We investigated the photophysical properties of fac-Ir(pmp)₃, mer-Ir (pmp)₃, fac-Ir(dmpmp)₃, and mer-Ir(dmpmp)₃ (where pmp = 3-methyl-1-phenyl-2,3-dihydro-1H-imidazo[4,5-b]pyridine and dmpmp = 1-(2',6'-dimethylbiphenyl-2-yl)-3-methyl-2,3-dihydro-1H-imidazo[4,5-b]pyridine). At 77 K, the fac-isomers showed blue emission with a vibronic structure, while the mer-isomers showed less structured emissions. At 300 K, all complexes showed broad and markedly red-shifted emission. The quantum yields of the Ir(dmpmp)₃ isomers were very low, and their emission lifetimes were very short compared to those of Ir(pmp)₃. In order to understand the large differences between the photodynamic properties of Ir(pmp)₃ and Ir(dmpmp)₃, we performed femtosecond time-resolved transient absorption (TA) spectroscopic measurements. The TA spectra of Ir(dmpmp)₃ were almost the same as those of Ir(pmp)₃ at a short delay time. However, Ir(dmpmp)₃ showed a new broad TA band at around 720 nm with increasing delay time.