Azobenzene Based Smart Materials-Synthesis and Studies

Abstract

Azobenzene-based materials exhibit a unique and smart behavior due to the reversible photo-isomerization of azo-chromophores and hence have attracted considerable attention for various potential applications. Keeping in mind this exciting property, four series of poly(azobenzene) esters containing organometallic, aromatic, alkyl, and silyl units have been successfully synthesized using solution poly-condensation reactions. Structural information of poly(azobenzene) esters was extracted using physical studies, elemental analysis, FTIR and 1H NMR spectroscopic techniques, which confirmed the presence of all the expected functional groups in the core polymer chain. The entire poly(azobenzene) esters series showed good solubility in common organic solvents hence possessed increased processability. Thermal behavior was monitored using TGA and DSC techniques. The entire poly(azobenzene) esters series exhibited good thermal stability and moderate to high Tg depending on the polymer backbone. Poly(azobenzene) esters having a ferrocene and azobenzene based backbone showed good fire retarding behavior. Surface morphology was monitored using SEM whereas XRD revealed semi crystalline to amorphous nature. Owing to the exciting light responsive behavior of azobenzene unit, poly(azobenzene) esters were subjected to various light responsive techniques including tunable wettability, holography and birefringence. All synthesized materials showed striking results including a change in wettability of polymer films with the change in wavelength of incident light, successful inscription of surface relief gratings (SRG) using holography and liquid crystalline birefringent phases under polarized optical microscope (POM). Besides, conductivity behavior was also monitored to see the effect of azobenzene units on the conductivity of polymer chains. Highest conductivity up to 10-6 Scm-1 was observed for the poly(azobenzene) ester having an azobenzene backbone proving that azobenzene unit facilitates the conduction in polymer chains. The rest of the polymers showed conductivity between 10-6-10-10 S/cm classifying the poly(azobenzene) esters in conducting polymers range. At the end, biological activity of poly(azobenzene) esters was monitored against cell lines and bacteria. Cell cyto-compatibility was achieved up to 100% against L-929 Fibroblast. Anticancer activity was monitored against Hep-G2 which was observed up to higher than 90% activity difference. Antibacterial activity against E.coli bacterial strain was achieved up to 97%, showing potential applications of poly(azobenzene)-esters as antibacterial material.