Development of chromic molecule that can change color and absorption/fluorescence wavelengths largely in response to external stimuli

Aminobenzopyranoxanthene (ABPX) dye, developed by our group, exhibits two-step color change in solution through a spiro-ring opening/closing process in response to chemical stimuli such as acids, metal ions and phenols. Using this unique characteristic, we have developed ABPX-based colorimetric sensor that change color depending on Cu²⁺ concentration, enabling visualization by spectrophotometry and the naked eye. Furthermore, an efficient and practical method to prepare ABPX with various nitrogen-containing fused rings was developed. Using a simple acid-catalyzed reaction consisting of 1,3-diisopropoxybenzene and CH 3SO 3H, a variety of benzophenones gave ABPX directly in excellent yields. We discovered that ABPX is a new type of mechanochromic organic molecule with a large wavelength difference of fluorescence (near-IR/blue). Detailed spectrophotometric and single-crystal X-ray analyses revealed that the near-IR fluorescence is attributable to fluorescence from slip-stacked dimeric structures in crystals, while the blue fluorescence is attributable to fluorescence from the monomer. Switching between the two is achieved by dynamic structural interconversion in response to mechanical grinding and exposure to the vapor of solvents.