Variable Temperature Coloration Study of Phenolphthalein Derivatives with Alkali Metals

Abstract

Recently, we reported an artificial receptor 1, which is a hybrid molecule consist of phenolphthalein and two crown ethers. In this system, the length of α,ω-diamines could be recognized by developing purple color. In addition, the coloration was so sensitive to temperature that receptor 1 could visualize "temperature". We found that the variable temperature coloration of receptor 1 with alkali metal ions significantly depends on the metal. As the temperature rises, the coloration of receptor 1 with NaOH becomes weaker, in contrast with KOH becomes more intense. Based on the variable temperature UV, NMR, and IR spectra, we propose that equilibrium between colored and colorless complex of receptor 1 with alkali metal ions is responsible for the observed phenomena.