The photoisomerization of azobenzene at 77°K in a rigid solvent and at room temperature

The photoisomerization of azobenzene has been studied at room temperature in ethanol and P. Me.H., and at 77°K in a P.Me.H. rigid solvent. At room temperature, the photostationary state composition is 74% trans (and 26 % cis) in ethanol and 77 % trans in P.Me.H.; it is 98 % trans in P.Me.H. at 77°K. It has been shown that both the trans to cis and the cis to trans photoisomerizations occur in the rigid solvent at liquid nitrogen temperature. The spectra and molar extinction coefficients have been determined at room temperature for trans azobenzene in ethanol and P.Me.H. Other spectra were taken of azobenzene: at the photostationary state, at room temperature in ethanol and P.Me.H., and at 77°K in P.Me.H.; at 77°K of 100 % and 77 % trans in P.Me.H. It has been shown that the photoisomerization occurs more readily by irradiation in the visible, than in the ultraviolet region. A new low temperature cell has been designed and used