Design and synthesis of 1,1,4,4- tetracyanobutadiene (TCBD) based donor acceptor D-A pyrazabole systems

Abstract

In this work, we have designed and synthesized donor-acceptor D-A pyrazabole (PY-A) systems using different donors like triphenylamine (TPA-D), phenothiazine (PTZ-D') and ferrocene (Fc-D'’) with the help of Sonogashira cross-coupling reaction. The 1,1,4,4-tetracyanobutadiene (TCBD, A′) derivatives of the D-A pyrazabole systems are formed followed by a [2 + 2] cycloaddition–retroelectrocyclization reaction on treatment with tetracyanoethylene (TCNE). The incorporation of TCBD act as an acceptor (A′) can further modulate the donor-acceptor strength, electronic and photophysical properties of the pyrazabole systems. The opted design helps up in opening new possibilities for development of near infrared (NIR) absorbing systems with various opto-electronic systems.