Abstract
Photocyclization of diphenylamine (DPA) in cyclohexane is accelerated by the addition of hydrogen-bonding agents (Q). Laser photolysis studies reveal that Q principally affects the S 1 state of DPA. DPA in its S 1 state forms a stable hydrogen-bonding complex with Q in which DPA acts as a proton donor. The estimated value of the intersystem crossing (ISC) rate constant ( k ∞ ISC) of excited hydrogen-bonded DPA is higher than that of free DPA, whereas the non-radiative deactivation rate constant ( k ∞ d) of hydrogen-bonded DPA is somewhat lower than that of free DPA. The value of k ∞ ISC is markedly dependent on the nature of Q, especially on the electron-donating tendency of Q. The detailed mechanism for the enhancement of the photocyclization of DPA by Q is discussed on the basis of the increase in the electron-donating ability of the NH group of DPA caused by the formation of the hydrogen-bonding complex.
Published Version
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