Two-step resonance energy transfer between dyes in layered silicate films

Single- and two-step fluorescence resonance energy transfer (FRET) was investigated between laser dyes rhodamine 123 (R123), rhodamine 610 (R610), and oxazine 4 (Ox4). The dye molecules played the role of molecular antennas and energy donors (ED, R123), energy acceptors (EA, Ox4), or both (R610). The dye cations were embedded in the films based on layered silicate laponite (Lap) with the thickness of several μm. Optically homogeneous films were prepared directly from dye/Lap colloids. Dye concentration in the films was high enough for FRET to occur but sufficiently low to prevent the formation of large amounts of molecular aggregates. The films were characterized by absorption and fluorescence spectroscopies, and their optical properties were compared with colloid precursors and dye aqueous solutions. The phenomenon of FRET was confirmed by means of steady-state and time-resolved fluorescence spectroscopies. Significant quenching of ED emission in favor of the luminescence from EA molecules was observed. FRET led to the decrease in the lifetimes of excited states of ED molecules. Molecular orientation of dye molecules was determined by polarized absorption and fluorescence spectroscopies. Almost parallel orientation with respect to silicate surface (～30°) was determined for all fluorescent species of the dyes. Theoretical model on relationship between anisotropy and molecular orientation of the fluorophores fits well with measured data. The analysis of anisotropy measurements confirmed the significant role of FRET in the phenomenon of light depolarization.     

Fluorescence resonance energy transfer between two cationic laser dyes in presence of the series of reduced-charge montmorillonites: effect of the layer charge

Series of montmorillonites with systematically reduced layer charges represent a suitable model for studying various properties and interactions of layered inorganic compounds. The reduced-charge montmorillonites (RCMs) used in this study were prepared by a standard method of Li+-fixation in Nanocor montmorillonite at 100-300 degrees C. The layer charge gradually decreased with increasing temperature of RCM preparation. Li+-fixation led in some cases to the loss of expandability due to the formation of mixed swelling/nonswelling and homogeneous nonswelling phases. The interaction of two cationic dyes-rhodamine 3B (R3B) and oxazine 4 (Ox4)-with reduced-charge montmorillonites in dispersions was studied by means of UV/vis absorption and fluorescence spectroscopy. Montmorillonite with the highest charge density induced the formation of H-aggregates of the dye cations characterized by a sandwich-type structure. As the layer charge decreased, the amount of the H-aggregates was reduced in favor of H-dimers and monomers. RCMs with low charge density suppressed dye cation aggregation and mainly monomeric forms were detected. The process of energy transfer from R3B to Ox4 was detected as decreasing the emission from the energy donor and increasing the emission from the energy acceptor. The energy transfer was clearly influenced by the properties of RCM templates. The dye cations adsorbed at the surface of the highest-charge specimen formed H-aggregates, which were efficient luminescence quenchers. Fluorescence resonance energy transfer (FRET) gradually increased with the charge reduction to be optimal at the templates with medium layer charge. Substantial decrease of the layer charge and reduction of clay mineral swelling led to the decrease of both the luminescence and the efficiency of FRET. The relations of energy transfer processes to the layer charges and swelling properties of montmorillonite are analyzed in detail.     

Inverted Opal Fluorescent Film Chemosensor for the Detection of Explosive Nitroaromatic Vapors through Fluorescence Resonance Energy Transfer

This paper reports an inverted opal fluorescence chemosensor for the ultrasensitive detection of explosive nitroaromatic vapors through resonance‐energy‐transfer‐amplified fluorescence quenching. The inverted opal silica film with amino ligands was first fabricated by the acid–base interaction between 3‐aminopropyltriethoxysilane and surface sulfonic groups on polystyrene microsphere templates. The fluorescent dye was then chemically anchored onto the interconnected porous surface to form a hybrid monolayer of amino ligands and dye molecules. The amino ligands can efficiently capture vapor molecules of nitroaromatics such as 2,4,6‐trinitrotoluene (TNT) through the charge‐transfer complexing interaction between electron‐rich amino ligands and electron‐deficient aromatic rings. Meanwhile, the resultant TNT–amine complexes can strongly suppress the fluorescence emission of the chosen dye by the fluorescent resonance energy transfer (FRET) from the dye donor to the irradiative TNT–amino acceptor through intermolecular polar–polar resonance at spatial proximity. The quenching response of the highly ordered porous films with TNT is greatly amplified by at least 10‐fold that of the amorphous silica films, due to the interconnected porous structure and large surface‐to‐volume ratio. The inverted opal film with a stable fluorescence brightness and strong analyte affinity has lead to an ultrasensitive detection of several ppb of TNT vapor in air.     

Photocontrolled Intramolecular Charge/Energy Transfer and Fluorescence Switching of Tetraphenylethene‐Dithienylethene‐Perylenemonoimide Triad with Donor–Bridge–Acceptor Structure

Photochromic 1,2‐dithienylethene (DTE) derivatives with a high thermal stability and fatigue resistance are appealing for optical switching of fluorescence. Here, we introduce a donor–photochromic bridge–acceptor tetraphenylethene‐dithienylethene‐perylenemonoimide (TPE‐DTE‐PMI) triad, in which TPE acts as the electron donor, PMI as the electron acceptor, and DTE as the photochromic bridge. In this system, the localized and intramolecular charge transfer emission of TPE‐DTE‐PMI with various Stokes shifts have been observed due to the photoinduced intramolecular charge transfer in different solvents. Upon UV irradiation, the fluorescence quenching resulting from photochromic fluorescence resonance energy transfer in TPE‐DTE‐PMI has been demonstrated in solution and in solid films. The fluorescence on/off switching ratio in polymethylacrylate film exceeds 100, a value much higher than in polymethylmethacrylate film, thus indicating that the fluorescence switching is dependent on matrices.     

Fluorodynamers Displaying Tunable Fluorescence on Constitutional Exchanges in Solution and at Solid Film–Solution Interface

Dynamic covalent polymers—dynamers—are adaptive materials that offer timely variant adaptive macroscopic organization across extended scales. In the current study, imine exchange reactions and fluorescence transfer can occur at the interfaces between various solutions and solid state dynameric films. The fluorescence quenching upon imine formations for designed fluorogen was successfully demonstrated, and this tunable fluorescence was further used to study the re-composition of a solid film. Moreover, the dynamic covalent films also exhibited responsiveness to competing amines and acid/base conditions, both in solutions and solid film–solution interface. This work can provide more insights into interface dynamic chemistry and holds great potential for further applications in optical and biomedical materials.     

8-羟基喹啉铝高分子薄膜的荧光特性

In this paper, the solid state. polymer thin films of 8-hydroxylquinoline aluminum (Alq3) were made by spinning coat method. The fluorescence efficiencies and the luminescence spectra of them were measured via the laser systems. Various experimental factors were considered and tested. It was found that the peak wavelength of the luminescence spectra of the Alq3 polymer films shifted and that the purity of the samples affected its fluorescence efficiencies: the fluorescence efficiencies of impure samples were about three-fourth of that of the purified ones; fluorescence efficiencies of Alq3 doped in PMMA polymer was higher than that doped in PC and PEO. Under certain conditions, transparent thin film 10 layers can be achieved. This kind of polymer thin film of Alq3 exhibits well fluorescence response, but also has good stability. Spin coat method can greatly reduce the technical requirements comparing with the vacuum plating method.     

Photo-quenched luminescence in Co(II)-doped sol–gel zirconia

The quenching process of the laser-induced luminescence of Co(II)-doped zirconia samples prepared by the sol–gel method is reported. Zirconia monoliths doped with Co(II) at different concentrations, were laser irradiated producing fluorescence; its intensity, measured by the slope at the low energy side of the Raman spectra, is reduced with the irradiation time. The rate the fluorescence decays can be modeled as a double exponential function of the irradiation time; the characteristic times involved in this quenching process are in the range of seconds. The suppression of the luminescence has been associated to the local heating produced when the laser beam is focused in a small area (≈2 microns in diameter) on the sample. This heating process reduces physical (such as grain boundaries and surface states) and chemical (oxygen vacancies) defects; however, some residual fluorescence still remains after long periods of illumination. R. Rodríguez is on sabbatical leave at Cinvestav, Unidad Queretaro.     

Injecting electronic excitation energy into an artificial antenna system through an Ru2+ complex

The Ru2+ complex [Ru(bpy)2(bpy-ph4-Si(CH3)3)]2+ can be electrostatically bound to the negatively charged channel entrances of dye-loaded zeolite L crystals where it acts as a functional stopcock molecule. Impressive electronic triplet-singlet excitation energy transfer from the Ru2+ complex to the acceptor dye oxazine 1 (Ox1) located inside the channels can be observed when the donor molecule is selectively excited. Time-resolved luminescence experiments have been performed on the separate components and on the assembled donor-acceptor material. The luminescence lifetime of the Ru2+ complex attached to the zeolite is reduced by a factor of 30 when Ox1 acceptor molecules are present. The fluorescence decay of Ox1 incorporated in zeolite L is single exponential with a lifetime of 3 ns. The much longer lifetime in zeolite L than in solution is due to the fact, that the diethyl groups are sterically restricted when the dye is inside the host.     

Low-energy electron-stimulated luminescence of thin H2O and D2O layers on Pt(111)

The electron-stimulated luminescence (ESL) from amorphous solid water and crystalline ice films deposited on Pt(111) at 100 K is investigated as a function of the film thickness, incident electron energy (5-1000 eV), isotopic composition, and film structure. The ESL emission spectrum has a characteristic double-peaked shape that has been attributed to a transition between a superexcited state (C) and the dissociative, first excited state (A) in water: C --> A. Comparing the electron-stimulated luminescence and O2 electron-stimulated desorption (ESD) yields versus incident electron energy, we find the ESL threshold is approximately 3 eV higher than the O2 ESD threshold, which is close to the center of the emission spectrum near 400 nm and supports the C --> A assignment for the ESL. For thin films, radiative and nonradiative interactions with the substrate tend to quench the luminescence. The luminescence yield increases with coverage since the interactions with the substrate become less important. The ESL yield from D2O is approximately 4-5 times higher than that from H2O. With use of layered films of H2O and D2O, this sizable isotopic effect on the ESL is exploited to spatially profile the luminescence emission within the ASW films. These experiments show that most of the luminescence is emitted from within the penetration depth of the incident electron. However, the results depend on the order of the isotopes in the film and can be modeled by assuming some migration of the electronically excited states within the film. The ESL is very sensitive to defects and structural changes in solid water, and the emission yield is significantly higher from amorphous films than from crystalline ice.     

Fluorescent lifetime quenching near d = 1.5 nm gold nanoparticles: probing NSET validity

The fluorescence behavior of molecular dyes at discrete distances from 1.5 nm diameter gold nanoparticles as a function of distance and energy is investigated. Photoluminescence and luminescence lifetime measurements both demonstrate quenching behavior consistent with 1/d(4) separation distance from dye to the surface of the nanoparticle. In agreement with the model of Persson and Lang, all experimental data show that energy transfer to the metal surface is the dominant quenching mechanism, and the radiative rate is unchanged throughout the experiment.     

具有聚集诱导发光性能的乙烯基衍生物的合成及其对DNT的检测

采用Wittig-Horner反应合成了两种具有聚集诱导发光(AIE)性能的乙烯基衍生物.紫外及荧光光谱显示,两种化合物在聚集态时分子间的π-π相互作用很弱,二者在聚集态时都展示了很强的荧光增强发光性能.由于二者所具有的扭曲的分子构型提供了2,4-二硝基甲苯(DNT)气态分子扩散所需的分子通道,因此对DNT蒸气的检测均显示了较高的荧光猝灭效率,且其荧光猝灭具有较好的可逆性.     

Upconversion properties of Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses

Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses emitting blue, green and red upconversion luminescence at 970 nm laser diode excitation were studied. It was shown that Tm3+ behaves as the sensitizer to Er3+ for the green upconversion luminescence through the energy transfer process: Tm3+:3H4+Er3+:4I 15/2-->Er3+:4I 9/2+Tm3+:3H6, and for the red upconversion luminescence through the energy transfer process: Tm3+:3F4+Er3+:4I 11/2-->Tm3+:3H6+Er3+:4F 9/2. Moreover, Er3+ acts as quenching center for the blue upconversion luminescence of Tm3+. The sensitization of Tm3+ to Er3+ depends on the concentration of Yb3+. The intensity of blue, green and red emissions can be changed by adjusting the concentrations of the three kinds of rare earth ions. This research may provide useful information for the development of high color and spatial resolution devices and white light simulation.     

Preparation and Characterization of Ternary Europium ComplexDoped Thin SolGel Hybrid Film by Fluorescence Spectroscopy*

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Rhodamine B nanocrystals: elaborations,characterizations and functionalizations for biosensing applications

A biological sensor based on fluorescent organic nanocrystals (NCs) of Rhodamine B grown in sol–gel thin films was developed. The original signalization function is based on fluorescence contrasts of NCs, which exhibit a simple fluorescence signature, good photostability and higher fluorescence intensities compared to dispersed dye molecules. Thanks to a well-controlled dissolution process of the sol–gel surface, accurately followed by atomic force microscopy, the NCs were made emerging just a few nanometers above the silicate thin films to be directly accessible to biological macromolecules. Thus, hairpin-shaped DNA, functionalized by a probe-molecule (DNA probe), has been grafted onto nanocrystal surfaces leading to a fluorescence quenching by Forster resonance energy transfer. After hybridization of these hairpin-shaped DNA probes with their complementary DNA-target, the molecular probes and NCs are pulled apart, stopping thus the quenching. This “turn-on” of nanocrystal fluorescence allows thus a label-free DNA detection. The preparation methodology of the signalization function, its functionalization by hairpin-shaped DNA probes and first DNA-sensor experiments are presented.     

Laser spectroscopic studies of Tb3+-doped oxyfluoroborate glass

Tb3+-doped oxyfluoroborate glasses have been prepared for different concentrations of Tb. The absorption, fluorescence and photoacoustic spectra of these have been recorded and studied. It is marked that the fluorescence intensity of different fluorescence transitions decreases with the increase of Tb ion concentration in the glass. This quenching at higher concentration is due to the energy transfer among the excited and nearest neighbor unexcited Tb ions in the glass. The lifetime measurement confirms it, as the lifetime of a particular state was found to decrease with the increase of Tb ion concentration in the glass. The mechanism of the energy transfer process was determined to involve quadrupole quadrupole interaction. We have also studied the energy transfer from Tb3+-->Pr3+ when both the rare earths are doped together in the glass. A decrease in the lifetime of the 5D4 level of Tb3+ with the increase of Pr3+ concentration confirms this.     

Inherent Photon Energy Recycling Effects in the Up‐Converted Delayed Luminescence Dynamics of Poly(fluorene)–PtIIoctaethyl Porphyrin Blends

We present results of steady‐state and transient photoluminescence studies of molecularly doped poly(fluorene) films. We study blends with increasing content of the triplet emitter (2,3,7,8,12,13,17,18‐octaethyl‐porphyrinato)Pt^II (PtOEP) when dispersed in the polymeric poly(fluorene) matrix of the poly[9,9‐di‐(2‐ethylhexyl)‐fluorenyl‐2,7‐diyl] (PF26) derivative. We carry out a unified study of the photophysical reactions that are involved in the energy transfer processes in this system by probing the three luminescence processes of a) PF26 fluorescence, b) triplet–triplet annihilation (TTA) induced up‐converted PF26 delayed fluorescence and c) PtOEP phosphorescence. With increasing PtOEP content, the process of photon energy recycling in the PF26:PtOEP system is manifested from the quenching of the TTA‐induced up‐converted PF26 delayed fluorescence and it is rationalized with the use of Forster theory of resonant energy transfer. Based on the combined results of the photophysical and the transmission electron microscopy characterization of the as‐spun PF26:PtOEP films, we determine the onset of PtOEP aggregation at 2–3 wt % PtOEP content. The analysis of the photophysical data is based on the use of modified Stern–Volmer photokinetic models that are appropriate for the solid state. A static component in the PL quenching of PF26 is revealed for PtOEP contents below 2 wt %. The modified Stern–Volmer kinetic scheme further suggests that co‐aggregation effects between PF26 and PtOEP are operative with an association constant of ground state complex formation k_bind ～15–17 M ^?1. The involvement of the ground state heterospecies in the TTA‐mediated PF26 up‐converted luminescence is discussed. The participation of an electron‐exchange step, in the excited state energy transfer pathway between PtOEP and PF26, is proposed for the activation mechanism of the PF26 up‐converted fluorescence.     

Ca_4GdO(BO_3)_3:Eu~(3 ),Sm~(3 )的发光及离子间的能量转移

Ca4 RO( BO3 ) 3 ( R=La,Ln,Y)三硼酸盐具有优良的非线性特征 . Khamaganova等[1] 以Pb O作助熔剂在合成 Ca4 Sm2 ( BO3 ) 4的过程中发现了一种新相 ,经过结构分析判定是一种新的化合物 .Norrestam等通过高温固相反应合成出此类三硼酸盐 .Iiykhuin[2 ] 对 Ca4 RO( BO3 ) 3( R=Lu,Tb,Gd)的结构进行了研究 .Dirkse等 [3 ]报道了 Ca4 Gd O( BO3 ) 3 粉末的发光特性 .1 996年 ,Aka[4 ] 采用提拉法 ( Czochralski)首次生长出较大尺寸的 Ca4 Gd O( BO3 ) 3 单晶 .孟宪林等 [5]报道了 Ca4 YO( BO3 ) 3 :Nd晶体的激光发射和自倍…     

金纳米颗粒表面能量转移及巯基化合物的检测

二氧化硅稳定的金纳米颗粒(Au-SiO₂)与罗丹明B之间发生表面能量转移,使罗丹明B荧光猝灭。 金纳米颗粒对罗丹明B的Stern-Volmer猝灭常数为4.3×10³ L/mol。 当荧光猝灭的混合体系中加入巯基化合物时,巯基化合物与金纳米颗粒发生强相互作用阻断罗丹明B-金纳米颗粒之间的能量转移,罗丹明B荧光恢复。 基于罗丹明B-Au-SiO₂体系对巯基化合物的单一响应,建立了一种简单快速检测巯基化合物的方法;并且由于二氧化硅对金纳米颗粒的稳定作用,金纳米颗粒成为一种可以回收利用的检测探针。     

基于上转换发光共振能量转移的CRISPR/Cas12a生物传感系统用于HPV16 DNA双信号检测

传统的纯核结构的上转换纳米材料用于生物传感时, 存在表面猝灭效应或者因发光共振能量转移(LRET)效率不高导致灵敏度低等缺点, 对目标物的灵敏检测有一定的局限性. 本文通过多步高温共沉淀, 介导壳层外延成长法, 合成了NaYF₄∶Yb³⁺,Er³⁺(C-UCNPs)核层发光和NaYF₄@NaYF₄∶Yb³⁺,Er³⁺@NaYF₄(CSS-UCNPs)内壳层发光能量限域型上转换纳米材料, 并表征了材料的晶型、 形貌、 表面配体、 元素组成和发光共振能量转移效率. 结果表明, 该材料具有表面猝灭效应低、 发光共振转移效率较高的优势, 随后将其与成簇规律间隔的短回文重复序列及其相关蛋白(CRISPR/Cas)12a-纳米金系统结合, 实现了人乳头瘤病毒DNA(HPV16 DNA)的比色定性和上转换发光定量分析, 检出限为69.8 pmol/L, 双信号检测有效提高了检测结果的准确性. 此外, 本方法不仅特异性强, 还能识别单碱基错配的HPV16 DNA, 提高了DNA片段的容错率.     

Three‐Component Langmuir–Blodgett Films Consisting of Surfactant,Clay Mineral,and Lysozyme: Construction and Characterization

The Langmuir–Blodgett (L–B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant–clay L–B film at the air–water interface without phase transition. The UV‐visible spectra of the hybrid film ODAH–saponite–Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3±0.2) ng mm^?2. The average surface area (Ω) per molecule of lysozyme is approximately 18.2 nm² in the saponite layer. For the multilayer film (ODAH–saponite–Lys)_n, the average amount of lysozyme per layer is (1.0±0.1) ng mm^?2. The amount of lysozyme found in the hybrid films of ODAH–laponite–Lys is at the detection limit of about 0.4 ng mm^?2. Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm^?1 band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mN m^?1.