Communication
ChemComm
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The decomposition temperature of Y-form is lower than that
of both B- and G-forms, which should be attributed to the
amorphous nature of Y-form (Fig. 3b). Moreover, there are no
endothermic or exothermic peaks prior to the decomposition
temperature in the differential scanning calorimetry (DSC) curves
of B-form or G-form (Fig. 3c). Upon heating Y-form to ca. 220 1C,
the DSC curve only shows an endothermic melting point peak
due to different molecular aggregation states.23 Indeed, without
the indispensable solvent molecules, the transformation among
the different forms cannot be achieved by thermal treatment,
which further validates the essential role of solvent molecules.
By exploiting the tricolour switching property of complex 1, a
simple patterned optical recording system visualized as a tree
was fabricated in an agate mortar (Fig. 3d). The procedure was
as follows: first, Y-form was spread evenly on the mortar,
exhibiting a yellow emission under photoexcitation. Then, a
green-emitting crown and a blue-emitting sky were drawn by
using a glass capillary with ethanol or toluene. A part of the
Y-form sample was retained as a tree-trunk. Finally, this pattern
could be erased by mechanical grinding with hand pressure,
recovering the original yellow background. This drawing and
erasing process was repeated for many cycles without any
obvious performance degradation.
In summary, tricolour luminescence switching has been
observed in an Ir(III) complex for the first time. Complex 1
can form two different crystal structures, and the transforma-
tion between two crystalline states and an amorphous state
leads to tricolour switching behaviour. Solvent molecules are
shown to play a crucial role in the crystallization and lumines-
cence processes. It is proposed that the different emission
characteristics of B-form and G-form should be ascribed to
their distinctions in molecular arrangement, conformation and
intermolecular interactions. The clear and reversible tricolour
luminescence switching feature makes complex 1 a competitive
candidate for practical applications. More importantly, it is
envisioned that our molecular design strategies will provide
valuable guidelines for developing ideal multicolour switching
luminescent materials in the future.
13 Iridium(III) in Optoelectronic and Photonics Applications, ed. E. Zysman-
Colman, J. Wiley & Sons, Ltd, 2017.
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This work was funded by NSFC (no. 51473028), the Key
Scientific and Technological Project of Jilin Province
(20190701010GH), and the Development and Reform Commis-
sion of Jilin Province (20160058). M. R. B. thanks EPSRC grant
EL/L02621X/1 for funding.
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Conflicts of interest
There are no conflicts to declare.
Notes and references
1 (a) Y. Liu, Q. Zeng, B. Zou, Y. Liu, B. Xu and W. Tian, Angew. Chem., 23 J. Bernstein, Polymorphism in Molecular Crystals, Oxford University
Int. Ed., 2018, 57, 15670; (b) S. K. Park, I. Cho, J. Gierschner,
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This journal is ©The Royal Society of Chemistry 2019
Chem. Commun., 2019, 55, 14582--14585 | 14585