Novel azobenzene-phthalocyanine dyads—design of photo-modulated J-aggregation

Based on the J-aggregation mechanism of α-aryl/alkoxy-substituted zinc phthalocyanines(Pcs) in non-coordinating solvents, two novel azobenzene-phthalocyanine dyads (3-azo-ZnPc and 4-azo-ZnPc) were synthesized with the aim of developing Pc compounds whose ability to form J-aggregation could be photo-modulated. It was found that 3-azo-ZnPc in chloroform could be effectively photo-controlled in a wide range. This phenomenon could be explained by the changes in the geometry and dipole moment of azobenzene during the photo-isomerization process. 4-azo-ZnPc did not have this ability at all, with or without UV light illumination. The positions of the oxygen atoms to which the aryl/alkoxy substitution was attached relatively were found important in determining the aggregation ability.