Fluorene Chromophore Research Articles

Photo-degradation of Di- and Trifunctional Oxime Ethers Bearing Polyphthalaldehyde Arms

Polyphthalaldehyde (PPA) is a representative degradable polymer that can be end-to-end depolymerized. Herein polymers bearing two and three PPA chains have been prepared, and their photochemical behaviors were investigated. The PPA chains were linked to fluorene and truxene cores via oxime ether units that are photoreactive moiety. Di- and trifunctional PPAs were obtained by anionic polymerization of phthalaldehyde monomer (o-PA) initiated by corresponding oximes and 1,8-diazabicyclo[5.4.0]undec-7-ene, even though the conversion of was low after purification. From the 1H NMR spectral changes of CDCl3 solutions of both PPA on irradiation with Hg-Xe lamp, it was found that PPAs decreased along with the formation of o-PA, and then the o-PA reduced along with the formation of phthalide. PPAs were also coated on CaF2 substrates and irradiated with the lamp. UV spectral changes of the films showed the photochemical reaction of oxime ether moieties, and IR spectral changes indicated the formation of phthalide. These results clearly show that depolymerization and following photo-isomerization into phthalide proceeded both in solution and solid state. 2,7-Diacetylfluorene O,O'-dibenzyldioxime was newly prepared to discuss the photochemical reaction of oxime ether with fluorene chromophore.

New Electroactive Polymers with Electronically Isolated 4,7-Diarylfluorene Chromophores as Positive Charge Transporting Layer Materials for OLEDs.

A group of polyethers containing electroactive pendent 4,7-diarylfluorene chromophores have been prepared by the multi-step synthetic route. Full characterization of their structures has been presented. The polymeric materials represent derivatives of high thermal stability with initial thermal degradation temperatures in a range of 392–397 °C. Glass transition temperatures of the amorphous polymers range from 28 °C to 63 °C and depend on structures of the 4,7-diarylfluorene chromophores. Electron photoemission spectra of thin layers of the electroactive derivatives showed ionization potentials in the range of 5.8–6.0 eV. Hole injecting/transporting properties of the prepared polymeric materials were confirmed during formation of organic light-emitting diodes with tris(quinolin-8-olato)aluminium (Alq3) as a green emitter, which also serves as an electron transporting layer. The device using hole-transporting polymer with electronically isolated 2,7-di(4-biphenyl)fluorene chromophores demonstrated the best overall performance with low turn on voltage of 3 V, high current efficiency exceeding 1.7 cd/A, and with maximum brightness over 200 cd/m2. The organic light-emitting diode (OLED) characteristics were measured in non-optimized test devices. The efficiencies could be further improved by an optimization of device structure, formation conditions, and encapsulation of the devices.

Poly(azomethine-phenothiazine)s with efficient emission in solid state

A series of poly(azomethine-phenothiazine)s was synthesized by using the reaction of 10-methyl-phenothiazine-3,7-dicarbaldehyde with diamines containing fluorene chromophore or polyethylene glycol (PEG) flexible spacer. The polymers were structurally characterized by 1H NMR and FTIR spectral techniques, elemental analysis and wide angle X-ray diffraction. Their thermal properties were monitored by using variable temperature polarized light microscopy whilst their photophysical behaviour was demonstrated by using UV–vis absorption and photoluminescence spectroscopy. All of these polymers were found to emit green light with high quantum yield, in both solution and solid state. The emission efficiency in solid state was further improved by mixing the fluorene containing polymers with the PEG containing one, when continuous films with quantum efficiency of up to 16% were obtained.

Synthesis and spectral properties of fluorene substituted cyclic and polymeric phosphazenes

Two new fluorene chromophores were prepared by the Suzuki cross-coupling reactions of 9,9-dimethylfluorene-2-boronic acid pinacol ester with bromophenol or 3,5-dibromophenol, respectively. The cyclic compounds were obtained by the reactions of chromophores with hexachlorocyclotriphosphazene (N3P3Cl6). For the comparison of spectral properties of cyclic compounds, the poly(bis-fluorenyl)phosphazene was also prepared from nucleophilic displacement reactions of chromophore with polydichlorophosphazene (Cl2PN)n. The synthesized compounds were characterized by standard spectroscopic methods (MALDI-TOF mass spectrometry, gel permeation chromatography for poly(bis-fluorenyl)phosphazene, FT-IR, 1H, 13C and 31P NMR spectroscopy) and their structure was confirmed by elemental analysis. The spectral properties were analysised by UV–Vis and fluorescence spectroscopy, thermogravimetric analysis, differential scanning calorimetry and cyclic voltammetry.

Synthesis and morphology of new asymmetric star polymers of poly[4-(9,9-dihexylfloren-2-yl)styrene]-block-poly(2-vinylpyridine) and their non-volatile memory device applications

We report the synthesis, morphology, and properties of new 3-arm AB22 and 5-arm AB44 asymmetric amphiphilic star polymers of poly[4-(9,9-dihexylfloren-2-yl)styrene]-block-poly(2-vinylpyridine) (P(St-Fl)-b-P2VP), with narrow molecular weight distributions (Mw/Mn < 1.11). The asymmetric star polymers were synthesized by living anionic polymerization using 1,1-diphenylethylene (DPE)-functionalized P(St-Fl) with two or four benzyl bromide moieties, followed by linking reaction with a living anionic P2VP. Depending on the arm numbers of P2VP, lamellar and hexagonally perforated lamellae morphologies were observed for the AB22 and AB44P(St-Fl)-b-P2VP from the results of SAXS, WAXS, and TEM. The [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) incorporated in the polymer matrix increased the order degree of the liquid-crystal-like morphology in the P(St-Fl) block. The prepared AB22 and AB44P(St-Fl)-b-P2VP could be blended with PCBM for electrical write-once-read-many times (WORM) memory devices application. The threshold voltage (−2.8 to −3.9 V) and ON/OFF ratio (103 to 106) of the WORM characteristic were obtained by tuning the PCBM content. The ON or OFF state of the WORM memory devices could remain over 104 s without any degradation. The optical absorption and photoluminescence results indicated the formation of charge transfer complexation between PCBM and the 2-vinylpyridine or pendent fluorene chromophores. The switching behavior was further explained by the charge injection dominated thermionic emission in the OFF state and field-induced charge transfer in the ON state. These experimental results provide a new strategy to prepare a conjugated moiety containing asymmetric star polymers and their potential electrical memory device applications.

Vectorial Photoinduced Energy Transfer Between Boron–Dipyrromethene (Bodipy) Chromophores Across a Fluorene Bridge

A series of novel multichromophoric, luminescent compounds has been prepared, and their absorption spectra, luminescence properties (both at 77 K in rigid matrix and at 298 K in fluid solution), and photoinduced intercomponent energy-transfer processes have been studied. The series contains two new multichromophoric systems 1 and 2, each one containing two different boron-dipyrromethene (Bodipy) subunits and one bridging fluorene species, and two fluorene-Bodipy bichromophoric species, 6 and 7. Three monochromophoric compounds, 3, 4, and 5, used as precursors in the synthetic process, were also fully characterized. The absorption spectra of the multichromophoric compounds are roughly the summation of the absorption spectra of their individual components, thus demonstrating the supramolecular nature of the assemblies. Luminescence studies show that quantitative energy transfer occurs in 6 and 7 from the fluorene chromophore to the Bodipy dyes. Luminescence studies, complemented by transient-absorption spectroscopy studies, also indicate that efficient inter-Bodipy energy transfer across the rigid fluorene spacer takes place in 1 and 2, with rate constants, evaluated by several experimental methods, between 2.0 and 7.0 x 10(9) s(-1). Such an inter-Bodipy energy transfer appears to be governed by the Förster mechanism. By taking advantage of the presence of various protonable sites in the substituents of the lower-energy Bodipy subunit of 1 and 2, the effect of protonation on the energy-transfer rates has also been investigated. The results suggest that control of energy-transfer rate and efficiency of inter-Bodipy energy transfer in this type of systems can be achieved by an external, reversible input.

Synthesis and Physical Properties of Polyfluorene Derivative with Imidazolium Units

A new polyfluorene derivative (PF-ImBr) with imidazole cations as side chains was synthesized to achieve a bidirectional photo-electro conversion by single-component polymer light-emitting electrochemical cell and photovoltaic cell with frozen p-i-n junction at room temperature. Various physical properties of this polymer such as UV-vis absorption and fluorescence spectra, transient absorption, fluorescence lifetime, and thermograms were studied. The optical band gap value of PF-ImBr was estimated as 2.9 eV. The transient absorption spectra and fluorescence lifetime results strongly suggested no electronic interactions between fluorene chromophores in the main chain and imidazolium cations in the side chain. PF-ImBr film with a fluorescent chromophore and two cations in the repeating units can form a single component frozen p-i-n junction after being heated above 130°C.

Metal−Organic Framework Based on [Zn4O(COO)6] Clusters: Rare 3D Kagomé Topology and Luminescence

A 2-fold interpenetrated metal−organic framework displaying intense yellow fluorescence is constructed from [Zn4O(COO)6] clusters and a new dicarboxylate ligand bearing the fluorene chromophore fluorene-2,7-dicarboxylic acid. The [Zn4O(COO)6] secondary building unit exhibits unusual coordination features and leads to the rare 3D pillared kagome net topology (324865).

Synthesis of Dendritic Oligo-Spiro(fluorene-9,9′-xanthene) Derivatives with Carbazole and Fluorene Pendants and their Thermal, Optical, and Electroluminescent Properties

Two novel spiro-configured ter(arylene-ethynylene) derivatives, TSF-Cz and TSF-F, have been designed and synthesized using spiro(fluorene-9,9'-xanthene) (SFX) as building blocks, introducing a hole-transporting carbazole and a fluorene chromophore as the peripheral functional group into the backbone through an oxygen atom. The two well-defined oligomers possess good solubility, film-forming quality, and high T(g) 's at 140 and 126 °C, respectively. In addition, these oligomers exhibit blue photoluminescence (PL) emission both in solution and solid states. The double-layered devices fabricated using the two materials as the emitter show a sky-blue emission with a brightness and a current efficiency of 7 613 cd · m(-2) and 1.11 cd · A(-1) for TSF-Cz, and 1 507 cd · m(-2) and 0.36 cd · A(-1) for TSF-F, respectively.

Fluorene–fullerene dyads: Modulation of interaction

Two new fullerene[C 60]–fluorene dyads, N-methyl-2-(9-fluorenyl)-3,4-fulleropyrrolydine and N-methyl-2-(2-fluorenyl)-3,4-fulleropyrrolydine, were synthesized and investigated. Cyclic voltammetry, fluorescence experiments, electronic spectra and Density Functional Theory (DFT) calculations, all indicate ground and excited state interactions when fluorene is linked at carbon 9, whereas linkage through position 2 does not affect the ground and excited state of the fulleropyrrolidine moiety. As a consequence, only changing the position of the fluorene chromophore linkage, opens the way to modulate interactions, choosing between a simple spacer and an active unit.

Morphology and properties of a polyrotaxane based on γ-cyclodextrin and a polyfluorene copolymer

The effect of complexation of a poly[2,7-(9,9-dioctylfluorene- alt-2,7-fluorene)] copolymer into the inner cavity of γ-cyclodextrin on the morphology, the optical and the electrical properties was investigated. The fluorescence spectra of the rotaxane copolymer and of a reference, non complexed copolymer exhibit typical well resolved blue emission bands arising from the fluorene chromophore units. The complexation of the fluorene copolymer chain increases the fluorescence lifetime from 0.54 to 0.59 ns and decreases the activation energy of the electrical conduction from 2.41 to 1.49 eV. The rotaxane copolymer presents higher semiconducting properties as compared to the reference copolymer.

Polyfluorene copolymer with a multiply blocked rotaxane architecture in the main chain: Synthesis and characterization

AbstractTo improve the physical properties of polymer materials, a novel copolymer with a multiply blocked rotaxane architecture in the main chain was synthesized through Suzuki dehalogenative polycondensation from a 2,7‐dibromofluorene/γ‐cyclodextrin (γ‐CD) inclusion complex and 9,9‐dioctylfluorene‐2,7‐trimethylene diborate in the presence of a tetrakis(triphenylphosphine)palladium(0) catalyst. As demonstrated by computational calculations, the dioctyl groups were large enough to prevent the dethreading of γ‐CD molecules. A copolymer polyrotaxane with a γ‐CD/structural unit ratio as high as 1/1.4 and a bimodal molecular weight distribution was obtained, as proved by its 1H‐NMR spectrum and size exclusion chromatography curve, respectively. The polyrotaxane showed lower thermal stability and higher solubility in polar solvents in comparison with the noncomplexed homologue. The fluorescence spectra of both the complexed and noncomplexed copolymers exhibited typical well‐resolved blue emission bands that arose from the fluorene chromophore units. In dimethylformamide solutions, the ratio of the intensities of the peaks of the emission spectra (emission spectra intensities413 for the 0–0 band and emission spectra intensities437 for the 0–1 band) was higher for the polyrotaxane than the noncomplexed copolymer, and this demonstrated a reduced quenching effect of the environment induced by the protection of the polymer chain by the macrocycle. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and characterization of fluorene end-labeled polymers prepared by nitroxide-mediated polymerization

The fluorene-based alkoxyamine 9-(2,2,6,6-tetramethyl-4-hydroxypiperidinyloxy)fluorene was prepared and investigated as a unimolecular initiator in the nitroxide-mediated polymerization (NMP) of styrene. Reactions performed in either bulk or ethereal solvents at 125°C generated polymers possessing low polydispersity indices (PDIs) and number average molecular weight (Mn) values close to those anticipated based on monomer-to-initiator ratios. A linear relationship between monomer conversion and Mn values was observed by analysis of reaction aliquots with 1H NMR and gel permeation chromatography (GPC), while PDI values remained low throughout. Analysis of the polymers by UV–vis spectroscopy indicated that approximately 80% of the polymer chains were labeled with the fluorene chromophore, while fluorescence spectroscopy was used to verify that the fluorene was polymer-bound.

A Chemical/Computational Approach to the Determination of Absolute Configuration of Flexible and Transparent Molecules: Aliphatic Diols As a Case Study

By reacting flexible and optically transparent in UV-vis molecules such as 1,2-, syn- and anti-1,3-diols, 1,3-sulfanylalcohols of known absolute configuration (AC) with fluorenone dimethyl acetal, the corresponding ketals are obtained. They are conformationally well-defined (only one conformer in most cases) compounds exhibiting medium-high optical rotation (OR) values, which are independent of the solvent, and electronic circular dichroism (ECD) spectra, which show several (up to five) Cotton effects in the 350-200 nm range due to valence shell pi-->pi* transitions. These features allow simulation of the chiroptical properties of these compounds at the TDDFT/B3LYP/6-31G* level of theory to obtain, using the known ACs of these compounds, a satisfactory reproduction of the OR values (sign and order of magnitude; quantitatively, the predicted values are twice the experimental ones), and a more than satisfactory reproduction of the ECD spectra (sign, intensity, and position of the lowest-energy four Cotton effects) for all the compounds studied. Therefore, this approach can be used to assign the AC of such flexible molecules, in particular, syn-1,3-diols, which are important substrates in organic synthesis and for which nonempirical methods of AC assignment have not been devised so far. Furthermore, since the fluorene chromophore leads to the presence of several Cotton effects from, say, 350 to 200 nm, their correct simulation of sign, intensity, and position is a guarantee of the correct assignment of AC: in this way, ECD spectroscopy gains the same advantages of VCD spectroscopy, that is, the need of reproducing many ECD bands and then a solid guarantee of a correct AC assignment.

Large Cross-Section Enhancement and Intramolecular Energy Transfer upon Multiphoton Absorption of Hindered Diphenylaminofluorene-C60 Dyads and Triads

Sterically hindered fullerenyl chromophore dyad and triads, C60(>DPAF-C9)x (x = 1 and 2, respectively), in an acceptor−donor (A−D) molecular linkage of C60-(keto-fluorene)x were synthesized and fully characterized. Attachment of two 3,5,5-trimethylhexyl groups on C9 of the fluorene ring moiety greatly improves their solubility and makes direct intermolecular aromatic stacking contacts more difficult. They are the first series of fullerene derivatives showing high three-photon absorptivity (3PA). Accordingly, C60(>DPAF-C9)2 exhibits 2PA and 3PA cross sections in the values of 0.824 × 10-48 cm4 s (or 82.4 GM) and 6.30 × 10-25 cm6/GW2, respectively, in femtosecond region among the highest ones reported for many diphenylaminofluorene-derived AFX chromophores. Utilization of a keto linker located immediately between C60 cage and fluorene chromophore moieties facilitates molecular polarization of the DPAF ring toward the C60 cage. That may serve as the fundamental cause for correlation of enhanced A−D electron interactions to, ultimately, observed multiphoton absorption cross sections. By using nanosecond laser flash photolysis results taken at 355 nm as the reference, transient absorption data obtained from femtosecond pump−probe experiments at 800 nm unambiguously verified the occurrence of two-photon excitation processes of C60(>DPAF-C9) in air-saturated benzene and subsequent efficient energy transfer from the two-photon pumped DPAF-C9 moiety to the C60 cage moiety.

Synthesis, theoretical characterisation and spectra of thiophene–fluorene π-conjugated derivatives

The syntheses, spectral measurements and the theoretical study of 2-((9H-fluoren-9-ylidene)methyl)thiophene ( A), ((9H-fluoren-9-ylidene)methyl)-5-(thiophen-2-yl)thiophene ( B), 1-(5-((9H-fluoren-9-ylidene)methyl)thiophen-2-yl)propan-1-one ( C), 1- (5-((9H-fluoren-9-ylidene)methyl)thiophen-2-yl)pentan-1-one ( D), 1,2-bis(1-(5-((9H-fluoren-9-ylidene) methyl)thiophen-2-yl)propylidene)hydrazine ( E) and 1,2-bis(1-(5-((9H-fluoren-9-ylidene)methyl)thiophen-2-yl)pentylidene)hydrazine ( F) are presented. The electron absorption and fluorescence spectra of prepared molecules are measured in polymer matrix and solution. The influence of the conformation (e.g. cis- and trans-forms in the case of E and F molecules) on electronic spectra are interpreted by ZINDO/S method. Our results indicate that the thiophene rings connected with terminal fluorene chromophores through the double bounded carbon atom seem to be suitable candidates for the subsequent preparation of the electro-optical materials.

Studies of the antenna effect in polymer molecules. 28. Photo-Fries rearrangement of 1-naphthyl acetate in aqueous solutions of poly(sodium styrenesulfonate-co-2-vinylfluorene)

The photo-Fries rearrangement of 1-naphthyl acetate (NA) in aqueous solutions of the novel antenna polyelectrolyte, poly(sodium styrenesulfonate-co-2-vinylfluorene) (PSSS-VF), was studied. Three copolymers with different fluorene (Fl) chromophore contents were synthesized. The solubilizing abilities of the PSSS-VF copolymers in aqueous solution were tested using perylene as a probe. The polarity of the polymeric medium was shown to be lower than that of the interior of typical surfactant micelles. It was demonstrated that electronic excitation energy can migrate along the polymer chain before being transferred to the solubilized probe molecule. The reaction of NA is sensitized efficiently by light absorbed by the polymeric fluorene chromophores. It was found that the product distribution of the reaction strongly depends on the content of fluorene in the copolymer. The reaction in aqueous solutions of PSSS-VF rich in Fl chromophores occurs with high selectivity to form the cage product, 2-acetonaphthol (2-AN) in 95% yield. Polymeric sensitizers with low fluorene content (∽5%) gave 90% yields of the non-cage product 1-naphthol. Both are more selective than when the Fries reaction is carried out in methanol solution.

Neutral and cation spectroscopy of fluorene–Arn clusters

Fluorene–Arn complexes formed in a pulsed supersonic jet have been studied in their S1 state using two color REMPI spectroscopy with mass resolved detection. The appearance and shifts of the S1 origins relative to the fluorene monomer are measured for cluster sizes up to n = 30. The shifts and appearance of these bands are used to identify multiple conformations at low n and have indicated a shift from two sided clustering by Ar at low n to primarily one sided clustering at large n. The ionic ground state of the smaller clusters (n⩽6) are studied using mass analyzed threshold ionization (MATI) spectroscopy. The change of the ionization potentials as a function of cluster size has been determined. In the case of the fluorene–Ar4 cluster, the MATI spectrum of two separate cluster conformations was measured, revealing significantly different ionization potentials. Vibrational dynamics has been studied in several smaller clusters (n⩽3) by measuring MATI and ZEKE spectra when pumping vibronic transitions in the fluorene chromophore. Significantly enhanced coupling of the chromophore to van der Waals modes is observed in going from n = 1 to n = 3.

Photochemical studies of Langmuir-Blodgett films fabricated from N-alkylacrylamide copolymers with various vinyl aromatic monomers

Various aromatic chromophores were incorporated into polymer Langmuir-Blodgett (LB) multilayers as comonomers of copolymers of N-alkylacrylamides (AA). The monolayer formation of the naphthalene copolymers is investigated in detail by measurement of the surface pressure-area isotherms. The fluorescence spectra for the LB multilayers were measured as functions of the deposited layer and the alkyl chain length of AA. The excimer emission intensity increased with increasing number of deposited layers when the effective intralayer and interlayer energy transfer to the excimer forming sites is taking place. The efficiency of vertical energy transfer in the Y-type LB films for naphthalene, pyrene, carbazole and fluorene chromophores was safely judged from the increase in the excimer emission intensity as a function of the type of deposited layer in the fluorescence spectra. The limiting energy transfer distances for each chromophores are correlated with critical energy transfer distances of Förster type.

Fluorenyl fatty acids as fluorescent probes for depth-dependent analysis of artificial and natural membranes.

The main objective of depth-dependent fluorescent probes is to provide information at a distinct position in the membrane hydrophobic core. We report here a series of fluorenyl fatty acids which can probe both artificial and natural membranes at different depths. Long-chain acids (C4, C6, and C8) are attached to fluorene chromophore on one side, and a hydrophobic tail (C4) is attached on the other side, so that on incorporation in membranes the carboxyl end of the molecule is oriented toward the membrane-water interface and the hydrophobic tail points toward the membrane interior. These acids can be readily partitioned into membranes. The disposition of these fluorenyl fatty acids in membranes was studied by fluorescence quenching using iodide as a water-soluble and 9,10-dibromostearic acid as a lipid-soluble quencher. The results obtained indicate that attachment of a hydrophobic tail is essential for effective alignment of depth-dependent fluorescent probes. The length of the hydrophobic tail was varied and an n-butyl chain was found to be most effective. In all cases, the compounds with a hydrophobic tail were found to be probing the membrane deeper than their counterparts with no hydrophobic tail. Further, the compounds with hydrophobic tails were more strongly immobilized in the membrane as indicated by fluorescence polarization studies. However, the effect of such a tail varied with membrane type. Thus in artificial membranes an n-butyl chain was found to be extremely important for effective monitoring by shallow probes like 4-(2'-fluorenyl)butyric acid, whereas in erythrocyte ghost membranes the same n-butyl tail was found to be more desirable for deeper probes like 8-(2'-fluorenyl)octanoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)