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 ).