Distorted forms of metalloporphyrins probed by Raman and high resolution luminescent spectroscopy

Aleksandr S. Starukhin 1,2Mikalai M. Kruk 1Jacek Waluk 2

1. B.I. Stepanov Institute of Physiscs National Academy of Sci. of Belarus (IF), Independence Av., 68, Minsk 220072, Belarus
2. Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 52/56, Warszawa 01-224, Poland

Abstract

In our report the spectral manifestation of different spectral forms obtained for Mg-, Zn-, Pd- and Pt-porphins in different solid matrices at cryogenic temperatures have been discussed. The planar and two kinds of distorted conformations of Mg-, Zn-porphins in highly-resolved fluorescence spectra were detected. Distorted forms of “saddle” and “dome” types have been detected in the luminescence and absorption spectra. For Zn-porphin distorted forms have been detected in the fluorescence and phosphorescence spectra simultaneously. In the phosphorescence spectra of the Pd- and Pt-porphins the manifestation of the two forms in the ground state has been proved also. Energy splitting in the phosphorescence spectrum of the Pd-porphin in n-octane at 4,2 K comes to 78 cm-1 for two forms. Under selective excitation in singlet-singlet channel the large set of sharp lines was detected for each of two forms and vibrational frequencies have been determined. In highly-resolved phosphorescence spectra of Pt-porphin in n-octane at 4,2 K we have detected similar manifestation of the two spectral forms in the phosphorescence spectrum. The set of temperature activated bands in phosphorescence spectra were found. Analysis of phosphorescence spectra at elevated temperatures and excitation of phosphorescence spectra under direct excitation in the singlet-triplet channel make possible the value of zero-field splitting of quasi-degenerate triplet states for two forms to be determined. The splitting values in n-octane matrix amount to 40 and 57 сm-1 for planar and nonplanar conformations of PdP, respectively. To estimate the type of molecule distortion the information about the frequencies of vibronic modes from well-resolved spectra of metalloporphins have been used. For distorted forms of metalloporphyrins the greatest shifts are observed for the lines in the range 1500-1650 cm-1 that well correlate with data of resonance Raman spectra of metalloporphyrins with Ni, Pd, Fe, Zn etc..

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium A, by Aleksandr S. Starukhin
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 17:42
Revised:   2008-06-13 16:32
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