ИСТИНА

Cyclometalated iridium(III) complexes can be utilized as more stable analogs of ruthenium(II) dyes in dye-sensitized solar cells (DSSC). Still, poor light absorption of iridium(III) photosensitizers prevent their widespread application in solar panels. The extension of the conjugated π-system of ligands is usually considered to be an effective tool for improving light-harvesting and emission properties of iridium(III) complexes. However, use of sterically hindered 2-aryl-N-phenylphenanthro[9,10-d]imidazoles as cyclometalated ligands results in significant distortions of the iridium(III) octahedron greatly reducing the stability of the target compounds without significant increase in their absorption[1]. Based on this study, we have assumed that benzimidazole ligands bearing the aryl unit with the extended π-system should be used. In this work, a number of new cyclometalated ligands with different number of fused rings in the aryl fragment of N-phenyl-benzimidazoles and corresponding heteroleptic iridium(III) complexes were synthesized. A thorough structural study of the compounds along with the study of their optical and electrochemical properties revealed the limits in which the conjugated π-system can be varied without any negative effect on light-harvesting properties of the complexes. Moreover, the results allowed us to modulate the geometry of cyclometalated complexes (five- or six-membered metallacycles, various degree of distortions of the iridium octahedron) by changing the size of the conjugated π-system of ligands. Finally, we succeeded in isolation of a mono-cyclometalated iridium(III) complex with unprecedented square-pyramidal geometry.