Anthracene Fluorescence Research Articles

Red shift in fluorescence of naphthalene doped by anthracene and perylene

The fluorescence in naphthalene is investigated systematically by doping it with different amounts of anthracene and perylene with a view to obtain luminophors emitting at longer wavelengths. The fluorescence spectra of naphthalene luminophors are recorded on recording spectrofluorophotometer. It is observed that the addition of small amount of anthracene completely quenches the weak violet fluorescence of naphthalene and new anthracene like emission band appears in the fluorescence spectra of doped naphthalene. The intensity of anthracene like emission band is maximum at 10−2mol anthracene per mole naphthalene. The addition of perylene as another impurity not only quenches the anthracene like emission but also acts as wavelength shifter. Thus, the fluorescence spectra of naphthalene containing anthracene and perylene shows anthracene like emission followed by a broad tail towards red. The anthracene like emission is explained on the basis of fluorescence sensitization while red side of the spectrum is attributed to emission arising from charge transfer complex formed in the excited state.

Energy Migration and Excimer Formation in Quasi-Two-Dimensional Polymer Films As Revealed by the Time-Resolved Fluorescence Depolarization Measurement

Excitation energy migration and subsequent energy transfer to excimer-forming sites occurring in a quasi-two-dimensional plane of poly(isobutyl methacrylate) Langmuir−Blodgett films were investigated through the time-resolved analyses of anthracene fluorescence. Fluorescence anisotropy decays showed that the energy migration occurred more efficiently as the anthracene fraction increased. A further increase of the anthracene gave rise to the excimer-forming sites acting as energy traps, and finally the anthracene fluorescence was markedly quenched from the energy transfer to the traps. The migration process was quantitatively analyzed by a computer simulation based on the Monte Carlo method, which allowed estimation of the number of hopping and the mean-square displacement of excitons. The initial growth of the mean-square displacement with time became gradually gentle, while the number of hopping linearly increased with time. This result shows that the excitons are not diffusive and tend to stay within a small cluster of chromophores, especially for small chromophore density at short times.

Action of a Fluorescent Chemosensor for Cu2+ Encapsulated in Silica Xerogel

The fluorescent chemosensor of the type Ant-NH-O-O-NH-Ant for Cu2+ ions has been designed by means of a supramolecular approach, as follows: two anthracene (Ant) fragments as fluorophore subunits have been linked by a noncyclic NH-O-O-NH quadridentate ligand as a receptor. The interaction of Cu2+ - receptor is signalled through the enhancement of the anthracene fluorescence when the receptor, i.e., the dioxodiamine chain subunit of the sensor is able to stop a photoinduced electron-transfer mechanism. The experiments with the chemosensor encapsulated in silica xerogel by the sol-gel processing are described.

Mapping phases of poly(vinyl alcohol) and poly(vinyl acetate) blends by FTIR microspectroscopy and optical fluorescence microscopy

Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) blends in compositions 9/1, 1/1, and 1/9 (w/w) show that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as PVA-richer domains by green fluorescence of fluorescein and PVAc-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in the solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed us to obtain spectra for both PVA-richer and PVAc-richer domains. These spectra demonstrated that partial miscibility could occur only for blends with a higher PVAc content and, in these cases, we observed interchain hydrogen-bonded carbonyl groups. Fluorescence microscopy of blends with this partial miscibility exhibited small interconnected domains produced by coalescence of droplets during the polymer phase separation process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 645–655, 1998

Local motion of crosslinks for poly (methyl methacrylate) gels by the fluorescence depolarization method

Poly(methyl methacrylate) (PMMA) gels labeled at crosslinks with anthracene were prepared. Anthracene fluorescence depolarization was monitored to probe the local motion of crosslinks for PMMA gels at different equilibrium swelling states. The relaxation times and the activation energies of local motion were measured for PMMA gels at the swollen states in various solvents through fluorescence anisotropy decays. The local motion of PMMA gel at crosslinks became faster with the increase of swelling ratio. When the swelling ratios were almost the same, the mobility of crosslinks was the same irrespective of the molecular weights between crosslinks. These results indicate that the local motion of crosslinks for PMMA gel is mainly governed by the segment density of network chains in the vicinity of crosslinks.

Three-photon excitation fluorescence imaging of biological specimens using an all-solid-state laser

We demonstrate that three-photon excitation images of both fixed and living biological specimens can be readily obtained using an all-solid-state Nd:YLF laser excitation source. Optically sectioned images of fixed Caenorhabditis elegans embryos stained with DAPI and embryos triple-labeled with DAPI, fluorescein and Texas Red are presented. Time series images of a living LLC-PK cell stained with Hoechst 33342 during the progression from metaphase to telophase are also presented. The mode of excitation was inferred from the power-law of anthracene and Hoechst 33342 fluorescence versus incident laser power and an axial resolution comparison of anthracene fluorescence with two-photon excited Calcium Crimson fluorescence. Multiphoton excitation imaging is an attractive method for optically sectioning live specimens because of the lower levels of phototoxicity produced compared to other optical sectioning techniques. The combination of two- and three-photon excitation extends the capabilities of a multiple- photon imaging system since a single wavelength can provide localized excitation of a wide variety of fluorophores whose collective emission spectra can span the entire visible spectrum.

Three‐photon excitation fluorescence imaging of biological specimens using an all‐solid‐state laser

We demonstrate that three-photon excitation images of both fixed and living biological specimens can be readily obtained using an all-solid-state Nd:YLF laser excitation source. Optically sectioned images of fixed Caenorhabditis elegans embryos stained with DAPI and embryos triple-labeled with DAPI, fluorescein and Texas Red are presented. Time series images of a living LLC-PK cell stained with Hoechst 33342 during the progression from metaphase to telophase are also presented. The mode of excitation was inferred from the power-law of anthracene and Hoechst 33342 fluorescence versus incident laser power and an axial resolution comparison of anthracene fluorescence with two-photon excited Calcium Crimson fluorescence. Multiphoton excitation imaging is an attractive method for optically sectioning live specimens because of the lower levels of phototoxicity produced compared to other optical sectioning techniques. The combination of two- and three-photon excitation extends the capabilities of a multiple- photon imaging system since a single wavelength can provide localized excitation of a wide variety of fluorophores whose collective emission spectra can span the entire visible spectrum.

Chelation-enhanced fluorescence chemosensing of Pb(II), an inherently quenching metal ion

Pb(II) ion serves as a quencher of anthracene fluorescence both intermolecularly and in intracomplex systems reported to date. The advantages of intensimetric analyses showing increasing signal require the design of mechanistically novel fluorescent chemosensors capable of yielding enhanced fluorescence upon chelation of inherently quenching metals. We synthesized both 2- and 9-derivatives of anthracene bearing the N-methylthiohydroxamate ligand, which is capable of quenching fluorescence in the uncomplexed form and which shows some selectivity for Pb(II). Complexation of the 2-derivative to Pb(II) results in rapid metal ion-catalyzed hydrolysis, rendering this compound useless as a sensor with real-time response. However, complexation of the 9-derivative with Pb(II) results in a 13-fold fluorescence increase, reversible upon dissociation of the metal ion. While blood lead analysis is a major potential application for fluorescent chemosensors, the present compound is insufficiently selective for this use.

Supramolecular assemblies containing metallocyclam subunits

Abstract The synthetic approach to supramolecular systems containing one or more metallocyclam subunits is reviewed. In particular, the template synthesis of azacyclam complexes has been used to design supramolecular coordination compounds displaying multi-electron redox activity. Moreover, it is shown that whenever the supramolecular design requires a component able to provide a fast and reversible redox change, a metallocyclam subunit should be used. Finally, the design of supramolecular systems in which a light-emitting fragment (anthracene) has been linked to a metallocyclam subunit has been considered. In particular, anthracene fluorescence can be switched on/off through the CuI/CuII redox couple inside a tetra-thia-macrocyclic environment, via an electron transfer mechanism.

An aqueous ratiometric fluorescence probe for Zn(II)

We report herein the first example of the use of metal promoted intramolecular excimer formation using a system derived from a simple linear polyamine. The system demonstrates that considerably less preorganization is necessary than that used in cyclic systems. The water solubility results in the first aqueous operative ratiometric fluorosensor for Zn 2+ ions.Bis-9-anthrylpolyamines (e.g. 2) were prepared by the 4Å molecular sieve promoted condensation of the polyamine with a stoichiometrically appropriate amount of 9-anthraldehyde in CHCl 2. Compound 2 (25μ M) was titrated with Zn(ClO 4) 2 in CAPS buffer (0.05 M) at pH 10.5. The most notable feature of this titration is the nearly 4-fold increase in fluorescence intensity at about 495 nm. In fact, after the addition of 1 equivalent of Zn +2 the normal anthracene fluorescence profile is no longer the dominant feature of the spectrum. Subtracting the spectrum with no Zn +2 from that with 1 equivalent reveals the dominant excimer spectrum. The mono substituted control shows only the expected chelation enhanced fluorescence based upon the complexation state of the benzylic amine nitrogen.

Fluorescent Sensors for Transition Metals Based on Electron‐Transfer and Energy‐Transfer Mechanisms

AbstractFluorescent sensors for 3d divalent metal ions have been designed by means of a supramolecular approach: an anthracene fragment (the signalling subunit) has been linked to either a cyclic or a noncyclic quadridentate ligand (the receptor). Occurrence of the metal‐receptor interaction is signalled through the quenching of anthracene fluorescence. When the receptor (i.e., the dioxotetramine subunit of sensors 2 and 3) is able to promote the one‐electron oxidation of the metal, quenching takes place through a photoinduced metal‐to‐fluorophore electron‐transfer mechanism. In the case of sensors containing a tetraamine binding subunit (4 and 5), quenching proceeds by an energy‐transfer process. Selective metal binding and recognition can be achieved by varying the pH, and metal ions can be distinguished (e.g., CuII from NiII) by spectrofluorimetric titration experiments in buffered solutions. Whereas systems 2, 3 and 5 show reversible metal binding behaviour, the cyclam‐containing system 4 irreversibly incorporates transition metals (due to the kinetic macrocyclic effect) and cannot work properly as a sensor.

Intramolecular deactivation of photoexcited anthracenes by aromatic ketones. Part 2.—Charge-transfer deactivation of ω-(9-anthryl)ketones in different solvents and binary solvent mixtures and at different temperatures

The solvent and temperature dependence of the excited state properties of anthracenes non-conjugatively linked to various aromatic phenones have been investigated by determination of the quantum yields of fluorescence and intersystem crossing. In a series of substituted bichromophoric ω-(9-anthryl)propiophenones, the degree of intramolecular quenching of the anthracene fluorescence by the phenones was not compensated for by increasing intersystem-crossing efficiency in the anthracene chromophore, but was found to be associated with the standard free-energy change for intramolecular charge separation, the solvent polarity and the temperature. In contrast, in monochromophoric anthracene reference compounds neither remarkable solvent polarity nor temperature dependence of the fluorescence emission was detected. For example, for one bichromophoric compound [ω-(9-anthryl)-4′-methoxypropiophenone] an analysis within the framework of the Marcus electron-transfer theory was performed and a dependence of the nuclear Franck–Condon factor for the intramolecular charge-separation reaction on the solvent polarity was found. Shortening the linking non-conjugative bridge in one bichromophore [ω-(9-anthryl)propiophenone] resulted in an increased charge-separation rate constant by more than one order of magnitude in ω-(9-anthryl)acetophenone.

Redox Switching of Anthracene Fluorescence through the CuII/CuI Couple

Redox Switching of Anthracene Fluorescence through the CuII/CuI Couple

Diffusion of molecular oxygen in glassy matrices, studied by luminescence quenching

Abstract Oxygen diffusion in low temperature squalane glasses was studied by phenanthrene phosphorescence quenching and anthracene fluorescence quenching in geminate pairs (anthracene 3. O 2 ). The oxygen mobility can be described by continuous diffusion. Anthracene fluorescence quenching in geminate pairs allow to measure diffusion coefficients till 10 −23 cm 2 /s.

Distance-Dependent Quenching of Anthracene Fluorescence by N,N-Diethylaniline Observed by Frequency-Domain Fluorometry

We measured the time-dependent fluorescence intensity decays of anthracene and 9,10-dimethylanthracene in propylene glycol quenched by N,N-diethylaniline by frequency-domain fluorometry. The frequency-domain data, for a range of temperatures and diffusion coefficients, are consistent with a rate of quenching which depends exponentially on the fluorophore-quencher separation distance. This type of quenching interaction explains upward curvature in the Stern-Volmer plots. In total, the steady-state and time-resolved data are consistent with a mechanism of quenching due to the electron transfer process from DEA to the singlet excited anthracene molecules.

Fluorescence studies on a supramolecular porphyrin bearing anthracene donor moieties

A tetraphenylporhyrin bearing four anthracene donor moieties (5,10,15,20-tetra(3-(9-methyloxyanthracenyl)phenyl)porphyrin, I) was synthesized and fully characterized. Spectroscopic and electrochemical data and results of metallation and intermolecular fluorescence quenching experiments suggest that there is no appreciable interaction between the porphyrin and anthracene moieties in I. Although intermolecular quenching of anthracene fluorescence by 5,10,15,20-(tetraphenyl)porphyrin is not obvious, the fluorescence of the anthracene donors in I is quenched by more than 90%. On the basis of the fluorescence excitation pectral data, the quenching observed is attributed to intramolecular singlet-singlet energy transfer from anthracene to the porphyrin. However, neither Förster's dipole-dipole formalism nor Dexter's electron exchange mechanism can explain adequately this intramolecular energy transfer. Thermodynamic considerations and solvent-dependent fluorescence data indicate that photoinduced electron transfer from singlet anthracene to the porphyrin can compete with energy transfer in this supramolecular system.

Intramolecular excitation energy transfer in anthracene appended porphyrins

Free-base and zinc(II) derivatives of supermolecular porphyrins bearing one or four anthracene subunits have been synthesized and fully characterized. It was observed that, in methylene chloride solutions, fluorescence due to the anthracene subunit of these systems has been quenched in comparison with the fluorescence of free anthracene and that the extent of quenching depends on the number and site of attachment of the anthracerte/s at the porphyrin periphery. Based on the fluorescence emission and excitation spectral data, the observed quenching has been attributed to the singletsinglet energy transfer, from the anthracene donor subunits to the porphyrin. A detailed analysis of the results suggested that the energy transfer process proceeds predominantly through Forster's dipole-dipole mechanism in these systems. Further, in the light of structural and thermodynamic data, other possible mechanisms for the observed quenching were considered. A photoinduced electron transfer reaction has been found-to effectively compete with the energy transfer in polar solvents. The results obtained in this study are discussed in comparison with the results of other porphyrin based energy transfer model systems and also with relevance to the carotene function of the photosynthetic antenna pigments.

Electronic and photochemical behavior of some conformationally restricted intramolecular charge transfer systems

Abstract Two series of conformationally restricted intramolecular charge transfer (CT) systems with very different potential for through-space interaction between an anthracene electron donor (D) and a series of pyridinium acceptor (A) moieties were synthesized. A comparison of the electronic absorption and emission behavior of these two systems indicated that CT absorption and intramolecular exciplex emission were more important in the series in which close proximity and coplanarity between D and A could be achieved. The electron-withdrawing pyridinium moiety was found to be a very efficient quencher of anthracene fluorescence. CT absorption and emission are dependent on the solvent polarity, the redox behavior of D and A and the ability of D and A to interact electronically either through bond or through space. In general, CT absorption is enhanced and red shifted as the solvent polarity decreases, while the reverse is true for intramolecular exciplex emission, i.e. the wavelength of exciplex emission shifts to the red and decreases in intensity as the solvent polarity increases. All of the intramolecular CT systems investigated were found to be photochemically inert.

Structural requirements for efficient photoinduced electron transfer (PET) quenching in 9-aminoalkylanthracenes

The structure-quenching relationship in 9-aminoalkylanthracenes is examined by the synthesis and fluorescence evaluation of five derivatives; it is observed that benzylic 2° and 3° amines lead to ≥95% quenching of anthracene fluorescence in water, while other amines afford substantially lower quenching efficiencies.

A matrix isolation study of the fluorescence of anthracene and anthracene—ammonia adducts in solid argon

The UV absorption and emission spectra of anthracene in an argon matrix were measured. Three major spectroscopic systems were observed, assignable to anthracene molecules occupying distinct sites. The origins of these systems were red-shifted with respect to the isolated molecule by 535,691 and 722 cm −1. At 17 K all lines were well resolved, with about 8 cm −1 fwhm. Addition of a small amount of ammonia leads to the observation of three new band systems, red-shifted with respect to the previously mentioned ones. These observations are discussed in relation to recent studies of anthracene—argon and anthracene—ammonia clusters in supersonic jets.