Luminescent behaviors of salts based on 2–phenyl–1H–benzimidazole

Abstract

Three new benzimidazole salts, namely, [HPBI]+ ClO4–·H2O (1), [HPBI]33+ 3Cl–·H2O (2), [HPBI]22+ SO42–·H2O (3) [PBI = 2–phenyl–1H–benzimidazole], were obtained by the reaction of PBI and the different inorganic acid, respectively. The maximal emission peaks of compounds 1–3 were observed at 419, 424 and 434 nm in the solid state, respectively. Compared with the free PBI, the emission maxima of compounds 1–3 are obviously red-shifted about 45, 50 and 60 nm, respectively, indicating that the luminescent properties were tuned by the anions, but also the maximal emission bands are proportional to the intermolecular packing interactions. Their photoluminescent lifetime are 0.72, 2.36, 5.44 and 3.56 ns, respectively; their luminescent quantum yields are 2.06%, 13.66%, 3.91% and 4.14%, respectively. Compounds 1–3 were structurally characterized by single crystal X–ray diffraction, FT-IR, UV–vis spectra and thermogravimetric analysis (TGA). Single crystal X-ray diffraction reveals that in these compounds, there exist a variety of hydrogen bonds (N–H⋯Cl, C–H⋯Cl, O–H⋯Cl, N–H⋯O, O–H⋯O and C–H⋯O) and stacking interactions (C–H⋯π and π⋯π), through which three-dimensional architectures are formed. In compound 1, a three–dimensional (3D) supramolecular architecture through intermolecular X–H⋯Cl (X = N, C and O) hydrogen bonds and π⋯π stacking interactions. Compound 2 exhibits intermolecular N/C–H⋯O hydrogen bonds and π⋯π stacking interactions. Compound 3 displays hydrogen bonding interactions, which further results into generating a three–dimensional supramolecular architecture. The shortest distances of π⋯π stacking interactions are 3.793, 3.690 and 3.466 Å in compounds 1–3, respectively. In an addition, the thermal properties of compounds 1–3 were investigated in detail.