Monolayers Langmuir–Schaefer films and acidichromism of a nonamphiphilic acetone derivative containing carbazole

Abstract

A carbazole-containing compound, di(3-N-ethylcarbazoylidene) acetone (dNECa), which has no long substituted alkyl chain, was found to form a stable monolayer at the air–water interface when spread from a chloroform solution. The monolayer can be transferred onto solid substrates by the horizontal lifting method to form a uniform ultrathin film (Langmuir–Schaefer film or LS film). Quartz-crystal microbalance measurements of the transferred LS film confirmed monolayer formation at lower surface pressures (10 mN m−1) and the collapse at higher surface pressures (20 mN m−1). The transferred LS film showed a strong color change from yellow to blue when exposed to HCl gas. The film returns to its original yellow color spontaneously in air or on exposure to NH3 gas. These color changes can be repeated many times in the transferred films by alternative exposure to HCl and NH3 gases. It is suggested that the color change or acidichromism is due to the keto-enol tautomerization of the compound in the film. Fluorescence spectra have been used to confirm our conclusions.