The emission properties of bmimBF4 determined using an HPLC system. Significant influence of emission of impurities

• HPLC system for determining the real emission properties of ionic liquid is proposed.
• The real ΦE value is by about ten times smaller than previously published.
• The contribution of the emission of impurities is as great as ≥70%.

Determination of the real emission properties of imidazolium room temperature ionic liquids (RTILs) is highly desirable because many of their applications are based on the exact knowledge of their emission properties. Unfortunately, it has not been possible to obtain even two identical emission spectra for any of imidazolium RTILs! In this study an innovative use of a high performance liquid chromatography (HPLC) system coupled with a PDA spectrophotometer and fluorescence detector has been employed. This system allows a separation of impurities from 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), and to a high degree, a separation of bmimBF4-related species, which makes it an irreplaceable setup for determining real absorption and emission properties of a compound studied. Thus, it was possible to calculate the emission quantum yield, ΦE < 9 × 10−4 (HPLC system) which is by about ten times (!) smaller than ΦE ∼ 10‐2 (spectrofluorometer). It was also possible to calculate the contribution of the emission of impurities to the total emission observed, which was as high as ≥70%. This clearly shows that the influence of emission of impurities on the emission spectrum and the ΦE of bmimBF4 is astoundingly great.

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