Synthesis, structure and photophysical properties of cationic Ir(III) complexes with functionalized 1,10-phenanthroline ancillary ligands

A series of substituted phenanthroline ancillary ligands with different degrees of steric hindrance, namely, 4,7-di(1H-pyrrol-1-yl)-1,10-phenanthroline (L1), 4,7-di(1H-indol-1-yl)-1,10-phenanthroline (L2) and 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline (L3), were synthesized in order to prepare cationic Ir(III) complexes. The results of photophysical studies revealed that functionalization with higher degree of steric hindrance L3 led to significant improvement of photoluminescence quantum yields (PLQYs) in neat film for these Ir(III) complexes, which may be attributed to the decrease of the intermolecular interactions. The mechanism of photophysical properties were rationalized with the help of quantum chemical calculations. Moreover, the complexes with L3 as ancillary ligands possessed good thermal stability, indicating their potential application as candidate for light-emitting electrochemical cells (LECs).