Synthesis, Structure, and Optical Properties of Cyclometalated Iridium(III) Complexes with 2-Arylbenzimidazoles and Pyrazino[2,3-f][1,10]Phenanthroline

Two new iridium(III) complexes with benzimidazole ligands differing in the size of the aromatic system and an auxiliary N-donor ligand with extended conjugated system have been synthesized and studied structurally and spectroscopically. Comparison of the results of crystal packing analysis and data of electronic absorption spectroscopy, diffuse reflectance spectroscopy, and luminescence spectroscopy shows that intermolecular π−π interactions between the benzimidazole ligands have little effect on the optical characteristics of the complexes. Both compounds exhibit light absorption in the range of 250–550 nm (ε = 58 000−1 000 Мcm) both in solution and in the solid phase ( = 2.14−2.16 eV) and emit in the orange region (λ = 558−585 nm), with the solid-state emission maxima systematically red-shifted by about 25 nm. The results of the work allow a better understanding of the influence of crystal packing on the optical properties of iridium(III) complexes and will be used for further development of approaches to the crystal chemistry design of luminescent iridium compounds in the long-wavelength range.