Synthesis and photophysical characterization of novel Ir(III) complexes with a dipyridophenazine analogue (ppdh) as ancillary ligand

Two new complexes [Ir(ppy)2ppdh](PF6) (C1) and [Ir(F2ppy)2ppdh](PF6) (C2), where ppy is 2-phenylpyridine, F2ppy is 2-(2,4-difluorophenyl)pyridine, and ppdh is pteridino[7,6–f][1,10]phenanthroline-1,13(10H,12H)-dihydroxy have been synthesized. Their photophysical properties have been characterized by means of steady-state and time-resolved emission techniques and supported by TD-DFT calculations. Both complexes C1 and C2 are luminescent in fluid solutions at room temperature with quantum yields around ca 1%, and the nature of the emitting excited state has a predominant 3MLCT/3LLCT character with some mixed contributions from a 3LC state on the ancillary ligand. However, in C2 the contribution from the 3LC state becomes dominating, as was identified from a dual emission observed in CH2Cl2 arising from a slow equilibration between the 3MLCT/3LLCT and 3LC states. Therefore, the corresponding luminescence is indeed composed of two different patterns (respective maxima at 533 and 580 nm) and two different lifetimes, whose contributions in the whole emission spectrum is strongly dependent on the excitation wavelength. Overall, the results here presented add further fundamental knowledge on the photophysical properties of iridium(III) complexes of potential interest for applications in diverse research fields such as optoelectronics, bioimaging, and theranostics.