Towards NIR emission: 2-(1H-tetrazol-1-yl)pyridine as versatile ligand for the synthesis of two new families of cationic and neutral Ir(III) complexes.

In the last decades, cyclometalated Ir(III) complexes have drawn a large interest for their unique properties: they are excellent triplet state emitters, thus the emission is phosphorescent in nature; typically high quantum yields and good stability make them good candidates for luminescent materials. Moreover, through an opportune choice of the ligands, it is possible to tune the emission along the whole visible spectra. Thanks to these interesting features, Ir(III) complexes have found different applications in several areas of applied science, from OLEDs to bioimaging. In particular, regarding the second application, a remarkable red-shift in the emission is required, in order to minimize the problem of the tissue penetration and the possible damages for the organisms. With the aim of synthesizing a new family of NIR emitting Ir(III) complexes, we envisaged the possibility to use for the first time 2-(1H-tetrazol-1-yl)pyridine as bidentate ligand able to provide the required red-shift of the emission of the final complexes. Exploiting the versatility of the ligand, I prepared two different families of heteroleptic Ir(III) complexes. In detail, in the first case the 2-(1H-tetrazol-1-yl)pyridine was used as bis-chelating N^N ligand, leading to cationic complexes, while in the second case it was used as cyclometalating C^N ligand, giving neutral complexes. The structures of the prepared molecules have been characterised by NMR spectroscopy and mass spectrometry. Moreover, the neutral complexes’ emissive properties have been measured: emission spectra have been recorded in solution at both room temperature and 77K, as well as in PMMA matrix. DFT calculation has then been performed and the obtained results have been compared to experimental ones.

Inverse and regular phenyl-azole ligands for luminescent Iridium(III) complexes

In the modern society, light is mostly powered by electricity which lead to a significant increase of the global energy consumption. In order to reduce it, different kinds of electric lamps have been developed over the years; it is now accepted that phosphorescence-based OLEDs offer many advantages over existing light technologies. Iridium complexes are considered excellent candidates for bright materials by virtue of the possibility to easily tune the wavelength of the emitted radiation, by appropriate modifications of the nature of the ligands. It is important to note that the synthesis of Ir(III) blue-emitting complexes is a very challenging goal, because of wide HOMO-LUMO gaps needed for produce a deep blue emission. During my thesis I planned the synthesis of two different series of new Ir(III) heteroleptic complexes, the C and the N series, using cyclometalating ligands containing an increasing number of nitrogens in inverse and regular position. I successfully performed in the synthesis of the required four ligands, i.e. 1-methyl-4-phenyl-1H-imidazole (2), 4-phenyl-1-methyl-1,2,3-triazole (3), 1-phenyl-1H-1,2,3-triazole (6) and 1-phenyl-1H-tetrazole (7), that differ in the number of nitrogens present in the heterocyclic ring and in the position of the phenyl ring. Therefore the cyclometalation of the obtained ligands to get the corresponding Ir(III)-complexes was attempted. I succeeded in the synthesis of two Ir(III)-complexes of the C series, and I carried out various attempts to set up the appropriate reaction conditions to get the remaining desired derivatives. The work is still in progress, and once all the desired complexes will be synthesized and characterized, a correlation between their structure and their emitting properties could be formulated analysing and comparing the photophysical data of the real compounds.