Luminescent Dendrimers Composed of Quinacridone Core and Carbazole Dendrons: Structure, Electrochemical, and Photophysical Properties

A series of pi-conjugated dendrimers Cn-QA and Tn-QA (n = 1-3) composed of quinacridone core and carbazole dendrons have been designed and synthesized. These dumbbell-like dendrimers with carbazole dendrons from first to third generation were achieved by convergent synthetic strategy. Their H-1 NMR spectra, electrochemical, photophysical properties, and film formation behaviors as well as aggregation structures in solid states have been fully investigated. The relationships between the structures and properties of dendrimers have been established. The electron-withdrawing substituent effects and the limited conjugations of the carbazole dendrons have been studied. Compared with the parent molecule N,N'-di(n-butyl)quinacridone (DBQA), the HOMO levels of the dendrimers increased and the LUMO levels decreased due to the carbazole dendrons substitution. The absorptions and emissions of dendrimers displayed red-shift feature compared with that of DBQA, while the higher generation dendrimer displayed slightly blue-shift tendency compared with the lower one. The aggregation structures of films and solid powder samples could be efficiently modulated by the carbazole dendrons and tert-butyl groups. In particular, dendrimers C2-QA and C3-QA exhibited piezochromic luminescence phenomenon, and the mechanism was preliminarily investigated.