Fluorescent dye guest-host effects in advanced ferroelectric liquid crystals

Abstract

Previous work has shown that guest-host ferroelectric systems incorporating dichroically absorbing dyes are suitable for use in colour display applications. These utilize either the dichroic absorption of a conventional dye, or the emission of a fluorescent dye. We present here the electrooptical properties of several advanced ferroelectric liquid crystals doped with a new fluorescent dye, coloured blue in emission. The data consists of measurements of tilt angle, response time, spontaneous polarization, and rotational viscosity, from which we conclude that certain hosts are not adversely affected by the fluorescent dopants. These results are then discussed in connection with the use of these mixtures in two novel colour display configurations, which are also presented, utilizing either the dichroic absorption or the polarized fluorescence of the fluorophore guests.     

Dye guest-host effects in ferroelectric liquid crystals

Here we present the optic and electro-optic characteristics of ferroelectric dye guest-host devices incorporating different dye and S*_C host materials. We demonstrate fast response time (< 100 μs) single polarizer and zero-polarizer device configurations for high order parameter dichroic dyes and single polarizer fluorescent dye devices. The dynamic data include measurements of response times as functions of voltage, temperature and dye concentration, from which we conclude that the inclusion of certain dyes does not adversely affect the ferroelectric phase. The contrast ratios of these novel guest-host devices are also presented and are shown, as expected, to be functions of tilt angle (and therefore temperature). However, we demonstrate that the high tilt angle of 45° is not necessary for high contrast devices, and in fact for certain devices configurations θ = 22½° is optimum. These results are discussed.     

Polarized fluorescence and electroluminescence from rubbing-aligned conjugated polymers and their composites with fluorescent dyes

Polarized fluorescence and optical absorption studies of rubbing-treated poly(2,5-diheptyloxybenzene) and poly (3-alkylthiophene)s (PATs) were carried out with the aim of obtaining polarized electroluminescence (EL). It was revealed that there exists an optimum alkyl chain length in PATs for the effect of rubbing. Polarized EL with a dichroic ratio of 2.6 was observed from a rubbing-aligned PAT-12 film. It was also demonstrated that the rubbing treatment of composite films of PAT and several fluorescent dyes such as 1,4-bis (2-methylstyryl)benzene enabled us to obtain polarized emission from oriented dye molecules. © 1997 John Wiley & Sons, Ltd.     

Fast polarisation-insensitive optical shutter supported by backflow in dichroic dye-doped dual-frequency liquid crystal

This paper describes a novel implementation of a dual-frequency liquid crystal optical shutter of the guest–host type. The transmissive state of the filter is obtained by applying a low-frequency electric field that brings the dichroic dye in a homeotropic orientation. The light-absorbing state is realised by a twisted planar configuration for which the absorption is quasi-independent of the polarisation. Switching between the two states occurs in about 1 ms and the devices show no scattering for wavelengths inside or outside the absorption band of the dichroic dye. Simulations and experiments reveal how a twisted state is obtained through the backflow phenomenon.     

Highly polarized absorption and emission from polymer-stabilized smectic guest-host systems

ABSTRACT

The optical properties of luminescent molecules dissolved in liquid crystals have led to their proposed use in luminescent thin-film polarizers. These molecules are typically required to fulfil a range of criteria related to their absorption and emission properties, degree of alignment and stability; however, concurrently satisfying these requirements has proven a barrier in their practical use. We obtained highly polarized absorption and emission luminescent thin-film polarizer using reactive liquid crystalline monomers and highly dichroic luminescent dyes, both of which have polymerizable end groups. In situ photopolymerization of the liquid crystalline mixtures in the highly ordered SmB phase resulted in the formation of cross-linked polymeric networks in which the anisotropic absorption and emission of the film were fixed. The as-obtained product exhibited a high dichroic ratio (DR = 30) with a large fluorescence quantum yield (?_F = 0.77). The device is both cheap and easy to fabricate and has the potential to be used in practical electro-optic applications.     

Effect of polymer binding on the spectroscopic properties of stilbene-based fluorescent dyes

Studies utilizing absorption and emission spectrophotometry have been carried out to observe the effect of various polymer substrates on the spectral characteristics of several stilbene-based fluorescent dyes. Poly(vinyl alcohol), cellulose acetate, cellulose fiber, and bovine serum albumin were used as substrates for two common fluorescent whitening agents and for two model compounds. Binding of these molecules to polymers leads to a marked red shift in the absorption spectra and an increase in vibrational structure. These effects are attributed to an increase in molecular planarity induced by the polymer environment. For the case of bovine serum albumin, it is concluded that the dye molecules bind to the protein largely through electrostatic interaction involving the dye sulfonate groups. The spectral characteristics of the dye molecules on wool fibers are interpreted in light of these results.     

LED-compatible fluorosensor for measurement of near-neutral pH values

We report on an optical sensor material suitable for fluorimetric measurement of pH in the 6–9 range using a new, fully LED-compatible fluorescent dye. Its base form has a strong absorption between 580 and 630 nm that matches the emission band of conventional yellow or orange light-emitting diodes. Two kinds of dye immobilization are reported. The first is based on covalent binding to a cellulosic matrix and the resulting material is intended for use in sensing membranes. The second involves physical entrapment of the dye in a sol-gel matrix which can be used for optical fiber tip coating as well as in evanescent wave type sensors. Both kinds of sensor materials are studied with respect to dynamic pH ranges, response times, sensitivity toward ion strength, and stability.Dedicated to Professor G. Werner, Leipzig, on the occasion of his 60th birthday.     

新型近红外试剂的合成及其现场二聚体与DNA作用的研究

合成了一种新型近红外阴离子染料,并对其水溶液及阳离子表面活性剂ＣＴＡＢ存在下的吸收荧光光谱进行了研究。结果表明,低浓度的ＣＴＡＢ与该近红外阴离子染料形成离子缔合物而使阴离子染料的荧光强度降低,当ＣＴＡＢ的浓度进一步加大时,其胶束前预聚集促使该染料形成非荧光二聚体,导致荧光急剧猝灭。     

Dichroic properties of bis(benzoxazolyl)stilbene and bis(benzoxazolyl)thiophene dispersed into oriented polyethylene films: a combined experimental and density functional theory approach

In this work, a combination of experimental and quantum mechanical investigations is performed for the study of dichroic absorption properties of melt-processed linear low-density polyethylene (LLDPE) oriented films containing < or =0.5 wt % of either 4,4'-bis(2-benzoxazolyl)stilbene (BBS) or 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene (BTBBT). The data acquired reveal that the film optical anisotropy and the performances as linear polarizer are strongly dependent on the molecular structure of the chromophore. In particular, the rodlike structure of BBS favors the alignment of the dye along the drawing direction of the PE film, providing dichroic ratios as high as 100 and optical performances as linear polarizer close to the pseudo-affine deformation scheme. On the contrary BTBBT, although characterized by huge anisotropic potentialities, confers the oriented film very poor dichroism and is unsuitable for linear polarizer applications. This behavior is attributed to the more complex banana-shaped structure of BTBBT dye caused by the thiophene 2,5-functionalization that limits the molecule parallel orientation to the drawing direction.     

Bulky Barbiturates as Non-Toxic Ionic Dye Insulators for Enhanced Emission in Polymeric Nanoparticles

Bulky hydrophobic counterions (weakly coordinating anions) can insulate ionic dyes against aggregation-caused quenching (ACQ) and enable preparation of highly fluorescent dye-loaded nanoparticles (NPs) for bioimaging, biosensing and light harvesting. Here, we introduce a family of hydrophobic anions based on fluorinated C-acyl barbiturates with delocalized negative charge and bulky non-polar groups. Similarly to fluorinated tetraphenylborates, these barbiturates prevent ACQ of cationic dye alkyl rhodamine B inside polymer NPs made of biodegradable poly(lactic-co-glycolic acid) (PLGA). Their efficiency to prevent ACQ increases for analogues with higher acidity and bulkiness. Their structure controls dye-dye communication, yielding bright NPs with on/off switching or stable emission. They enhance dye encapsulation inside NPs, allowing intracellular imaging without dye leakage. Compared to fluorinated tetraphenylborates known as cytotoxic transmembrane ion transporters, the barbiturates display a significantly lower cytotoxicity. These chemically available and versatile barbiturate derivatives are promising counterion scaffolds for preparation of bright non-toxic fluorescent nanomaterials.     

The synthesis and spectral properties of a stimuli-responsive D-π-A charge transfer dye

A new donor-π-acceptor (D-π-A) type isophorone dye was synthesized by the condensation reaction between 2-(3,5,5-trimethylcyclohex-2-enylidene)-malononitrile and indole-3-carboxaldehyde. The chemical structure of the dye was characterized by 1H NMR, EA and MS. A novel, chromogenic, fluorescent dye based on indol as donor unit and isophorone as acceptor unit displayed marked UV-visible absorption changes and highly selective fluorescence quenching in the presence of fluoride ion. The dye also exhibited sizeable colour changes when used as a pH-induced molecular switch and as a detector for volatile organic compounds. The absorption and fluorescent intensity of the dye can be reversibly selected by protonation/deprotonation of the amine moiety via control of intramolecular charge transfer (ICT), leading to a molecular switch with "on" and "off" states.     

Ratiometric Fluorescent Probe Based on Novel Red-emission BODIPY for Determination of Bovine Serum Albumin

A novel red-emission boron-dipyrromethene（BODIPY） dye with a pyrrole ring was synthesized simply via one-pot reaction. The spectral properties of it were investigated under the conditions of different solvents. The results show that the as-prepared BODIPY dye is extremely sensitive to solvent polarity, and the fluorescent emission enhances with the decrease of solvent polarity. In aqueous buffer, the addition of bovine serum albumin leads to a ratiometric change in absorption spectra with an association constant of 1.16×10^6 L/mol. Meanwhile, the fluorescence emission increases greatly at 622 nm but changes slightly at 575 nm. The response time is very short（less than 3 min）, and the changes of color can be noticed by naked eyes. Bovine serum albumin can be detected by this ratiometric fluorescence probe, but other proteins or enzymes cannot be detected by this method, which indicates that this novel dye has high selectivity towards bovine serum albumin. The reason is that bovine serum albumin has suitable hydro- phobic cavities for binding with the dye. In addition, the dye molecule can penetrate cell membrane easily and make a fast fluorescent stain, which makes it a potential probe for living-cell fluorescence imaging.     

Organically modified silica nanoparticles co-encapsulating photosensitizing drug and aggregation-enhanced two-photon absorbing fluorescent dye aggregates for two-photon photodynamic therapy

We report energy-transferring organically modified silica nanoparticles for two-photon photodynamic therapy. These nanoparticles co-encapsulate two-photon fluorescent dye nanoaggregates as an energy up-converting donor and a photosensitizing PDT drug as an acceptor. They combine two features: (i) aggregation-enhanced two-photon absorption and emission properties of a novel two-photon dye and (ii) nanoscopic fluorescence resonance energy transfer between this nanoaggregate and a photosensitizer, 2-devinyl-2-(1-hexyloxyethyl)pyropheophorbide. Stable aqueous dispersions of the co-encapsulating nanoparticles (diameter < or = 30 nm) have been prepared in the nonpolar interior of micelles by coprecipitating an organically modified silica sol with the photosensitizer and an excess amount of the two-photon dye which forms fluorescent aggregates by phase separation from the particle matrix. Using a multidisciplinary nanophotonic approach, we show: (i) indirect excitation of the photosensitizer through efficient two-photon excited intraparticle energy transfer from the dye aggregates in the intracellular environment of tumor cells and (ii) generation of singlet oxygen and in vitro cytotoxic effect in tumor cells by photosensitization under two-photon irradiation.     

Achiral Dichroic Dyes-mediated Circularly Polarized Emission Regulated by Orientational Order Parameter through Cholesteric Liquid Crystals

It is noteworthy that cholesteric liquid crystal (CLC) platforms have been witnessed in high-performance circularly polarized luminescence (CPL) behaviors through the highly organized chiral co-assembled arrangement of achiral dyes. However, most CPL-active design strategies are closely relative to the helix co-assembly structure of CLC rather than achiral dyes. Herein, we developed an intriguing regulation strategy for CPL-active CLC materials. They were regulated using the orientational order parameter (S_F) of achiral dichroic dyes as an incisive probe for the order arrangement degree of achiral dyes in CLC media. The I-shaped phenothiazine derivative PHECN dye (S_F=0.30) emitted a strong CPL signal (|g_lum|=0.47). In contrast, the T-shaped derivative (PHEBen) dye (S_F=0.09) showed a weak circular polarization level (|g_lum|=0.07) at similar CLC textures. Most interestingly, this kind of dichroic PHECN dye with a higher S_F could greatly improve the contrast ratio of CPL (Δg_lum=0.47) and emission intensity (ΔFL=46.0 %) at direct-current electric field compared with the T-shaped PHEBen (Δg_lum=0.07 and ΔFL=1.0 %) in CLC. This work demonstrates that an induced CPL emission can be mediated using achiral dichroic dye, which will open a new avenue for developing excellent CPL-active display materials.     

嘧啶基双光子荧光染料的设计合成与生物成像

生理条件下光学性质稳定的双光子荧光染料在生物成像领域具有广阔的应用前景。我们使用2,4-二甲基-6-羟基嘧啶与4-(N,N-二甲氨基)苯甲醛进行缩合反应,设计合成了具有双光子荧光性质的化合物2-[(1E)-2-[4-(二甲氨基)苯基]乙烯基]-6-甲基-4(3H)-嘧啶(NHP)。通过质谱(MS)、核磁共振波谱(NMR)、紫外可见吸收光谱和荧光发射光谱等技术手段表征了其结构,研究了其光物理性质,以及外部环境改变对其发射光谱的影响。结果表明,化合物NHP的最佳吸收峰位于400 nm,最佳发射峰位于540 nm左右,且荧光发射不受金属离子、氨基酸和pH等环境因素的影响。生物实验结果表明,化合物NHP细胞毒性较小,且具有很好的活细胞和果蝇脑组织成像效果,是一种较为理想的双光子荧光生物成像染料。     

A sensitive fluorescent chemosensor for anions based on a styryl-boradiazaindacene framework

Long wavelength emitting, extended conjugation boradiazaindacenes are novel dyes with considerable ICT character. By appending a dipicolylaminylethylamine group, the parent compound was transformed into a fluorescent dye with a strong chelating ability for Zn(II) ions. The zinc complex which has bright orange fluorescence, reversibly signals anions with very large changes in both the absorption and the emission spectra. The remarkable change in the emission intensity is explained in relation to the electron donating capacity of the substituent on the styryl functionality.     

Red–Green–Blue Trichromophoric Nanoparticles with Dual Fluorescence Resonance Energy Transfer: Highly Sensitive Fluorogenic Response Toward Polyanions

A red–green–blue (RGB) trichromophoric fluorescent organic nanoparticle exhibiting multi‐colour emission was constructed; the blue‐emitting cationic oligofluorene nanoparticle acted as an energy‐donor scaffold to undergo fluorescence resonance energy transfer (FRET) to a red‐emitting dye embedded in the nanoparticle (interior FRET) and to a green‐emitting dye adsorbed on the surface through electrostatic interactions (exterior FRET). Each FRET event occurs independently and is free from sequential FRET, thus the resultant dual‐FRET system exhibits multi‐colour emission, including white, in aqueous solution and film state. A characteristic white‐emissive nanoparticle showed visible responses upon perturbation of the exterior FRET efficiency by acceptor displacement, leading to highly sensitive responses toward polyanions in a ratiometric manner. Specifically, our system exhibits high sensitivity toward heparin with an extremely low detection limit.     

聚合物与有机染料多层复合膜电致发光颜色的直流电压调制

聚合物与有机染料多层复合膜电致发光颜色的直流电压调制马於光，薛善华，黄劲松，田文晶，刘式墉，沈家骢，刘晓冬（吉林大学分子光谱与分子结构开放实验室，集成光电子学国家重点实验室，长春，１３００２３）（白求恩医科大学，长春，１３００２３）关键词聚合物，发光...     

Indocyanine green as a noncovalent, pseudofluorogenic label for protein determination by capillary electrophoresis

Indocyanine green (ICG)--a negatively charged, polymethine dye--can interact noncovalently with proteins to form fluorescent complexes, with excitation and emission maxima near 780 and 820 nm, respectively. This behavior was realized utilizing either a 100 mM phosphate buffer or a 25 mM citric acid buffer, both at pH 3.1. The behavior of ICG under these conditions, termed pseudofluorogenic, rendered the dye suitable for use as a label for protein determination in capillary electrophoresis with diode laser-induced fluorescence detection (CE-LIF). To this end, pseudofluorogenic ICG was used both as an on-column label for human serum albumin (HSA) and as a precolumn label for a model mixture of proteins, including ribonuclease A, transferrin, and cytochrome c. These ICG-labeled proteins were successfully resolved in less than 11 min, with no interference from excess, unbound dye.     

High-contrast electrically switchable light-emitting liquid crystal displays based on α-cyanostilbenic derivative

Light-emitting liquid crystal displays (LE-LCDs), serving as emissive displays, are considered as promising alternatives to conventional LCDs because of their superior power efficiency. A dichroic fluorescent dye (Z)-2-(4-aminophenyl)-3-(4-(fluorophenyl)acrylonitrile (CN-AFAN) is synthesised, which exhibits strong fluorescence in the solution and solid states. Moreover, an electrically switchable optical switch based on CN-AFAN and a cholesteric liquid crystal is demonstrated, which combines the internal scattering of excitation light and the dichroism of CN-AFAN to improve fluorescence contrast. The photoluminescence and transmittance of the optical switch is modulated by an electric field between the planar state, focal conic state, and homeotropic state. The resultant device is cost-effective and easy to fabricate, thereby demonstrating immense potential for security and display applications.