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Effect of Medium on Transients and on Observed Quantum Yields in Photoreduction of Benzophenone by 2‐Propanol
Author(s) -
Cohen S.G.,
Cohen J.I.
Publication year - 1968
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.196800093
Subject(s) - quantum yield , benzophenone , chemistry , propanol , benzene , photochemistry , hydrocarbon , yield (engineering) , quenching (fluorescence) , alcohol , naphthalene , acetonitrile , ethanol , fluorescence , organic chemistry , thermodynamics , physics , optics
The quantum yield for photoreduction of 0.1 M benzophenone by 2‐propanol, at 313 mμ, light intensity 1 × 10 16 quanta/sec cm 2 is −1.16. The quantum yield increases on dilution with benzene to 1.70 at 3.13 M 2‐propanol. A Stern‐Volmer plot of data below 3 M 2‐propanol leads to an extrapolated limiting quantum yield of ˜1.9. The quantum yield in 2‐propanol decreases with extent of conversion from 1.1 at 17% to 0.74 at 37% photoreduction. Quantum yields for photoreduction of 0.1 M benzophenone by 1 M 2‐propanol and by 1 M benzhydrol in benzene remain constant with conversion. A light absorbing transient builds up strongly and progressively during photoreduction in 2‐propanol, and to a much lesser extent in 1 M 2‐propanol and 1 M benzhydrol in benzene. Photoreduction in 1 M 2‐propanol in t‐butyl alcohol appears to behave like that in 2‐propanol; 1 M 2‐propanol in acetonitrile shows behavior intermediate between that in alcoholic and in hydrocarbon solutions. Efficiency of quenching by naphthalene in alcoholic and in hydrocarbon media indicates that k r is about twice as great in the hydrocarbon as in the alcohol solvents. The effect of the hydrocarbon in diminishing build up of the light absorbing intermediate, which may mask and possibly quench, is largely responsible for the increase in quantum yield on dilution with hydrocarbon.