Photoluminescent Properties and Antimycobacterial Activity of Imidazo[1,5-a]quinolines

Abstract

One factor that characterizes our modern world is the ubiquity of electrical devices and light. These light sources are increasingly linked to the integration of organic light-emitting diode (OLED) materials and will continue to gain in importance due to their color purity, color volume and contrast. One challenge of these emitter materials is often their service life and durability. The main reason for this is the blue emitters used, which represent the lifetime-limiting component of the OLED. The wide band gap required for blue emission leads to equally high energy absorption and so-called hot excited energy states. This results in degeneration of the blue emitter material as well as other components. One class of blue organic emitter molecules are imidazo[1,5-a]quinolines, which are also characterized by oxidative stability and structural simplicity. A central objective of every emitter material is to achieve the highest possible quantum efficiency. The publications in this work have demonstrated that a strong dependence of the quantum yield (QY) on the substitution pattern on the imidazole ring can be observed. The combination of a sterically demanding electron-donating moiety in position 1 of the imidazole ring and an electron-poor 2-N-heteroaromatic in position 3 showed the highest QY. However, other physical properties such as extinction maxima, emission maxima, HOMO and LUMO energies showed minimal dependence on the substituents. Further investigations focused on the transferability of QY in solution to the solid phase. A considerable reduction was observed as soon as measurements were made in crystalline form. Nevertheless, molecules were identified that exhibit a comparable QY in the solid phase to the emitter materials already in technical use. In addition, further investigations revealed that imidazo[1,5-a]quinoline showed biological activity against Myobacterium tuberculosis (Mtb). Tuberculosis, the main bacterial infectious disease agent, is an important medical target because of the emergence of resistant strains. Pathogens that are not only resistant to two, but three of the standard preparations are being detected more frequently. Chelating imidazo[1,5-a]quinolines have shown good activity, which could be significantly increased by incorporation into a zinc complex. Molecules with a sterically demanding residue in the first position and a 2-pyridinyl moiety in the third position of the imidazole ring were particularly active. Another advantage of this class of compounds is a lack of toxicity towards lung and liver cell lines, which could qualify them as potential therapeutics.