Interaction of long wavelength light with phenanthrene triplets in crystalline benzophenone

Illumination by light at 750 nm depopulates the triplet state of phenanthrene d-10 dissolved in crystalline benzophenone. The effect is revealed by studies of the kinetics of formation and disappearance of triplets and by a direct spectroscopic observation. Neither the benzophenone nor the phenanthrene alone in the lowest triplet or singlet state absorbs at 750 nm. The effect may be produced by a phenanthrene triplet-benzophenone excimer.     

Monomer and excimer triplet states in glassy phenanthrene

Phosphorescence spectra recorded with vapor-deposited glassy phenanthrene layers reveal the existence of several inhomogeneously broadened monomeric triplet traps of structural origin and two excimeric triplet traps. Temperature-dependent studies yield estimates for both the triplet excimer binding energies and the parameters governing triplet trapping kinetics.     

ENERGY TRANSFER IN PHENANTHRENE-DOPED NAPHTHALENE CRYSTALS

Abstract— Measurements at 77°K and room temperature are described on naphthalene crystals containing varying concentrations of phenanthrene. The lowest excited singlet and triplet states of phenanthrene iie between the singlet and triplet exciton bands of the host crystal. Triplet-triplet annihilation in the host was studied by absorbing radiation purely into the guest molecules; the absence of any phosphorescence or delayed naphthalene fluorescence allowed the radiationless processes out of the naphthalene triplet to be discussed. Singlet-singlet energy transfer was studied using radiation absorbed by the naphthalene. Two separate mechanisms of transfer were observed: (A) free exciton motion in the naphthalene band till encounter with a phenanthrene trap, the last step having an activation energy of 65 cm^-1, and (B) defect traps in the naphthalene transferring energy by a resonance mechanism to the phenanthrene; the average depth of the defect traps was calculated at 200 cm^-1.     

ESR study of the hyperfine structure of the triplet state in crystalline donor acceptor complexes: A probe for the degree of charge transfer in the excited state

The hyperfine tensors of the triplet states of several guest donor molecules in naphthalene/tetracyanobenzene host crystals have been measured by EPR spectroscopy. From these data the degree of charge transfer (b²) in the excited state can be derived in a straightforward way. Whereas anthracene yields values almost identical with those characteristic for the isolated molecule (b² ≈ 0.05), phenanthrene shown a significant degree of charge transfer in the triplet state (b² ≈ 0.47).     

Deuteration effects on the phosphorescence of aromatic hydrocarbons

Observations of the phosphorescence decay of isotopic mixtures of naphthalene-h_s and -d_s, phenanthrene-h₁₀ and -d₁₀, and chrysene-h₁₂ and -d₁₂, in ethanol solutions at 77 K are analysed to determine the ratio k_PT^H/k_PT^D of the triplet radiative rate parameters of the perprotonated and perdeuterated compounds. The ratio is 1.20 (±0.07) for naphthalene, 1.39 (±0.06) for phenanthrene, and 0.98 (±0.04) for chrysene.     

Charge density flow as a driving force of distortion in excited protonated azaaromatics

The INDO method was used to calculate electronic charge densities in the ground and lowest excited singlet and triplet states of neutral and protonated 2,3- and 1,4-diaza derivatives of naphthalene and phenanthrene, and benzo (a) phenazine. Experiniental changes of pK_a upon excitation can be correlated with the values of electron density flow into the heterocy- clic ring. Electron-density increase turns out to be a major factor which causes distortion in some excited protonated species.     

Delayed Fluorescent Emission from Pyrene Doped Phenanthrene Nanoparticles Based on Triplet-triplet Energy Transfer

Doped nanoparticles were prepared from pyrene and phenanthrene using a facile reprecipitation method. The doped nanoparticles presented unique delayed fluorescent emissions of pyrene under the unprotected condition. The ratio of the intensity of delayed fluorescence (I_DF) to that of phosphorescence (I_P) is about 4:1, which almost keeps unchanged with the decrease of pyrene content at room temperature. The intensity of the delayed fluorescence emissions is dependent on the relative content of pyrene, as well as the aggregation degree of nanoparticles. The delayed emissions are contributed to efficient triplet‐triplet energy transfer from phenanthrene (donor) to pyrene (acceptor). Steady fluorescence measurement have proved that the singlet‐singlet energy transfer process was also existent dominated by the radiation energy transfer mechanism.     

Static luminescence quenching by oxygen and nitric oxide for phenanthrene in glassy matrices

Steady-state and pulsed methods have been applied to static phosphorescence and fluorescence quenching for phenanthrene caused by oxygen and nitric oxide. The characteristic fluorescence quenching distances have been determined for oxygen (8.7±0.5 Å) and nitric oxide (8.9±0,5 Å); the phosphorescence quenching involves an exchange mechanism, and measurements have been made on the characteristic quenching distances R₀ and exchange-interaction attenuation parameters L. Estimates have been made on the rate constants for dynamic quenching of the triplet excited states of phenanthrene in low-viscosity liquids, which agree well with the measured values for hexane.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 667–672, November–December, 1988.     

Synthesis and characterization of phenanthrylphosphine gold complex: observation of Au-induced blue-green phosphorescence at room temperature

A new 9-diphenylphosphinophenanthrene ligand (9DPP, 1), its oxide (9DPPO, 2), and its gold complex [(AuCl(9DPP)] (3) were synthesized. The Au(I) complex 3 was found to exhibit intense blue-green, room-temperature phosphorescence (Phip = 0.06 and tauT = 22.7 micros) originating in the locally excited triplet of the phenanthrene moiety (3LE) in degassed 2-methyltetrahydrofuran solution. On the assumption that PhiST = 1.0 for 3, the radiative rate constant (kr) in the triplet state is calculated to be 2.6 x 10(3) s(-1). This value is 4 orders of magnitude larger than the radiative rate constant of the triplet phenanthrene (0.26 s(-1)). Thus, the coordinated Au(I) atom is concluded to have a markedly large heavy-atom effect on kr of the phenanthrene chromophore in 3.     

Heat capacities and volumes of interaction between mixtures of alcohols in water at 298.15 K

The heat capacities and densities of mixtures of aqueous solutions of normal alcohols (methanol to n-butanol) and t-butanol were measured at 298.15 K at low molalities. The results were used to calculate the thermodynamic pair and triplet interaction parameters between solutes for heat capacities and volumes. The pair parameters are approximately a linear function of the total number of carbon atoms of the two solutes. The enthalpic pair and triplet interaction parameters for (ROH + H₂O) are also reported. The temperature dependence of the pair parameters for Gibbs free energies, enthalpies, entropies, heat capacities, and volumes are discussed in terms of structural changes in the aqueous solutions.     

Properties of the low-lying electronic states of phenanthrene: Exact PPP results

We report properties of the exact low-lying states of phenanthrene, its anion and dianion within the Pariser-Parr-Pople (PPP ) model. The experimentally known singlet states of the neutral molecule are well reproduced by the model. The intensities for one and two photon absorption to various singlet states are also in good agreement with experiment. From the bond orders of these states, we predict the equilibrium geometries. The relaxation energies of these states, computed from charge-charge correlations and bond orders, are presented. We also present results of ring current calculations in the singlet ground state of phenanthrene. We have also reported energies, spin densities, bond orders, and relaxation energies of several triplet states and compared them with experiments as well as with other calculations, where available. The fine structure constants D and E, computed in the lowest triplet state, compare well with those obtained from experiments. These properties are also presented for the anions and the dianions. The PPP model in these cases predicts a low-energy (<1 eV) dipole excitation. © 1996 John Wiley & Sons, Inc.     

EXCITED-STATE REACTIONS OF OXIDIZED FLAVIN DERIVATIVES

Abstract— The reactivity of flavin mononucleotide and of lumiflavin triplets was studied by flash and laser photolysis. The rate constants of the triplets with oxygen, with flavin ground-state molecules, and with Br^- ions were determined. Although in solution at room temperature, the protonated flavin triplet, ³F1H⁺, is not formed directly from its very short lived singlet state, a transient, which we think is this triplet, results from protonation of the neutral triplet. This conclusion is based on a comparison between the neutral and the protonated triplet spectra in a low-temperature glass. It is proposed that the protonated triplet can also be formed by sensitization via the phenanthrene triplet.     

ESR study of the photoexcited triplet state of substituted 2-acetonaphthones

Electron spin resonance of phosphorescent triplet states of a number of 6-substituted-2-acetonaphthones is studied at 77 K in toluene glass. The life-times of the triplet states and zero-field parameter D* have been measured from Δm_s = ± 2 resonance. The life-times and the zero-field splitting parameters indicate that the lowest triplet states have mainly π, π* character.     

Triplet triplet absorption of biphenyl and related compounds

Triplet triplet absorption spectra of biphenyl, carbazole and phenanthrene have been studied in rigid glass at 77 K. Oscillator strengths and polarizations are reported. A theoretical study has been performed using the Pariser-Parr-Pople approximation in order to support the band assignments.Phenanthrene is shown to be definitely not related to the other members of the series. Triplet-triplet oscillator strengths are decreased in carbazole, as compared to biphenyl. This effect is discussed in terms of a possible dilution of the ground triplet, in addition to the spectral dilution of the upper triplet states, as previously observed in derivatives of alternant molecules.     

Zero field splittings in the lowest excited triplet states of aza- and diazaphenanthrenes and their protonated species

ESR spectra of the lowest excited ππP^* triplet states of a series of azaphenanthrenes (AP) and diazaphenanthrenes (DAP) are measured in rigid glasses. The zfs parameters are evaluated for 4-AP, 1,7-DAP, 4,7-DAP, 1,10-DAP and for their mono- and diprotonated species, BH⁺ and BH²⁺₂. The zfs parametesr of the bases are a litte higher than those of phenanthrene. On single protonation they fall below the latter values. Second protonation causes again an increase in zfs, with the exception of the 1,10-DAP divalent cation which behaves peculiarly. Spin-orbi contributions to the zfs seem not to be responsible for the observed differences.     

Time-resolved ESR study of the lowest excited triplet states of para-quinones in glassy matrices at 77 k

The lowest excited nπ* triplet of 9.10-anthraquinone, 1.4-naphthoquinone and 1,4-benzoquinone were studied in glassy matrices at 77 K using a time-resolved ESR method. The D value of the triplet state of 9,10-anthraquinone varied from ?0.351 cm^?1 in a polar solvent to ?0.318 cm^?1 in a non-polar solvent. Both 1,4-naphthoquinone and 1,4-benzoquinone in polar solvents showed triplet state spectra with a D value of ?0.330 cm^?1. A computer simulation revealed the existence of widely distributed zero-field splitting parameters in the glassy condition. These data are compared with an analysis of CIDEP results of para-quinones.     

The triplet state of picene in p-terphenyl crystals by EPR

Spin-hamiltonian parameters of the triplet state of picene in p-terphenyl crystals are determined. Optical spin polarization and transient nutations are also observed using pulsed light sources.     

Influence of a magnetic field on delayed fluorescence of aromatic hydrocarbons in solution: I. Dependence on temperature,solvent and solute

The relative magnetic field effects on the total triplet—triplet annihilation (TTA) rate constant, on the rate constant for production of a singlet monomer and on the rate constant for production of a singlet excimer have been measured in a magnetic field range from 0 to 6000 gauss for the hydrocarbons pyrene, 3,4-benzopyrene, 1,2-benzanthracene and phenanthrene in solvents of different polarity between room temperature and 120 K. A qualitative discussion of the experimental results yields the following information on the mechanism of TTA: (i) The ratio of singlet to triplet products decreases with decreasing temperature or increasing viscosity of the solvent. (ii) The magnetic field effect depends much more on viscosity than on temperature. (iii) Singlet monomers and excimers are predominantly formed from different initial triplet—triplet pair configurations. (iv) Ionic radical pair states do not seem to play an important role in the TTA mechanism between equal molecules.     

Dynamic nuclear polarization of proton spins via photoexcited triplet states: the system phenanthrene in fluorene

The proton spins in a single crystal of fluorene have been polarized by dynamic nuclear polarization via the photoexcited triplet state of phenanthrene guest molecules. It is possible to reach an enhancement of the proton polarization of 90 at 1.2 K where the thermal equilibrium polarization is 0.033%.