Investigation of vapochromism of 3,3′,5,5′-tetramethylbenzidine-tetrasilicicfluormica intercalation compounds through visible diffuse reflection and powder X-ray diffraction

In this study, we synthesized intercalation compounds of 3,3′,5,5′-tetramethylbenzidine (TMB) and tetrasilicicfluormica (TSFM) via a commonly used cation exchange method with TMB2+/TSFM cation exchange capacity (CEC) ratios of 1.0, 2.0, 2.7, and 5.4. These materials were characterized using powder X-ray diffraction (XRD), X-ray fluorescence, thermogravimetric-differential thermal analysis, scanning electron microscopy, and visible absorption spectroscopy. The vapochromism of each sample was assessed directly from the exterior of the glass sample tube using diffuse reflectance spectroscopy. All specimens vacuum-dried at 50 °C appeared yellow but turned green under water vapor at TMB/CEC = 2.0, 2.7, and 5.4, and blue under acetonitrile vapor at all TMB/CEC ratios. The sample with TMB/CEC = 2.0, in particular, exhibited clear vapochromic effects towards water and acetonitrile. Methanol and formic acid induced color changes similar to that of water vapor but less intense, except at TMB/CEC = 2.0. The color of each sample faded upon exposure to gaseous ammonia, whereas ethanol, acetone, iodomethane, and nonpolar solvents did not induce any color changes. The powder XRD pattern suggested changes in the array structures of TMB in the interlayer spaces due to vapor exposure.