SYMMETRIES OF SINGLET AND TRIPLET MANIFOLDS IN PLATINUM PHTHALOCYANINE BY USE OF SHPOL'SKII MATRIX SPECTROSCOPY
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Date
1978
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Ohio State University
Abstract
We report here the first detailed analysis of the Shpol’ skii structures in the phosphorescence, phosphorescence excitation, and abosorption spectra of a metal phthalocyanine (pc) molecule, PtPc, in mixtures of $\alpha$-chloronaphthalene and n-octane. Previous work on this $molecule^{1}$ indicated that the symmetry is not the expected one for metal Pc’s, i.e. $D_{4h}$. The spectra reported here show that PtPc molecules occupy preferentially three distinct sites in a rapidly frozen matrix of Che mixed solvent. The predominant site was selected and found to have (0-0) phosphorescences at 9411 {\AA} (weak/9475 {\AA} (strong), 9740 {\AA}. (extremely weak), 9767 {\AA} (very weak), 10192 {\AA}. (very weak), and 10247 {\AA} (extremely weak) at $55^{\circ} $K, The first two transitions are attributed, following Van der Waals et al.,$^{2}$ to the removal of the degeneracy of the lowest $E_{u}$ triplet of a $D_{4h}$ symmetry. Interstate vibronic coupling exists between these two split triplets which are separated by a low activation barrier, $9 \pm 3 cm^{-1}$ Such coupling also exists, to a less extent between the split singlets. The other (0-0) phosphorescences are accounted for and are further differentiated from the split triplets by their temperature dependence. The vibronic bands in the excitation and absorption spectra correspond to those in the phosphorescence spectra. The energies of the vibronic bands in the phosphorescence progressions agree with the resonance Raman vibrations observed at $77^{\circ} k$ The equilibrium position of the ground state potential surface is only slightly shifted from that of the first excited state. The lower portions of the ground state potential surface and those of the first excited states are for all practical purposes identical in shape. The PtPc symmtry in the ground and in the first excited singlets is indistinguishable between $D_{2h}.C_{2v}$, or $D_{2}{^{1}}$ in agreement with the conclusions of earlier work. $^{1,3}$ The symmetry of the triplets is as low as that of the first excited singlets.
Description
$^{1}$ ``Resonance Raman in Platinum Phthalocyanine'', Tzer-hsiang Huang, Klaus E. Riecfchoff, and Eva-Maria Voigt, accepted by Can. J. Chem. $^{2}$ G. W. Canterst G. Janson, M. Noort, and J. H, Van der Waals, J. Phys. Chem. 80, 2253 (1976). $^{3}$ Tzer-hsiang Huang, Klaus E. Rieckhoff, Eva-Maria Voigt, and E. Roland Menzel, Chem, Phys. 19, 25 (1977).""
Author Institution: Departments of Physics and Chemistry
Author Institution: Departments of Physics and Chemistry