Synthesis of photoisomeric azobenzene monomers and model compound effect on electric-optical properties in PDLC films

A series of azobenzene monomers and related model compounds with various side-chain lengths were synthesized. The electrooptical properties of a polymer-dispersed liquid crystal (PDLC) were verified by side-chain methoxy azobenzene in various chain lengths (n = 3, 6,11). The properties under various voltages were measured and the effect of extra voltage on the transmittance of PDLC was researched as well. The experiment demonstrated the validity of employing these side chain methoxy azobenzene materials in electrooptical devices. The azobenzene model compound showed better electric-optical and thermal-optical properties, having a higher contrast ratio (CR = 689) and a lower saturation voltage (4.7 V/μm). All the azobenzene molecules, can be photoisomerized through UV light irradiation, following the mechanism of isomerization. The reversible photo and heat isomerization property was stud ied. The cis-azobenzene that was transformed from the trans-azobenzene irradiated by UV light can decrease the clearing point of the liquid crystal phase. We used this unique characteristic to record image patterns and it worked successfully. We synthesized the azobenzene monomers can stabilize the PDLC and their relative model compounds with various alkyl chain lengths even got better electric-optical effects. We found that azobenzene monomer shows different behaviors in the electric-optical property from its relative model compound. The difference between the systems were explained using a proposed model.