Fluorene Ring Research Articles

Enrichment of highly pure large-diameter semiconducting SWCNTs by polyfluorene-containing pyrimidine ring.

The use of copolymers to extract and purify semiconducting SWCNTs (sc-SWCNTs) and metallic SWCNTs (m-SWCNTs) is widely employed. In this paper, the performances of two pyrimidine-alt-dioctylfluorene conjugated polymers in the enrichment of semiconducting SWCNTs are compared, and the subtle structural effects on them are discussed. It was found that both pyrimidine-polymers were more effective in wrapping the semiconducting SWCNTs than the metallic SWCNTs under the co-action of the pyrimidine and fluorene rings. Moreover, methyl groups on the pyrimidine ring of the polymer slightly contributed to the semiconducting purity, and the minor differences of sc-SWCNTs extraction between two pyrimidine-polymers are compared. Additionally, the average diameter of the selected SWCNTs is larger than that of the raw SWCNTs. The experimental results show the excellent selectivity for sc-SWCNT from both co-polymers: the index Φi values for determining the purity of sc-SWCNTs were increased from 0.408 for P2 to 0.465 for P1, of which the selected sc-SWCNT purity is up to 99.9%. The resulting purity and the inexpensive availability of pyrimidine co-polymers make them suitable to be considered for effective sc-SWCNT enrichment.

Questions of Mirror Symmetry at the Photoexcited and Ground States of Non-Rigid Luminophores Raised by Circularly Polarized Luminescence and Circular Dichroism Spectroscopy: Part 1. Oligofluorenes, Oligophenylenes, Binaphthyls and Fused Aromatics.

We report experimental tests of whether non-rigid, π-conjugated luminophores in the photoexcited (S1) and ground (S0) states dissolved in achiral liquids are mirror symmetrical by means of circularly polarized luminescence (CPL) and circular dichroism (CD) spectroscopy. Herein, we chose ten oligofluorenes, eleven linear/cyclic oligo-p-arylenes, three binaphthyls and five fused aromatics, substituted with alkyl, alkoxy, phenyl and phenylethynyl groups and also with no substituents. Without exception, all these non-rigid luminophores showed negative-sign CPL signals in the UV-visible region, suggesting temporal generation of energetically non-equivalent non-mirror image structures as far-from equilibrium open-flow systems at the S1 state. For comparison, unsubstituted naphthalene, anthracene, tetracene and pyrene, which are achiral, rigid, planar luminophores, did not obviously show CPL/CD signals. However, camphor, which is a rigid chiral luminophore, showed mirror-image CPL/CD signals. The dissymmetry ratio of CPL (glum) for the oligofluorenes increased discontinuously, ranging from ≈ −(0.2 to 2.0) × 10−3, when the viscosity of the liquids increased. When the fluorene ring number increased, the glum value extrapolated at [η] = 0 reached −0.8 × 10−3 at 420 nm, leading to (–)-CPL signals predicted in the vacuum state. Our comprehensive CPL and CD study should provide a possible answer to the molecular parity violation hypothesis arising due to the weak neutral current mediated by the Z0-boson.

(Sila)Difluoromethylation of Fluorenyllithium with CF3H and CF3TMS

Difluoromethylation of the C9-H site of the fluorene ring using lithium base and fluoroform (CF3H), which is one of the most cost-effective difluoromethylating reagents, is attained to give difluoromethylated fluorenes with an all-carbon quaternary center. The Ruppert–Prakash reagent (CF3TMS) can also be applied to the present reaction system, providing siladifluoromethylated fluorenes that can be utilized for sequential carbon–carbon bond-forming reactions through activation of the silyl group.

Synthesis, Structure and Anion Sensing Properties of a Dicationic Bis(imidazolium)‐Based Cyclophane

AbstractThe preparation and sensing properties of a tetracyclic cyclophane receptor containing two imidazolium rings as anion binding sites and two fluorene rings as fluorescent signaling units, are reported. The receptor behaves as a selective fluorescent chemosensor molecule for inorganic phosphates. 1H‐NMR spectroscopical data clearly indicate the simultaneous occurrence of charge‐assisted aromatic and aliphatic C−H noncovalent interactions. PCM/DFT calculations have been carried out to predict the structures of the complexes formed with one and two molecules of PF6−, H2PO4− and HP2O73−

Molecular weight-dependent physisorption of non-charged poly(9,9-dioctylfluorene) onto the neutral surface of cuboidal γ-alumina in toluene

To understand how polymers physisorb onto solid surfaces, we investigated the physisorption behavior of non-charged, semiflexible poly(9,9-dioctylfluorene) (PF8) with three different number-average degrees of polymerization (DPn) as photoluminescent and chromophoric probes onto cuboidal γ-alumina in toluene at 5, 25, and 50 °C. PF8 revealed noticeable DPn and temperature dependencies in its physisorption behaviors. Molecular mechanics (MM)/molecular dynamics (MD) simulations [consistent valence force field (CVFF)] and Moller–Plesset second-order perturbation theory (MP2) with 6-31 G(d,p) calculations suggested that the PF8 in toluene has multiple interactions from CH/π to C–H/O interactions on the (110) surface of γ-alumina. The competition between multiple intermolecular CH/π and C–H/O interactions was crucial for the spontaneous physisorption of PF8 to occur in the presence of a solvent quantity of toluene. Calculations by time-dependent density functional theory (TD-DFT) with Becke three parameter Lee-Yang-Par (B3LYP) method and 6–31 G(d,p) basis set of a model fluorene 9-mer indicated that the π–π* absorption wavelength largely depends on the regularity of the dihedral angles between fluorene rings, while the intensity and spectral width of the π–π* absorption band are largely influenced by the regularity of the dihedral angles. Solution-phase physisorption systems are a result of the inherent nature of several competitive weak intermolecular interactions coexisting among the polymers, surface, and solvents. Noticeable molecular weight and temperature dependency for physisorption behavior of semiflexible, non-charged poly(9,9-n-dioctylfluorene) (PF8) onto cuboidal γ-alumina in toluene were found. MM/MD simulations (CVFF) and quantum mechanical (MP2/6-31G(d,p)) calculations suggested that PF8 swaps interacting toluene for (110) surface of γ-alumina by changing the interaction from CH/π interactions to C-H/O interactions of γ-alumina in toluene. The competition between multiple intermolecular CH/π and C-H/O interactions was crucial whether the spontaneous physisorption of PF8 occurs in place of solvent quantity of toluene. The solution-phase physisorption systems should be the consequence of several weak attractive intermolecular interactions coexisting between polymers, surface, and solvents

Effect of deprotonation on the magnetic exchange coupling constant of fluorene‐based verdazyl diradical: A computational study

AbstractThe magnetic behavior of the fluorene bridged verdazyl diradicals has been studied theoretically in their neutral and deprotonated states. The deprotonation of C9‐H site of the fluorene ring opens a new coupling pathway, which changes the nature of magnetic coupling. The transmission spectra analysis reveals that the transmission through fluorine has also increased due to the opening of a new coupling path after deprotonation.

New 3D-stereoconfigurated cis-tris(fluorenylphenylamino)-benzene with large steric hindrance to minimize π–π stacking in thin-film devices

Highly fluorescent trans- and cis-tris(fluorenylphenylamino)benzene stereo-isomeric derivatives, trans- and cis-tris(DPAF-C9), respectively, were designed and synthesized to minimize facile planar fluorene ring stacking in the solid state during thin-film device fabrications. Resulting tris-cup cis- and tris-chair trans-conformers were hypothesized to be capable of reducing direct packing contact of light-harvesting fluorene moieties from each other that should reduce the aggregation-related self-quenching effect derived from the π–π stacking packing arrangement. By the fact of closely matching photophysical characteristics of them to those of poly(N-vinylcarbazole) (PVK), we applied the former conformer as the secondary blue hole-transporting material in the study of its electroluminescence properties, using a tricomponent system of PVK‒cis-tris(DPAF-C9)‒tris(2-phenylpyridine)iridium (III) [Ir(ppy)3], as an example. Accordingly, several prototype single-layered or multilayered devices were fabricated with their electroluminescence and external quantum efficiency demonstrated. These analogous 3D-stereoconformers can also be used in other fluorescence-related thin-film applications.

Investigation of the Intra-CH/π Interaction in Dibromo-9,9′-dialkylfluorenes

Polyfluorenes are well-known derivatives that exhibit electrical conductivity, electroluminescence, and liquid crystallinity, but its crystallization process is not well understood. To investigate the role of intra-CH/π interaction in the process, 2,7-dibromo-9,9′-dialkylfluorenes (DBFs) with various dialkyl side chains (alkyl group = methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, 2-methylpropyl, and 2-ethylbutyl) were prepared. Systematic observation of the single-crystal structure revealed that DBF with a methyl group does not possess intra-CH/π interactions, whereas DBFs with straight side chains that are equal to or longer than an ethyl group exhibit CH/π interactions between Hβ and the fluorene ring. For DBFs with branched side chains, one Hβ and one Hγ interact with the fluorene ring. The computations at the MP2/cc-pVTZ//MP2/6-31G(d) level with a polarizable continuum model revealed that the close proximity of Hγ and the fluorene ring in the branched DBF crystals was caused by the geo...

Packing of Large Two- and Three-Photon Activity Into Smallest Possible Unsymmetrical Fluorene Chromophores.

The quantum chemical study of one-, two-, and three-photon absorption (1PA, 2PA, and 3PA) properties for a set of compact fluorene derivatives (FD) with combination of different donor and acceptor moieties on both sides of fluorene ring system is presented. The main goal of the study is to pack large two-photon (2P) and three-photon (3P) activity into smallest possible chromophore. Linear, quadratic, and cubic response time-dependent density functional theory was used to calculate 1PA, 2PA, and 3PA properties, respectively. We used CAMB3LYP/cc-pVDZ level of theory for all the property calculations. The 2P and 3P transition probabilities were recalculated using two-state model approach and found to be in good agreement with the response theory results for first excited state. To include the contributions from higher states, the three-state model was also employed to recalculate the 2P transition probabilities and found to be in excellent agreement with response theory. The 2P/3P tensor elements were also analyzed to find reasons behind large 2P/3P activities. All the orbitals involved in transition processes were studied in detail by both molecular orbital pictures (qualitatively) and overlap diagnostic Λ-values (quantitatively). The study reveals that the novel fluorene derivatives FD-12 and FD-13 have shown large 2PA cross-section values of 1100 G.M. and 1030 G.M.; and 3PA transition probabilities of 6.10 × 10(10) a.u. and 4.85 × 10(10) a.u., respectively, for transition S0 → S1. The largest 3PA transition probability of 4.04 × 10(11) a.u. was found with FD-12 for S0 → S2 excitation. The linear relationship between Λ-values and 2PA cross-section values was also studied.

Design, synthesis and properties of near-infrared molecular switches containing a fluorene ring.

Three molecular switches containing a fluorene ring were designed and synthesized. The introduction of the amino group substituted fluorene ring resulted in the target molecular switches having some optical properties in the near-infrared region. It was demonstrated that the N-substituents on the fluorene rings and the switch units both had great influence on the molecular switch optical properties including the absorption maximum, absorption intensity and fluorescence quantum yield. The open-ring forms and showed obvious solvatochromic behaviour. The closed-ring forms and showed obvious hydrochromic behaviour in MeCN/water binary solvent systems and acidichromic behaviour in MeCN solution with high reversibility. Especially, the distinct off-on fluorescence signal in the near-infrared region using the stimuli of acid means that the designed compounds have great potential application value in the field of biological sensing.

New low band-gap conjugated organic materials based on fluorene, thiophene and phenylene for photovoltaic applications: Theoretical study

We use the density functional theory (B3LYP/6-31G(d)) to determine structural parameters band gap, absorption and photovoltaic properties of several conjugated organic materials. The chemical structure of these molecules contains fluorene, thiophene and phenylene rings, together with different unities (e.g. Ethylenedioxythiophene EDOT). The theoretical calculations were performed by using Gaussian 09 program supported by GaussView 5.0.8 Interface. The results reveal that the geometrical parameters (dihedral angles, bond lengths) of all molecules possess nearly planar conformations.Moreover, the optoelectronic properties (HOMO, LUMO, Egap…) were determined from the fully optimized structures by using B3LYP/6-31G(d) level. The absorption data (λmax, Etr, OS) of these systems were obtained by TD-B3LYP/6-31G(d) method.The studied molecules Mol-i (with i = 1-6) have low band-gaps with appropriate energy levels of HOMO and LUMO which are desired in photovoltaic applications, especially the Molecules with acceptor unities in their chain. We conclude that these materials are good candidates for bulk heterojunctions used in organic solar cells.

Ring-Expanded Phthalocyanines Fused with Fluorene Skeleton for Light-Harvesting in the Near-IR Region

Organic photovoltaic devices (OPVs) based on thin films of organic semiconductors have been intensely investigated as a promising candidate for low-cost, lightweight, and scalable solar cells. While OPVs have achieved high conversion efficiencies, their organic semiconductors mainly absorb the light in visible range. To enhance their efficiency, the expansion of light-harvesting range is a key issue in this field. Phthalocyanines (Pcs) and their metal complexes (MPcs), synthetic porphyrin analogues, have been widely investigated as near-IR absorbing dyes because of their intense Q band (600-700 nm), high molar extinction coefficients (e > 100000 M-1 cm-1), and excellent thermal, chemical, and photolytic stabilities. The electronic structure and properties of MPcs can be tailored by modifying the macrocyclic ligands and changing the central metals [1]. We present here designed and synthesized novel ring-expanded zinc phthalocyanine (ZnFc , Figure1), in which four fluorene rings were fused with porphyrazine ring. Fusing fluorene rings with the porphyrazine rings lead to red-shifting the Q band and tailoring of the HOMO and LUMO energy levels as well as an expansion of p-system. We demonstrated the expansion of the light-harvesting area in BHJ solar cells based on poly(3-hexylthiophen) (P3HT) and 1-(3-methoxycalbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) by co-sensitizing with ZnFc. When the ZnFc decorated with eight alkyl chains was added to P3HT/PCBM BHJ solar cells, the solar cells showed a higher device efficiency with 16 % enhancement of JSC as compared with that of the reference P3HT/PCBM BHJ solar cells due to the expansion of light-harvesting range [2]. We also synthesized an asymmetrical fluorene-fused phthalocyanine (FcS1, Figure1), which containing three fused fluorene rings and one carboxylic acid. FcS1 indicated a potential for near-IR sensitizer in DSSCs. The absorption spectrum of FcS1 adsorbed onto a nano-crystalline TiO2 film suggested the formation of J-aggregation with tilted orientation of macrocyclic ligands. While the DSSC cells sensitized by FcS1 showed a modest efficiency of 3.2 % under simulated air mass 1.5 global sunlight, FcS1 could convert the red and near-IR light regions between 600 and 860 nm [3]. Reference [1] J. Mack, N. Kobayashi, Chem. Rev. 2011, 111, 281-321. [2] S. Yamamoto, M. Kimura, ACS Appl. Mater. Interfaces 2013, 5, 4367-4373. [3] S. Yamamoto, T. Ikeuchi, S. Mori, M. Kimura, Asian J. Org. Chem. 2014, 10, 1083-1088. Figure 1

Carbon Anionic Chiral Initiators for Asymmetric Anionic Polymerization of Achiral Isocyanates.

Novel optically active carbon anionic initiators bearing a chiral oxazole substituent on fluorene ring, (S)-1-(9H-fluoren-2-yl)-4-isopropyl-4, 5-dihydrooxazole lithium ((S)-1-FIDD-Li) and (S)-2-(9H-fluoren-2-yl)-4-isopropyl-4, 5-dihydrooxazole lithium ((S)-2-FIDD-Li), were synthesized. Anionic polymerizations of achiral polyisocyanates with the chiral initiators were investigated and optical rotation of the obtained polymers were attributed to asymmetric induction of the chiral initiators. The crowded substituent of initiator ((S)-2-FIDD-Li) seems to reduce the polymerizability of isocyanates and yet enhances the chiral induced ability in polymerization.

Homopolymerization and copolymerization of N‐substituted maleimides with chiral anionic initiators

AbstractNovel optically active anionic initiators bearing a chiral oxazole substituent on the fluorene ring, (S)‐1‐(9H‐fluoren‐2‐yl)‐4‐isopropyl‐4,5‐dihydrooxazole lithium (Li‐(S)‐1‐FIDH) and (S)‐2‐(9H‐fluoren‐2‐yl)‐4‐isopropyl‐4,5‐dihydrooxazole lithium (Li‐(S)‐2‐FIDH), were prepared. Anionic homopolymerizations of achiral N‐substituted maleimide (RMI) with the chiral initiators were investigated. The optically active polymers obtained were attributed to asymmetric induction of the chiral initiators. The very crowded chiral initiator Li‐(S)‐1‐FIDH was found to play a better asymmetric induction role in the polymers than Li‐(S)‐2‐FIDH. Anionic copolymerization of (R)‐(+)‐N‐1‐phenylethyl maleimide and optically inactive RMI with Li‐(S)‐1‐FIDH were also studied. © 2014 Society of Chemical Industry

Light-Harvesting in the Near-Infrared Region: Dye-Sensitized Solar Cells Sensitized with Asymmetric Ring-Expanded Zinc(II) Phthalocyanines

A near-IR absorbing dye (FcS1), in which three fluorene rings were fused with a porphyrazine ring, has been designed and synthesized as a photosensitizer for dye-sensitized solar cells (DSSCs). The fusion of the fluorene rings led to tailoring of the HOMO and LUMO energy levels as well as an expansion of the π-system. The absorption spectrum of FcS1 adsorbed onto a nanocrystalline TiO2 film suggested the formation of J-aggregates with tilted orientation of the macrocyclic ligands. While the power conversion efficiency of DSSCs sensitized with FcS1 was a modest 3.2 % under simulated air mass 1.5 global sunlight, FcS1 can convert the red and near-IR light regions between 600 and 860 nm into electricity.

Synthesis and structure–activity relationships of new carbonyl guanidine derivatives as novel dual 5-HT2B and 5-HT7 receptor antagonists. Part 2

We previously reported that the novel dual 5-HT2B and 5-HT7 receptor antagonist N-(9-hydroxy-9H-fluorene-2-carbonyl)guanidine (4) exerted a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs. To develop a synthetic strategy, we performed docking studies of lead compound 4 bound to 5-HT2B and 5-HT7 receptors, and observed that the carbonyl guanidine group forms a tight interaction network with an active center Asp (D135:5-HT2B, D162:5-HT7), Tyr (Y370:5-HT2B, Y374:5-HT7) and aromatic residue (W131:5-HT2B, F158:5-HT7). Based on molecular modeling results, we optimized the substituents at the 5- to 8-position and 9-position of the fluorene ring and identified N-(diaminomethylene)-9-hydroxy-9-methyl-9H-fluorene-2-carboxamide (24a) exhibits potent affinity for 5-HT2B (Ki=4.3nM) and 5-HT7 receptor (Ki=4.3nM) with high selectivity over 5-HT2A, 5-HT2C, α1, D2 and M1 receptors. Compound 24a reversed the hypothermic effect of 5-carboxamidotryptamine (5-CT) in mice and also showed a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs when orally administered at 30mg/kg. Compound 24a is therefore a promising candidate for a novel class of anti-migraine agent without any adverse effects.

Synthesis and characterization of polybrominated fluorenes and their conversion to polyphenylated fluorenes and cyclopenta[def]triphenylene

We report the synthesis and characterization of polyphenylated fluorene derivatives and a ring cyclized product containing cyclopenta[def]triphenylene core. Polybromination on fluorene was achieved either by solid state reaction with bromine or utilizing Br2/KBrO3 in AcOH/H2SO4 mixture. The bromofluorenes were converted to the corresponding polyphenylated fluorenes by Suzuki coupling protocol. A hexabromofluorene underwent a multifold Suzuki coupling followed by C–H activation to produce a cyclopenta[def]triphenylene derivative. Fluorene ring showed a severe distortion from planarity beyond tetra-substitution which manifested in the optical properties.

Fluoren-9-one oxime.

In the title mol­ecule, C13H9NO, the fluorene system and the oxime group non-H atoms are essentially coplanar, with a maximum deviation from the fluorene mean plane of 0.079 (2) Å for the oxime O atom. A short intra­molecular C—H⋯O generates an S(6) ring. In the crystal, mol­ecules related by a twofold screw axis are connected by O—H⋯N hydrogen bonds, forming [100] chains Within these chains, mol­ecules related by a unit translation along [100] show π–π stacking inter­actions between their fluorene ring systems with an inter­planar distance of 3.347 (2) Å. The dihedral angle between the fluorene units of adjacent mol­ecules along the helix is 88.40 (2)°. There is a short C—H⋯π contact between the fluorene groups belonging to neighbouring chains.

2,2'-Bi(9,9-di-ethyl-fluorene).

The title compound, C34H34, systematic name 9,9,9′,9′-tetra­ethyl-2,2′-bi(9H-fluorene), crystallized with two crystallographically independent mol­ecules (A and B) in the asymmetric unit. These differ mainly in the orientation of the lateral ethyl chains: in mol­ecule A, they are both on the same side of the mol­ecule whereas in mol­ecule B, one di­ethyl­fluorene moiety has undergone a 180° rotation such that the two pairs of ethyl residues appear on opposite sides of the mol­ecule. The fluorene ring systems subtend dihedral angles of 31.37 (4) and 43.18 (3)° in mol­ecules A and B, respectively. Hence the two fluorene moieties are tilted slightly toward one another. This may be due to the presence of inter­molecular C—H⋯π inter­actions between neighboring mol­ecules. The lateral ethyl chains (excluding H atoms) are also almost planar, with each pair almost perpendicular to the plane of the fluorene system to which they are attached with dihedral angles between the ethyl and fluorene planes in the range 86.04 (8)–89.5 (1)°.

N-[(9H-Fluoren-9-yl-idene)(2-meth-oxy-phen-yl)meth-yl]-1,1,1-tri-methyl-silanamine.

The title mol­ecule, C24H25NOSi, is a hydrolysis product of the reaction between 9-tri­methyl­silyfluorenyl lithium and 2-meth­oxy­benzo­nitrile. The fluorene ring system is substanti­ally planar, with an r.m.s. deviation of 0.0288 Å from the best-fit plane through its 13 C atoms. This plane forms a dihedral angle of 58.07 (7)° with the 2-meth­oxy­benzyl­amine ring plane. In the crystal, mol­ecules are linked by N—H⋯π and C—H⋯π inter­actions, which leads to the formation of two-dimensional network lying parallel to the bc plane.