Zeeman effect in the Q-band absorption spectrum of palladiumporphin in an n-octane single crystal

Electron spin resonance of the lowest triplet state of palladiumporphin in a n-octane crystal at 1·3 K

“…data to be described below. The angle which the direction of the field in this experiment made with the a-axis of the crystal (27~ 3 ~ ) proved to be equal to the angle which the (out-of-plane) molecular z-direction of a number of porphyrins has been found to make with the a-axis of the n-octane host [2,7,15]. It was therefore concluded that in this experiment the field was aligned along the molecular z-axis.…”

“…From optical experiments on the lower singlet states of ZnP and PdP, which also are degenerate, we know that the crystal field lifts the degeneracy of those states and introduces a splitting between the two orbital components of which the wavefunctions Ix) and ]y) transform like the unit vectors along two mutually perpendicular directions in the molecular plane [2,4,8]. (If it is assumed that the Jahn-Teller distortion of the molecule and the crystal field together do not lower the symmetry of the molecule in the host to less than D~h , these axes must either pass through the nitrogen atoms or the methine groups.)…”

“…The fact that metalloporphins (MeP's), when incorporated in very low concentrations in single crystals of the n-alkanes, give sharp optical spectra at low temperatures has been found to be very ~useful for the study of the electronic properties of the porphin molecule and the influence of the metal on them [1][2][3][4]. The lower excited states of the MeP's arc orbitally degenerate (they bear the symmetry label E u of the point group Dab of the isolated molecule [5]) and magneto-optical experiments have demonstrated the existence of a large orbital angular momentum in some of these states [6][7][8][9].…”

Observation of the distorted form of Pd-porphin in single site spectra at low temperatures

“…(see for example, Refs. [7][8][9]). The spectroscopic investigations of porphyrins at low temperatures may be very effective for studies of distortions of their planar structure under influence of matrices, different kinds of substitution in porphyrin macrocycle, interaction of metal ions with extra-ligands, etc.…”

Analytical application of laser excited Shpol'skii spectroscopy: direct identification and quantitation of polynuclear aromatic compounds

“…Also, as the temperature is decreased, electronphonon coupling is reduced and enhancements of the zero-phonon bands are achieved. In some cases, it is sufficient to decrease the temperature to 77 K, e.g., for n-alkane solutions of a large number of aromatic hydrocarbons (130,131) while in other cases, it is necessary to cool the solution tested to 20 K or 4 K (e.g., porphyrins (132), chlorophyll (133), diphenyl polyene (134), and benzophenone solutes (135)). …”