Alkyl and dendron substituted quinacridones: synthesis, structures, and luminescent properties

The synthesis of two alkyl substituted quinacridone derivatives, N,N'-di(n-hexyl)-1,3,8,10-tetramethylquinacridone (1) and N,N'-di(n-hexyl)-2,9-di(t-butyl)quinacridone (2), and four dendritic quinacridone derivatives, N,N'-didendritic-1,3,8,10-tetramethylquinacridones (3-G1 and 3-G2) and N,N'-didendritic-2,9-di(tert-butyl)quinacridones (4-G1 and 4-G2) are reported. X-ray crystal structure and thermal analysis revealed that the quinacridone derivatives reported in this paper exhibit the evolution from crystalline phase to amorphous phase upon varying from alkyl substituted quinacridones to dendritic quinacridones. The concentration-dependent 1H NMR, UV-vis, and photoluminescence (PL) spectroscopic studies demonstrated the aggregation properties of the quinacridone derivatives in solution. For dendritic quinacridones with the sufficient shield of dendrons, the fluorescence concentration quenching can be significantly suppressed and emission intensity in concentrated solution and solid state could be greatly enhanced. Compound 4-G2 displays good solution process property and higher PL yield in concentrated solution, suggesting that it is a potential candidate for the fabrication of high-performance organic electroluminescent devices (OLEDs) on the basis of low-cost solution process technique.