Donor Substituted Pyrazabole Monomers and Dimers: Design, Synthesis and Properties

We report the design and synthesis of ferrocene and triphenylamine substituted D–π– A–π–D and D–π–A–π–A–π–D type of symmetrical pyrazabole monomers (3 and 5) and dimers (6 and 7). Their optical, thermal, electrochemical and computational properties were investigated. The electronic absorption spectra of pyrazaboles 3−7 exhibit absorption bands in UV region. The TGA study reveals that pyrazaboles 3−7 show good thermal stability and pyrazabole monomers are thermally more stable as compared to pyrazabole dimers. The electrochemical studies show that pyrazaboles 3−7 exhibits one reversible oxidation and two reduction waves. The theoretical investigation shows that the triphenylamine substituted pyrazaboles (5 and 7) exhibit low HOMO − LUMO gap values compared to ferrocenyl pyrazaboles (3 and 6). Herein we have synthesized ferrocene and triphenylamine substituted D–π– A–π–D and D–π–A–π–A–π–D type of pyrazabole monomers and dimers by Pd‐catalyzed Sonogashira and Stille coupling reactions respectively. Their photophysical, thermal, electrochemical and computational properties were investigated which show good thermal stability, absorption spectra in UV region with red shift in monomers compared to their dimer analogues. The electrochemical investigation exhibited one reversible oxidation and two reduction waves for monomers and dimers. The theoretical investigation supports to red shifted absorption in triphenylamine substituted pyrazaboles with low HOMO ‐ LUMO gap values compared to ferrocenyl pyrazaboles.