Maximum Fluorescence Wavelength Research Articles

Solvatochromic fluorescence properties of pyrazine-boron complex bearing a β-iminoenolate ligand.

Pyrazine-based monoboron complexes bearing two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex) on the boron atom were synthesized, and the fluorescence properties were investigated. The BPh2 complexes exhibited red-shifted maximum absorption and maximum fluorescence wavelengths and lower molar absorption coefficients than the corresponding BF2 complexes in n-hexane. The fluorescence quantum yields of the BPh2 complexes were higher than or comparable to the corresponding BF2 complexes owing to the relatively low nonradiative rate constants. Although the nonsubstituted and trifluoromethyl-substituted derivatives did not show solvatochromism, the dimethylamino-substituted BF2 and BPh2 complexes exhibited pronounced solvatochromism in the fluorescence spectra. Dual fluorescence was observed for the dimethylamino-substituted BF2 complex in toluene, 1,4-dioxane, and chloroform, corresponding to locally excited (LE) and twisted intramolecular charge-transfer (TICT) states.

Combined use of two membrane-potential-sensitive dyes for determination of the Galvani potential difference across a biomimetic oil/water interface

The fluorescence behavior of anionic membrane-potential-sensitive dyes, bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4(3)) and bis-(1,3-diethylthiobarbituric acid)trimethine oxonol (DiSBAC2(3)), at a biomimetic 1,2-dichloroethane (DCE)/water (W) interface was studied by the mean of potential-modulated fluorescence (PMF) spectroscopy. The respective dyes gave a well-defined PMF signal due to the adsorption/desorption at the DCE/W interface. It was also found that the potentials where the two dyes gave the PMF signals were different by about 100mV. We then attempted a combined use of the two dyes for determination of the Galvani potential difference across the DCE/W interface. When 40μM DiBAC4(3) and 15μM DiSBAC2(3) were initially added to the W phase, distinctly different spectra were obtained for different interfacial potentials. The ratio of the PMF signal intensities at 530 and 575nm (the fluorescence maximum wavelengths for the respective dyes) showed a clear dependence on the interfacial potential. These results suggested the potential utility of the combined use of two dyes for the determination of membrane potentials in vivo.

Synthesis and Properties of Photochromic Dithienylethene Compounds with Triphenylamine Units

Combining dithienylethene photochromic unit with triphenylamine unit, three new photochromic dithienylethene compounds 1a~1c were successfully synthesized using 5-chloro-2-methyl-3-acetylthiophene and diphenylaminobenzalde- hydes as starting materials through Aldol condensation reaction, Michael addition reaction and McMurry coupling reaction, the structures of which were characterized by MS, 1 H NMR and 13 C NMR. Different from majority of previous studies that introduce different functional groups through thiophene rings, we bridged the triphenylamine unit with fluorescence property to the cyclopentene at β-position via C—C single bond, which will maintain the activation of photochromism and prevent other functional groups affecting the dithienylethene backbone. Their photochromic and fluorescence properties in solutions and polymethylmethacrylate films were investigated by UV-Vis and fluorescence spectra, respectively. The colorless solu- tions and films of 1a~1c switch to yellow upon irradiation with 302 nm UV light and reach the photostationary state fast, while bleaching of the colored solutions happen upon irradiation with 450 nm blue light. When 1a~1c are excited by UV light, the maximum fluorescence wavelengths of 1a~1c increase along with the enhancement of the abilities of electron donating of substituent R, and 1a~1c emit strong fluorescence in n-hexane, toluene and ethyl acetate, while weak in acetoni- trile and none in chloroform. Moreover, upon irradiation at 302 nm, Forster resonance energy transfer occurs between triphenylamine unit and dithienylcyclopentene unit of 1a~1c. Thus, the fluorescence intensities of 1a~1c decrease along with the prolonging of irradiation time, which indicates the potential application of these compounds as fluorescence mo- lecular switches. Keywords dithienylethene; triphenylamine; photochromic; fluorescence molecular switch; Forster resonance energy trans- fer

Synthesis and Fluorescence Properties of Pyrimidine Mono- and Bisboron Complexes

Novel fluorescent mono- and bisboron complexes based on pyrimidine bearing β-iminoenolate ligands were synthesized, and their fluorescence properties were investigated. The nonsubstituted and trifluoromethyl-substituted monoboron complexes showed higher fluorescence quantum yield in solid state than in solution. The dimethylamino derivative of the monoboron complex exhibited positive solvatochromism in the fluorescence spectra. The bisboron complex showed significantly higher molar absorption coefficient and red-shifted maximum absorption and maximum fluorescence wavelengths than the corresponding monoboron complex.

Measuring the spatial distribution of dielectric constants in polymers through quasi-single molecule microscopy.

The variation in dielectric constant is measured for thin films of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) using confocal fluorescence microscopy. Spatial variation in the local dielectric constant of the polymer films on the ~250 nm length scale is measured using the solvochromatic emission from incorporated nile red (NR) at "quasi-single molecule" (10(-7) M) and true single molecule (SM) concentrations (10(-9) M). Correlation of the NR fluorescence wavelength maximum with dielectric constant is used to transform images of NR's emission maxima to spatial variation in local dielectric constant. We demonstrate that the distributions of dielectric environments measured in the quasi- and true SM approaches are equivalent; however, the enhanced signal rates present in the quasi-SM approach result in this technique being more efficient. In addition, the quasi-SM technique reports directly on the continuous spatial variation in dielectric constant, information that is difficult to obtain in true SM studies. With regards to the polymers of interest, the results presented here demonstrate that a limited distribution of dielectric environments is present in PMMA; however, a broad distribution of environments exists in PVDF consistent with this polymer existing as a distribution of structural phases.

Optical properties of the hybrid nanocomposites consisting of poly-n-phenylvinylene and cadmium sulfide

Thin-film hybrid nanocomposites based on poly-n-phenylvinylene with various contents of the CdS semiconductor nanoparticles are obtained using the pyrolytic polymerization of dichloro-n-xylene from the gas phase and the simultaneous sedimentation of the CdS vapor with the subsequent thermal processing of the precursor. The structure of the nanocomposite is studied, and the optical properties of the materials are analyzed. It is demonstrated that a variation in the concentration of the inorganic component in the polymer matrix leads to a variation in the maximum fluorescence wavelength and optical band gap. The material parameters (degree of conjugation of poly-n-phenylvinylene, band gap, Huang-Rhys factor, Stokes shift, and vibronic energy of molecules) are determined.

Fluorescence Micropatterning Based on the Polymeric Photobase Generator Containing Oxime-Urethane Groups by Dansylation

A polymeric photobase generator containing oxime-urethane groups is applied to a fluorescence micropatterning material. Polymer bearing oxime-urethane groups was prepared by copolymerization of methyl methacrylate with methacryloyloxyethyl benzophenoneoxime urethane (MBU). The reaction of amino groups in the irradiated copolymer film with dansyl chloride (Dns-Cl) was monitored by using UV absorption, IR absorption and fluorescence spectroscopy. The fluorescence spectrum of the Dns-Cl-treated irradiated copolymer film shows a strong fluorescence with a fluorescence maximum wavelength at 510 nm. A blue fluorescent micropattern with a line width of <TEX>$2{\sim}3{\mu}m$</TEX> was obtained. Treatment of the irradiated copolymer film with Dns-Cl and rhodamine B mixture led to the formation of green, red, and orange-colored fluorescence micropatterns. Thus, various colored micropatterns on a single polymer film can be obtained by selective excitation of each dye molecules.

Trimethine cyanine dyes with an indole nucleus: Synthesis and spectral properties studies

A series of trimethine quinoline cyanine dyes with an indole nucleus were designed and synthesized based on the chemical structures of Cy3 and TO. The structures of all dyes were confirmed by 1HNMR and MS. Studies on their spectral properties showed that the trimethine cyanine dyes had properties of both the embedded dye TO and the bonded dye Cy3. The maximum fluorescence wavelength of the final cyanine dyes shifted red compared with those of Cy3 and TO alone.When we changed the substituent groups on the indole ring of the dye, both the fluorescence intensity and wavelength exhibited corresponding changes. The fluorescence wavelength of indole quinoline with an electron donor group shifted red and the fluorescence intensity was enhanced with good photostability. When labeled with BSA, a significant fluorescence enhancement could be observed.

Fluorescent properties of coumarins with dual functions constructed by two sequential reactions

A series of coumarins with two aryl moieties was constructed from 3-azide-6-bromocoumarin scaffold by means of two sequential reactions, Huisgen 1,3-cycloaddition and Suzuki–Miyaura coupling reactions. Evaluation of their fluorescence properties indicated that the mode of fluorescent change by substituted group on each aryl group would be different. So this structure could be promising candidates as multi-analyte type fluorescent sensors, whose mode of spectroscopic changes, such as fluorescence intensity, and absorption or fluorescence maximum wavelength, are different for each analyte.

Gel Formation Driven by Tunable Hydrophobic Domain: Design of Acrylamide Macromonomer with Oligo Hydrophobic Segment

Nowadays, biomaterials with amphiphilic properties are undergoing remarkable development. Here, we present one such development, in which we prepared amphiphilic graft copolymers, with a main chain composed of hydroxyethyl acrylamide (HEAA), to introduce hydrophilicity, and a side chain composed of poly(trimethylene carbonate) (PTMC) to introduce tunable hydrophobicity. These macromonomers were created with a novel molecular design, which introduced a ring-opening polymerization by the hydroxyl end group of HEAA in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, and were analyzed by (1)H NMR and gel permeation chromatography. The amphiphilic graft copolymers were shown to form a hydrogel, the swelling ratio of which was greatly influenced by the number of trimethylene carbonate units. These copolymers also exhibited the Tyndall phenomenon in aqueous solution; they aggregated spontaneously due to hydrogen bonding and hydrophobic interactions, and a sodium 8-anilino-1-naphthalenesulfonate (ANS) fluorescence probe was introduced into the hydrophobic domain. The solution property of ANS in the polymer solution was analyzed by fluorescence measurement and (1)H NMR. The maximum fluorescence wavelength of ANS shifted to shorter wavelengths as the degree of polymerization of the hydrophobic PTMC, the composition of the macromonomer, and the concentration of the copolymer increased. The resulting copolymer formed a polymer micelle structure due to the tunable hydrophobic domain formation in selected solvents. Therefore, these amphiphilic graft copolymers containing a PTMC segment are excellent candidates for use as hydrophobic drug delivery carriers.

The fibrillogenic L178H variant of apolipoprotein A-I forms helical fibrils

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. Previously, we showed that the G26R mutation of apoA-I leads to increased β-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. In vivo, this and other variants mutated in the N-terminal domain (residues 26 to ∼90) lead to renal and hepatic accumulation. In contrast, several mutations identified within residues 170 to 178 lead to cardiac, laryngeal, and cutaneous protein deposition. Here, we describe the structural changes in the fibrillogenic variant L178H. Like G26R, the initial structure of the protein exhibits altered tertiary conformation relative to wild-type protein along with decreased stability and an altered lipid binding profile. However, in contrast to G26R, L178H undergoes an increase in helical structure upon incubation at 37°C with a half time (t1/2) of about 12 days. Upon prolonged incubation, the L178H mutant forms fibrils of a diameter of 10 nm that ranges in length from 30 to 120 nm. These results show that apoA-I, known for its dynamic properties, has the ability to form multiple fibrillar conformations, which may play a role in the tissue-specific deposition of the individual variants.

Fluorescence Behavior of Dyes in Thin Films of Various Polymers

We have studied the fluorescence behavior of a dye, 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid (NBD), in thin films of polymers with various polarities, such as poly(methyl methacrylate) (PMMA), Arton, poly(styrene) (PS), hydrogenated polystyrene (H-PS), and Zeonex. In the case of well-dispersed systems, the fluorescence behavior of NBD could be explained in terms of the mobility of the polymer matrix. This was the case for PMMA, Arton, and PS. On the other hand, when H-PS or Zeonex was used, NBD aggregated in the films, leading to unusual fluorescence behavior: the fluorescence lifetime and maximum wavelength increased with a decrease in the film thickness. Time- and space-resolved fluorescence spectroscopy using an evanescent wave excitation revealed that the aggregation states of NBD near the interface varied with the film thickness. While NBD molecules near the interface aggregated in a thick film, such was not the case in a thin film. Angular-dependent X-ray photoelectron spectroscop...

Synthesis of Coumarin Conjugates of Biological Thiols for Fluorescent Detection and Estimation

Coumarin-labeled thioesters are efficiently prepared from biological thiols using N-coumarin-3-carbonyl benzotriazoles. Absorption (λabs), fluorescence (λem) wavelength maxima and quantum yields (φ) for the thioesters are measured in buffer solution at physiological pH 7.4. Quantum yields (φ = 0.0318-0.1068) of four of the products are higher than their precursor 7-methoxy-3-(1H-benzotriazol-1-ylcarbonyl)-2H-chromen-2-one (φ = 0.0195), suggesting that derivatives of this type could be suitable for quantitative thiol assays.

Effect of method of preparation and drying time on photophysical properties of coumarin 1 laser dye embedded in HCl catalysed sol–gel glasses

Coumarin 1 (C1) dye is impregnated in transparent sol–gel glass samples prepared by sol–gel process using three methods – (I) using HCl as catalyst and glycerol as a drying control chemical additive (DCCA), (II) using HCl as catalyst at 60 °C subsequent drying at room temperature, and (III) using HCl as catalyst at 60 °C and heated at 600 °C for 3 h. The sol–gel matrices prepared by Methods I and II are given dip treatment with methanol/distilled water (50/50 volume) for 16 h before dipping into dye solution. The effect of method and drying time of matrix on spectroscopic properties of C1 dye doped glass samples has been studied. The optical density (OD) at absorption maximum wavelength and fluorescence intensity (FI) at fluorescence maximum wavelength of all C1 dye doped samples prepared by Methods I and II decrease, where as there is no change in photophysical properties (OD/FI) is observed in samples prepared by Method III with the time of drying of the sol–gel samples. These absorption/fluorescence properties of C1 dye in sol–gel glass matrices are compared with its respective properties in methanolic solution in acidic environment.

Facile Synthesis and Systematic Investigations of a Series of Novel Bent‐Shaped Two‐Photon Absorption Chromophores Based on Pyrimidine

The synthesis, structure, and single- and two-photon spectroscopic properties of a series of pyrimidine-based (bent-shaped) molecules are reported. All these stable heterocyclic compounds are fully characterized, and exhibit intense single- and two-photon excited fluorescence (SPEF and TPEF) over a wide spectral range from blue to red, with the spectral peak position of the SPEF being basically the same as that of the TPEF. The well-conjugated pi-systems, observed from the crystal structure, indicate the charge transfer feature of the ground state. Meanwhile, the theoretical and experimental studies indicate that the charge transfer from donor to acceptor is greatly enhanced in the excited states and the different substituted donor groups on the pyrimidine have a large effect on the optical and electrochemical properties. Based on typical structure data and comprehensive spectral data, the following structure-property relationships can be determined: for such bent-shaped chromophores, the absorption and the fluorescence wavelength maximum of the SPEF and TPEF, and two-photon absorption cross sections show a similar trend with increasing electron-donating strength of the corresponding terminal group and the number of branches, while the average bond lengths of the pi-linkage and HOMO-LUMO energy levels show an inverse trend. Experimental data and theoretical calculation provide a coherent picture. With these findings, bent-shaped quadrupolar chromophores combining peak TPA cross sections (up to 2280 GM), broad TPA bands throughout the whole 700-900 nm range, and high fluorescence quantum yields could, thus, be obtained. Such compounds are of particular interest for TPEF microscopy, as well as optical data storage in the visible and NIR regions. A data recording experiment proved the potential application of these materials.

Effect of Matrix Treatment on Spectroscopic Properties of HCl Catalysed Sol-Gel Glasses Containing Coumarin Laser Dyes

Coumarin 1, Coumarin 2 and Coumarin 120 are embedded in transparent sol-gel glass samples prepared by sol-gel process using dip method. The sol-gel matrix is given dip treatment with Methanol /Distilled Water (50/50 vol) for 1 to 16 h before dipping into dye solution. The effect of dipping time of matrix in Methanol/ Distilled Water on spectroscopic properties of coumarin dye doped glass samples has been studied. The Optical Density (OD) at absorption maximum wavelength and Fluorescence Intensity (FI) at fluorescence maximum wavelength of all coumarin dyes increase with the time of dipping of the sol-gel sample. These absorption/fluorescence properties of coumarin dyes in sol-gel glass matrices are compared with its respective properties in methanolic solution in acidic environment. The cause of these changes in OD/FI with dipping time is discussed by taking into account the absorption / fluorescence of dye in acidified methanol.

Molecular Features Governing the Stability and Specificity of Functional Complex Formation by Mycobacterium tuberculosis CFP-10/ESAT-6 Family Proteins

The Mycobacterium tuberculosis complex CFP-10/ESAT-6 family proteins play essential but poorly defined roles in tuberculosis pathogenesis. In this article we report the results of detailed spectroscopic studies of several members of the CFP-10/ESAT-6 family. This work shows that the CFP-10/ESAT-6 related proteins, Rv0287 and Rv0288, form a tight 1:1 complex, which is predominantly helical in structure and is predicted to closely resemble the complex formed by CFP-10 and ESAT-6. In addition, the Rv0287.Rv0288 complex was found to be significantly more stable to both chemical and temperature induced denaturation than CFP-10.ESAT-6. This approach demonstrated that neither Rv0287.Rv0288 nor the CFP-10.ESAT-6 complexes are destabilized at low pH (4.5), indicating that even in low pH environments, such as the mature phagosome, both Rv0287.Rv0288 and CFP-10.ESAT-6 undoubtedly function as complexes rather than individual proteins. Analysis of the structure of the CFP-10.ESAT-6 complex and optimized amino acid sequence alignments of M. tuberculosis CFP-10/ESAT-6 family proteins revealed that residues involved in the intramolecular contacts between helices are conserved across the CFP-10/ESAT-6 family, but not those involved in primarily intermolecular contacts. This analysis identified the molecular basis for the specificity and stability of complex formation between CFP-10/ESAT-6 family proteins, and indicates that the formation of functional complexes with key roles in pathogenesis will be limited to genome partners, or very closely related family members, such as Rv0287/Rv0288 and Rv3019c/Rv3020c.

Polar Laser Dyes Dispersed in Polymer Matrices: Reverification of Charge Transfer Character and New Optical Functions

In this paper, we describe the photophysical properties and new functions of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) and its derivative, 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl)-ethenyl]-4H-pyran-4-ylidene)propane dinitrile (DCM2) in various polymer matrices, with respect to intramolecular charge transfer (ICT). The maximum fluorescence wavelengths of DCM and DCM2 shifted to red with an increase in the dielectric constant of the polymer matrix. The fluorescence lifetime shortened according to the matrix polarity. When a polymer with a dielectric constant varying according to its crystalline structure, poly(vinylidenefluoride-co-trifluoroethylene) (PVdF-co-TrFE), was used as a matrix, we were able to thermally tune the fluorescence wavelength as well as the fluorescence intensity of DCM2. The locked molecular structure of DCM2 was very effective for maintaining the charge transfer character during thermal stimulation.

Specific Binding Effects for Cucurbit[8]uril in 2,4,6‐Triphenylpyrylium–Cucurbit[8]uril Host–Guest Complexes: Observation of Room‐Temperature Phosphorescence and their Application in Electroluminescence

2,4,6-Triphenylpyrylium (TP(+)) forms host-guest complexes with cucurbiturils (CBs) in acidic aqueous solutions. (1)H NMR spectroscopic data indicates that complexation takes place by encapsulation of the phenyl ring at the four position within CB. Formation of the complex with CB[6] and CB[7] leads to minor shifts in the fluorescence wavelength maximum (lambda(fl)) or quantum yield (Phi(fl)). In sharp contrast, for complexes with CB[8], the emission results in the simultaneous observation of fluorescence (lambda(fl)=480 nm, Phi(fl)=0.05) and room-temperature phosphorescence (lambda(ph)=590 nm, Phi(ph)=0.15). The occurrence of room-temperature phosphorescence can be used to detect the presence of CB[8] visually in solution. Molecular modeling and MM2 molecular mechanics calculations suggest that this effect arises from locking the conformational mobility of the 2- and 6-phenyl rings as a result of CB[8] encapsulation. The remarkably high room-temperature phosphorescence quantum yield of the TP(+)@CB[8] complex has been advantageously applied to develop an electroluminescent cell that contains this host-guest complex. In contrast, analogous cells prepared with TP(+) or TP(+)@CB[7] fail to exhibit electroluminescence.

Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 1: Synthesis, Vibrational Properties and Excited‐state Decay Characteristics

Understanding the effects of substituents on the spectra of chlorins is essential for a wide variety of applications. Recent developments in synthetic methodology have made possible systematic studies of the properties of the chlorin macrocycle as a function of diverse types and patterns of substituents. In this paper, the spectral, vibrational and excited-state decay characteristics are examined for a set of synthetic chlorins. The chlorins bear substituents at the 5,10,15 (meso) positions or the 3,13 (beta) positions (plus 10-mesityl in a series of compounds) and include 24 zinc chlorins, 18 free base (Fb) analogs and one Fb or zinc oxophorbine. The oxophorbine contains the keto-bearing isocyclic ring present in the natural photosynthetic pigments (e.g. chlorophyll a). The substituents cause no significant perturbation to the structure of the chlorin macrocycle, as evidenced by the vibrational properties investigated using resonance Raman spectroscopy. In contrast, the fluorescence properties are significantly altered due to the electronic effects of substituents. For example, the fluorescence wavelength maximum, quantum yield and lifetime for a zinc chlorin bearing 3,13-diacetyl and 10-mesityl groups (662 nm, 0.28, 6.0 ns) differ substantially from those of the parent unsubstituted chlorin (602 nm, 0.062, 1.7 ns). Each of these properties of the lowest singlet excited state can be progressively stepped between these two extremes by incorporating different substituents. These perturbations are associated with significant changes in the rate constants of the decay pathways of the lowest excited singlet state. In this regard, the zinc chlorins with the red-most fluorescence also have the greatest radiative decay rate constant and are expected to have the fastest nonradiative internal conversion to the ground state. Nonetheless, these complexes have the longest singlet excited-state lifetime. The Fb chlorins bearing the same substituents exhibit similar fluorescence properties. Such combinations of factors render the chlorins suitable for a range of applications that require tunable coverage of the solar spectrum, long-lived excited states and red-region fluorescence.