New deep blue emissive materials are crucially important for development OLED technology, because of the most useful iridium containing complexes, which are applied as blue emitters, suffer from degradation during exploitation and do not show required color characteristics. One potential methodology for the design of blue emitters is synthesis of indium(III) complexes, due to the absence of metal-associated transitions. The coordination of an organic ligand to In3+ may result in enhanced ligand fluorescence (CHEF effect), and these emitters may also be phosphorescent. The reaction of InCl3 with 3-chloro-6-(1H-pyrazol-1-yl)pyridazine (LH) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (LMe) afforded two new complexes [In(LH)(H2O)Cl3] (1) and [In(LMe)2Cl2][InCl4] (2). The crystal structures of compounds 1 and 2 were determined by X-ray diffraction analysis. Complex 1 is octahedral neutral with one coordinated LH ligand. Complex 2 has an ionic structure, the structure consists of a octahedral complex cation +, which contains two coordinated LMe ligands, and a tetrahedral complex anion -. The UV-Vis spectra of complexes 1 and 2 are similar and consist of a main intense signal at 258 nm for 1 and 261 nm for 2 and a less intense signal at 286 nm for 1 and 309 nm for 2. Quantum chemical calculations were performed using TD-DFT method for assigning electron transitions. It is shown that the most intense transition in complex 1 is mainly intraligand (ILCT). The main transition in complex 2 is mixed interligand (LL'CT) and intraligand (ILCT) character. Photoluminescent properties of 1 and 2 investigated in both solid state and solution at room temperature. In the solid state the indium complexes demonstrate excitation-dependent emission, namely the complexes display blue fluorescence at λmax = 375 nm upon excitation of 340 nm, but upon excitation of 420 nm fluorescent bands in green region at 500-510 nm can be detected.

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