*4.1. Polymorph Identification*

In general, changes in crystal morphology are probable to occur when polymorphism exists. Numerous cases [40–42] indicated various crystal forms with diverse habits in different solvent environments. Therefore, it is necessary to examine the crystal polymorphism of the products obtained from different solutions. As illustrated in Figure 2, the catechol products crystallized from isopropanol, methyl acetate and ethyl acetate have similar characteristic peaks with the raw material, proving that all the samples were in the same crystal form as reported [43]. In addition, the simulated powder X-ray diffraction (PXRD) pattern of the catechol obtained from CSD was consistent with the patterns of the experimental crystals (Supplementary Materials Figure S1). The results suggest that no polymorphic phenomenon occurred in our study, and it is reasonable to simulate crystal habits using the structure obtained from CSD.

**Figure 2.** Powder X-ray diffraction (PXRD) patterns of the catechol crystals: (**a**) the raw material and the products crystallized from (**b**) ethyl acetate, (**c**) methyl acetate, and (**d**) isopropanol.
