Acid–base equilibrium in non-aqueous medium: colorimetric visualization, estimation of acidity constants and construction of molecular logic gates

Abstract

A reversible acid–base probe, (N¹E, N⁴E)-N¹, N⁴-bis((Z)-3-(4-(dimethylamino)phenyl)allylidene)benzene-1,4-diamine (MM1), is introduced for the colorimetric visualization of acid–base equilibria in non-aqueous media. MM1 displays reversible acidochromic behavior, showing exciting colorimetric change varying from weak to strong acid. Also, we have fabricated a colorimetric paper strip-based test kit to visualize acid–base equilibria. A dipstick experiment has been demonstrated to visualize the acid–base equilibria in the gaseous state. This acid–base probe has also been employed to estimate the pK_a values of several acidic compounds in a non-aqueous medium using overlapping indicator methods. Based on reversible acidochromic UV-visible absorption spectral and colorimetric behavior, we have constructed a reconfigurable dual input and dual output combinational logic circuit and set-reset memorized device employing acid and base as chemically encoded inputs and corresponding optical outputs. The current report evokes a new protocol for developing various reversible acidochromic probes and its implication for constructing opto-chemical molecular logic gates and estimating the acid dissociation constants of various acidic compounds in non-aqueous media.