Synthesis, Photophysical, Electrochemical, and Halochromic Properties of <i>peri</i>-Naphthoindigo

A facile synthesis of <i>peri</i>-naphthoindigo (PNI) was reported for the first time from simple precursor. Installation of a chromophore at the <i>peri</i>-position of naphthalene is very unique in terms of synthetic challenges and properties. PNI exists in monoenol form, undergoes halochromism in acidic medium, and displays a wide and strong absorption band (ε = 33390 M^–1cm^–1) with maxima at 632 nm (chloroform). The dye undergoes oxidation and reduction at +0.30 and −0.58 V (vs Fc/Fc⁺), respectively, in chloroform