Abstract
In this manuscript, synthesis and optical properties, such as crystallization-induced emission (CIE) and room-temperature phosphorescence (RTP), and the substituent effect on the central element are reported based on β-diketiminate aluminum complexes. Although luminescent aluminum compounds have been utilized for emitting and electron transporting layers in organic light-emitting diodes, most of them often exhibit not phosphorescence but fluorescence with low photoluminescent quantum yields in the aggregated state than those in the amorphous state due to concentration quenching. In this study, the π-conjugated β-diketiminate ligand was employed for constructing four-coordinated complexes with dialkyl- or dihaloaluminum moieties, and the dihaloaluminum complexes were found to exhibit the CIE property. Moreover, we found that the diiodoaluminum complex provided RTP, while the dialkylaluminum complexes hardly showed emission at room temperature. From theoretical calculations, it was suggested that undesired structural relaxation in the singlet excited state of dialkyl complexes should be suppressed by introducing electronegative halogens instead of alkyl groups. Our findings might be useful for establishing a new molecular design not only for obtaining luminescent complexes but also for achieving triplet-harvesting materials.