Communication
ChemComm
stable in the range of 5 ns (t1) and presented CPL-activity, being Conflicts of interest
probably correlated with a folded structure in solution. The
apparent glum value is modest due to the presence of species
There are no conflicts to declare.
with non-polarized emissions (t2 and t3). In the case of (S,S)-2
the contribution of the CPL-active excited state species is
practically irrelevant. Taking into account the practically null
Notes and references
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CPL-response of free (S,S)-2, a build-up of CPL from zero could
be observed in (S,S)-2 upon metal coordination, especially in
the case of Sc(III). For the complexes (S,S)-1:Zn (Fig. 5a, bottom
left) and (S,S)-2:Sc (Fig. 5b, bottom right) we may again attri-
bute the CPL emission (DI, black lines) to the species with
the longest lifetime ((t1), purple line). The presence of non-
polarized emissions from shorter lifetimes in the SAEMS spec-
tra suggested that oligomeric material could also be present in
solution. This seems to be the case for the (S,S)-2:Zn complex
(Fig. 5b, bottom left). Additionally, in the case of the (S,S)-1:Sc
complex (Fig. 5a, bottom right), the CPL emission could not be
exclusively attributed to one species but to the combination of
two close emissive species with the longest lifetimes (t1 purple
and t2 green). All these studies suggested that the operating
mechanism of the increased CPL activity of the diamagnetic
complexes was the strengthening of the intrinsic contributions
of the longest lifetime (t1) to the global emission by coordina-
tion with the ligand. For paramagnetic metals, the difference
from the free ligand appears to be related to the presence of
unpaired electrons, which affect particularly the CPL-active
emission, as could be observed in the corresponding TRES
and SAEMS analysis. The stability of the complexes was finally
checked in different solvents. Remarkably, the complexes are
formed and stable even in MeCN. Nevertheless, MeOH is able
to reverse the equilibrium to the free ligand leading to an
OFF/ON CPL switch.
In conclusion, we have shown that compounds (S,S)-1 and
especially (S,S)-2 are able to fold by a novel oxophilic metal-
mediated coordination mechanism, leading to stable com-
plexes that present both high glum values and high QYs. A
representative example is the (S,S)-2:Sc(III) complex, which has a
glum value of À7.1 Â 10À3 and keeps a good QY value of 0.38.
Moreover, we have observed that the chiroptical properties of
these complexes are influenced by the magnetic nature of the
metal. These findings have been rationalized on the basis of the
complete photophysical characterization of these systems. It is
worth noting that these structures can finally act as CPL
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profile in both ON and OFF states.
mixture of CH2Cl2 : acetone was used as solvent.
´
We thank the Ministerio de Economıa y Competitividad
(MINECO, Spain) (CTQ2017-85454-C2-1-P, CTQ2017-85454-C2-
2-P, CTQ2015-70283-P) for funding. We also thank the UGR
12 The additional ligands in the crystal are two water molecules, which
come from the crystallization conditions. In solution, acetone
molecules may play the same role, and have been used as additional
ligands during the theoretical calculations.
13 However, the carbophilic silver induces a large wavenumber shift in
the CRC stretching Raman modes of (S,S)-1, and shows a strong
interaction with CRC bonds (Fig. S28, ESI†).
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15 The CRC bonds of (S,S)-2 are not influenced by Ag(I). Thus (S,S)-1
presents a unique hosting cavity for Ag(I) formed by the cooperative
interaction of the three alkynes (Fig. S29, ESI†).
´
‘‘Unidad de Excelencia Quımica’’ and PP2016-VS01 for support.
A. G. C., P. R., S. R., and A. O. also acknowledge funding from
MINECO and MECD (Spain) for RyC-2013-12943 and FPU
contracts. Fondazione Cariplo and Regione Lombardia (Big &
Open Data Innovation Laboratory, BODaI-Lab, University of
Brescia), the Computing Center CINECA (Bologna), Italy, and
CSIRC (UGR) are also acknowledged for access to computa-
tional facilities.
16 H. Tanaka, Y. Inoue and T. Mori, ChemPhotoChem, 2018, 2, 386.
13988 | Chem. Commun., 2018, 54, 13985--13988
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