Anisotropy of the T-T absorption spectra of naphthalene and phenanthrene

The naphthalene absorption in the spectral region of 3500–4100 Å consists of two perpendicularly polarized band systems. This can be shown by polarization measurements. The arguments given do not allow a decision as to whether or not the short axis polarized band is the ³A_g⁻ ← ³B_iu⁺ transition or an induced vibronic band of the ³B_3g⁻ ← ³B_iu⁺ transition generated by a b_3g vibration mode. The T-T polarization of phenanthrene as a function of the excitation wavenumber is quantitatively compared with the equivalent S₁ ← S₀ fluorescence polarization. There is a good agreement between the calculated and the measured curve.     

Threshold photoelectron study of naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene

Threshold photoelectron spectra (TPESs) were obtained for naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene using imaging photoelectron photoion coincidence spectroscopy, from threshold to a photon energy of ～20 eV. Outer valence Green's function calculations at the OVGF∕cc-pVTZ level of theory were used to assign molecular orbitals to the observed TPES features. There is generally good agreement between the predicted and observed bands. Threshold regions for each molecule exhibit vibrational structure which is readily assigned based on previous PES studies. While the measured adiabatic ionization energies (IE(a)) for naphthalene, anthracene, and pyrene are in good agreement with previous works, new values are reported for the two dihydro species (1,2-dihydronaphthalene, 8.010 ± 0.010 eV and 9,10-dihydroanthracene, 8.335 ± 0.010 eV). A comparison is also made with the G3∕∕B3LYP composite method, which consistently overestimates the IE values by 0.06-0.09 eV. The double ionization energies for anthracene and pyrene have been measured to be 19.3 ± 0.2 and 19.8 ± 0.2 eV, respectively.     

Orientation of anthracene molecules in naphthalene and tetracene molecules in anthracene single crystals

The orientation of isolated anthracene and tetracene molecules in naphthalene and anthracene single crystals, respectively, was determined using electron spin resonance. The result indicates only small deviations of less than 60° from that of a molecule in a substitutional position.     

Optical T-T absorption of salicylidene-p-toluidine in solution

The observation of triplet-triplet absorption of salicylidene-p-toluidine, is complicated by the possible colored isomer formation during the optical pumping. The short-lived (singlet-singlet) and long-lived (triplet-triplet) absorption spectra were recorded phographically by microsecond flash and nanosecond laser flash photolysis techniques. Salicylidene-aniline complexes were purified by repeated recrystallisation until further recrystallisation produced no further changes for X-ray diffraction pattern and optical absorption, emission properties.     

One-pot synthesis of partially fluorinated naphthalene, anthracene, and chrysene derivatives

A series of partially fluorinated naphthalene, anthracene, and chrysene derivatives have been synthesized by a convenient one-pot reaction of multi-fluorinated aromatics and 1,4-dilithio-1,2,3,4-tetraaryl-1,3-butadiene that was generated in situ from the reduction of diphenylacetylene derivatives with lithium naphthalenide.     

Electrodimerization of cyano-substituted derivatives of anthracene and naphthalene

The electrochemistry of cyano-substituted derivatives of naphthalene and anthracene was studied at different temperatures (298–233 K) using slow and fast scan voltammetry with a maximum scan rate of 500 V s⁻¹. All experimental evidence indicates the formation of a dimer by an E_revC_2rev process at the monoanion level. Rate constants for dimerization process were evaluated in six different polar solvents using theoretical working curves for an E_revC_2rev mechanism. Digital simulation was used to verify the accuracy of these rate constants. The results show that the polarity of the solvent influences the rate of dimerization reactions and that radical anions of the studied compounds dimerize under diffusion control.     

Electronic structure and chemical bond in naphthalene and anthracene

We investigated the electronic structure of crystalline naphthalene and anthracene within the framework of density functional theory including van der Waals interactions (DFT-D). It is established that for better agreement with experimental values it is necessary to use the increased values of the van der Waals radii, which is caused by an overestimated value of the van der Waals interactions in crystalline linear oligoacenes. Utilization of the DFT-D leads to a correct account of the dispersion forces, which results in a high precision of the computed lattice parameters and cohesive energy. Based on the relaxed crystal structures, we have computed the total and deformation electron density and determined the mechanism of chemical bonds formation in crystals of naphthalene and anthracene. It has been established that the chemical bond in molecular crystals is formed under the influence of not only intramolecular but also intermolecular interactions. On the basis of the Mulliken population analysis it was revealed that two C(3) atoms in naphthalene (or C(3) and C(4) in anthracene) have a positive charge and the population of the rest of the carbon atoms increased, as compared with isolated molecule.     

Infrared absorption spectra of naphthalene and anthracene anion-radicals

The infrared spectra of naphthalene and anthracene anion-radicals and their completely deuterated analogs have been studied. The most intense bands have been assigned, and it has been shown that the frequencies of the bending and stretching vibrations of the ring and the C-H (D) bond are less than the corresponding frequencies for the hydrocarbons. The decrease in the frequencies has been attributed to the fact that the unpaired electron of the anionradical, present in an antibonding orbital, decreases the force constants of the bonds; this is analogous to an excited state of the hydrocarbon molecule. A product rule has been proposed for the anion-radicals and their original hydrocarbons.     

Intra- and inter-ring haptotropic rearrangements in (naphthalene and anthracene)nickel complexes: a DFT study

Density functional quantum chemical calculations of the mechanisms of metallotropic η²,η²-intra- and η²,η²-inter-ring haptotropic rearrangements (HRs) in 16e zero-valent η²-(naphthalene and anthracene)nickel complexes involving migration of the organometallic group within the same ring or from one aromatic ring to the other were carried out. The structures of the initial complexes, transition states, and intermediates were determined. The intra-ring HRs in these systems proceed via low-energy η⁴-cis-butadiene transition states. The inter-ring HRs proceed along the periphery of the naphthalene and anthracene ligands via high-energy η³-allylic transition states. In contrast to well-investigated η⁶,η⁶-inter-ring HRs in (naphthalene and anthracene)tricarbonylchromium complexes, the activation barriers to the η²,η²-inter-ring HRs in the corresponding nickel complexes are much lower. Transition states of these processes are characterized by higher hapticity compared to the initial complexes. This also distinguishes the nickel complexes from the corresponding Cr(CO)₃ complexes for which the hapticities of transition states of the η⁶,η⁶-inter-ring HRs are lower than those of the initial complexes. The calculated activation barriers to the η²,η²-intra-ring HRs in the (naphthalene and anthracene)nickel complexes as well as the barrier to rotation of the organonickel group in the naphthalene complex are in good agreement with the experimental data. The calculated barriers to the η²,η²-inter-ring HRs in the naphthalene and anthracene complexes are 3–5 kcal mol⁻¹ lower than the experimental values. This is probably due to the competition between two mechanisms of this process, a low-energy intramolecular mechanism and a high-energy intermolecular dissociative mechanism.     

Orientation of anthracene molecules in naphthalene single crystals

The orientation of anthracene in naphthalene matrix has been determined by EPR of the triplet state of the guest molecule. It differs from the host molecule orientation mainly by a rotation of 25° about the z axis.     

Hydrogenation of naphthalene and anthracene on Pt/C catalysts

Hydrogenation of naphthalene and anthracene deposited on Sibunit and active carbon was studied. The reactions were carried out at a temperature of 280 °C and a pressure of 90 atm. The directions for the complete hydrogenation of the investigated substrates were studied. Correlations between the structures of naphthalene and anthracene and their activity in hydrogen absorption are presented. The hydrogenation rates decrease as the substrate is saturated with hydrogen.     

The radical anions and the electron affinities of perfluorinated benzene,naphthalene and anthracene

Although benzene and naphthalene do not have electron affinities in the conventional sense, perfluorobenzene and perfluoronaphthalene have nonzero electron affinities. Theoretical methods extensively calibrated with experiment for the prediction of electron affinities (EAs) predict the EAs of perfluorobenzene, perfluoronaphthalene and perfluoroanthracene as 0.69, 1.02 and 1.84 eV, respectively. A rough estimate of 2.39 eV is made for the electron affinity of perfluorotetracene. Thus the perfluoro polycyclic aromatic hydrocarbons (PAHs) are predicted to be effective electron acceptors.     

Emission spectra of naphthalene,anthracene and naphthacene oriented in stretched polyethylene and in shpolskii matrices

Emission spectra of naphthalene, anthracene and naphthacene, oriented in stretched polyethylene sheets, have been studied. Absolute polarization of the bands and symmetry assignments of the vibrational modes are deduced and progressions of bands are drawn up. A comparison with other polarization investigation is given.To support the interpretation of the film spectra the molecules have also been measured (20 K) in suitable crystalline solvents (Shpolskú matries). Discrepancies with the literature are discussed. The anomalous behavior of the environment multiplet structure of naphthacene in n-nonane is described.     

Ultraviolet spectrophotometric method for the determination of anthracene,naphthalene and pyrene in coal tars

A rapid method determination of the abovemetioned three compounds directly in coal tar solutions has been developed, using a baseline technique λ_max = 376, 335 and 220 nm, respectively. In the case of anthracene the standard addition method and first derivative spectra were used. The precision of the results was calculated. The accuracy of the method was evaluated by comparison of the results obtained by means of different instrumental techniques for coal tar and its fraction.     

Two-photon spectroscopy of the low-lying singlet states of naphthalene and acenaphthene

Two-photon excitation spectra of naphthalene and acenaphthene have been measured up to 50000 cm^?1. In naphthalene. three two-photon allowed states are observed for which the symmetry assignment is confirmed by polarization. The corre- sponding transitions are also seen in acenaphthene. The experimental data are in excellent agreement with theoretical predictions.     

Two-photon excitation into low-energy singlet states of anthracene in mixed crystals

The two-photon excitation spectrum of the first excited state of anthracene in fluorene and biphenyl at 4.2 K has been measured. Intensity is induced into the origin by the static dipole moment of fluorene, and into b_1u vibrons through coupling to an A_g state near 29400 cm⁻¹; the nature of this A_g state is discussed.     

Line widths of the 3800 Å singlet transitions in crystalline anthracene

The theory of resonance coupling of Frenkel excitons and phonons is extended to two molecules per unit cell. Intra- and inter-band scattering for the two Davydov components can thus be dealt with on the same footing. Restrictions to nearest neighbour interactions have been removed. Application to anthracene shows that the contribution of librational phonons to the scattering is approximately one hundred times larger than that of translational phonons. The widths of the anthracene components are shown to fit the calculated coupling and known phonon frequencies satisfactorily.     

On singlet exciton fission in anthracene and tetracene at 77°K

Relative variations of prompt flourescence yield, on application of a magnetic field are studied at 77°K for anthracene and tetracene crystals excited by light with wavenumbers up to 50,000 cm^-1. The results obtained for anthacene, as compared to those previously reported at 300°K, indicate a very small temperature dependence. The variations observed for tetracene at 77°K are comparable in magnitude to those for anthracene. The singlet exciton fission process, responsible for the experimental observations, does not involve a thermally relaxed lowest bound or charge transfer singlet exciton. The possible role of upper excited vibronic states is discussed.