Anthracene Molecules Research Articles

Systematic Investigation of Molecular Arrangements and Solid‐State Fluorescence Properties on Salts of Anthracene‐2,6‐disulfonic Acid with Aliphatic Primary Amines

Organic salts of anthracene-2,6-disulfonic acid (ADS) with a wide variety of primary amines have been fabricated, and their arrangements of anthracene molecules and solid-state fluorescence properties investigated. Single-crystal X-ray studies reveal that the salts show seven types of crystal forms and corresponding molecular arrangements of anthracene moieties depending on the amine, while anthracene shows only one form and arrangement in the solid state. Depending on the molecular arrangements, the ADS salts exhibit various solid-state fluorescence properties: spectral shift (30 nm) and suppression and enhancement of the fluorescence intensity. Especially the ADS salt with n-heptylamine (nHepA), which shows discrete anthracene moieties in the crystal, exhibits the highest quantum yield (Phi(F)=46.1+/-0.2%) in the series of ADS salts, which exceeds that of anthracene crystal (Phi(F)=42.9+/-0.2%). From these systematic investigations on the arrangements and the solid-state properties, the following factors are essential for high fluorescence quantum yield in the solid state: prevention of contact between pi planes of anthracene moieties and immobilization of anthracene rings. In addition, such organic salts have potential as a system for modulating the molecular arrangements of fluorophores and the concomitant solid-state properties. Thus, systematic investigation of this system constructs a library of arrangements and properties, and the library leads to remarkable strategies for the development of organic solid materials.

Optical study of anthracene molecules doped in fluorene single crystals

Properties of two luminescence centers, which are observed in anthracene-doped fluorene crystal as concentration increases, have been investigated to clarify their origin. Excitation spectra and concentration dependence of absorption spectra were measured and two types of luminescence are attributed to anthracene molecule pair centers with weak and strong interaction. Dipole–dipole interactions between two anthracence molecules of various configurations are estimated and possible configuration for two types of luminescence is proposed.

Structure and excited-state dynamics of anthracene: Ultrahigh-resolution spectroscopy and theoretical calculation

Rotationally resolved ultrahigh-resolution spectra of the S(1) (1)B(2u)<--S(0) (1)A(g) transition of anthracene-h(10) and anthracene-d(10) have been observed using a single-mode UV laser and a collimated supersonic jet. We have determined rotational constants of the zero-vibrational levels of the S(0) and S(1) states by analyzing the precisely calibrated transition wavenumbers of rotational lines. We measured Zeeman splitting of each rotational line in the external magnetic field, of which the magnitude was small and strongly dependent on the rotational quantum numbers. We have shown that the magnetic moment in the S(1) (1)B(2u) state arises from J-L coupling with the S(2) (1)B(3u) state and that mixing with the triplet state is negligibly small. We concluded that the main radiationless transition in the S(1) state of anthracene is not intersystem crossing to the triplet state but internal conversion to the ground state. We also examined methods of ab initio theoretical calculation to determine which method most closely yielded the same values of rotational constants as the experimentally obtained ones. Moller-Plesset second-order perturbation method with a 6-31G(d,p) basis set yielded approximately the same values for the S(0) (1)A(g) state with an error of less than 0.04%. Geometrical structure in the S(0) (1)A(g) state of the isolated anthracene molecule has been accurately determined by this calculation. However, configurational-interaction with single excitations, time-dependent Hartree-Fock, and time-dependent density-function-theory methods did not yield satisfactory results for the excitation energy of the S(1) (1)B(2u) state. Symmetry-adapted-cluster configuration-interaction calculation was sufficiently good for the excitation energy and rotational constants.

Effect of cluster formation of solvent molecules on the preferential solvatation of anthracene in binary alcoholic solutions

The formation of the solvatation shell of anthracene molecule was investigated in binary mixtures of protic alcoholic solvents by solvent-relaxation measurements, anisotropy decay studies and quantum-chemical modeling. Results show significant change of the solvatation shell of anthracene dissolved in binary solutions of methanol, ethanol or n-propanol with n-butanol when the molar fraction of n-butanol in the bulk solution exceeds a critical value. Both the solvent relaxation and anisotropy decay data suggest clusterization process in the solvatation shell of the anthracene probe. Quantum chemical calculation supports formation of energetically preferred heteromolecular (X 2(BuOH) 2, X = MeOH, EtOH or PrOH) clusters around the solute.

Optical properties of anthracene‐fluorene mixed crystals fabricated by cell method

AbstractAnthracene‐fluorene mixed crystals with anthracene mole fraction of 0.1 to 100% are fabricated using a cell method and their optical properties are studied. In contrast to sharp luminescence due to isolated anthracene molecules in a 0.1% doped sample and in a pure anthracene bulk crystal, broad luminescence bands are observed in the middle concentration samples. For samples with less than 50% anthracene, broad luminescence bands are attributable to localized excited state at anthracene molecule pair which is accompanied by lattice relaxation. For samples with higher anthracene concentration, observed broad luminescence has lower peak energy than that of an anthracene bulk crystal. Origin of the luminescence is proposed to be excitation localized at fluorene impurity induced X‐traps in anthracene clusters. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Large Negative Differential Resistance in a Molecular Junction of Carbon Nanotube and Anthracene

We propose a novel molecular junction with single walled carbon nanotube (SWNT) as electrodes bridged by an anthracene molecule. It is found that when the coupling between the molecule and the SWNT is noncovalent, the current-voltage (I-V) curve shows a striking nonlinear feature and a large negative differential resistance (NDR) at small bias. While in covalent adsorption site, the I-V curve behaves nearly linear. Theoretical studies based on the nonequilibrium Green's function method demonstrate that mechanism of the NDR is due to the narrow features of the local density of states (LDOS) of the SWNT as well as the alignment between the peak of LDOS of the electrodes and the molecular energy levels.

Resonant Rayleigh scattering from an anisotropic organic single-crystal microcavity

Resonant Rayleigh scattering (RRS) is observed upon excitation of a microcavity containing a single crystal of the organic molecule anthracene. The RRS profile is obtained for a range of excitation energies and angles. In contrast to the circular profile observed for inorganic microcavities, the scattered light pattern is elliptical when projected normal to the sample surface. The profile shape provides a direct visual representation of the anisotropic microcavity polariton dispersion characteristic of organic crystals.

One-step catalyst-free generation of carbon nanospheres via laser-induced pyrolysis of anthracene

Carbon nanospheres with diameters between 100 and 400 nm have been successfully synthesized via low-power laser-assisted pyrolysis of anthracene in a nitrogen atmosphere. The developed facile route yields homogeneous nanoparticles and requires no supplementary carbon feedstock or catalyst. The sharp thermal gradient afforded by the laser results in two kinds of carbon products that differ in crystallinity and mean particle size. Our detailed findings point to the carbon nanospheres being comprised of small-unclosed aromatic layers that are connected together by simple organic linkers. C–H bonds in the anthracene molecules are partially broken by the laser beam energy, and as the newly created large radicals aggregate, carbon nanospheres are formed.

On the mechanism of mechanochemical dimerization of anthracene. Quantum-chemical calculation of the electronic structure of anthracene and its dimer

The electronic structure of anthracene, its dimer, and intermediate structures composed of two anthracene molecules were calculated in the density functional theory. The calculated potential barrier to anthracene dimerization is ∼55 kcal/mol; the dissociation barrier is ∼45 kcal/mol. The pressure required for the reaction to reach the transition state and acting on the anthracene crystal is ∼60 kbar. Lower pressures, ∼10 kbar, are required for molecules to approach each other to distances of ∼3 A, at which tunnel dimerization is possible for photoexcited molecules.

Intersystem Crossing Mediated by Photoinduced Intramolecular Charge Transfer: Julolidine−Anthracene Molecules with Perpendicular π Systems

Time-resolved electron paramagnetic resonance studies show that the primary mechanism of triplet formation following photoexcitation of julolidine-anthracene molecules linked by a single bond and having perpendicular pi systems is a spin-orbit, charge-transfer intersystem crossing mechanism (SOCT-ISC). This mechanism depends on the degree of charge transfer from julolidine to anthracene, the dihedral angle (theta1) between their pi systems, and the magnitude of the electronic coupling between julolidine and anthracene. We compare 4-(9-anthracenyl)-julolidine with the more sterically encumbered 4-(9-anthracenyl)-3,5-dimethyljulolidine and find that fixing theta1 congruent with 90 degrees serves to enhance SOCT-ISC by increasing the change in orbital angular momentum accompanying charge transfer. Given that the requirements for the SOCT-ISC mechanism are quite general, we expect it to occur in a variety of electron donor-acceptor systems.

Physical origins of interactions in dimers of polycyclic aromatic hydrocarbons

Dimers of several polycyclic aromatic hydrocarbons (PAHs): naphthalene, anthracene and pyrene have been investigated by symmetry-adapted perturbation theory based on the density functional description of the monomers [SAPT(DFT)]. Calculations have been performed for a number of radial cross-sections of selected stacked and T-shaped configurations. The interaction energies at the minima of stacked configurations of the benzene, naphthalene, anthracene and pyrene dimers increase with the number of rings, but -- in contrast to literature findings -- the rate of increase is somewhat irregular. In particular, the anthracene molecules interact slightly stronger than indicated by the number of rings and the pyrene molecules interact significantly weaker (although the latter do interact stronger than the former). These trends can be partly rationalized by the physical decomposition of the interaction energies given by SAPT. We find the stacked structures to be significantly more stable than the T-shaped ones, with the relative stability of the former structures increasing as the size of the system increases. This observation extends to the benzene dimer where the two structures are nearly isoenergetic and a tilted T-shaped structure actually becomes the global minimum. For the naphthalene dimer, the greater stability of the stacked configuration than of the T-shaped one is in disagreement with recent experiments observing only the latter structure. For the anthracene dimer, theory is in agreement with experiments.

High-resolution laser spectroscopy on the S1←S transition of jet-cooled anthracene: Rotational structure and Stark effect

We present rotationally resolved spectra of the S(1)<--S(0) transition of anthracene at 27,687.153(4) cm(-1) as well as Stark effect measurements of the free anthracene molecule in electric fields of up to 85 kV/cm. The molecule is rotationally cooled in a supersonic jet expansion to a temperature of 4 K. The rotational constants of the electronic states S(0) and S(1) are determined by a simplex fit comparing the experimental spectra with simulations for an asymmetric rigid rotor. The measured and simulated energies are in very good agreement and the estimated accuracy of the rotational constants is 1 per thousand. Furthermore, the polarizabilities of the electronic states S(0) and S(1) are investigated. At an electric field of 85 kV/cm, line shifts of up to 150 MHz caused by a change in the polarizability of Deltaalpha=123(7) a.u. and broadenings due to the anisotropy are observed. The components of the tensor polarizabilities of the electronic states S(0) and S(1) are determined by simulating the complete spectra using second-order perturbation theory.

Detection of one base mismatch using photochemical ligation

We attached anthracene molecules covalently to one end of oligodeoxyribonucleotides to form three pairs of anthracene-ODN conjugates. The sequences of each pair of the conjugates were designed to bind adjacent sequences of the template with the anthracene units directed such that they stacked each other. The conjugates dimerized only in the presence of the template by light irradiation. We found that the ligation yields largely depended on the substituted position of anthracene groups. Sequence selectivity in the dimerization yield was preserved even in the system with highest reactivity. SNP bases could be discriminated rapidly by combining the techniques of MS spectroscopy.

Single Dibenzoterrylene Molecules in an Anthracene Crystal: Main Insertion Sites

We present a spectroscopic study of the properties of the two principal insertion sites (at 785.1 and 794.3 nm) of single dibenzoterrylene molecules in anthracene single crystals at cryogenic temperatures. We measured the temperature dependence of the line width, the orientation of the transition dipole moments, and the Stark effect. We performed molecular dynamics simulations, which show that one dibenzoterrylene molecule preferably replaces three anthracene molecules. From simulated annealing, we derive the molecular conformations in the most stable insertion sites and the orientations of the transition dipole moments. The good agreement between the spectroscopic results and the simulations allows us to propose unambiguous structures for the two principal spectroscopic sites.

Quantum Chemical Modeling of the Oxidation of Dihydroanthracene by the Biomimetic Nonheme Iron Catalyst [(TMC)FeIV(O)]2+

Hybrid density functional theory has been employed to model the oxidation of dihydroanthracene (DHA = C14H12) to anthracene (C14H10) by the biomimetic iron complex [(TMC)FeIV(O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Experimentally, the reaction has been studied in a solution of the reactants and the counterion trifluoroacetate (CF3C ) in the solvent acetonitrile (CH3CN). Depending on the concentration of trifluoroacetate, different coordination situations have been observed by NMR spectroscopy. The complexity of the chemical environment offers a challenging modeling problem, and five different models were initially considered. The effects of the coordination of either a counterion or a solvent molecule were found to be rather small. The reaction was found to be a two-step process in which the first step is rate-limiting. The free energy of activation (ΔG⧧) for the first H-abstraction was found to be between 14.5 and 16.9 kcal mol-1 depending on the model, in reasonable agreement with experimental data. The second step has a much lower free-energy barrier, found to be completely entropic in origin. In all models, the system is found to have a triplet ground state in the FeIV(O) reactant. A spin-crossing of the triplet and quintet potential energy surfaces occurs before the first transition state, and the system is found to end up in the FeII quintet state, releasing a water molecule and the anthracene product. Because of the formation of the aromatic anthracene molecule, the reaction is very exothermic.

On the aromagnetism and anapole moment of anthracene nanocrystals

We report the results of the study of orientation of small anthracene crystals (suspended in liquid) by static and oscillating magnetic fields. They contradict the previous claim that magnetic response of such crystals displays aromagnetism associated with the static toroidal (anapole) moments of the aromatic molecule. The existence of strong aromagnetism in anthracene would be a fundamental result of high importance for the understanding of interactions on the molecular and bio-molecular levels. Instead, our observations are fully consistent with conventional diamagnetism of anthracene molecules.

Heterogeneous triplet-triplet annihilation of erythrosine and anthracene molecules on a fractal anodized aluminum surface

We have studied exchange resonance processes of homogeneous triplet-triplet annihilation and heterogeneous triplet-triplet annihilation for erythrosine and anthracene molecules on an anodized aluminum surface over a broad temperature range. We have shown that the kinetics of the considered processes are determined by the dimensionality of the molecular clusters on the porous anodized aluminum surface.

Nanostructured Thin films of Anthracene by Liquid-Liquid Interface Recrystallization Technique

Herein, we report the fabrication of anthracene nanostructures and, in turn, their thin films at the air-water interface by recrystallization at the liquid-liquid interface. This method is simple, inexpensive and allows the deposition of anthracene nanoparticulate thin films on large and a variety of substrates. The virgin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Hot Stage Polarizing Microscopy and UV-Visible spectroscopy. Interestingly, it was found that these thin films are comprised of nanosized bushy clusters of anthracene molecules as revealed by TEM. Also, with increase in the thickness of the films, the formation of irregular microtapes was evinced by SEM. The absorption spectra reveals the presence of 2 excitonic peaks for the lowest dip sample (10 dips) whereas the spectra recorded for higher dip samples (20 dips, 30dips, 40dips) closely match with that of pure anthracene in chloroform solution. The dramatic reduction in the melting point as revealed by hot stage polarizing microscopy is the salient feature of the work.

Luminescence of anthracene molecules in single crystal matrices

AbstractOptical properties of single fluorene/phenanthrene crystals doped with various mole fraction of anthracene, 10–5 to a few %, were investigated at 10 K. In low concentration samples, sharp structures attributed to isolated anthracene molecules were observed. Inhomogeneous width in their 0‐0 energy were found to be ∼20 cm–1. When concentration is higher, spectral species, which are distinctly different from the isolated molecule spectrum, were observed and their origins are discussed. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Photophysics of anthracene–indole systems in unilamellar vesicles of DMPC and POPC: Exciplex formation and temperature effects

The quenching of anthracene fluorescence by indole (IN), 1,2-dimethylindole (DMI), tryptophan (Trp) and indole 3-acetic acid (IAA) in dimiristoylphophatidylcholine (DMPC) and palmitoyloleoylphosphatidylcholine (POPC) lipid bilayers was investigated. The studies were carried out at 25 °C in POPC vesicles and below (15 °C) and above (35 °C) the phase transition temperature (24 °C) of DMPC. A very efficient quenching of the anthracene fluorescence by IN and DMI in the lipid membrane is observed in all cases. It is less efficient in the case of Trp and IAA. 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. Partition constants of the quenchers were obtained from the changes in the fluorescence emission of the indole moiety caused by the presence of the phospholipid. Using the partition constants bimolecular quenching rate constants were determined in terms of the local concentration of quencher in the lipid bilayer. These corrected rate constants are lower than those in homogeneous solvents. In the case of DMPC values the gel phase are higher than in the liquid-crystalline phase. In the quenching by IN and DMI a new, red shifted, emission band appears which could be assigned to an exciplex emission. The exciplex band is absent in the quenching by IAA and Trp.