Electronic spectra of cationic forms of meso-tetrapropylporphin in a nanoporous silicate gel matrix |
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Authors: | S M Arabei D V Novik T A Pavich K N Solov’ev |
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Institution: | (1) Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 prosp. Nezavisimosti, Minsk, 220072 |
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Abstract: | We have studied the fluorescence and fluorescence excitation spectra at 300 K, 77 K, and 4.2 K for silicate gel matrices colored
with meso-tetrapropylporphin by impregnation of the matrix with a solution of the pigment. Comparison of the data obtained
with the absorption spectra in acidified solutions and analysis of the low-temperature fine-structure vibronic spectra, and
also taking into account data obtained earlier for octaethylporphin in a xerogel showed formation of two cationic forms of
meso-tetrapropylporphin in the gel matrix: the short-wavelength form has a dicationic structure, while the long-wavelength form
has a monocationic structure. We have traced out the correlations of the vibrational structure in the spectra of the dicationic
form with data for the porphin dication, and we have drawn a number of conclusions concerning the normal vibrational modes
that are active in the vibronic fluorescence and absorption spectra of the studied cationic forms. Using the AM1 semiempirical
quantum chemical method, we optimized the geometry of the mesotetrapropylporphin dication: the most stable of the possible
conformers is the dication structure with saddleshaped macrocycle nonplanarity.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 453–461, July–August, 2006. |
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Keywords: | silicate gel matrix meso-tetrapropylporphin dication monocation fine-structure fluorescence spectrum normal vibrations nonplanar distortions |
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