Detailed procedures of synthesis and characterization of compounds 2a - 2c, Fig. S1 - S6 (DSC curves no shown in text), Fig. S7 - S34 (NMR), Fig. S35 - S45 (HRMS). from New azobenzene liquid crystal with dihydropyrazole heterocycle and photoisomerization studies

New azobenzene derivatives with dihydropyrazole heterocycle have been prepared and characterized. According to thermal polarizing microscopy and differential scanning calorimetry studies, the compounds consisting four linearly linked rings and a long alkoxy chain on the azobenzene side (3a-8 and 3a-14) displayed no liquid crystal properties. When the length of mesogenic unit increased to five rings, except for compound 5a-8, all compounds from 5a-10 to 5a-16 containing a long chain of ten 10–16 carbon atoms on the side of ester group displayed liquid crystalline properties, and the mesogenic domain gradually narrowed with increase of the chain length. However, in the case of the molecular with long alkoxy chains on both sides, only 5c-16 with a long chain of sixteen carbon atoms exhibited liquid crystal behaviour. In addition, these azo compounds underwent isomerization from E to Z under ultraviolet irradiation and then thermal back relaxation slowly in the dark, which can be recycled many times.