Supramolecular structures and assembly and luminescent properties of quinacridone derivatives

Abstract

The synthesis and single-crystal X-ray structures of two quinacridone derivatives, N,N′-di(/i-butyl)quinacridone (1) and N,N′-di(n-butyl)- 1,3,8,10-tetramethylquinacridone (2), are reported, and the 1H NMR, absorption, photoluminescent (PL), and electroluminescent (EL) characteristics are presented. Both these crystal structures are characterized by intermolecular π⋯π and hydrogen bonding interactions. The intermolecular π⋯π interactions lead to the formation of molecular columns in the solids of 1 and 2, and the interplanar contact distances between two adjacent molecules are 3.48 and 3.55 Å, respectively. Crystals of I display shorter intermolecular π⋯π contacts and higher density than 2. These results suggest that tighter intermolecular interactions exist in 1. The 1H NMR, absorption, and PL spectra of 1 and 2 in solutions exhibit concentration-dependent properties. The PL quantum yields of 1 in solutions decrease more quickly with the increase of concentration compared to that of 2 in solutions. For solid thin films of Alq 3:1 (Alq 3 = tris(8-hydroxyquinolinato)aluminum), emission intensities dramatically decrease and obvious red shifts are observed when the dopant concentration is above 4.2%, while for films of Alq 3:2, a similar phenomenon occurs when the concentration is above 6.7%. EL devices with Alq 3:1 as emitting layer only show high efficiencies (20.3-14.5 cd/A) within the narrow dopant concentration range of 0.5-1.0%. In contrast, high efficiencies (21.5-12.0 cd/A) are achieved for a wider dopant concentration range of 0.5-5.0% when Alq 3:2 films are employed as emitting layer. The different PL and EL concentration-dependent properties of the solid thin films Alq 3:1 and Alq 3:2 are attributed to their different molecular packing characteristics in the solid state. © 2005 American Chemical Society.