Photoactive hyperbranched poly(azo‐ester) urethanes as fluorescent staining agent for plant cells

A new AB2‐type blocked isocyanate monomer containing azo‐ester linkages and N,N′‐diethanol amine groups was successfully synthesized. Deblocking of this monomer in DMF resulted corresponding hyperbranched poly(azo‐ester)urethanes (HBPAEUs). These polymers were characterized by UV–visible spectroscopy, GPC, TGA, and DSC methods. The molecular weights (Mw) of the polymers were in the range of 5500–25,500 g/mol. The effect of reaction temperature on Mw was found significant. The polymers were found thermally stable up to 240 °C and showed Tg between 150 and 153 °C. These polymers absorbed UV light at 407 nm in THF solvent and also exhibited high absorption coefficients. The photo induced trans to cis isomerization of HBPAEU in THF was also studied and found λmax of cis form of the polymer was shifted to 526 nm, which suggested that the stability of this isomer was good. And, the polymer showed aggregation induced enhanced emission. In addition, the monomer and HBPAEU were found to exhibit maximal antibacterial activity against various Gram‐positive and Gram‐negative bacteria. In‐vitro bio‐imaging studies of this monomer and polymer were carried out in onion epidermal and fungal cells and the results revealed that the polymer was more efficient for staining and imaging plant cells.