A review of the photochromic behavior of metal complexes embedded in conjugated (–N=N–C=N–) and non-conjugated azo-imine-based ligands

Abstract

Photochromic compounds are well known and attract tremendous necessity for their versatile applications in various fields of science. When exposed to light, metal complexes containing potentially photoswitchable azo (–N=N–) and imine (–C=N–) based ligands can be switched between trans (E) and cis (Z) two isomers, as well as energy manipulation and energy level modulation. Then the cis (Z) isomers underwent slow thermal isomerization back to the more stable trans (Z) isomers. The quantum efficiency of metal complexes has been tuned by modifying the ligands’ structures and altering metal substrates. Herein our review encompasses the photochromic behavior of a few conjugated azo-imine (–N=N–C=N–), ligands such as arylazoimidazoles, phenylazopyridine, azobispyridine, arylazopyrozoles, as well as a few non-conjugated azo-imine or Schiff base ligands with their metal complexes.