Synthesis and luminescence of indium(iii) complexes with (1H-pyrazol-1-yl)pyridazines

Abstract

New deep-blue-emitting materials are crucial for the development of OLED technology because of the most useful iridium-containing complexes, which are applied as blue emitters. However, they suffer from degradation during operation and do not show the required color characteristics. One potential methodology for the design of blue emitters is the 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 (L^H) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (L^Me) afforded two new complexes, namely, [In(L^H)(H₂O)Cl₃] (1) and [In(L^Me)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 L^H ligand. Complex 2 has an ionic structure, which consists of a octahedral complex cation {In(L₂)₂Cl₂}⁺ containing two coordinated L^Me ligands and one tetrahedral complex anion {InCl₄}⁻. 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 the TD-DFT method for assigning electron transitions. It was shown that the most intense transition in complex 1 was mainly intraligand (ILCT). The main transition in complex 2 was a mixed interligand (LL'CT) and intraligand (ILCT) characteristic. The photoluminescent properties of 1 and 2 were investigated in both solid state and solution at room temperature. In the solid state, the indium complexes demonstrated excitation-dependent emission, that is, the complexes displayed blue fluorescence at λ_max = 375 nm upon 340 nm excitation, but upon 420 nm excitation, fluorescence bands can be detected in the green region at 500–510 nm.