Ultrasound responsive organogels based on cholesterol-appended quinacridone derivatives with mechanochromic behaviors

A series of cholesterol-appended quinacridone (QA) derivatives 1a-1d have been synthesized, in which 1b and 1c could form stable organogels in a wide range of organic solvents upon ultrasound irradiation. Field emission scanning electronic microscope (FESEM) and transmission electron microscopy (TEM) of xerogels or precipitates indicated that 1b and 1c formed 1D fibrous nanostructure, while 1a assembled into 3D flower-like microstructures. The ultrasound-induced organogel process was characterized by kinetic UV-vis and photoluminescence spectroscopic methods suggesting the formation of pi-pi aggregates in the gel state. Experimental results demonstrated that the ultrasound could promote molecules to contact frequently in the solution and induce semistable initial aggregates, which propagate to form nano/micro superstructures. The aggregation model was optimized by semiempirical AM1 calculation suggesting the hierarchical self-assembly process. In addition, the formed xerogel film exhibited mechanochromic property, and the phase transition process was accompanied by the fluorescence changes between yellowish green and orange.