Magnetooptical Spectroscopy of Zinc Octaethylporphyrin in an Argon Matrix

Abstract

Magnetic circular dichroism, magnetic circularly polarized luminescence, emission, and absorption spectra have been measured over the range 12 500-50 000 cm-' for zinc octaethylporphyrin isolated in an argon matrix at -6 K. The spectra arise from transitions at a single matrix site. Values of gll for the Q, B, and N states are 7.0 f 0.7, 1.0 f 0.3, and 1.2 f 0.9, respectively. The degeneracy of the Q state (IE, in D4h symmetry) is lowered by Jahn-Teller and crystal-field effects, with the splitting of the Q(0,O) band being -30 cm-'. Analysis of the spectra in the Q-band region yields Jahn-Teller parameters YJT = 140 f 4 cm-I, AJT = 1.27 f 0.5, and EJT = 26 f 3 cm-' and suggests that the crystal-field distortion is of the same symmetry as the Jahn-Teller effect and of magnitude 30 f 4 cm-I. Qualitative indications are that Jahn-Teller effects in the B and P (lowest triplet) states are weaker than that in the Q state.

Weak Temperature Dependence in the Magnetic Circular Dichroism of Matrix-Isolated Copper Phthalocyanine

“…The substantial literature that has since accumulated on the MCD of porphyrins and Pcs has been the subject of several reviews. − Most of these studies involve the determination of electronic symmetries and angular momenta, and correlations of these properties against central metal ion or substituents. However, when used in conjunction with the method of moments and/or analysis of the spectral dispersion, the technique is capable of much more, for example, the elucidation of vibronic and crystal-field effects. − For paramagnetic systems, information can also be obtained by following the magnetic-field and temperature dependencies of the MCD. The former has been used in investigations of hemoproteins, but there are surprisingly few examples where the temperature dependence has been utilized.…”

MCD and MCPL Characterization of Luminescent Si(IV) and P(V) Tritolylcorroles: The Role of Coordination Number

“…Magnetic optical activity can be observed also in emission. , Such a phenomenon is called magnetic circularly polarized luminescence (MCPL) and measures the difference between right and left circularly polarized emission due to the external magnetic field. Even if the number of recorded MCPL spectra is still limited, data produced by this technique have been spreading lately. − …”

“…Furthermore, MCD spectroscopy, being particularly sensitive to metal coordination, , is found to be the ideal method to follow the axial interaction of metal complexes with various ligands, thus complementing the information obtained with other optical spectroscopies. Finally, corroles, showing an intense MCD signal in the Q region and being efficiently excited in correspondence with the Soret band, are good candidates to provide easily detectable magnetic circularly polarized luminescence (MCPL) signals. − …”

An analytical data inversion method for magnetic circular dichroism spectra dominated by the “B-term”

“…13,14 In a symmetric molecule (e.g., zinc porphyrin) having equivalent x and y axes, doubly degenerate electronic transitions will appear that have an ''A''-type MCD spectrum. 15,16 However, chemical substitution usually breaks this degeneracy so that two independent bands emerge, and in porphyrins and chlorophylls these component bands are named Q x and Q y . Typically the induced energy separation DE is larger than the widths of the inhomogeneously broadened electronic origins, changing the MCD spectra to ''B'' type spectra that may be represented simply as weighted sums of individual spectral components for each state.…”