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.

The nearest distances between phenyl groups in (ppy)2Ir(pmip) crystal is more than 4.723 Å, too long to create π–π interactions whereas in (ppy)2Ir(dbm) crystal, the distance is around 4 Å, near enough to create π–π interactions to bathochromically shift the emission and increase the quantum efficiency.Figure optionsDownload as PowerPoint slide