10.1002/anie.202002646
Angewandte Chemie International Edition
COMMUNICATION
monomer emission became more evident. Further heating at 45
ºC, 65 ºC and 85 ºC gave equivalent results, causing the
concomitant decrease of the excimer emission band with a
progressive increase of the monomer emission. This ultimately
turned the emission of the system, from orange (25 ºC) to yellow
(85 ºC) (Fig. S13).
In summary, we have synthesized 1-PtII, a cyclometalated
complex with a neutral and rigid structure that is responsive-at-
metal. The use of oxidizing agents allowed for the controlled and
selective transformation of 1-PtII into 1-PtIII or 1-PtIV thus turning
photoluminescence OFF. Both 1-PtIII or 1-PtIV could be converted
into 1-PtII to turn emission back ON. Complex 1-PtII showed
dramatic solvatochromism in the solid state, with a different color
observed in the DCM solvate than from other solvents. SCXRD
analysis of different solvates confirmed that the DCM solvate
allows for a close Pt‧‧‧Pt interaction, which we believe is
responsible for the intense coloration of the DCM solvate. Beyond
the solid-state solvatochromism, the complex shows a dramatic
change in its emission properties in polar solvents that enable
metal‧‧‧metal interactions between 1-PtII units in aggregates. We
anticipate that the incorporation of 1-PtII (or 1‧H2) species into
structured materials (as repeating units or links) may allow for the
development of responsive-at-metal materials able to, e.g., sense,
cross-link, actuate, or heal on demand.
Figure 3. Aggregation-induced emission switch. a) a series of photographs
showing the emission change, from green to red-orange, as water content
increases from 0 to 90% (left to right); [1-PtII] = 1 × 10-5 M. b) Selected emission
spectra collected at different DMSO:water ratios (exc = 315 nm). c) CIE plot
showing the path followed as DMSO:water ratio is changed.
Acknowledgements
molecules. This must impact on the MMLCT of the materials in
the solid-state and ultimately dictate their apparent color. SCXRD
data of a chloroform solvate, which appeared yellow in color,
resembled those characteristics observed in the TCE solvate. In
the asymmetric unit of the chloroform solvate, there are two Pt(II)
units that generate two independent dimers (Fig. S12); both of
them show greater Pt---Pt distances (4.26 Å and 3.66 Å) than that
observed in the DCM solvate.
M.A.S. thanks Conacyt for a postdoctoral fellowship. M.J.M.
thanks NSERC (Discovery Grant; CREATE NanoMat) and the
World Premier International Research Initiative (WPI), MEXT,
Japan for funding.
Keywords: platinum • luminescence • solvatochromism • X-ray
diffraction • dimers
In stark contrast to the solid state, where the red excimer
emission dominates, 1-PtII emits green light in DCM solutions
when irradiated at 315 nm (em = 500 nm, Figure 2c,d); this
emission is ascribed to the monomeric form of the complex. We
did not observe solvatochromism at different concentrations (50
M to 3 mM) and solvents that included DMSO, acetonitrile and
chloroform. Given this dual photoluminescence of 1-PtII (solid
state vs. solution), we anticipated that an emission switch
between both states would be accessible through solvent-induced
aggregation.
As observed for DCM, 1-PtII is green emissive in DMSO (em
= 515 nm, ex = 315 nm); however, continuous addition of water
to the solution causes a progressive emission change from green
to red, showing a critical water content of 40% (Figure 3a). The
recorded emission spectra showed the structured monomer
emission band (515 nm) when only DMSO was present (Figure
3b), while no obvious excimer emission was detected. As the
proportion of water in DMSO increased, a new broad band
appeared at ca. 630 nm, and at a limiting water content of 90%
the monomer emission was barely observed whereas the broad
excimer band was visible and intense. The CIE coordinates
(Figure 3c) show a clear non-linear pathway that goes from green
(0.3, 0.6) to red (0.6, 0.4) emission passing through pale orange
(0.5, 0.4) as the proportion of water increased. Interestingly, the
1-PtII aggregates could be thermally disrupted in high water-
content samples. When heating a 1-PtII sample (90% water), the
excimer emission was partially quenched, whereas the structured
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