Anthracene Fluorescence Research Articles

Regulating the fluorescence intensity of an anthracene boronic acid system: a B–N bond or a hydrolysis mechanism?

An anthracene-based fluorescent boronic acid system developed by the Shinkai group has been widely used for the preparation of fluorescent sensors for carbohydrates. Such application is based on the significant fluorescence intensity increase of this system upon binding with a carbohydrate. The mechanism through which this fluorescence intensity change happens was originally proposed to go through a B–N bond formation mechanism, which masks the nitrogen lone pair electrons. However, our own fluorescence studies suggest a possible alternative mechanism for the fluorescence change upon the formation of a boronic acid ( 1a) complex with diols. In this new proposed mechanism, complex formation induces solvolysis, which results in the protonation of the amine nitrogen if the reactions are carried out in a protic solvent such as water. This protonation prevents the photoinduced electron transfer, resulting in reduced quenching of the anthracene fluorescence. Such a solvolysis mechanism is supported by evidence from various types of experiments and theoretical calculations.

Electron transfer processes of coadsorbed Anthracene and N,N‐Dimethylaniline on titania‐silica

The effect of titania‐silica binaries on the processes of PET and the decay kinetics of the Anthracene (An) fluorescence and An radical cation in presence of the co‐adsorbed electron donor N,Ndimethylaniline (DMA) has been studied. The fluorescence of excited An adsorbed on pure silica is quenched by the addition of DMA, while co‐adsorption of DMA on Ti/Si binaries resulted in increase of fluorescence intensity of adsorbed An. We suggest that competitive adsorption between DMA and An results in DMA occupying more active “titania” sites causing the shift of An molecules to weaker adsorption sites located on the silica support. An and DMA molecules being adsorbed simultaneously on the surface, effectively produce reduced titanium ions due to an electron transfer process. These data appear to lend weight to the suggestion of a pre‐exciplex An‐DMA state on the surface and effective PET from the excited molecular pair to the acceptor sites on the surface. These sites may be titania aggregates, or titania ions when there is a low content of Ti in the binaries.

Application of Smoluchowski's generalized theory to the kinetics of triplet–triplet annihilation of anthracene in viscous solution after long-pulse excitation

The validity of Smoluchowski's theory is demonstrated by its application to the bimolecular triplet–triplet annihilation (TTA) T1 + T1 → S0 + S1 in viscous solution. For that purpose the delayed S1 → S0 fluorescence of anthracene in cis-1,3-dimethylcyclohexane/trans-1,4-dimethylcyclohexane (1∶1) was measured after UV excitation with long laser pulses (∼30 μs) in a temperature range where TTA is completely diffusion controlled. Through the adequate treatment of the kinetics of TTA upon spatially homogeneous and spatially periodic excitation (which is partially based on the results of previous publications) absolute values for the diffusion coefficients D of triplet molecules, for the effective annihilation distance RA and for the Forster radius RST of heterogeneous annihilation S1 + T1 → S0 + Tn were determined. The temperature dependence of all three parameters (D, RA and RST) is discussed. From the decrease of RA with increasing temperature, the parameters A and L can be determined, which define the exponential distance dependence of the annihilation of a triplet pair in the kinetic model of Butler and Pilling (1977). Differences of the two models and applicability criteria are discussed.

Anti-Stokes delayed fluorescence from metal–organic bichromophores

Long wavelength excitation of [Ru(dmb)(2)(bpy-An)](2+) (dmb is 4,4'-dimethyl-2,2'-bipyridine and bpy-An is 4-methyl-4'-(9-anthrylethyl)-2,2'-bipyridine) in CH(3)CN solution produces upconverted delayed singlet anthracene fluorescence via bimolecular triplet-triplet annihilation.

Spectroscopic and nonlinear characteristics of anthracene-containing silicon-organic polymers in solution

Spectroscopic characteristics, i.e. absorption, fluorescence, fluorescence excitation spectra, fluorescence decay time, fluorescence polarization degree of novel silicon-containing organic polymers including main chain anthracene groups were investigated. Three kinds of emission spectra were revealed and assigned to polaron–exciton, anthracene and anthracene dimer. The measured fluorescence polarization spectra gave evidence of directed excitation energy migration along the disordered polymeric chain. Strong quenching of anthracene fluorescence during the polaron–exciton lifetime was interpreted as a result of the interaction between two excitations that causes anthracene anion-radical formation. The third-order nonlinear susceptibility of the polymers in solution measured by the Z-scan technique at 1054 nm is 190×10 −14 cm 2 W −1.

A new family of donor-acceptor systems comprising tin(IV) porphyrin and anthracene subunits: Synthesis, spectroscopy and energy transfer studies

A new family of covalently linked ‘Sn(IV) porphyrin-anthracene’ diad (1), triad (2) and tetrad (3) donor-acceptor (D-A) systems have been designed and synthesized in good-to-moderate yields. While diad 1 possesses one anthracene subunit at the peripheral (meso) position of the tin(IV) porphyrin scaffold, triad 2 possesses twotrans axial anthracene subunits at the tin(IV) centre. On the other hand, tetrad 3 is endowed with both the peripheral and axial anthracene subunits in its architecture. These D-A systems have been fully characterised by elemental analysis, FAB-MS, UV-Vis,1H and13C NMR and electrochemical methods. UV-Vis,NMR and redox data suggest the absence of intramolecular π-π interaction between the porphyrin and the anthracene/s in 1–3. Fluorescence from the anthracene subunit in 1 and 3 is found to be quenched in comparison with the fluorescence of free anthracene in four different solvents. This is not the case with compound 2. Excitation spectral data provides evidence for an intramolecular excitation energy transfer (EET) from the singlet anthracene to the porphyrin in 1 and 3. The energy transfer efficiency is in the order: 2 (almost negligible) < 3 (~30%) < 1 (nearly quantitative), with the peripheral anthracene → porphyrin pathway being largely favoured. This orientation dependence of EET could be analysed using Forster's dipole dipole mechanism.

Fluorescence emission and photooxidation studies with 5,6- and 6,7-benzocoumarins and a 5,6-benzochromone under direct and concentrated sun light

4-Methyl-8-hydroxy-benzo(6,7)coumarin, I, 4-methyl-6-hydroxy-benzo(5,6)coumarin, II, and 2-methyl-6-hydroxy-benzo(5,6)chromone, III, have shown similar absorption and fluorescence emission spectra. Fluorescence emission quantum yields for I and III are found to be very low, φ f=0.02, but 4-methyl-6-hydroxy-benzo(5,6)coumarin, II, has a eight-fold higher fluorescence quantum yield of the other two specie, in acetonitrile solution, φ f=0.16. Quenching of anthracene fluorescence emission by I, II and III are found to give k q values of 1.0×10 7–1.2×10 9 M −1 s −1. Benzo(5,6)coumarin, II, which gives the most intense fluorescence also presents the highest quenching rate, k q=1.2×10 9 M −1 s −1. Experimentally determined k q values are seen to correlate well with the free energy of electron transfer (Δ G ET) which are calculated to be in the range of −8.0 to −9.4 kcal/mol, where benzo(5,6)coumarin, II, gives the lowest free energy of electron transfer Δ G ET=−9.4 kcal/mol. These results indicate that I–III behave as electron acceptor moieties toward a condensed aromatic ring, anthracene. The Stokes shift values of 88–105 nm and broad fluorescence emission bands respect to absorption–excitation bands, indicates a molecular structure change in the excited states of I–III. Fluorescence lifetimes of 0.1–0.9 ns in I–III, singlet oxygen quantum yields of 0.15 and 0.40 for I and II, respectively, may be taken as evidence of singlet–triplet intersystem crossings. The photooxidation products of α-terpinene, sensitised by II, under direct and concentrated sun light conditions that are mainly p-cymene and ascaridole. In accordance with literature data on coumarin derivatives, benzocoumarins also seem to produce singlet oxygen and beside singlet oxygen, in addition super oxide anion radical production appear to be dominant especially under concentrated sun light. Under direct sun light conditions ascaridole is the major product. Some by-products of α-terpinene photooxidation are also determined at GC–MS analysis. Those by-products are assumed to be generated from ascaridole decomposition.

Photoionization and Ion-Radical Decay of Anthracene in a Water Swollen Nafion Network. Effect of Different Counterions on the SO3-−Water Clusters

The formation of anthracene ion radicals in the H + -, Na + -, Fe 2 + -, and Fe 3 + -Nafion membrane was established by laser kinetic spectroscopy. The formation of ion radicals was observed to be due to (1) the two photon ionization of the anthracene molecule with the formation of the radical cation An + . radical and a fast electron scavenging by H + , Na + , Fe 2 + , and Fe 3 + acting as efficient electron traps in solution and (2) the quenching of the excited anthracene by Fe 3 + that leads by a redox process to the formation of An + . and Fe 2 + . It is shown that the ensuing kinetics of the ion-radical decay depends on the chemical nature of the traps. The lifetime of T An becomes shorter after Fe 2 + or Fe 3 + is introduced in the Nafion. The steady-state anthracene fluorescence is quenched by Fe 3 + or Fe 2 + and followed the logarithmic decay law ln(I 0 /I) where the decay in solution was seen to be proportional to the [Fe 3 + ] or [Fe 2 + ]. The counterions of SO 3 - -water clusters as well as of oxygen in the reaction media strongly affect the kinetics of ion-radical reactions occurring in the Nafion membrane. The counterions and oxygen are suggested to be the traps for the generated electrons in solution. The excited state of An was shown to react with Fe 3 + through electron transfer. Triplet excited anthracene molecules are quenched by Fe 3 + and Fe 2 + with rate constants k q (Fe 3 + ) = (1.9 ′ 0.19) × 10 8 M - 1 s - 1 and k q (Fe 2 + ) = (1.4 ′ 0.11) × 10 9 M - 1 s - 1 . Anthracene ion radicals are formed in the reaction with Fe 3 + but not with Fe 2 + on thermodynamic grounds. Fe 2 + or Fe 3 + being different chemical species quench with similar rates the An probe inside the Nafion membrane. Treatment of Fe 3 + -Nafion with NaOH leads to precipitation of iron particles in the membrane having as consequences (1) the decrease of the observed rate for the triplet excited anthracene quenching with a concomitant decrease in the observed An + . yields and (2) a significant decrease of the An + . decay time because of the lowering of the mobility of the iron ions in solution.

Synthesis of heteroleptic anthryl-substituted beta-ketoenolates of rhodium(III) and iridium(III): photophysical, electrochemical, and EPR study of the fluorophore-metal interaction.

The anthryl-substituted rhodium(III) and iridium(III) heteroleptic beta-ketoenolato derivatives of general formula [M(acac)(2)(anCOacac)] [acac = pentane-2,4-dionate; anCOacac = 3-(9-anthroyl)pentane-2,4-dionate], 3 (M = Rh) and 4 (M = Ir), and [M(acac)(2)(anCH(2)acac)] [anCH(2)acac = 3-(9-anthrylmethyl)pentane-2,4-dionate], 5 (M = Rh) and 6 (M = Ir), were prepared by reacting the corresponding tris(pentane-2,4-dionate)metal complexes, [M(acac)(3)], with 9-anthroyl chloride and 9-chloromethylanthracene, respectively, under Friedel-Crafts conditions. 3-6 were characterized by elemental analysis, ion spray mass spectrometry (IS-MS), (1)H NMR, and UV-vis spectroscopy. The structure of 3 was also elucidated by single-crystal X-ray analysis. When excited at 365 nm, 3-6 result to be poorly luminescent compounds; while the free diketone, i.e., 3-(9-anthrylmethyl)pentane-2,4-dione 1, whose structure was established also by single-crystal X-ray analysis, results to be a strongly light emitting molecule. The study of the electrochemical behavior of 3-6 as well as of the corresponding tris-acetylacetonates of rhodium(III) and iridium(III) allows a satisfactory interpretation of their electrode process mechanism, and gives information about the location of the redox sites along with the thermodynamic and kinetic characterization of the corresponding redox processes. All data are in agreement with the hypothesis that the quenching of the anthracene fluorescence, observed for compounds 3-6, can be due to an intramolecular electron transfer process between the anthryl moiety and the metal-beta-ketoenolato component. Moreover, a study was carried out of the redox behavior of the dyads 3-6 under chemical activation. The one-electron oxidation of compounds 3-6 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, 3(+)-6(+), whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.

Anthrylmethylamines and anthrylmethylazamacrocycles as fluorescent pH sensors—a systematic study of their static and dynamic properties

The pH dependent fluorescence of various 9-mono- and 9,10-disubstituded anthracenes is reported. They have a compartmental structure: fluorophore (anthracene)–spacer (methylene)–and ionophore (mono-, polyamines, azamacrocycles). In these n-basic anthrylmethylamines the fluorescence of anthracene is intramolecularly quenched by unprotonated amine groups. The pKA values have been evaluated by titration in order to calculate the amount (mole fraction) of each of the n + 1 differently charged species and their dependence on the pH. The fluorescence–pH profiles (intensities and lifetime versus pH) have been determined, and interpreted as the formation of differently protonated species with different fluorescence intensities and hence different fluorescence lifetimes. The experimentally determined fluorescence lifetime–pH profiles can be described by three lifetimes. This is corroborated by global analysis. The measurement of the fluorescence quantum yields of the completely protonated species yielded the radiative lifetimes. The rate constants and quantum yields of the photoinduced electron transfer (PET) are calculated for the species with shorter lifetimes and hence smaller fluorescence intensities.

Phase transitions and relaxation processes in ethylene-vinyl acetate copolymers probed by fluorescence spectroscopy

The steady-state fluorescence of pyrene and anthracene are used to investigate the relaxation processes of several random ethylene-co-vinyl acetate copolymers, EVA, with defined comonomer compositions (EVA-9, EVA-18, EVA-25, EVA-33 and EVA-40). The temperature of the relaxation processes are compared with those of low-density polyethylene (LDPE) and poly(vinyl acetate) (PVAc). The polymer relaxation processes are assigned to T g=300–310 K (glass transition temperature of the PVAc); T α =270–300 K (relaxation processes of the ethylene units present in LDPE and EVA); T g=220–250 K (glass transition of the LDPE and of the EVA); T γ or T β =160–190 K (relaxation processes of interfacial defects of methylenic chains of LDPE and rotation of the acetate group of the PVAc and the EVA); and T γ =90–130 K (relaxation processes of small sequences of methylene units of LDPE and end groups of PVAc). An Arrhenius-type function was employed as an attempt to represent the experimental data of fluorescence intensity versus temperature above the γ-relaxation temperature. As obtained with other techniques, there is not a simple relationship between the polymer relaxation processes and the vinyl acetate content that can be explained by the morphology in these copolymers.

Molecular weight effect on swelling of polymer gels in homopolymer solutions: a fluorescence study

A novel technique based on in situ steady state fluorescence measurements is introduced for studying swelling processes of gels formed by free radical crosslinking copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in homopolymer solutions. Gels were prepared at 55±2 °C for various EGDM contents. After drying these gels, swelling experiments were performed in chloroform solution of anthracene labeled poly(methyl methacrylate) (An-PMMA) in various molecular weights at room temperature by real time monitoring of anthracene fluorescence intensity. Anthracene labeled PMMA chains having various molecular weights were prepared by atom transfer radical polymerization at 90 °C. During the swelling experiments, it was observed that anthracene emission intensities increased due to trapping of An-PMMA chains into the gel as the swelling time is increased. The trapping of An-PMMA chains in swollen gel, increase by obeying parabolic law in time. Penetration time constant, τ of PMMA chains were measured and found to be increased as the crosslinker density of gel is increased. It is observed that τ values are much higher for high molecular weight An-PMMA chains than low molecular weight chains in all gel samples.

Fluorescent photoinduced electron transfer (PET) sensing of anions using charge neutral chemosensorsElectronic supplementary data (ESI) available: 1H, 13C NMR for 1a–c and UV-Vis and NMR titration results for 1a are available as electronic supplementary information (ESI). See http://www.rsc.org/suppdata/cc/b1/b107608f/

We demonstrate for the first time that the charge neutral anthracene based fluorescent sensors 1a–c, having an aromatic or aliphatic thiourea moiety as an anion receptor, show ideal PET sensor behaviour where the anthracene fluorescence emission is selectively quenched upon titration with AcO−, H2PO4− and F− but not by Cl− and Br− in DMSO.

Strongly UV absorbing bifunctional azoalkanes.

[structure: see text] Two new anthracene-containing azoalkanes (1 and 2) absorb UV light 600 times more strongly than simple azoalkanes. Intramolecular energy transfer from excited singlet anthracene to the azo group is nearly complete, but despite the close proximity of the two chromophores, 1 and 2 continue to exhibit anthracene fluorescence. Thermolysis of these compounds in the presence of monomers affords fluorescent labeled polymers. Compounds 1 and 2 are the first azoalkanes to undergo induced decomposition in solution.

Anthracene as the Origin of the Red-Shifted Emission from Commercial Zone-Refined Phenanthrene Sorbed on Mineral Surfaces

The origin of the red-shifted fluorescence emission spectra observed for commercial zone-refined phenanthrene (purity 99.5+%) in concentrated cyclohexane solution and as sorbates on porous silica at high loading levels was studied by absorption and fluorescence spectroscopy as well as fluorescence quenching measurements. The absorption and fluorescence spectra indicate that a small amount of anthracene is present in the zone-refined phenanthrene. In concentrated phenanthrene solution and highly phenanthrene-loaded porous silica, excitation energy transfer from phenanthrene to the anthracene impurity results in the reduction of the phenanthrene fluorescence intensity and the appearance of the anthracene fluorescence emission at longer wavelength. A Stern−Volmer plot for quenching of phenanthrene fluorescence by anthracene in cyclohexane indicates both dynamic and static energy transfer mechanisms. For phenanthrene sorbed on mineral surfaces, the dynamic pathway is limited. Therefore, the appearance of anthracene fluorescence due to energy transfer from excited phenanthrene can serve as a spectral probe for polyaromatic hydrocarbon (PAH) aggregation and association on mineral surfaces.

Fluorescence quenching of anthracene by indole derivatives in phospholipid bilayers

The quenching of anthracene fluorescence by indole, 1,2-dimethylindole (DMI), tryptophan (Trp) and indole 3-acetic acid (IAA) in palmitoyloleoylphosphatidylcholine (POPC) lipid bilayers was investigated. A very efficient quenching of the anthracene fluorescence in the lipid membrane is observed. Stern–Volmer plots are linear for DMI but present a downward curvature for the other quenchers. This was interpreted as an indication of the presence of an inaccessible fraction of anthracene molecules. By a modified Stern–Volmer analysis the fraction accessible to the quenchers and the quenching constant were determined. The changes in the fluorescence emission spectrum of indole and DMI have been used to calculate the partition constants of these probes into the membranes, and bimolecular quenching rate constants were determined in terms of the local concentration of quencher in the lipid bilayer. The rate constants are lower than those in homogeneous solvents, which may be ascribed to a higher viscosity of the bilayer. No changes in the emission spectra of Trp and IAA are observed in the presence of vesicles, indicating that these probes locate preferentially in the aqueous phase, or in close proximity to the vesicular external interface in a medium resembling pure water. In these cases quenching rate constants were determined in terms of the analytical concentration. In the quenching by DMI a new, red shifted, emission band appears; it is similar to that observed in non-polar solvents and it is ascribable to an exciplex emission. The exciplex band is absent in the quenching by IAA and Trp and only very weakly present when the quencher is indole. From the position of the maximum of the exciplex emission, a relatively high local polarity could be estimated for the region of the bilayer where the quenching reaction takes place.

Enhanced Quenching of Anthracene Fluorescence by Nitroalkanes in Zeolite X and Y

Quenching of the first excited singlet state of anthracene (1An*) by nitromethane (NM) and 2-methyl-2-nitropropane (2M2NP) has been evaluated by picosecond, fluorescence-based methodologies in alka...

Investigation of the anthracene-nitroxide hybrid molecule as a probe for hydroxyl radicals.

A new method for the determination of hydroxyl radicals is proposed. The method is based on the use of a hybrid molecule consisting of a fluorescent chromophore, anthracene, and a nitroxide radical. In the hybrid molecule, the nitroxide quenches the fluorescence of anthracene strongly. The reaction of hydroxyl radicals with dimethyl sulfoxide generates quantitatively methyl radicals, which then combine with the nitroxide moiety of the hybrid molecules to result in an increase in the fluorescence intensity. The fluorescence increase is proportional to the concentration of hydroxyl radicals. The proposed method is capable of detecting hydroxyl radicals generated in the Fenton system. It is a simple and sensitive technique for the determination of hydroxyl radicals.

Determination of N-Phenylmaleimide by a Decrease in the Intensity of Anthracene Fluorescence

A highly sensitive method for the determination of N-phenylmaleimide was described. The method is based on the quenching of the fluorescence of an anthracene solution in dioxane in the presence of the analyte. The determination limit is 0.17 ng/mL.

Experimental measurement and calculation of the line intensities in vibronic spectra of jet-cooled anthracene

The intensities of vibronic lines are experimentally measured in fluorescence and fluorescence excitation spectra of jet-cooled anthracene. An original method is developed for calculating geometrical parameters of benzene hydrocarbons in the ground and excited electronic states. Using these parameters, the intensities of vibronic lines in fluorescence and absorption spectra of anthracene are calculated in the Franck-Condon approximation taking into account the mixing of all the twelve normal coordinates of totally symmetric vibrational modes. After correction for the quantum yield of fluorescence, good agreement is obtained between the calculated line intensities in the absorption spectrum and the measured line intensities in the fluorescence excitation spectrum. Based on these data, a new assignment of the lines in the fluorescence excitation spectrum corresponding to totally symmetric modes 7 and 8 is suggested.