Monitoring i-motif transitions through the exciplex emission of a fluorescent probe incorporating two (Py)A units

Pairs of pyrene-modified deoxyadenosine ((Py)A) units induce a stable interstrand i-motif structure, which can be characterized by a change in the fluorescence λ(max), with an exciplex emission that is not observable in its single-strand structure.     

Controlled synthesis and fluorescent properties of poly(9-(4-vinylbenzyl)-9H-carbazole) via nitroxide-mediated living free-radical polymerization

The functional polymer containing carbazole unit, [(poly(9-(4-vinylbenzyl)-9H-carbazole) (PVBK)], was successfully prepared via nitroxide-mediated living free-radical polymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK). The controlled features of the polymerization were confirmed by the linear increase in the molecular weight with the monomer conversion while keeping the relative narrow molecular weight distribution (M_w/M_n ? 1.51), and successful chain extension with styrene. The resulting polymer absorbed light in the 305-355 nm range and exhibited fluorescent emission at 350 nm. The fluorescent intensity of the polymer was lower than that of monomer and was affected by the properties of the different solvents, which decreased in the following order: DMF > THF > CHCl₃ at the same concentration of carbazole units. The fluorescence intensity of the polymer was apparently influenced by chromophore concentration, and the maximum value was obtained when the carbazole unit concentration was around 8 × 10⁻⁵ mol/L. Moreover, it was shown that the strong fluorescence of PVBK can be quenched by methyl acrylate (MA).     

一种蓝光单体的合成及其荧光性能研究

吡唑啉衍生物在生物医药[1,2]应用的领域非常广泛.吡唑啉还是一种优质的发光材料[3],其发射波长位于450nm左右,具有很高的荧光量子效率,且发光波长窄,色纯度好,是一种纯正的蓝光.当吡唑啉环3位引入给电子基时,化合物则具有很高的荧光量子产率,可制得具有高热稳定性的空穴传输蓝光发光材料[4-6]和荧光探针[7].它还可以将吸收的不可见的紫外光转变为蓝色的可见光反射出来,从而增加了光线的反射率,使被其处理过的物体白度和光泽提高,所以吡唑啉又被做为荧光增白剂和荧光染料[8,9]进行广泛地应用.     

Preparation and fluorescent properties of poly(vinyl alcohol) bearing coumarin

A novel water‐soluble fluorescent material was prepared via ring‐opening reaction between 4‐methyl‐7‐(2,3‐expoxypropoxy) coumarin (MEC) and poly(vinyl alcohol) (PVA). The fluorescent behaviors of this material (PVA–MEC) in solution, solid and film were studied in detail. The results showed that the fluorescence of PVA–MEC arose from isolated dye molecules and had a good film forming ability. In addition, the effects of acid/base environments on PVA–MEC were studied and the results showed that it was less affected by environment than 7‐HMC. Moreover, relative fluorescence intensity of PVA–MEC had an excellent linear response in the temperature range of 0–60°C. These observations suggest that PVA–MEC is an excellent fluorescent macromolecular material with a convenient method of preparation and had a good water‐soluble ability. Copyright © 2007 John Wiley & Sons, Ltd.     

Electronic spectroscopy, photophysical properties, and emission quenching studies of an oxidatively robust perfluorinated platinum porphyrin

The highly electron-deficient, beta-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H(2)F(28)TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF(28)TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF(28)TPP] in CH(2)Cl(2) displays a near-UV Soret band (B) at 383 nm (epsilon = 2.85 x 10(5) dm(3) mol(-1) cm(-1)) and two visible Q(1,0) and Q(0,0) bands at 501 (epsilon = 1.45 x 10(4) dm(3) mol(-1) cm(-1)) and 533 (epsilon = 1.36 x 10(4) dm(3) mol(-1) cm(-1)) nm, respectively. These absorption bands of [PtF(28)TPP] are blue-shifted from those in [PtF(20)TPP] (390, 504, and 538 nm, respectively) and [PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF(28)TPP] (complex concentration = 1.5 x 10(-6) mol dm(-3)) in dichloromethane at the Soret or Q(1,0) or Q(0,0) band gave a phosphorescence with peak maximum at 650 nm (lifetime = 5.8 micros) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with solvent polarity, and plots of tau versus E(K) and Phi versus E(K) (where E(K) is the empirical solvent polarity parameter based on the hypsochromic shift of the longest wavelength absorption of the [Mo(CO)(4)[(C(5)H(4)N)HC[double bond]NCH(2)C(6)H(5)]] complex with increasing solvent polarity; see: Kamlet, M. J.; Abboud, J. L. M.; Taft, R. W. Prog. Phys. Org. Chem. 1981, 13, pp 485-630) show linear correlation, indicating that the emission is sensitive to the local environment/medium. Electrochemical studies on [PtF(28)TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at potential < or = 1.5 V versus Ag/AgNO(3), demonstrating that [PtF(28)TPP] is more resistant toward oxidation than [PtF(20)TPP] (E(1/2) = 1.33 V) and [PtTPP] (E(1/2) = 0.97 V). The porphyrin-centered reduction of [PtF(28)TPP] occurs at -0.75 and -1.18 V, which is anodically shifted from those at -1.06 and -1.55 V in [PtF(20)TPP], and -1.51 V in [PtTPP], respectively. The excited-state reduction potential of [PtF(28)TPP] is estimated to be 1.49 V versus Ag/AgNO(3). Over 97% of the emission intensity of [PtF(28)TPP] was retained after irradiation with a high power mercury arc lamp (500 W) for 14 h, compared to 90% and 12% for [PtF(20)TPP] and [PtTPP], respectively; hence, [PtF(28)TPP] exhibits superior photostability. Quenching of the emission of [PtF(28)TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF(28)TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.     

Preparation and properties of cross-linked fluorescent poly(methyl methacrylate) latex colloids

We report a single step preparation of monodisperse fluorescent poly(methyl)methacrylate (PMMA) lattices cross-linked with ethylene glycol dimethacrylate with radii in the range 150-1000 nm using dispersion polymerization. The particles are applied as fluorescent cores in core-shell PMMA particles for confocal microscopy (Dullens et al. Langmuir 2003, 19, 5963). Contrary to un-cross-linked particles, these cross-linked colloids are stable in good solvents for PMMA as well. Therefore we studied the properties of the cross-linked PMMA particles in the good solvents tetrahydrofuran (THF), chloroform, and toluene using light scattering and confocal scanning laser microscopy. We show that the particles swell instantaneously and that their volume can increase up to more than seven times their volume in poor solvents. Further, it is very likely that the particles are charged in THF.     

Blends of poly(carbonate) with poly(styrene) and poly(methylmethacrylate): phase morphology,mechanical, and thermal properties

This paper is concerned with the dependence of mechanical and thermal properties of heterogeneous blends of poly(carbonate) (PC) with poly(methyl-methacrylate) (PMMA) and with poly(styrene) (PS) on the concentration of the components. PS displays a very weak phase coupling in blends with PC, whereas PMMA is characterized by a strong coupling to PC. Experimental results as well as predictions based on composite theories are reported. The general finding is that mechanical properties, such as the tensile modulus and the dynamic shear modulus, as well as thermal properties, such as thermal expansion, are (i) only weakly affected by the occurrence of a phase inversion and of a continuous phase morphology, (ii) vary continuously with the concentration of the components, and (iii) are rather insensitive to the strength of the phase coupling. The theoretical predictions on the concentration—property relationship for these properties, based on a self-consistent approach, agree very well with those observed experimentally. The elongation at break as well as the yield stress, on the other hand, are strongly influenced by the nature of the phase coupling: a discontinuous variation of these properties with the composition is observed for PS/PC blends but not for PMMA/PC blends. The general conclusion is that a set of mechanical and thermal properties of heterogeneous blends can satisfactorily be predicted on the basis of rather simple composite theories.     

Synthesis and absorption/emission properties of novel poly(silylenearylenevinylene)s

Polymerization of p-(dimethylsilyl)phenylacetylene in toluene at 25 and 80 °C with RhI(PPh₃)₃ catalyst afforded highly regio- and stereoregular poly(dimethylsilylene-1,4-phenylenevinylene)s [cis- and trans-poly( 1a )s] containing 98% cis- and 99% trans-vinylene moieties, respectively. The trans-type polymers exhibited redshifts and hyperchromic effects in the ultraviolet–visible spectrum as compared with the cis-type counterparts. Photoirradiation of cis- and trans-poly( 1a )s gave cis-rich mixtures at equilibrium states. The trans and cis polymers exhibited different emission properties, for example—trans polymer, emissn λ_max = 400 nm, quantum yield: 3.4 × 10⁻³ and cis polymer, emissn λ_max = 380 nm, quantum yield: 1.5 × 10⁻³. Besides poly( 1a ), poly(dimethylsilylenearylenevinylene)s containing biphenylene and phenylenesilylenephenylene units [poly( 3 )] were prepared. The extent of conjugation in these polymers decreased in the orders of biphenylene > phenylene > phenylenesilylenephenylene as well as trans-vinylene > cis-vinylene. The quantum yield of the trans-rich polymer with biphenylene moiety was fairly large and 0.15. Polyaddition of 1,4-bis(dimethylsilyl)benzene and three types of diethynylarenes (4,4′-diethynylbiphenyl, 2,7-diethynylfluorene, and 2,6-diethynylnaphthalene) catalyzed by RhI(PPh₃)₃ provided novel regio- and stereoregular polymers [poly( 6 )]. These polymers displayed blue light emission with high quantum yields (4–81%). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3615–3624, 2003     

Steady state and laser spectroscopic investigations on the intramolecular exciplex formation of 1-(N-p-anisyl-N-methyl)-amino-3-anthryl-(9)-propane

The photophysical processes of 1-(N-p-anisyl-N-methyl)-amino-3-anthryl-(9)-propane, I, in methylcyclohexane/isopentane at different temperatures were investigated by steady state and time resolved fluorescence measurements. Structurally, I has a higher tendency to intramolecular exciplex formation than 1-p-dimethylaminophenyl-3-anthryl-(9)-propane, a compound of an isomeric type studied by Mataga and Eisenthal.     

Syntheses and characterization of poly(iminophenol)s derived from 4-bromobenzaldehyde: Thermal, optical, electrochemical and fluorescent properties

Schiff base monomers[2-（4-bromobenzylideneamino）phenol and 2-（4-bromobenzylideneamino）-5-methylphenol] were synthesized by the condensation reaction of 4-bromobenzaldehyde with aromatic aminophenols.Then,the monomers were converted to their polyphenol derivatives by oxidative polycondensation reactions（OP） in an aqueous alkaline medium. The structures of the synthesized compounds were characterized by solubility tests,FT-IR,NMR,TG-DTA,DSC and SEC techniques.The HOMO-LUMO energy levels and electrochemical（E_g ） and optical（E_g） band gaps were calculated from cyclic voltammetry（CV） and UV-Vis measurements,respectively.Cyclic voltammetry（CV） was used to determine the electrochemical oxidation-reduction characteristics.Optical properties were investigated by UV-Vis and fluorescence analyses.Solid state electrical conductivities were measured on polymer films by four point probe technique using a Keifhley 2400 electrometer.The effects of electron-donating（-CH₃） group at p-position of -NH₂ group in aminophenol on electrochemical and thermal properties were also discussed.Photoluminescence（PL） properties of the synthesized materials were determined in solution forms using different solvents.Fluorescence measurements were carried out in various concentrated solutions to determine the optimum concentrations to obtain the maximal PL intensities.     

N-n-butyl-N,N-di(2-naphthylmethyl)amine: A compound exhibiting intramolecular excimer and exciplex formation

The dinaphthylamine (3) is unique in that it exhibits both intramolecular excimer and exciplex formation. The relative amounts of each is dependent upon the solvent polarity. Highly polar solvents, e.g. methanol, lead to the emission being entirely that of the exciplex but addition of acid to these solutions prevents exciplex formation and only excimer is observed.     

A ratiometric fluorescent metal ion indicator based on dansyl labeled poly(N-isopropylacrylamide) responds to a quenching metal ion

The fluorescence emission of poly(N-isopropylacrylamide) (PNIPAM) covalently tagged with a 5-(dimethylamino)naphthalene-1-sulfonyl (dansyl) fluorophore and an iminodiacetic acid (IDA) chelator changes with temperature and with Cu(II) complexation. Increasing the temperature above the lower critical solution temperature (LCST) causes the polymer to collapse from a coil to a compact globule. This changes the environment experienced by the fluorophore causing a shift in maximum emission wavelength from 546 to 508 nm and an increase in the ratio of emission intensity at 508 nm to emission intensity at 546 nm from 0.70 to almost 1.40. Metal ions can be sensed by working at a temperature where the uncomplexed polymer is in an expanded state due to the charges on the ligand. Complexation with a metal ion such as Cu(II) neutralizes the charges on the ligand causing the polymer to collapse. At 35 °C, the emission intensity maximum shifted from 535 to 510 nm as Cu(II) concentration was increased and the intensity ratio increased from 0.84 to 1.28. By decoupling complexation from fluorescence, we have prepared a ratiometric fluorescent indicator for a metal ion that normally quenches fluorescence. The affinity for Cu(II) was found to be thermally tunable. The log apparent formation constants for the indicator-Cu(II) complex were estimated as the half way point in the intensity ratio vs. pCu curve. The values were determined to be 4.3 at 35 °C and 3.2 at 34 °C respectively.     

A multifunctional poly(aryl ether) with oligoaniline and fluorene pendants: Synthesis,electrochromic performance,and tunable fluorescent properties

A novel multifunctional poly(aryl ether) with both pendant oligoaniline and fluorene groups (PAE‐p‐OF) was synthesized by nucleophilic polycondensation and characterized by ¹H NMR, Fourier‐transform infrared spectra, and gel permeation chromatography. The polymer showed excellent solubility in common organic solvents and good thermal stability. Electrochemical and photophysical properties were also investigated using cyclic voltammetry, UV–vis, and fluorescence spectroscopies. The obtained PAE‐p‐OF exhibits satisfactory electrochromic properties with high contrast value, acceptable coloration efficiency, and moderate switching times. Moreover, the fluorescence intensity of PAE‐p‐OF was modulated by controlling oxidation degree of oligoaniline moiety, due to the energy migration occurring between oligoaniline and fluorene groups. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Base-discriminating fluorescent (BDF) nucleoside: distinction of thymine by fluorescence quenching

A novel fluorescence BDF probe containing pyrene-labeled 7-deaza-2[prime or minute]-deoxyadenosine has been developed for the detection of thymine base on a target DNA.     

Synthesis of substituted poly(1-vinylpyrene)s and investigation of their fluorescent properties

A series of functionalized linear poly(1-vinylpyrene) (PVP) polymers bearing substituents such as ? NO₂, ? CHO, ? NH₂, ? Br, and ? CH?C(CN)₂, were prepared by chemical modification of PVP in solution. The degree of substitution in PVP? CH?C(CN)₂ was varied from 40% to nearly 100% by control of the reaction conditions. The other polymers were partially functionalized. The UV-visible and fluorescence spectroscopy of the polymers were studied in solution. The influence of solvent polarity, excitation energy, and degree of substitution on the fluorescence of the polymers were examined. © 1993 John Wiley & Sons, In     

Preparation and emission properties of various poly(dimethylsilylenearylenevinylene)s: Effects of geometric structures and π units on their emission properties

trans‐Poly(dimethylsilylenearylenevinylene)s (trans‐rich) and cis‐poly(dimethylsilylenearylenevinylene)s (cis‐rich) containing phenylene, biphenylene, and phenylenesilylenephenylene units were prepared by hydrosilylation catalyzed with the RhI(PPh₃)₃ complex. The addition of a phenylene π unit to poly(silylenephenylenevinylene) expanded the conjugation in the main chain, whereas the insertion of a dimethylsilylene σ unit in the biphenylene moiety reduced the conjugation. UV spectra of the trans‐type polymers showed redshifts and hyperchromic effects with respect to those of the cis‐type polymers, indicating wider conjugation, and the quantum yields of emission of the former polymers were much higher than those of the latter polymers. The quantum yield of the trans‐rich polymer with the biphenylene moiety reached 0.15, which was about 10² times as large as those of trans‐type polymers with phenylene (3.4 × 10^?3) and phenylenesilylenephenylene (1.9 × 10^?3) moieties. The effects of the geometric structure and π unit on the absorption and emission properties of these polymers were examined with molecular orbital methods. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 535–543, 2002; DOI 10.1002/pola.10139     

Kinetic studies on the formation of cyclic oligomers in poly(ethylene terephthalate)

The mechanism of cyclic oligomer formation has been kinetically studied by determining the rate of the formation of cyclic oligomers during melt of poly(ethylene terephthalate) (PET) at several levels of average molecular weight, which were obtained by fractionation and did not initially contain oligomers. The experimental rate equation of cyclic oligomer formation was introduced and then compared with the rate equation derived theoretically. The close agreement between the two equations suggested that the cyclic oligomer formation takes place according to cyclodepolymerization by the action of hydroxyl end groups in PET. The relation is represented as [C] = m·[OH]₀·t^1–n, where [C] is the concentration of cyclic oligomers, [OH]₀ is the initial concentration of hydroxyl end groups, m and n are constants, and t is melting time. A method has also been developed for separating cyclic oligomers from PET using dimethylformamide (DMF) as a solvent.     

Synthesis and properties of poly(1‐naphthylacetylene) and poly(9‐anthrylacetylene)

Polymerizations of 1‐naphthylacetylene (1‐NA) and 9‐anthrylacetylene (9‐AA) by various transition metal catalysts were studied, and properties of the polymers were clarified. 1‐NA polymerized with WCl₆‐based catalysts to offer dark purple polymers in good yield. Especially, a binary catalyst composed of WCl₆ and Ph₃Bi gave a polymer with high molecular weight (M_w = 140×10³) and sufficient solubility in common solvents. The use of Mo and Rh catalysts, in contrast, resulted in the formation of insoluble red poly(1‐NA)s. 9‐AA gave insoluble polymers by both WCl₆‐ and MoCl₅‐based catalysts in moderate to good yields. Copolymerization of 9‐AA with 1‐NA by WCl₆–Ph₃Bi provided a soluble copolymer which exhibited the largest third‐order nonlinear optical susceptibilities (χ⁽³⁾(−3ω; ω, ω, ω) = 40×10⁻¹²) among all the substituted polyacetylenes synthesized so far. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 277–282, 1999     

The photochemistry of 2-(1-naphthyl)ethyl benzoates: cycloaddition and intramolecular exciplex formation

The photochemistry of the 2-(1-naphthyl)ethyl benzoates 6 and 7 was examined in order to compare them to previously studied 2-arylethyl 4-cyanobenzoates that underwent a Norrish Type II fragmentation. The 1-naphthyl group was incorporated to provide a fluorescent chromophore for probing the intramolecular electron transfer proposed previously for the mechanism. The naphthalene fluorescence was quenched for both 6 and 7 although at very different rates. For 6, with the higher thermodynamic driving force (-68.9 kJ/mol), intramolecular electron transfer was fast in all solvents, independent of their polarity (cyclohexane to methanol). For 7, with the lower driving force (-26.5 kJ/mol) the process was fast only in polar solvents. Exciplex emission, observed for 6 (but not for 7), exhibited a large solvatochromic effect possibly indicating a high dipole moment (28 D) in polar solvents (stretched conformation) but a lower one (17 D) in nonpolar solvents (folded conformation). Finally, the 4-cyanobenzoate 6 was very unreactive photochemically. In contrast, benzoate 7 underwent a 2 + 2 cycloaddition of the ester carbonyl to the naphthalene ring to give products 8 and 9, a process for which we have found no precedent.