Synthesis, crystallography and photoluminescence of a new pyrazolonato iridium complex

By using 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone (pmip) as the ancillary ligand, the cyclometalated complex: bis-(2-phenylpyridine)-(pmip)-iridium [(ppy)2Ir(pmip)] was synthesized. Its crystal structure, absorption and emission were compared with those of its analogue, the frequently used electrophosphorescent material (ppy)2Ir(dbm) [bis-(2-phenylpyridine)-(dibenzoylmethane) iridium]. For (ppy)2Ir(pmip) in dichloromethane, the emission is highly structured and the intensity is 5 times higher than that of (ppy)2Ir(dbm). It is a result of the higher triplet energy level of pmip relative to that of dbm. In solid state, green emission of (ppy)2Ir(pmip) peaked at 550 nm was observed with a quantum efficiency 0.31% in contrast to the emission at 626 nm with a quantum efficiency of 0.76% for (ppy)2Ir(dbm). The bathochromical shift and higher efficiency in crystallized (ppy)2Ir(dbm) was explained by the stronger π–π intermolecular interactions which is unique to in solid state (ppy)2Ir(dbm) crystals.