Paramagnetic Resonance Absorption in Naphthalene in Its Phosphorescent State

Abstract

Paramagnetic resonance absorption has been observed in naphthalene in solid solution in a single crystal of durene when irradiated with light from an A-H6 mercury lamp. The fine structure of the spectrum at a frequency of ∼22.7×109 cps may be described by the spin-Hamiltonian H=|β|H·g·S+DSz2+E(Sx2−Sy2),,with S=1,g=2.0030±0.0004 (isotropic),D/hc=±0.1003±0.0006 cm−1,E/hc=∓0.0137±0.0002 cm−1.Observations at a different frequency, ∼9.7×109 cps, and also measurements on perdeuteronaphthalene are described by essentially the same parameters. The fine structure data identify the spectrum as arising from a triplet state and leave no doubt as to the triplet character of the phosphorescent state of naphthalene. The zero-field splitting of the triplet has its origin in the magnetic dipole-dipole interaction between the two unpaired electrons in the triplet state. These experimental results are in agreement with the theoretical estimates. Hyperfine structure has been observed and is interpretable on the basis of the anisotropic hyperfine interaction constants for a C–H fragment given by McConnell. The π-electron spin density on the α-carbons is found to be 0.209. The hyperfine structure results identify the spectrum as arising from naphthalene. In addition they show that the triplet state is 3B2u+ and that the naphthalene molecules are oriented in the crystals such that they are not only coplanar with the durene molecule which they replace but also have their long and short twofold axes in this plane parallel, respectively, to the long and short axes of durenes.

Electron Paramagnetic Resonance Studies of the Triplet State of Flavin and Pteridine Derivatives*

“…Apart from spin correlation factors for the triplet state, this statement holds for most alternant molecules due to the pairing of bonding and antibonding molecular orbitals. The normalized spindensities in the lowest triplet state of naphthaleneare practically the same as those observed in the negative ion (Hutchison and Mangum, 1961 ;Carrington et af., 1959). The epr measurements of Vincent and Maki showed that the fine structure of the triplet state of quinoxaline is practically identical with that of the naphthalene triplet state (Vincent and Maki, 1963).…”

Antisymmetric Magnetic Interactions in Oxo-Bridged Copper(II) Bimetallic Systems

“…1 and 2 are the atomic spin-orbit parameters of Cu 2+ and Cu 3+ , respectively. 3 to the wave function has such a small weight that the importance of this mechanism is negligible. At ϑ 1 ) 90°, only the 3d xy and 3d z 2 orbitals have nonzero copper contributions to the magnetic orbitals.…”

Zero‐field splitting in phosphorescent triplet states of aromatic hydrocarbons IV. Phenyl naphthalenes

“…I n the case of the 2-phenyl naphthalene, the results of the calculations were not unequivocal inasmuch as the calculated D* value was rather insensitive to the choice of @; in fact, all three sets of values for ,!I yielded results in good agreement with experiment for this molecule. This insensitivity in the calculation of D* for 2-phenyl naphthalene is probably due to the near-zero spin density at the 2 position of naphthalene in the triplet state [12]. AET is simply the difference between the observed and calculated values.…”