Naked-Eye Discrimination of Methanol from Ethanol Using Composite Film of Oxoporphyrinogen and Layered Double Hydroxide

Methanol is a highly toxic substance, but it is unfortunately very difficult to differentiate from other alcohols (especially ethanol) without performing chemical analyses. Here we report that a composite film prepared from oxoporphyrinogen,(OxP) and a layered double hydroxide (LDH) undergoes a visible color change (from, magenta to purple) when exposed to methanol, a change that does not occur upon exposure to ethanol. Interestingly, methanol induced color variation of the OxP-LDH composite film is retained even after removal of methanol under reduced pressure, a condition that does not occur in the case of conventional solvatothrornic dyes. The original state of the OxP-LDH composite film could be recovered by rinsing it with tetrahydrofuran (THE), enabling repeated usage of the composite film. The mechanism of color variation, based on solid-state C-13 CP/MAS NMR and solution state C-13-NMR studies, is proposed to be anion transfer from LDH to OxP triggered by methanol exposure.