H. Rau et D. Rottger, PHOTOCHROMIC AZOBENZENES WHICH ARE STABLE IN THE TRANS AND CIS FORMS, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 246, 1994, pp. 143-146
Azobenzenophanes with three-carbon bridges can be photoisomerized in b
oth trans to cis and cis to trans directions. Contrary to other aromat
ic azo compounds the cis,cis form is stable at room temperature with a
half life of about a year.