Most of the nonalkali MOFs containing NDI only turn darken after photoresponse, with a narrow color change range. To expand the color response range of photochromic materials, this work designs two novel metal-organic frameworks (Na/Cs-CMNDI) constructed by alkali metals (Na+, Cs+) and the photoresponsive linker N, N'-bis(carboxymethyl)-1,4,5,8-naphthalenedicarboximide (H2CMNDI). It was found that the thermally stable Cs-CMNDI exhibits a remarkable four-color transformation from yellow, gray to black and finally red under photothermal costimulation, surpassing the limitation of single-color change in traditional NDI-based MOFs. Based on this, a dynamic information encryption system was successfully established, which can generate specific passwords within a certain period of time, and a color-based encryption strategy was developed by using an 8888-type mold to brush the powder to encrypt specific four-digit numbers. Moreover, both AMOFs can be used as fluorescent sensors for the detection of the antibiotic cefuroxime, demonstrating good application potential in the fields of medicine and ecological protection.
Zhang et al. (Thu,) studied this question.