Supramolecular Structures and Assembly and Luminescent Properties of Quinacridone Derivatives

The synthesis and single-crystal X-ray structures of two quinacridone derivatives, N,N‘-di(n-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 1 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 Alq3:1 (Alq3 = 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 Alq3:2, a similar phenomenon occurs when
the concentration is above 6.7%. EL devices with Alq3:1 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 Alq3:2 films are employed
as emitting layer. The different PL and EL concentration-dependent properties of the solid thin films Alq3:1
and Alq3:2 are attributed to their different molecular packing characteristics in the solid state.