Tetracyanobutadiene bridged ferrocene and triphenylamine functionalized pyrazabole dimers

Abstract

Herein we have designed and synthesized tetracyanobutadiene (TCBD) bridged ferrocenyl pyrazabole dimer Fc-TCBD and triphenylamine pyrazabole dimer TPA-TCBD by [2+2] cycloaddition-retroelectrocyclization reaction of ferrocene and triphenylamine functionalized pyrazabole dimers 1 and 2, to evaluate the effect of TCBD on the photonic and electrochemical properties. The incorporation of TCBD shifts the absorption from ultraviolet region to visible region by 147 nm in TPA-TCBD. The TCBD derivatives Fc-TCBD and TPA-TCBD show red shifted broad charge-transfer (CT) bands with low HOMO – LUMO gap values compared to ethyne bridged pyrazabole dimers 1 and 2. The electrochemical study reveals that, the additional two successive one electron reduction waves at low potential in Fc-TCBD and TPA-TCBD corresponds to reduction of TCBD unit. The theoretical investigation supports the experimental observations of red shift in TCBD derivatives. The photophysical, electrochemical and computational studies show substantial donor–acceptor interaction between electron donor moiety (ferrocene and triphenylamine) and electron accepting TCBD unit. © 2017 Elsevier B.V.