The
dye encapsulated metal–organic frameworks (MOFs) are
of interest for their practical applications such as light-emitting
diodes, temperature sensing, and microlasers. However, very few MOFs
have been reported to date where the dye moiety is utilized as one
of the components of the framework. Fluorescein dye (FSD) doped materials
have an ability to emit various colors such as red, green, and yellow
depending upon their tautomeric form and external stimuli. In anticipation
of light-emitting devices, three FSD-based novel MOFs, namely, {[Co2(FSD)2(H2O)4]·H2O·MeOH}
n
, FSDCo; {[Mn2(FSD)2(H2O)4]·H2O·MeOH}
n
, FSDMn; and {[Cd2(FSD)2(H2O)3(MeOH)]·2(H2O)}
n
, FSDCd, have been designed
and synthesized. These crystalline materials were shown to exhibit
multicolor light-emitting behavior and reversible green to brown piezochromism,
implying their potential to act as fluorescent switches, mechanosensors,
and security papers. Further, these crystalline MOFs were also shown
to exhibit a rare optical phenomenon called pleochroism. The green
colored crystals displayed multiple colors under polarized light due
to the agglomeration of nano- and microcrystals at different angles
on the surface of macrocrystals.
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