Phenylene ethynylene azobenzenes with symmetrical peripheral chromophores: Synthesis, optical properties and photoisomerization behaviors study

A series of phenylene ethynylene azobenzenes bearing different symmetrical peripheral chromophores were synthesized by Sonogashira coupling and characterized by UV-vis absorption, fluorescence emission, cyclic voltammetry and cis-trans photoisomerization. All compounds exhibit strong ¹π,π (*) absorption bands in the UV region, which pronouncedly blue-shifts when the π-electron donating chromophore attached on the para-position of phenyl group. When excited at the ¹π,π (*) band, the compounds exhibit violet to blue emission (363 ∼ 430 nm), which is attributed to a ¹π,π (*) emission. All of these compounds show reversible trans-cis isomerization in dichloromethane solution, indicating that the π-conjugated phenylene ethynylene backbone does not prevent the occurrence of the photochemical processes of the azobenzene center. The photoisomerization properties were influenced by the peripheral chromophores in the conjugated system and the steric interactions. In addition, the kinetic investigation of the photoisomerization process was carried out.