Preparation and Characterization of Blue‐Luminescent Tris(8‐hydroxyquinoline)‐aluminum (Alq₃)

Abstract

Using differential scanning calorimetry (DSC) measurements in combination with structural and optical characterization we have investigated the formation conditions of different phases of tris(8‐hydroxyquinoline)aluminum (Alq3). We have identified the δ‐phase as a high‐temperature phase of Alq3 being composed of the facial stereoisomer, and report an efficient method to obtain blue luminescent Alq3 by a simple annealing process. This allows the preparation of large amounts of pure δ‐Alq3 by choosing appropriate annealing conditions, which is necessary for further characterization of this blue‐luminescent phase, and offers the possibility of fabricating blue organic light‐emitting devices (OLEDs) from this material.

Formation of Flower-Like Crystals of Tris(8-hydroxyquinoline)aluminum from 8-Hydroxyquinoline on Anodic Porous Alumina

“…To date, five crystalline phases ( , , , , and ) have been identified for Alq 3 [8][9][10]. To the best of our knowledge, -, -, and -Alq 3 are formed by meridional isomers, whileand -Alq 3 are formed by facial isomers [2,[5][6][7][10][11][12][13].…”

“…The preparation and characterization of Alq 3 have been widely studied [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Because of the bidentate ligand, Alq 3 complexes form two isomers, as shown in Figure 1: meridional and facial.…”

“…Because of the bidentate ligand, Alq 3 complexes form two isomers, as shown in Figure 1: meridional and facial. Interestingly, the two isomers exhibit different types of photoluminescence (PL): specifically, green [2,3] in the case of the meridional isomer and blue [4][5][6][7] for the facial isomer. To date, five crystalline phases ( , , , , and ) have been identified for Alq 3 [8][9][10].…”

Improved lifetime of an OLED using aluminum (III) tris (8-hydroxyquinolate)

“…These results seem to indicate that the amorphous phase in thin films is attributed to polymorphs composed only of mer-Alq 3 . Very recently, it has been reported that d-Alq 3 might be composed of fac isomers [7]. Therefore, there is now some disagreement about the amorphous structure based on the isomeric mixture of Alq 3 in thin films.…”

Organic Semiconductor Based Heterostructures for Optoelectronic Devices

“…This arrangement in the solid state generates a significant overlap of the orbitals of the aromatic rings belonging to molecules situated in different planes. In Alq3 the conduction properties depend on the dominant type of stereoisomer, meridian or facial (Cölle, 2003), and are generated by the overlapping degree of the orbitals of the hydroxyquinoline ligands belonging to the neighbouring molecules.…”