Anthracene Crystals Research Articles

Preparation and spectral characteristics of anthracene/tetracene mixed crystals

A series of tetracene-doped anthracene crystals with different doping concentrations (the highest molar ratio 100 1) are grown from solution. Crystal structures and optical characteristics of the above mixed crystals are investigated at room temperature. By changing the doping concentrations, the fluorescence can be adjusted from blue-green to green and even to yellow-green. The emission spectra of anthracene/tetracene (An/Te) mixed crystals reveal the sensitized fluorescence of tetracene and the partial quenching of anthracene emission. The data of transient photoluminescence (PL) decays illustrate that in An/Te mixed crystals, the decay of anthracene becomes faster, while the PL lifetime of tetracene is longer than that of the tetracene single crystals. All above experimental results suggest that there is excitation energy transfer from anthracene to tetracene in the mixed crystals.

High-Pressure Effects on the Electronic Structure of Anthracene Single Crystals: Role of Nonhydrostaticity

Optical spectroscopy methods were used to examine the effect of nonhydrostaticity on the electronic structure of anthracene single crystals compressed statically to 9 GPa. Two pressure-transmitting media, nitrogen (hydrostatic) and water (nonhydrostatic above approximately 5.5 GPa), were utilized. It was found that nonhydrostatic compression generates several new features both in the absorption and fluorescence spectra: (i) formation of new absorption and fluorescence bands, (ii) deviations in pressure shift of fluorescence peaks, (iii) extensive broadening of vibrational peaks, and (iv) irreversible changes in the spectra shape upon pressure unloading. Furthermore, the time-resolved fluorescence decay curves measured at the wavelength corresponding to the new fluorescence band show clear initial increase. These new features are accompanied by inhomogeneous color changes and macroscopic lines on the (001) plane of the crystal. All of the changes are discussed and correlated with microscopic transformations in the crystal. It is demonstrated that nonhydrostatic compression in anthracene crystal introduces inelastic changes in the form of dislocations along [110] and [110] directions. These dislocations lead to the development of dimeric structures and, consequently, to various changes in the electronic response of the compressed anthracene crystal.

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 & Co. KGaA, Weinheim)

Cavity polariton dispersion of a single‐crystalline anthracene film embedded in a microcavity

AbstractWe study anisotropic behavior of cavity polaritons in an organic microcavity composed of a single crystalline anthracene film grown into the gap of the Fabry‐Perot cavity by a method through capillary action. The anisotropic response of the cavity polariton appeared on the spectra depending on the linear polarized directions; two kinds of the polarization correspond to the principal axes of anthracene crystal. Transmission spectra were measured with various thickness of the anthracene film. The peak‐shift of the lower polariton mode depending on the thickness was obviously observed, whereas that of the upper polariton mode was not clearly observed be cause of the complicated shape of the spectra. This behavior for the upper polariton mode was analyzed on the basis of the convolution between the spectra of the cavity mode and the absorption due to the vibronic transition in anthracene. Cavity‐polariton dispersion as a function of thickness was obtained from peak‐shift on the spectra. Each thickness was determined by spectral fitting through calculation using the transfer matrix theory. Large vacuum Rabi splitting energies of this system were obtained from the dispersion as 0.20 and 0.34 eV for two kinds of the polarizations. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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.

Absence of toroidal moments in ‘aromagnetic’ anthracene

Colloidal suspensions of anthracene and other aromatic compounds have been shown to respond to a magnetic field as if they possessed a permanent magnetic moment. This phenomenon was named ‘aromagnetism’ by Spartakov and Tolstoi, and it was subsequently attributed to the interaction of an electric toroidal moment with a time-varying magnetic field. However, there has been no independent confirmation of the original work. Here, we have selected purified anthracene crystallites which respond to a low magnetic field and investigate how this response depends on the gradient and the time derivative of the field. We conclude that the anomaly cannot be attributed to a toroidal interaction but is due to a constant magnetic moment of the particles. Close examinations using magnetometry and scanning electron microscopy reveal metallic clusters of Fe and Ni up to a few hundred nanometres in size embedded in the anomalous crystallites. These inclusions represent 1.8 ppm by weight of the sample. The observed presence of ferromagnetic inclusions in the ppm range is sufficient to explain the anomalous magnetic properties of micron-sized anthracene crystals, including the reported optical properties of the colloidal suspensions.

Evolution of energy deposition processes in anthracene single crystal from photochemistry to radiation chemistry under excitation with synchrotron radiation from 3 to 700 eV

Absolute values of quantum yield Φ( hν) of singlet exciton formation in anthracene single crystals were measured as a function of photon energy hν, with the usage of synchrotron radiation (SR) in 3–700 eV region. Values of Φ( hν) were found to increase linearly for hν⩾75 eV. For hν⩽40 eV, values of Φ( hν) gave a wealth of structures and are not linear to hν. Because number of secondary electrons produced by radiation is thought to increase in proportional to the incident photon energy, it is natural to conclude that the radiation chemistry effect becomes dominant above 75 eV. On the other hand, values of Φ( hν) showed response due to resonance rather than linear dependence with hν, which implies that the photochemical effect is dominant below 40 eV.

Time-Resolved Electronic Spectroscopy To Examine Shock-Wave-Induced Changes in Anthracene Single Crystals

Shock-wave-induced electronic structure changes in anthracene single crystals were examined using time-resolved absorption and fluorescence spectroscopy. Crystals were subjected to stepwise loading normal to the (001) crystallographic plane to peak stresses between 2.5 and 6.0 GPa. Absorption experiments revealed (i) a monotonic shift of the absorption edge of the singlet state toward lower energies (red shift) and (ii) formation of a new band on the lower energy side of the red-shifted absorption edge. Furthermore, laser excitation to the new absorption band produced fluorescence with excimer-like characteristics. The combined absorption and fluorescence results indicate the formation of new electronic states as a consequence of shock-wave compression and the resulting plastic deformation. The new states are attributed to dimer-type defects formed in shocked anthracene crystals.

Self-trapping limited exciton diffusion in a monomeric perylene crystal as revealed by femtosecond transient absorption microscopy

Self-trapping and singlet-singlet annihilation of the free excitons in a monomeric (beta) perylene crystal were studied by using femtosecond transient absorption microscopy. The free exciton generated by the photo-excitation of the beta-perylene crystal relaxed to the self-trapped exciton with a rate constant of 7 x 10(10) s(-1). The singlet-singlet annihilation of the free exciton observed under the high excitation density conditions was competed with the self-trapping of the free exciton; we estimated the annihilation rate constant for the free exciton to be 1 x 10(-8) cm(3) s(-1) from the excitation density dependence of the free exciton decay. After self-trapping of the free exciton, no annihilation was observed in the 100 ps time range, suggesting that the diffusion coefficient was reduced drastically by self-trapping. The results show that the major factor limiting the exciton diffusion in the beta-perylene crystal is a relaxation of the free exciton to the self-trapped exciton, and not the lifetime of the exciton. Though the singlet-singlet annihilation rate constants and fluorescence lifetime of the beta-perylene crystal are similar to those of the anthracene crystal, the estimated exciton diffusion length (2 nm) in the beta-perylene crystal is much smaller than that (100 nm) in the anthracene crystal as a result of the exciton self-trapping.

Vibronic approach in the theory of the excitonic spectra of molecular crystals

The excitonic and vibronic spectra of a molecular chain have been studied on using a complete vibronic approach (without separation in Hilbert subspaces) which has been developed in this paper. The methods of canonical transformations and Green's functions are applied to find out analytical expressions as continued fractions for the linear optical susceptibility near the frequencies of the Frenkel exciton and its first and/or subsequent three vibronic replicas. The approximation of the dynamical theory, i.e., the case of a narrow exciton band compared with the energy of the vibrational quantum, is modified to treat vibronic spectra with totally symmetric phonons by considering both the linear and quadratic exciton-phonon coupling. The excitonic and vibrational parameters for anthracene, naphthalene, and benzene crystals as well as for three other models of molecular chains have been used in calculating the linear absorption spectra of the one-dimensional models of those crystals. The main results concern the shape of the absorption maxima and the manifestations of joint and unbound exciton-phonon configurations in the one-, two-, and three-phonon vibronic spectra depending on the dominant impact of the linear or (and) quadratic exciton-phonon coupling. The picture of the calculated spectra has been compared with the data of previous theoretical studies. It agrees with the available experimental data on the linear absorption in the three aromatic crystals.

Cover Picture: Single Dibenzoterrylene Molecules in an Anthracene Crystal: Spectroscopy and Photophysics (ChemPhysChem 8/2007)

The cover picture shows a sublimation‐grown anthracene crystal doped with dibenzoterrylene. The deep blue color is the anthracene crystal's intrinsic fluorescence, excited by a mercury line at 365 nm. The red color arises from scattered near‐infrared (785 nm) laser light used to excite dibenzoterrylene. Fluorescence exits the crystal dominantly through the edges, defects and cracks. The bottom of the figure presents a high‐resolution broad‐band fluorescence excitation spectrum of the sample at low temperature around 785 nm. Every sharp line marks the zero‐phonon transition of a single dibenzoterrylene molecule. The group of lines at 12 590 cm−1 is one of the two spectroscopic sites (the “red site”) whose photophysics are studied in the Article by Nicolet et al. on page 1215.

Single Dibenzoterrylene Molecules in an Anthracene Crystal: Spectroscopy and Photophysics

We study single dibenzoterrylene molecules in an anthracene single crystal at 1.4 K in two insertion sites at 785.1 and 794.3 nm. The single-molecule zero-phonon lines are narrow (about 30 MHz), intense (the detected fluorescence rates at saturation reach 100,000 counts s(-1)), and very photostable. The intersystem-crossing yield is extremely low (10(-7) or lower). All of these features are hallmarks of an excellent system for high-resolution spectroscopy and nanoscale probing at cryogenic temperatures.

Mechanochemical Doping of Tetracence into Anthracene Crystals by Milling Technique

The wet bead milling of anthracence with tiny amounts of tetracene in water results in mechanochemical doping to exhibit solid-state singlet energy transfer. Changes of emission spectra are sensitive to milling conditions so that the couple can act as a fluorescent probe for milling. Perylene displays similar behavior, whereas pentacene and rubrene lead to insufficient fluorescence quenching due to their poor solubility in host crystals.

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.

A novel portable system for detecting and measuring tritium

A novel tritium detector configuration is described based on the anthracene scintillation method. Tritium-bearing samples are applied to a plate-bearing finely sublimed anthracene crystals and viewed in a field-able PMT-based reader against a standard plate. A microprocessor-based control and signal analysis system delivers a reading with a sensitivity of better than 5 nCi 3H in approximately 3 min, and 2.3 nCi in 10 min of counting.

Specific Heat of Molecular Crystals from Atomic Mean Square Displacements with the Einstein, Debye, and Nernst−Lindemann Models

Analysis of atomic displacement parameters (ADPs) from multitemperature diffraction data provides mean-field molecular translation and libration frequencies. These quantities have been combined with molecular deformation frequencies calculated ab initio, e.g. by DFT methods, to calculate the specific heat Cv of molecular crystals of naphthalene, anthracene, and hexamethylenetetramine. If the difference Cp - Cv is represented by the Nernst-Lindemann relation, Cp curves from diffraction experiments and ab initio calculations agree well with those based on calorimetry. Agreement is better if the Debye rather than the Einstein model is chosen to represent the contribution of the translational vibrations. Compressibilities estimated from the differences Cp - Cv are 2-5 times higher than those obtained from compressibility measurements at 298 K and Grüneisen constants derived from the temperature dependence of ADPs.

Intermolecular intersystem crossing in single-molecule spectroscopy: Terrylene in anthracene crystal

We present a spectroscopic study of terrylene in anthracene crystals at the ensemble and single-molecule levels. In this matrix, single-molecule fluorescence is reduced by three orders of magnitude. Correlation measurements allow us to identify a new relaxation channel, matrix-enhanced intersystem crossing. This process starts with a singlet-to-triplet energy transfer from guest to host, after which the triplet exciton is transferred back to the guest. The intermolecular intersystem crossing is expected whenever the lowest triplet state of the host is located between the lowest singlet S(1) and lowest triplet T(1) excited states of the guest. It must be considered when searching for new host-guest systems for single-molecule spectroscopy.

DFT Calculation of Deuterium Quadrupolar Tensor in Crystal Anthracene

A DFT calculation of deuterium nuclear quadrupole tensors of crystal anthracene is presented. After a careful analysis of the DFT functionals and of the basis sets, the B3LYP/6-311+G(d,3p2d) level has been identified as the best compromise between accuracy and computational cost. To account for the crystal environment, three models are proposed: one represented by a cluster of five anthracene arranged as in the crystal, the other formed by an anthracene embedded in a dielectric continuum having the dielectric permittivity of the crystal, and the last represented by an embedded dimer of anthracene. It is shown that the pure continuum model (here represented by the Integral Equation Formalism version of the Polarizable Continuum Model) already accounts for a large part of the crystal effects and that the embedded dimer almost entirely recover all the details of the explicit 5-anthracene cluster.

Dynamics of the Intermolecular Transfer Integral in Crystalline Organic Semiconductors

In organic crystalline semiconductor molecular components are held together by very weak interactions and the transfer integrals between neighboring molecular orbitals are extremely sensitive to small nuclear displacements. We used a mixed quantum chemical and molecular dynamic methodology to assess the effect of nuclear dynamics on the modulation of the transfer integrals between close molecules. We have found that the fluctuations of the transfer integrals are of the same order of magnitude of their average value for pentacene and anthracene. Under these conditions the usual perturbative treatment of the electron-phonon coupling is invalid, the band description of the crystal breaks down and the charge carriers become localized. Organic crystals of pentacene and anthracene, even in the absence of defects, can be regarded as disordered media with respect to their charge transport properties. These results suggest that the dynamic electronic disorder can be the factor limiting the charge mobility in crystalline organic semiconductors.