Vibrational photochemistry of porphine imbedded in a n-hexane-d sub 14 Shpol'skii matrix

The near-infrared-induced tautomerization of free-base porphine incorporated in a n-hexane-d{sub 14} matrix is reported. Porphine occupies two sites in a n-hexane-d{sub 14} matrix as opposed to one site in a n-hexane matrix. Two spectroscopically distinct tautomers, differing by a 90{degree} rotatio...

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Bibliographic Details
Published in:Journal of physical chemistry (1952) 1990-10, Vol.94:20
Main Authors: Butenhoff, T.J., Chuck, R.S., Limbach, H.H., Moore, C.B.
Format: Article
Language:English
Subjects:
400500 - Photochemistry
ALKANES
CHEMISTRY
DATA
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
HEXANE
HYDROCARBONS
INFORMATION
INFRARED RADIATION
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
MEASURING INSTRUMENTS
MEASURING METHODS
NEAR INFRARED RADIATION
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOSPHORUS COMPOUNDS
PHOTOCHEMISTRY
RADIATIONS
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Summary:The near-infrared-induced tautomerization of free-base porphine incorporated in a n-hexane-d{sub 14} matrix is reported. Porphine occupies two sites in a n-hexane-d{sub 14} matrix as opposed to one site in a n-hexane matrix. Two spectroscopically distinct tautomers, differing by a 90{degree} rotation of the NH bond axes within the molecular plane, exist for each site. Nernst glower irradiation on the NH stretch fundamental does not induce tautomerization, but irradiation in the regions 4,000 < {nu} < 5,100 cm{sup {minus}1} and 5,630 < {nu} < 7,700 cm{sup {minus}1} does induce tautomerization. Narrow-band (8 cm{sup {minus}1} fwhm) laser irradiation studies in the NH symmetric plus antisymmetric stretch combination band region (6,300 < {nu} < 6,600 cm{sup {minus}1}) show that the near-infrared-induced tautomerization occurs at select wavelengths. Tautomer conversion in absence of site conversion is strong evidence that the observed photochemistry is due to absorption of light by porphine and not by hexane. The estimated quantum yield is roughly 5 {times} 10{sup {minus}4} for 6,530-cm{sup {minus}1} irradiation; this is 1-3 orders of magnitude larger than the quantum yield expected from RRKM theory.
ISSN:0022-3654
1541-5740
DOI:10.1021/j100383a021