core and two non-conjugated triarylamines dangling through the bridge methine moiety. These polyamines are amorphous in nature and display moderate emission properties that are either dependent on the nature of the arylamine segments or reminescent of the fluorene backbone. The phenyl, naphthyl, fluorenyl and carbazolyl amine based materials are blue emissive while the pyrenylamine based compound emits yellow-green color. We demonstrate a possibility of using blue-emitting fluorene derivatives (2 and 4) blended with poly(N-vinylcarbazole) (PVK) to fabricate organic light emitting diodes (OLEDs). Emissions in the EL devices purely originated from the fluorene derivatives alone (blue) are contaminated with those of complex species (electromer/electroplex) formed by intermolecular interactions.     

An efficient one-pot synthesis of spiro dihydrofuran fluorene and spiro 2-hydroxytetrahydrofuran fluorene derivatives via [3+2] oxidative cycloaddition mediated by CAN

Spiro dihydrofuran fluorene derivatives were prepared via [3+2] oxidative cycloaddition of 1,3-dicarbonyl compounds to 9-benzylidene-9H-fluorene and 2-(9H-fluorene-9-ylidene)-1-phenylethanone derivatives mediated by ceric ammonium nitrate. In the case of the reaction of 9-benzylidene-9H-fluorene with acyclic 1,3-dicarbonyl compounds, spiro 2-hydroxytetrahydrofuran fluorene derivatives were obtained.     

Novel fluorene/fluorenone DNA and RNA binders as efficient non-toxic ds-RNA selective fluorescent probes

A series of structurally similar 1-substitued heteroaryl fluorene derivatives were prepared in a simple single step reaction, oxidized to fluorenones and then both, fluorenes and fluorenones, were methylated to enhance the solubility and increase the affinity to DNA/RNA. Interactions of both, fluorene and fluorenone analogues with various ds-DNA, ds-RNA revealed strong ds-DNA/RNA binding, and various thermal stabilization effects. Most intriguingly, some fluorene derivatives showed opposite fluorescence change (increase for ds-RNA and decrease for ds-DNA), which was not previously reported for any fluorene analogue. CD experiments along with other methods support ds-DNA minor groove binding and major groove ds-RNA binding. All compounds showed negligible interaction with G-quadruplex DNA. Very low cell cytotoxicity of studied compounds combined with very efficient cellular uptake makes these fluorescent dyes safe for laboratory applications. Moreover, especially compounds which show opposite fluorescence response to ds-DNA and ds-RNA, are promising lead compounds for further studies aimed toward ds-RNA-specific fluorescence markers.     

Palladium(0)-catalyzed cyclization of 1,6-diyn-3-yl carbonates with a nucleophilic functionality: efficient synthesis of polycyclic benzo[b]fluorene derivatives via allene intermediates

We report in this paper an interesting tandem reaction involving sequential palladium(0)-catalyzed decarboxylation of diynylic carbonates, intramolecular nucleophilic cyclization and Schmittel reaction, which provides a facile method for the synthesis of a variety of polycyclic benzo[b]fluorene derivatives from easily accessible starting materials.     

Preparation of chiral cholestanofluorene and its electron-rich derivatives for isolation of a stable cation-radical salt

A simple and practical synthesis of a variety of chiral fluorene derivatives is described where a cholestane moiety is attached to the carbon 9 of the fluorene ring system from readily available starting materials. An appropriately substituted fluorene derivative (i.e., R = OMe) forms a highly colored (chiral) cation-radical that can be isolated as robust hexachloroantimonate salt. Interestingly, the simplest cholestanofluorene (i.e., R = H) can also be transformed into a dibromo derivative (i.e., R = Br), a precursor to the (poly)cholestanofluorenes where the cholestane moieties will serve not only as groups that impart chirality but also allow them to be soluble in common organic solvents. The details of these works are described.     

Enantioselective synthesis of fluorene derivatives by chiral N-triflyl phosphoramide catalyzed double Friedel-Crafts alkylation reaction

A highly efficient tandem double Friedel-Crafts reaction between indoles and 2-formylbiphenyl derivatives by chiral N-triflyl phosphoramide was realized. Under mild conditions, various 9-(3-indolyl) fluorene derivatives have been obtained in good yield and up to 94% ee. Comparing to their corresponding chiral phosphoric acids, chiral N-triflyl phosphoramides catalyzed reactions led to products with opposite absolute configuration.