Intramolecular energy transfer between the triplet of ancillary ligand and the metal to ligand charge transfer state existed in heterocyclometalated iridium (III) complexes

Abstract

Higher efficiency red organic light emitting devices (OLEDs) were obtained by employing Ir (III) complexes with 1-phenylbutane-1, 3-dione (ba) as the second ligand than that with acetylacetone (acac) as the second ligand, which were attributed to the intramolecular energy transfer existed in these complexes. The reason were attributed to the intramolecular energy transfer existed in these complexes and were approved by their photoluminescence characteristics at 77 K, as well the phosphorescence decay lifetime. Because of the lower triplet energy level of ba (Tba,19 230 cm−1) whose energy was suitable to transfer to the triplet of the metal to ligand charge transfer (MLCT) (M3LCT,16 260 cm−1) state compared to Tacac (25 500 cm−1), more efficient OLEDs were obtained (7.0 cd/A) using Ir[2-(4′-methanoxy-styryl)-benzothiazole]2ba (ba-2) than Ir[2-(4′-methanoxy-styryl)-benzothiazole]2acac acac-2 (6.1 cd/A).