Crystal structure, Hirshfeld surface, DFT calculations and photophysical properties of 2,4,5-tris(4-pyridyl)imidazole hydrogen chloride

Abstract The hydrogen chloride salt of 2,4,5-tris(2-pyridyl)imidazole (TPI), namely, [HTPI]Cl (1), was prepared and characterized by IR, UV–Vis and fluorescence spectroscopy, high-resolution mass spectrometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and single-crystal X-ray diffraction (scXRD) analysis accomplished by inspection of the Hirshfeld surface. The molecular crystal salt exhibits interesting blue photoluminescence in the solid state, which is achieved also in EtOH/THF solutions with the maximum emission corresponding to a 1:3 (v/v) solvent mixture. The supramolecular interactions in the solid-state structure are characterized by N–H⋯Cl− and C–H⋯N/Cl− hydrogen bonds, giving a 2D layer structure that in the third dimension is accomplished by π⋅⋅⋅π interactions. Based on the structural characterization and Hirshfeld surface analysis it is assumed that π-contacts are also dominant in ethanol solution with the antisolvent THF. According to TD-DFT calculations at the MO6-2X/6-31G(d) level of theory simulating an ethanol solvent environment showed that the emission properties are originated from π−π* and n−π* HOMO→LUMO transitions.