Effects of hydrogen bonding on the photocyclization of diphenylamines

✍ Scribed by Kazuo Amano; Tadao Hinohara; Mikio Hoshino

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 841 KB
• Volume: 59
• Category: Article
• ISSN: 1010-6030
• DOI: 10.1016/1010-6030(91)87067-6

✦ Synopsis

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 S1 state of DPA. DPA in its S1 state forms a stable hydrogen-bonding complex with Q in which DPA acts as a proton donor. The estimated value of the intersystem crossing (EC) rate constant (I$-) of excited hydrogen-bonded DPA is higher than that of free DPA, whereas the non-radiative deactivation rate constant (k;) of hydrogen-bonded DPA is somewhat lower than that of free DPA. The value of k,",, 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 N-H group of DPA caused by the formation of the hydrogen-bonding complex.