Spectroscopic and thermal isomerization characteristics of 3,3′-dialkoxy and dialkanoyloxy azobenzenes

The UV/visible spectra and activation parameters of thermal Z-to-E isomerization of several symmetrical 3,3'-dialkoxy and dialkanoyloxy azobenzenes were discussed in comparison to those of the corresponding 4,4'-disubstituted, unsubstituted and other substituted azobenzenes. It is shown that lambda (max) and molar extinction coefficient (epsilon) of the pi-pi (*) bands of these 3,3'-disubstituted azobenzenes are similar to that of an azobenzene. Thermal isomerization rates of these azobenzenes were found to be relatively slower than those of 4,4'-disubstituted azobenzenes. The isokinetic plots in solutions suggested the inversion mechanism for these azobenzenes. It is also assumed from thermal isomerization in the glassy state that the Z-isomers of these azobenzenes were less strained, probably due to the conformation that consumes less space during isomerization.