Aryl pyrazaboles: a new class of tunable and highly fluorescent materials

Novel aryl substituted pyrazaboles 2-9 with direct and acetylenic linkages were synthesized by Pd-catalyzed Suzuki or Sonogashira cross-coupling reactions. Their structural, thermal, and photonic properties were investigated. The results show that the aryl pyrazaboles 2-9 exhibit good thermal stability, high fluorescence quantum yield, and tunable photophysical properties. The aryl substituted acetylenic pyrazaboles 6-9 exhibit red shifted absorption, small Stokes shifts, and high quantum yields as compared to directly linked aryl pyrazaboles 2-5. The X-ray structures of the pyrazaboles 2, 5, and 7 are discussed. The computational studies were used to calculate the relative energy levels, and band gap in the pyrazaboles. The computational results show good agreement with the experimental results.