Solvatochromism Study of DCM Encapsulated in ZIF-90 and the Potential Application of DCM/ZIF-90 as the Fluorescence Down-Conversion Layer for an LED Chip

In this study, we have employed the laser dye, 4-(dicyano-methylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), to probe the microenvironment in ZIF-90 cavities. The steady-state and time-resolved studies suggested that the ZIF-90 provides a highly restricted but solvent-accessible environment for the encapsulated molecules. Because ZIF-90 can effectively prevent the aggregation quenching of the DCM in solid state, we have employed the DCM/ZIF-90 composite material as the fluorescence down-conversion layer for the blue light-emitting diode chips. The device provides stable white light illumination with the CIE 1931 chromaticity coordinate at (0.404, 0.355). When we mixed the DCM/ZIF-90 with Ag+ ion, the Ag+ ion was reduced and formed Ag nanoparticles on the DCM/ZIF-90 surface. Our study shows that the decoration of Ag nanoparticles on the ZIF-90 surface could ultimately change the spectroscopic properties of the DCM encapsulated in ZIF-90, and this unique phenomenon can be used to tune the optical properties of the dye molecules encapsulated in the ZIF-90.