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.

The figure shows the changes in the trans-fractions as a function of irradiation time for trans-to-cis photoisomerization in CH2Cl2 solution (10−5 mol/L) under 365 nm light irradiation. Inserts are the molecular structures of the phenylene ethynylene azobenzenes for photoisomerization investigation.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of a series of phenylene ethynylene azobenzenes bearing different symmetrical peripheral chromophores.
► Characterization by UV–vis absorption, emission, cyclic voltammetry and cis–trans photoisomerization.
► The determination of first-order rate constants for trans-to-cis and cis-to-trans photoisomerization.