The modulated luminescent materials based on benzimidazole and indazole skeletons: Synthesis, crystal structure and Hirshfeld surface analysis

To exploit new luminescent materials, three new compounds containing benzimidazoles and indazole moieties, namely, [H IZBI ] + · BS − ·H 2 O ( 1 ), [H IZBI ] + · MBS − ·2H 2 O ( 2 ) and [H IZBI ] + · SBS − ( 3 ) ( IZBI = 3-(1 H -benzimidazol-2-yl)-1 H -indazole, BS = benzene sulfonic acid, MBS = p -toluene sulfonic acid, SBS = 5-sulfonic salicylic acid), which were obtained through reacting IZBI and a set of aromatic sulfonic acid. Compounds 1 – 3 have been characterized by single–crystal X-ray diffraction, powder X-ray diffraction, IR, 1 H NMR, 13 C NMR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). In these compounds, there exist hydrogen bonds (N/O H⋯O/N) and the stacking interactions can be obviously observed. The luminescence behaviors of 1 – 3 reveal that the emission maxima are observed at 404, 448 and 410 nm, respectively, which is consistent with the intermolecular interactions and reverse-proportional to the dihedral angles between imidazole and pyrazole rings. Compared with IZBI itself, the emission peaks of compounds 1–3 are clearly hypsochromically ( 1, 3 ) or bathochromically ( 2 ) shifted by 26, 18 and 20 nm, respectively. The luminescence lifetimes can be found to be 1.12, 1.67, 1.21 and 1.56 ns for compounds IZBI, 1, 2 and 3, respectively. The absolute quantum yields were found to be 20.8 %, 23.5 %, 21.9 % and 22.7 % for compounds IZBI, 1, 2 and 3, respectively. The luminescence maxima are reverse proportional to the contribution of the H⋯C/C⋯H close contacts calculated by Hirshfeld surface analysis. The luminescence quantum yields and the decay lifetimes of the target compounds are proportional to the contribution of the H⋯C/C⋯H close contacts. The thermal behaviors of compounds 1–3 have been evaluated in detail.