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doi.org/10.1002/chem.202005481
Chemistry—A European Journal
us to study the performance of the CPL properties of these
host–guests mixed colloidal solutions.
nescence. Thus, the coordination interaction was taken into
consideration. Rh-COOH adopts a similar molecular structure
to Rh6G. The major difference in structure is the function
group 2-COOEt is replaced by 4-COOH. It is supposed that the
-COOH group may adopt coordination bonding with the ZnII in
the Zn-L1 colloid, considering the popular coordination bonds
observed between the -COO and ZnII in reported coordination
polymers or metal–organic frameworks (MOFs).[15] It is surpris-
ing that the Zn-L1+Rh-COOH shows a strong Cotton effect
with the intensity exceeding the limit of spectrometer at the
characteristic absorption band of Rh-COOH (Figure 5d, Fig-
ure S22 in the Supporting Information). The direction of the
Cotton effect for Zn-L1+Rh-COOH at 550 nm is opposite that
of Zn-L1+Rh6G with the same CCW stirring direction. Mean-
while, the CPL study of Zn-L1+Rh-COOH with stirring reveals
a negative CPL peak centered at 570 nm under the excitation
wavelength of 500 nm. The glum value at 570 nm is À0.046,
which is more than twice the glum value of Zn-L1+Rh6G at
570 nm and close to that of Zn-L1. Rh-COOH possesses a quan-
tum yield in solution of approximately 51%. When the Rh-
COOH is added into the Zn-L1 colloidal solution, the quantum
yield was maintained at 40%.
From host to guest: chiroptical transfer of CPL properties
ThT and PDI are fluorescence compounds in solution. However,
the luminescence property is greatly quenched in the Zn-L1
colloidal solution, making the CPL study difficult. Thus, the
Rhodamine family was chosen to study the potential CPL prop-
erties trigged by host–guest interactions and the vortex field.
Rhodamine 6G (Rh6G) is known for its high quantum yield
that is close to 100%. When Rh6G is added into the Zn-L1 col-
loidal solution (labeled as Zn-L1+Rh6G), the quantum yield for
Rh6G remains at 83%, which is pretty good for a fluorescence
material. Meanwhile, the CD spectroscopy study shows that
Rh6G in the stirring Zn-L1 colloidal solution possesses both CD
and LD properties in its characteristic absorption band (Fig-
ure 5c, Figure S21 in the Supporting Information). The CPL
spectrum of Zn-L1+Rh6G was taken by setting the excitation
wavelength to 500 nm. As shown in Figure 5b, there is a nega-
tive emission peak, the position of which (563 nm) is close to
the emission wavelength of Rh6G (573 nm). The glum of Zn-
L1+Rh6G at 563 nm is À0.02, which is almost half the value of
Zn-L1.
We wondered if the high value of glum for Rh-COOH in Zn-L1
colloidal solution is attributed to the coordination bonding.
Thus, the functional group 4-COOH was esterified into 4-
COOMe. The resulting Zn-L1+Rh-COOMe is also CD active in
its absorption band with in situ stirring (Figure S22 in the Sup-
porting Information). But the CD intensity is much weaker than
that of Zn-L1+Rh-COOH. In the meantime, the direction of the
Cotton effect is opposite to that of Zn-L1+Rh-COOH with the
same vortex direction (but the same as Zn-L1+Rh6G). It is as-
sumed that the esterification for Rh-COOMe may weaken the
molecular interaction with Zn-L1. The CPL study for Zn-L1+
Rh-COOMe suggests a negative emission difference band at
570 nm, with glum =À0.03 (Figure S22 in the Supporting Infor-
mation). The lower glum value of Rh-COOMe compared with
that of Rh-COOH confirms the coordination bonding plays a
key role in obtaining the high value of glum. In addi-
tion, the quantum yield maintenance for Rh-COOMe
(84%) in Zn-L1 is close to that of Rh-COOH (78%),
which indicates the presence of coordination bond-
ing may not diminish the quantum yield to a great
extent. On the other side of the coin, the fluores-
cence lifetime study shows equal lifetimes for Rh6G
in Zn-L1 colloid or in solution (both 4.4 ns, Figure S23
in the Supporting Information). Similar phenomena
were observed for Rh-COOH and Rh-COOMe, indicat-
ing the interaction between the dye molecules and
Zn-L1 colloid may not greatly influence the fluores-
cence properties, which results in the high F mainte-
nance.
It is assumed that the electrostatic interaction between
Rh6G and Zn-L1 colloids leads the small molecules of Rh6G
adopting a chiral arrangement in the vortex. If so, there is a
chance to strengthen the supramolecular interaction between
the Zn-L1 colloids and small guest molecules to improve the
glum. In the study of PDI, a fluorescence compound shown in
Figure 3d, the +2 charged nature of PDI may endow it with a
stronger electrostatic interaction with Zn-L1 colloids. However,
the photoluminescence of PDI is quenched greatly in the Zn-
L1, although the CD intensity for PDI in the stirring Zn-L1 is
quite high. It seems that the stronger electrostatic interaction
may encourage the small molecules to arrange orderly accord-
ing to the alignment of Zn-L1 colloids, but sacrifice the lumi-
In the previous study of CPL functional materials, it
was found that the chiral photoluminescence com-
pounds always possess poor glum but good quantum
yields, whereas the composites of chiral supramolec-
Figure 5. The UV/Vis absorption and PL spectra of Zn-L1+Rh6G (a) and Zn-L1+Rh-
COOH (b). The CD and CPL spectra of Zn-L1+Rh6G (c) and Zn-L1+Rh-COOH (d). ([Zn-
L1]=1.2510À3 M, [Rh6G]=[Rh-COOH]=3.010À5 M, stirring speed: 240 rpm for CD
spectra, 1000 rpm for CPL spectra).
ular architectures and photoluminescent molecules
may lead to improved glum but poor quantum yields.
Chem. Eur. J. 2021, 27, 6760 –6766
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