Temperature dependence of photoluminescence and hydrogen bonding revealed for the first time in a templated borate family: synthesis, structure and properties of a pentaborate [Emmim][B5O6(OH)4].

Herein, a templated borate, [Emmim][B5O6(OH)4] (denoted 1, Emmim = 1-ethyl-2,3-dimethylimidazolium), has been synthesized. It is unexpectedly observed that 1 exhibits a series of broadened luminescence curves from -183 to 75 °C, the emission intensities are measured as a decreasing function of temperature, and the line width of the PL emission is strongly enhanced when temperatures decrease below -100 °C. In addition to this, hydrogen bonding (H-B) in 1 with distinctly enlarging trends was observed as the temperature increased. The influence of temperature on H-Bs and physical properties was explored through single crystal X-ray diffraction analysis, theoretical calculations, PL, and dielectric constant test. The results indicate that the temperature can impact weak H-Bs interactions and the PL can be seen as a prober to the varying of structure such as H-Bs in borate crystal.