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

• 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
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100383a021

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.