Vinylene Bridge Research Articles

Microwave assisted synthesis, photophysical and redox properties of (phenothiazinyl)vinyl-pyridinium dyes

New cationic cyanine dyes, containing electron donor 10-alkyl-phenothiazine and electron acceptor pyridinium units connected through a vinylene bridge were conveniently synthesized by microwaves assisted condensation of phenothiazine carbaldehyde with methylpyridinium salts in dry media. Their photophysical properties revealing strong absorption bands in 440–470 nm region (ɛ ≈ 104–105) and large Stokes shifts of fluorescence emission (610–750 nm) in solid state were supported by computational data using TDDFT level of theory. The redox behavior of PVP was studied by means of electrochemical and biocatalytical oxidation processes.

Synthesis and spectroscopic characterisation of (E)-2-(2-(9-(4-(1H-1,2,4-triazol-1-yl)butyl)-9H-carbazol-3-yl)vinyl)-3-ethylbenzo[d]thiazol-3-ium, a new ligand and potential DNA intercalator

AbstractThree new compounds based on carbazole planar skeleton were synthesised. Among them there is a new ligand and a potential DNA intercalator which contains a benzothiazolium moiety connected to the carbazole ring by a vinyl bridge. The absorption and emission spectral properties of this new ligand have been studied by spectroscopic methods.

Spirooxazine-based multifunctional molecular switches with tunable photochromism and nonlinear optical response

A new type of organic photochromic spirooxazine has been synthesized, incorporating increasing numbers of thiophene units by vinyl bridges. These compounds exhibit tunable photochromic properties that are sensitive to low-energy visible light compared with traditional UV. Furthermore, the ring-opening mechanism is put in relation to the interaction of fragment molecular orbitals. The result shows that the effective excitation with significant intensity is centred mainly on the naphthoxazine part and vinyl thiophene plays a crucial role in the photochemical and photophysical process. Density functional calculations are performed to rationalize the “on and off” switching nonlinear optical behaviors of compounds, showing the potential for applying the materials in nonlinear optical switches.

An enhanced host–guest electro‐optical polymer system using poly(norbornene‐dicarboximides) via ROMP

AbstractHigh glass transition temperature poly(N‐cyclohexyl‐5‐norbornene‐2,3‐dicarboximide)s (NDI)s prepared by ring opening metathesis polymerization yielded polymers with a narrow polydispersity and well‐controlled molecular weight materials when using the Grubbs first generation initiator. Polymers produced using the Grubbs second generation initiator could not be controlled easily. By initiator selection it was also possible to synthesize polymers with either 98 or 52% trans microstructures. These materials were employed as electro‐optic (EO) polymer hosts for high molecular hyperpolarizability (β) phenyl vinylene thiophene vinylene bridge chromophores. This chromophore was modified by the incorporation of a tert‐butyldiphenylsilane group. The addition was able to further increase its EO coefficient (r33) to reach 93 pm/V in a trans rich poly(NDI) produced by the Grubbs first generation initiator, compared to a benchmark chromophore / polymer combination. We investigated in detail the relationship between polymer microstructure and their absolute molecular weight on forming the best host–guest with the high β chromophore. Our results indicate that by utilizing a very simple host–guest system a high r33 can be realized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

2,3,4,5‐Tetraphenylsilole‐Based Conjugated Polymers: Synthesis, Optical Properties, and as Sensors for Explosive Compounds

A series of linear 2,5-tetraphenylsilole-vinylene-type polymers were successfully synthesized for the first time. The tetraphenylsilole moieties were linked at their 2,5-positions through a vinylene bridge with p-dialkoxybenzenes to obtain polymer PSVB and with 3,6-carbazole to obtain polymer PSVC. For comparison, 2,5-tetraphenylsilole-ethyne-type polymer PSEB was also synthesized, in which the vinylene bridge of PSVB was replaced with an ethyne bridge. Very interestingly, the bridging group (vinylene or ethyne) had a significant effect on the photophysical properties of the corresponding polymers. The fluorescence peak of PSEB at 504 nm in solution originated from the emission of its silole moieties, whereas PSVB and PSVC emitted yellow light and no blueish-green emission from the silole moieties was observed, thus demonstrating that the emissions of PSVB and PSVC were due to their polymer backbones. More importantly, the 2,5-tetraphenylsilole-ethyne polymer exhibited a pronounced aggregation-enhanced emission (AEE) effect but the 2,5-tetraphenylsilole-vinylene polymer was AEE-inactive. Moreover, both AEE-active 2,5-tetraphenylsilole-ethyne polymer and AEE-inactive 2,5-tetraphenylsilole-vinylene polymers were successfully applied as fluorescent chemosensors for the detection of explosive compounds.

Synthesis and properties of trans-2-[2-(2-hetaryl)vinyl]benzothiazoles

Electrophilic substitution reactions (formylation and acylation) in the series of 2-[2-(2-furyl)vinyl]- and 2-[2-(2-thienyl)vinyl]benzothiazoles leads to the corresponding derivatives at the α-position of the furan or thiophene ring. The presence of a vinylene bridge weakens deshielding effect of the benzothiazole fragment on π-excessive heterocycles, so that such compounds react at a higher rate and under milder conditions as compared to hetarylbenzothiazoles having no vinylene bridge.

Nonlinear optical side‐chain polymers post‐functionalized with high‐β chromophores exhibiting large electro‐optic property

AbstractElectro‐optic side‐chain polymers have been synthesized by the post‐functionalization of methacrylate isocyanate polymers with novel phenyl vinylene thiophene vinylene bridge (FTC) nonlinear optical chromophores. For this application, FTC‐based chromophores were modified in their electronic donor structure, exhibiting much larger molecular hyperpolarizabilities compared with the benchmark FTC. Of these new chromophores, absorption spectra, hyper‐Rayleigh scattering experiment, and thermal analysis were carried out to confirm availability as effective nonlinear optical units for electro‐optic side‐chain polymers. The electro‐optic coefficients (r33) of obtained polymers were investigated in the process of in situ poling by monitoring the temperature, current flow, poling field, and electro‐optic signal. Compared with the nonsubstituted analogue, benxyloxy modified FTC chromophore significantly achieved higher nonlinear optical property, exhibiting molecular hyperpolarizability at 1.9 μm of 4600 × 10−30 esu and an r33 value of 150 pm/V at the wavelength of 1.31 μm. Synthesized electro‐optic polymers showed high glass transition temperature (Tg), so that the temporal stability examination exhibited >78% of the electro‐optic intensity remaining at 85 °C over 500 h. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Solution-Processable Star-Shaped Molecules with Triphenylamine Core and Dicyanovinyl Endgroups for Organic Solar Cells

Two new star-shaped D−π−A molecules with triphenylamine (TPA) as core and donor unit, dicyanovinyl (DCN) as end group and acceptor unit, and 4,4′-dihexyl-2,2′-bithiophene (bT) or 4,4′-dihexyl-2,2′-bithiophene vinylene (bTV) as π bridge, S(TPA-bT-DCN) and S(TPA-bTV-DCN), were synthesized for the application as donor materials in solution-processed bulk-heterojunction organic solar cells (OSCs). The two compounds are soluble in common organic solvents, because of the three-dimensional structure of the TPA unit and the two hexyl side chains on the bithiophene unit. S(TPA-bTV-DCN) film shows a broad absorption band from 360 to 750 nm. Absorption edge of S(TPA-bTV-DCN) film is red-shifted by ca. 78 nm than that of S(TPA-bT-DCN) film, benefitted from the vinylene bridges between TPA and bithiophene units in S(TPA-bTV-DCN). Power conversion efficiency (PCE) of the solution-processed bulk-heterojunction OSC based on a blend of S(TPA-bTV-DCN) and [6,6]-phenyl-C71-butyric acid methyl ester (1:2, w/w) reached 3.0% with a short circuit current density of 7.76 mA/cm2 and an open circuit voltage of 0.88 V, under the illumination of AM.1.5, 100 mW/cm2. In comparison, PCE of the OSC based on S(TPA-bT-DCN) as donor is 1.4% under the same experimental conditions. The PCE of 3.0% for S(TPA-bTV-DCN) is among the top values for the solution-processed molecule-based OSCs reported so far.

The synthesis and spectral properties of new DNA binding ligands

Two new ligands based on anthracene or carbazole planar skeletons, and a phenyloxazoline moiety linked by a vinyl bridge are synthesized as potential DNA-interacting drugs. Their spectral characteristics and DNA binding affinity are assessed.

Effects of the CN and NH 2 substitutions on the geometrical and optical properties of model vinylfluorenes, based on DFT calculations

A systematic study on the structural and photo-physical properties of model bifluorenevinylene compounds based on the density functional theory (DFT) and its time-dependent (TD-DFT) version is presented. The main aim of this work is to investigate the influence of substitution on bifluorenevinylene using strong electron acceptor CN or electron donor NH 2 groups on: (a) the optimal geometry, (b) torsional potentials and (c) photo-physical properties. Our results indicate that the substitution on the vinylene bridge, leads to the twisting of molecular fragment on the side of added group and are in good overall agreement with experiment. In the case of the amino mono-substituted bifluorenevinylene, the amino group leads to non-planarity at the non-substituted portion of the molecule. The chemical modification also have a pronounced impact on the electronic properties. The shape of the potential energy curves evaluated for the lowest vertically excited states is heavily dependent on the molecular conformation. Finally, we discuss how the structural and electronic information presented here can be useful in designing of novel optical materials as well as understanding of excitation–relaxation phenomena which may occur in various time-dependent optical experiments.

Efficient hybrid bulk heterojunction solar cells based on phenylenevinylene copolymer, perylene bisimide and TiO 2

A soluble alternating phenylenevinylene copolymer P containing a side anthracene, which was attached to the thiophene ring via a vinylene bridge, was synthesized by Heck coupling. The copolymer had relatively low glass transition temperature (61 °C) and decomposed above 400 °C. The absorption maximum of P was located at 387–402 nm with an optical band gap of 2.32 eV. The emission spectra of P indicated that an intramolecular energy transfer from the side anthracene to the main chain took place via the vinylene bridge. In addition, a new symmetrical compound A based on perylene–anthracene was synthesized and used as electron acceptor in the device. Photovoltaic devices were fabricated using a blend of copolymer P as donor and compound A as acceptor, as photoactive layer film sandwiched between indium tin oxide-coated glass and Al electrodes. This device showed a power conversion efficiency of 0.72%. However, when TiO 2 nanoparticles were incorporated on the pristine P: A blend, the power conversion efficiency of the device was enhanced up to 1.32%, which is attributed to the enhanced photoinduced excitons due to the increase of the interfacial area and improved charge carrier mobility. The power conversion efficiency of the P: A:TiO 2 based photovoltaic device was further improved up to 2.64%, when the hybrid composite was treated with a mixture of Li salt and 4-tert-butylpyridine, which is attributed to the reduction in the recombination of charge carriers.

Synthesis and Fluorescent Properties of Chiral Polymer Complexes Incorporating Bipyridine and Eu(III) or Gd(III)

AbstractChiral polymer P‐1 was synthesized by the polymerization of (R)‐5,5′‐dibromo‐6,6'‐di(4‐trifluoromethyl‐ phenyl)‐2,2′‐bisoctoxy‐1,1'‐binaphthyl (R‐M‐1) with 5,5′‐divinyl‐2,2′‐bipyridine (M‐2) via Pd‐catalyzed Heck reaction. The polymer complexes P‐2 and P‐3 could be obtained by the bipyridyl coordination of P‐1 with Eu(TTA)3·2H2O and Gd(TTA)3·2H2O (TTA−=1‐(2‐thenoyl)‐3,3,3‐trifluoroacetonate). The chiral polymer P‐1 shows strong blue fluorescence due to the extended ‐electronic structure between the chiral repeating unit (R)‐6,6'‐di(4‐trifluoromethyl‐phenyl)‐2,2′‐bisoctoxy‐1,1'‐binaphthyl and the conjugated linker 2,2′‐bipyridyl (bpy) group via vinylene bridge. The Eu(III)‐containing polymer complex P‐2 can not only emit the polymer fluorescence, but also have the characteristic fluorescence of Eu(III) (5D0→7F2) under different exciting wavelengths. The Gd(III)‐containing polymer complex P‐3 only emits the polymer fluorescence. Based on the fluorescent properties of the polymer and RE(III)‐containing polymer complexes, it can be concluded that the chiral polymer does not transfer energy to Eu(III) or Gd(III) complex moiety but emits its own fluorescence.

Synthesis and properties of chiral helical polymers based on optically active polybinaphthyls

The chiral polymer P-1 was synthesized by the polymerization of ( R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bisoctoxy-1,1′-binaphthyl ( R-M-1 ) with 5,5′-divinyl-2,2′-bipyridine ( M-1) via Pd-catalyzed Heck reaction. P-2 and P-2′ were prepared by Wittig–Horner reaction of ( R)-6,6′-dibutyl-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde ( R-M-2 ) with 5,5′-bis (diethylphosphonomethyl)-2,2′-bipyridine ( M-2) in the presence of EtONa or NaH, respectively. P-3 was synthesized by Wittig–Horner reaction of ( R)-6,6′-di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl-3,3′-dicarbaldehyde ( R-M-3 ) with M-2 using NaH as a base. The four polymers have strong blue-green fluorescence due to the extended π-electronic structure between the chiral model compounds ( R)-6,6′-dibutyl-/di(4-trifluoromethylphenyl)-2,2′-bisoctoxy-1,1′-binaphthyl ( R-1 or R-2 ) and the conjugated linker 2,2′-bipyridyl group via vinylene bridge. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV–vis spectroscopy, DSC–TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. Based on the great differences of specific rotation values and CD spectra, P-1 and P-2 may adopt a zigzag chain configuration, while P-2′ and P-3 may adopt a helical configuration. The responsive optical properties of the two chiral helical polymers P-2′ and P-3 on transition metal ions were investigated by fluorescence, UV–vis and CD spectra. The results show that Ag + and Ni 2+ lead to nearly complete fluorescence quenching of P-2′ and P-3, Cu 2+ and Fe 2+ can cause obvious fluorescence quenching, but Zn 2+ and Cd 2+ can only produce slight fluorescence quenching. Ag +, Ni 2+, Cu 2+ and Fe 2+ can also lead to the obvious changes of UV–vis spectra of P-2′ and P-3. On the contrary, Zn 2+ and Cd 2+ cause little changes. Most importantly, the CD intensities and wavelengths of the chiral helical polymers P-2′ and P-3 exhibit the pronounced changes upon addition of Ag + and Ni 2+.

Improving the Photostability of Membrane Probes through Fluorination

High photostability is a desired property for fluorescent probes, especially when long recording time is necessary. It becomes more crucial for long wavelength fluorescent dyes because they generally have lower fluorescence quantum yields and are more vulnerable to chemical and photochemical attacks. We have developed a series of optical probes with high membrane affinities that are able to report on their local membrane environment and act as sensors of membrane voltage. These dyes have hemicyanine chromophores with donor-bridge-acceptor structures. Following our recent success in developing near-infrared fluorescent membrane probes, we further tried to improve the performance of these dyes through fluorination. Synthetic pathways to hemicyanines with fluorine substitution at various positions have been developed and the performances of these fluorinated dyes have been evaluated. It was found that the effect of fluorination depends critically on the site of fluorination: donor, acceptor, or bridge. Fluorination on the vinylene bridge appears to give optimal outcomes: improvement in photostability, red-shifts in absorption and emission spectra, and increase in absorption cross section. On the other hand, fluorination on the pyridinium acceptor results in an undesirable outcome: the dye is much less stable than the nonfluorinated counterpart in PBS buffer. Fluorinated membrane dyes generally show response kinetics and voltage sensitivities similar to their nonfluorinated counterparts when tested in a voltage-clamped hemispherical lipid bilayer (HLB) apparatus and in nonlinear optical imaging. (Supported by NIH grants EB001963 and U54RR022232)

Fluorescent chemosensor based on the conjugated polymer incorporating 2,2′‐bipyridyl moiety for transition metal ions

AbstractA fluorescent conjugated polymer was synthesized by the polymerization of 1,4‐dibromo‐2,3‐bisbutoxynaphthalene (M‐2) with 5,5′‐divinyl‐2,2′‐bipyridine (M‐3) via Heck reaction. The conjugated polymer shows strong blue–green fluorescence because of the extended π‐electronic structure between the repeating unit 2,3‐bisbutoxynaphthyl group and the conjugated linker 2,2′‐bipyridyl (bpy = 2,2′‐bipyridine) moiety via vinylene bridge. The responsive properties of the conjugated polymer on transition metal ions were investigated by fluorescent and UV–vis spectra. The results show that Cu2+ and Ni2+ can form nonradiative metal‐to‐ligand charge‐transfer complexes with the polymer, whereas, Zn2+ and Cd2+ do not produce the pronounced differences from the polymer fluorescence and UV–vis spectra. The fluorescent quenching can probably be attributed to the intramolecular photoinduced electron transfer (PET) or photoinduced charge transfer (PCT). The results can also suggest that 2,2′‐bipyridyl moiety in the main chain backbone of the conjugated polymer can act as the recognition site of a special fluorescent chemosensor for sensitive detection of transition metal ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

SYNTHESIS AND CHARACTERIZATION OF THIOPHENE-CONTAINING CHROMOPHORES FOR NONLINEAR OPTICAL (NLO) MATERIALS

A series of chromophores based on benzene and thiophene moieties as π-conjugating spacers were designed and synthesized by Horner-Emmons-Wadsworth reaction and Vilsmeier-Haack reaction, followed by Knoevenagel reaction with different electron acceptors. Their structures were confirmed by 1HNMR, FT-IR, HPLC-Ms, UV-visible spectra, and the thermal properties were characterized by differential scanning calorimetry (DSC). Solvatochromic method was used to measure their nonlinear optical properties. The variation of chromophoric structures on NLO properties was investigated, indicating that the cyano substitution on the vinylene bridge of the chromophore produces a considerable red-shift of the absorption maximum, and would greatly enhance the molecular quadratic hyperpolarizability (βμ).

Synthesis, Luminescence Properties, and Explosives Sensing with 1,1-Tetraphenylsilole- and 1,1-Silafluorene-vinylene Polymers

The syntheses, spectroscopic characterizations, and fluorescence quenching efficiencies of polymers and copolymers containing tetraphenylsilole- or silafluorene-vinylene repeat units are reported. These materials were prepared by catalytic hydrosilylation reactions between appropriate monomeric metallole alkynes and hydrides. Trimeric model compounds methyl(tetraphenyl)silole-vinylene trimer (1), methyl(tetraphenyl)silole-silafluorene-vinylene cotrimer (2), and methylsilafluorene-vinylene trimer (3) were synthesized to provide detailed structural and spectroscopic characteristics of the polymer backbone and to assess the extent of delocalization in the luminescent excited state. Poly(tetraphenylsilole-vinylene) (4), poly(tetraphenylsilole-silafluorene-vinylene) (5), and poly(silafluorene-vinylene) (6) maintain a regio-regular trans-vinylene Si−C backbone with possible ground state σ*−π and excited state σ*−π* conjugation through the vinylene bridge between metallole units. Fluorescence spectra of the polymers show an ∼13 nm bathochromic shift in λflu from their respective model compounds. Molecular weights (Mn) for these polymers and copolymers are in the range of 4000–4500. Detection of nitroaromatic explosives by solution-phase fluorescence quenching of polymers 4−6 was observed with Stern−Volmer constants in the range of 400−20 000 for TNT, DNT, and picric acid (PA). A surface detection method for the analysis of solid particulates of TNT, DNT, PA, RDX, HMX, Tetryl, TNG, and PETN is also described for silafluorene-containing polymers. Polymer 6 exhibited detection for all the preceding types of explosive residues with a 200 pg cm−2 detection limit for Tetryl. Polymers 4 and 5 exhibited only luminescence quenching with nitroaromatic explosives, revealing that the excited-state energy of the sensor plays a key role in the fluorescence detection of explosives.

Synthesis, characterization, and electroluminescence of new conjugated PPV derivatives bearing triphenylamine side‐chain through a vinylene bridge

AbstractThree new conjugated poly(p‐phenylene vinylene) (PPV) derivatives bearing triphenylamine side‐chain through a vinylene bridge, poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylene‐vinylene) (DP‐PPV), poly(2‐(3′‐(3″,7″‐dimethyloctyloxy)phenyl)‐1,4‐phenylenevinylene‐alt‐2‐(4′‐ (diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene) (DODP‐PPV), and poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene‐co‐2‐(3′,5′‐bis(3″,7″‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (DP‐co‐BD‐PPV), were synthesized according to the Gilch or Wittig method. Among the three polymers, the copolymer DP‐co‐BD‐PPV is soluble in common solvents with good thermal stability with 5% weight loss at temperatures higher than 386°C. The weight‐average molecular weight (Mw) and polydispersity index (PDI) of DP‐co‐BD‐PPV were 1.83 × 105 and 2.33, respectively. The single‐layer polymer light‐emitting diodes (PLEDs) with the configuration of Indium tin oxide (ITO)/poly (3,4‐ethylenedioxythiophene): poly(4‐styrene sulfonate)(PEDOT:PSS)/DP‐co‐BD‐PPV/Ca/Al were fabricated. The PLED emitted yellow‐green light with the turn‐on voltage of ca. 4.9 V, the maximum luminance of ca. 990 cd/m2 at 15.8 V, and the maximum electroluminescence (EL) efficiency of 0.22 cd/A. Copyright © 2007 John Wiley & Sons, Ltd.

Inorganic−Organic Hybrid Nonlinear Optical Films Containing Bulky Alkoxysilane Dyes

Two bulky alkoxysilane dyes based on nonlinear optical (NLO)-active triphenylamino derivatives possessing high thermal stabilities, without and with a cyano group substitution on the vinylene moiety (TPAH and TPACN, respectively), were synthesized, characterized, and copolymerized with tetraalkoxysilane (TEOS) with the ratio of 1:5. After a poling and curing process, the resulting side-chain-type sol-gel films with excellent optical qualities were achieved. Second-order NLO coefficients, d33, of 10-20 pm/V have been obtained in the films incorporated with different types of NLO-active dyes. The variation of chromophoric structures on NLO properties was investigated, indicating that the cyano substitution on the vinylene bridge of the chromophore would greatly enhance the temporal stability. This work provides a potential design strategy based on molecular engineering which would lead to more stable dipole orientation.

Two-Photon Absorption in Quadrupolar Bis(acceptor)-Terminated Chromophores with Electron-Rich Bis(heterocycle)vinylene Bridges

Two-photon absorption spectra for a range of bis(acceptor)-substituted bis(dibutoxythienyl)ethene and bis(N-hexylpyrrolyl)ethene chromophores have been recorded using Z-scan and white-light-continuum pump−probe techniques. All the chromophores studied show strong near-infrared two-photon absorption with cross sections in the range of 2400−5900 GM (1 GM = 1 × 10-50 cm4 s/photon) at photon wavelengths between 1.0 and 1.3 μm; cross sections as high as 10000 GM can be accessed close to the one-photon absorption edge. Quantum-chemical calculations reproduce the experimentally observed variations of the two-photon properties with the chemical structure.