Isomérisation photosensibilisée par des colorants et photoréduction de l'azobenzène en solution. II

Abstract

The photochemical isomerization of azobenzene in solution can be sensitized by dyes which have low-lying triplet states (rose Bengal, eosin Y, fluorescein, methylene blue) but cannot be inhibited by such compounds. The two triplet levels, Tβc and Tαc of the cis form are indistinguishable experimentally. On the other hand, the experimental results verify the existence of two triplet levels, Tβt and Tαt, with different properties, in the trans form. Population, by energy transfer, of the lower triplet, Tαt, leads to isomerization with a quantum yield near 0.5, whereas population of the triplet Tβt only rarely leads to isomerization (quantum yield about 0.03).The photoreduction of azobenzene in isopropanol also has been studied. Only the cis form is photoreducible and it is very difficult experimentally to determine whether this photoreduction can be sensitized.A Jablonski diagram of the two forms of azobenzene is presented to correlate these observations. [Journal translation]