Photoinduced reaction of methylpolyynes H(C≡C)nCH3 (n = 5-7) and polyyne H(C≡C)5H with I2 molecules
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Methylpolyynes, H(C≡C) n CH3 (n = 5-7), were photo-irradiated under the presence of iodine molecules in hexane to confirm the formation of a series of molecular complexes, H(C≡C) n CH3(I6) (n = 5-7), by systematic changes in their UV absorption spectra. In order to investigate the reaction mechanism, solutions of hydrogen-capped polyyne, H(C≡C)5H, and I2 molecules in hexane were irradiated with a cw-laser beam at 532 nm, then their UV absorption spectra were recorded to obtain temporal decay profiles for the polyyne C10H2. At C10H2 concentrations of about 7 μmol L-1, the rate of reaction in the decay profile for C10H2 increased with increasing I2 concentration (8.2–126 μmol L-1) as well as with increasing laser power (0.34–6.2 mW). Based on a kinetic model, the degradation of C10H2 was shown to compete with the formation of the polyyne-iodine molecular complex, H(C≡C)5H(I6). The formation of the complex was found to be efficient under the condition that the I2 concentration is orders of magnitude higher than the C10H2 concentration as this suppresses the degradation process.
KeywordsLaser Power Molecular Complex Molar Equivalent Nanosecond Laser Pulse Iodine Molecule