Tuning the Circular Dichroism and Circular Polarized Luminescence Intensities of Chiral 2D Hybrid Organic–Inorganic Perovskites through Halogenation of the Organic Ions

Article abstract of DOI:10.1002/anie.202107239

Through the incorporation of various halogen-substituted chiral organic cations, the effects of chiral molecules on the chiroptical properties of hybrid organic–inorganic perovskites (HOIPs) are investigated. Among them, the HOIP having a Cl-substituted chiral cation exhibits the highest circular dichroism (CD) and circular polarized luminescence (CPL) intensities, indicating the existence of the largest rotatory strength, whereas the F-substituted HIOP shows the weakest intensities. The observed modulation can be correlated to the varied magnetic transition dipole of HOIPs, which is sensitive to the d-spacing between inorganic layers and the halogen–halogen interaction between organic cations and the inorganic sheets. These counteracting effects meet the optimal CD and CPL intensity with chlorine substitution, rendering the rotatory strength of HOIPs arranged in the order of (ClMBA)₂PbI₄>(BrMBA)₂PbI₄>(IMBA)₂PbI₄>(MBA)₂PbI₄>(FMBA)₂PbI₄.

Full text of DOI:10.1002/anie.202107239

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Accepted Article
Title: Tuning the Circular Dichroism and Circular Polarized
Luminescence Intensities of Chiral 2D Hybrid Organic-Inorganic
Perovskites through Halogenation of the Organic Ions
Authors: Jin-Tai Lin, Deng-Gao Chen, Lan-Sheng Yang, Tai-Chun Lin,
Yi-Hung Liu, Yu-Chiang Chao, Pi-Tai Chou, and Ching-Wen
Chiu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202107239
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10.1002/anie.202107239
Angewandte Chemie International Edition
RESEARCH ARTICLE
Tuning the Circular Dichroism and Circular Polarized
Luminescence Intensities of Chiral 2D Hybrid Organic-Inorganic
Perovskites through Halogenation of the Organic Ions
Jin-Tai Lin,1, x Deng-Gao Chen,1,x Lan-Sheng Yang,2 Tai-Chun Lin,1 Yi-Hung Liu,3 Yu-Chiang
Chao,*, 2 Pi-Tai Chou,*, 1,4 and Ching-Wen Chiu*, 1
Dedication ((optional))
Abstract: By incorporating various halogen (F, Cl, Br, and I)-
substituted chiral organic cations, the effects of chiral molecules on
chiroptical properties of hybrid organic inorganic perovskite (HOIP)
are investigated. Among them, the HOIP having Cl-substituted chiral
cation exhibits the highest circular dichroism (CD) and circular
polarized luminescence (CPL) intensities, indicating the existence of
the largest rotatory strength, whereas the F-substituted one shows the
weakest intensities. The observed modulation can be correlated to the
varied magnetic transition dipole of HOIPs, which is sensitive to the
d-spacing between inorganic layers and the halogen-halogen
interaction between organic cations and the inorganic sheets.
Although a larger angular momentum of organic cation is expected as
the atomic number of the para-substituent increases, the
simultaneous increase in atom size enlarges the d-spacing of the
HOIPs, thereby lowering the magnetic transition dipole. However, the
strong halogen-halogen interaction existing in Cl-substituted system
leads to a significantly increased rotational strength. These offsetting
effects meet the optimal CD and CPL intensity with chlorine
substitution, rendering the rotatory strength of HOIPs arranged in the
lengths,[1] high dielectric constants,[2] as well as tunable optical
absorption and emission wavelengths.[3] Accordingly, HOIPs have
found numerous applications in solar cells,[4] light-emitting diodes
(LEDs)[5] and field-effect transistors (FETs).[6] In addition to their
superb solar-electric conversion efficiency, the intrinsic strong
spin-orbital coupling,[7] large Rashba splitting[8] and magneto-
photoluminescence response[9] have rendered HOIPs promising
candidates for electronic and spintronic device.[10] Moreover, in
recent years, chiral-perovskites with non-centrosymmetric
property have been widely investigated due to its ferroelectricity,
circular dichroism (CD) and circular polarized photoluminescence
(CPL) responses, which have been regarded as promising
materials in chiroptoelectronics.[11] Among them, polarized
absorption (CD) and photoluminescence (CPL) responses arise
from asymmetric absorption/emission rates of left-handed
polarized and right-handed polarized lights according to different
Einstein coefficients.[12] Thence, the observed CD/CPL responses
imply asymmetric absorption/emission rates between electron
spin up and spin down species, which follows the selection rule in
spin polarized absorption/emission.[9b, 13] To be more specific, the
order
of
(ClMBA)2PbI4>(BrMBA)2PbI4>(IMBA)2PbI4>(MBA)2PbI4>(FMBA)2PbI4. efficient spin filtering created by chiral molecules allows
The modulation of the magnetic transition dipoles of HOIP paves the
new avenue for designing hybrid perovskite-based spintronic devices.
nanoscale manipulation of quantum spins, a process that is
critical for spintronic or chiroptoelectronic applications. Therefore,
the chiroptoelectronic device featuring chiral HOIPs brings the
perovskite materials to an intensively sought-after field.[11, 14]
In 2006, Billing's group reported the first chiral two-dimensional
(2D) perovskite by introducing either R- or S-form methyl-benzyl
ammonium (MBA) ion to lead iodide perovskite.[15] However, not
until 2017 were the chiroptical properties of these two chiral
HOIPs investigated with CD by Moon's group.[16] In the following
year, spin-polarized photoluminescence of chiral HOIPs was
observed in the absence of an external magnetic field.[9b] Since
then, the chiroptical properties of chiral HOIPs featuring various
metal ions, including lead,[17] tin,[14c] copper[18] and bismuth/silver
system[14d] have been investigated. However, most of these
studies focus on chiral MBA-based perovskites to probe their
chiroptical properties. A comprehensive understanding of the
influence of the chiral organic cation on the chiroptical properties
of HOIPs remains unexplored.
Introduction
Hybrid
organic-inorganic
perovskites
(HOIPs)
have
revolutionized the field of solution-processable optoelectronic
devices owing to their long-range charge carrier diffusion
[1]
J.-T. Lin, D.-G. Chen, T.-C. Lin, P.-T. Chou, C.-W. Chiu
Department of Chemistry, National Taiwan University, Taipei, 10617
Taiwan.
E-mail: cwchiu@ntu.edu.tw
E-mail: chop@ntu.edu.tw
L.-S. Yang, Y.-C. Chao
[2]
Department of Physics, National Taiwan Normal University, Taipei
116, Taiwan.
E-mail: ycchao@ntnu.edu.tw
[3]
[4]
[x]
Y.-H. Liu
Like a pair of enantiomers, circular polarization of transmitted
light exerted by a chiral HOIP built with R-form MBA results in
optical rotatory dispersion (ORD) curves in the CD spectrum with
opposite sign and equal strength to its S-form counterpart.[14b, 17]
Instrumentation Center, National Taiwan University, Taipei 10617
Taiwan.
P.-T. Chou
Center for Emerging Materials and Advanced Devices, National
Taiwan University, Taipei, 10617 Taiwan.
equal contribution
This article is protected by copyright. All rights reserved.

10.1002/anie.202107239
Angewandte Chemie International Edition
RESEARCH ARTICLE
Figure 1. (a) XRD pattern of all the fabricated (a) S-form and (b) R-form HOIPs films as depicted in the figure. SEM cross-section images of all the fabricated
(c) S-form and (d) R-form HOIPs films. Note that the estimated thicknesses are recorded in the figure.
The same spectral features are also captured in the CPL spectra
of a pair of chiral HOIPs.[14b, 19] As the ability of a material to induce
strong spin polarization of light is critical for effective
chiroptoelectronic applications, we herein demonstrate how to
manipulate spin polarization of chiral HOIPs through
functionalization of the chiral ammonium ion.
investigated experimentally by both CD and CPL spectra from the
absorption and emission spectra of HOIPs, respectively. On the
other hand, rotatory strength can be determined theoretically by
the scalar product between the electric transition dipole moment
ꢁ
ꢁ
(ꢀ(elec. dipole)) and the magnetic transition dipole moment (ꢀ(Mag.
dipole)) of the system as depicted in eq. (2):[20a]
As circularly polarized light passes an optically active material
(i.e. chiral HOIPs), the CD signals can be obtained from the
1
ˆ
ˆ
g
R
=
Im Yg M(elec.dipole)
(mag.dipole)Yedt
Y dt • òY M
theo
e
ò
2mc
eq. (2)
difference in absorption coefficient (Dε) between left- and right-
[14d, 20]
The derivation originated from the linear displacement of the
excited electron when the electric field of the incident light
interacts with the molecule. In the meantime, the magnetic field of
the excitation source leads to a circulation of the electron, bring
both translational and rotatory motions to the excited electron
simultaneously.[20a, 20b] In short, chiroptical properties such as CD
or CPL intensity should be harnessed by the electric and magnetic
transition dipole moments of the target material.[22] In this work,
we measure the chiroptical properties of a series of chiral HOIPs,
featuring different halogen-substituted MBA derivatives as the
chiral organic spacers, and demonstrate that the intensity of CD
handed light,
and the intensity of CD signal can be
illustrated with rotatory strength as depicted in eq. (1):
3hc103 ln(10)
32p3NA
ò De
Rexp
=
dn
n
...................................................... eq. (1)
where R represents the rotatory strength of the electronic
transition between two electronic states and Dε denotes the
absorption coefficient difference.[20b] The equation reveals a
positive correlation between the rotatory strength and the intensity
of CD signal. Furthermore, the circular polarization luminosity in
CPL spectra was also found to be proportional to the rotatory
strength.[21] Thus, the rotatory strength of the HOIPs can be
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10.1002/anie.202107239
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RESEARCH ARTICLE
Figure 2. (a) The absorption (solid circle line) and normalized photoluminescence (PL, solid line) spectra of the fabricated R- (blue), S- (red) and rac- (black)
HOIPs films including (a) (FMBA)2PbI4, (b) (ClMBA)2PbI4, (c) (BrMBA)2PbI4 and (d) (IMBA)2PbI4 series as depicted in the figure, respectively. (e) Schematic
energy diagram of HOIPs.
and CPL signal can be harnessed by the chiral organic cations in
a systematic manner.
microscope (SEM). As shown in Figure 1a-b (see Figure S15 for
Rac-forms XRD), all the HOIPs exhibit a set of strong 00l
reflections, demonstrating a layered 2D perovskite structure
composed of an inorganic framework and organic layers. It is
worth noting that the 2q angle of the 001 reflection patterns
decreases sequentially from (MBA)2PbI4 (6.13o) to (IMBA)2PbI4
(5.32o). Correspondingly, the estimated d-spacing of the HOIP
films are in the order of 1.441 nm ((MBA)2PbI4) < 1.487 nm
Results and Discussion
Prior to investigating the chiroptical properties of HOIPs, a
suitable selection of the chiral organic ligands is indispensable.
To avoid optical variation resulted from the structural disturbance
of the inorganic layers, we decided to focus on the derivatives of
MBA with halogen-substitution at the para-position of the phenyl
((FMBA)2PbI4)
< 1.615 nm ((ClMBA)2PbI4) < 1.635 nm
((BrMBA)2PbI4) < 1.658 nm ((IMBA)2PbI4), which is consistent
with the atomic size of the para-substituent, implying successful
incorporation of these chiral cations. Also, the reflection patterns
are independent of the chirality of the cation (R- or S-form). Apart
from this, SEM cross-sectional images (see Figure 1c-d) reveal
that the thicknesses of the fabricated HOIP films are independent
of the para-substituents for both R- and S- forms. Thus, the
observed difference in the chiroptical spectra of chiral HOIPs
should arise from their intrinsic properties rather than the film
thickness.
The absence of significant variation in both the I-Pb-I angle and
film thickness was further corroborated by the absorption and
photoluminescence spectra of the HOIPs shown in Figure 2a-d
and Figure S18 (see Figure S18 for (MBA)2PbI4). In all cases,
the title HOIPs exhibit a sharp absorption peak at 497 nm and an
emission peak at 515 nm, which are similar to those previously
reported for (MBA)2PbI4.[14b] Notably, the comparable bandgaps
group.[23]
These
derivatives
included
1-(4-
fluorophenyl)ethanamine (FMBA), 1-(4-chlorophenyl)ethanamine
(ClMBA), 1-(4-bromophenyl)ethanamine (BrMBA), and 1-(4-
iodophenyl)ethanamine (IMBA). For a fair comparison, in addition
to the enantiopure R- and S-form derivatives, HOIPs obtained
from the racemic mixture were also prepared. These chiral HOIPs
are then named according to the chirality of the organic cation
used. For example, (R-FMBA)2PbI4, (S-FMBA)2PbI4, and (rac-
FMBA)2PbI4 represent respectively the HOIP prepared from R-
FMBA, S-FMBA, and the racemic mixture of FMBA (see
Supporting Information for details of synthetic routes).
Before discussing the chiroptical spectra of the chiral HOIPs,
we have confirmed that all materials adopt layered structure with
chiral ammonium ions sitting in between lead-iodide sheets by
powder X-ray diffraction (PXRD) and scanning electron
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Figure 3. (a) CD spectra of the R- (blue), S- (red) and rac- (black) fabricated HOIPs films including (MBA)2PbI4, (FMBA)2PbI4, (ClMBA)2PbI4 (BrMBA)2PbI4 and
(IMBA)2PbI4 series as depicted in the figure. Circular polarized photoluminescence (CPL) spectra of the R-form (black) and S-form (red) fabricated films (b)
(FMBA)2PbI4 (c) (ClMBA)2PbI4 (d) (BrMBA)2PbI4 and (e) (IMBA)2PbI4.
of the chiral HOIPs prepared suggest that the influence of the
para-substituent of the ammonium cation on the structure of the
[PbI4]2− layer is negligible.[23] Thus, any observed variation in
chiroptical properties of the title HOIPs caused by structural
deformation of the inorganic part can be minimized. More
intensity of HOIPs dropped to 10 mdeg when the para-hydrogen
atom of MBA ligand was substituted by fluorine atom
((FMBA)2PbI4). Interestingly, a CD intensity value of 90 mdeg was
observed in the (ClMBA)2PbI4 series and decreased to 60 and 30
mdeg in the (BrMBA)2PbI4 and (IMBA)2PbI4 series, respectively.
The CD results clearly showed that the magnitude of the magnetic
a
ꢁ
importantly, the value of squared ꢀ(elec. dipole) possesses a positive
correlation with the absorption coefficient expressed in eq. (3):[24]
transition dipole moments (ꢀ (Mag. dipole)) of HOIPs is strongly
ꢁ
2
dependent on the chiral organic cation.
ˆ
òedl µ M
(elec.dipole)
A related dimensionless g-factor spectrum can be derived from
the CD spectrum of HOIP. The g-factor was obtained by dividing
the differential absorbance of the circularly polarized lights (left or
right-handed polarized light) by the absorbance along with the
wavelength, making g-factor independent of sample thickness,
concentration and molecular weight.[20c] More importantly, g-factor
.......................................................eq. (3)
Combining the SEM cross-sectional images (see Figure 1c-d),
the absorption coefficient of individual HOIP can be estimated by
dividing the measured absorbance by the film thickness.
Accordingly, all the HOIPs films exhibit a similar absorption
coefficient of 7.80*106 m-1 affirming that all chiral HOIPs have
comparable intrinsic electric transition dipole moments. Therefore,
any chiroptical property changes could be ascribed to the change
in the magnetic transition dipole moment of the perovskite
induced by the chiral ammonium cation.
ꢁ
is proportional to the magnetic transition dipole moment (ꢀ(Mag.
dipole)) but inversely proportional to the electric transition dipole
moment (ꢀ(elec. dipole)).[20a] As shown in Figure S20, (ClMBA)2PbI4
ꢁ
and (BrMBA)2PbI4 series exhibit the largest g-factor values about
3.1*10-3 and 2.2*10-3 among all investigated HOIPs, respectively.
On the other hand, the (FMBA)2PbI4 series exhibit the smallest g-
factor values of 3.0*10-4, which is an order of magnitude smaller
than that of (ClMBA)2PbI4 series. Together with the observations
By incorporating the chiral organics into HOIPs, all the
fabricated films exhibit spin-polarized absorptions in the visible
region ranging from 400 to 530 nm as illustrated in Figure 3a.
Note that the absorption bands of MBA salt derivatives are
centered around 275 nm (see Figure S19 for the absorption
spectra of the organic salts); the observed CD absorption in the
visible region of the chiral HOIPs should be viewed as an optical
response originating from the inorganic layers of HOIPs. Hence,
the detection of CD response in the visible region implies that the
chirality of the organic cations is successfully transferred to the
perovskite inorganic quantum sheets. In terms of the chiroptical
properties, the varied CD intensities are of particular interest. The
non-substituted chiral MBA perovskite film (i.e. (R-MBA)2PbI4 and
(S-MBA)2PbI4) exhibit a maxima CD value around 20 mdeg, which
is comparable to the previous report.[17] However, the maxima CD
ꢁ
in absorption spectra where similar ꢀ
has been
(elec. dipole)
confirmed (vide supra), it is unambiguous to conclude the larger
ꢁ
ꢀ(Mag. dipole) in (ClMBA)2PbI4 and (BrMBA)2PbI4 series among the
title HOIPs. In yet another approach, CPL spectra of the
fabricated films are also recorded in Figure 3b-e and Figure S21.
The results clearly indicate that the Cl-substituted HOIPs exhibit
the strongest CPL intensities, whereas the F-substituted ones
show the lowest CPL intensities, revealing the consistent
chiroptical properties of the films from the emission’s perspective.
The photophysical properties and the transition dipole moments
were estimated theoretically to gain more insight into the chiral
perovskites as tabulated in Table S1. The fitted lifetimes and the
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10.1002/anie.202107239
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RESEARCH ARTICLE
(a)
(b)
(c)
100
Title perovskite
Cl
Linear fit
Linear fit
80
60
40
20
0
Br
I
H
F
1.0 1.1 1.2 1.3 1.4 1.5 1.6
3rd power of d-spacing ratio (a.u.)
Figure 4. (a) Plots of the g value of CPL spectra at 535 nm (emission wavelength) versus the 3rd power of d-spacing of HOIPs. Herein, the black line represents
a linear regression for (MBA)2PbI4 and (FMBA)2PbI4. Also, the blue line corresponds to one with r2 = 0.9957 for (ClMBA)2PbI4, (BrMBA)2PbI4 and (IMBA)2PbI4
series. The red dashed square indicates the region of a significantly enhanced halogen-halogen interaction. Crystal structure of (b) Cl-substituted and (c) F-
substituted chiral perovskite, where dark gray, purple, green, yellow, blue, light gray, and white balls represent Pb, I, Cl, F, N, C and H atoms, respectively.
PLQYs were recorded and employed to calculate the radiative
rate constants and the electronic transition dipole moments of the
perovskite films. The calculated radiative rate constants are
ranging from 3.18×107 to 4.53×107 (s-1) for all the films, which are
similar with the reported perovskite systems (6.2×107 s-1).[25]
Meanwhile, the calculated electronic transition dipole moments
show no obvious variance in the MBA perovskite system,
affirming the experimental observation in absorption coefficient
(vide supra). Additionally, gPL values and the calculated electric
transition dipole moments were employed to estimate the
magnetic transition dipole moments.[25-26] The estimated magnetic
transition dipole moments show the trend of 1.43×10-1 µB
((ClMBA)2PbI4) > 9.58×10-2 µB ((BrMBA)2PbI4) > 6.33×10-2 µB
momentum resulted from electronic transition. Given that all
HIOPs investigated in this study display comparable absorption
and emission profiles with nearly identical absorption coefficients,
the obtained variation in gPL should originate from the magnetic
transition dipole moment term. Accordingly, the magnetic dipole
matrix element (Mif) expressed as eq. (4) can be related to the
⇀
sum of the orbital angular momentum (L )and the electron spin
⇀
⇀
⇀
angular momentum ( S ). However, the L and S of the chiral
HOIPs could not be determined with computational methods.
!
!
Mif = i L+2S f
.............................................................eq. (4)
Since the angular momentum of a single atom is positively
related to its atomic number, we decided to look for the correlation
between the gPL and the atomic properties of the para-
((IMBA)2PbI4) > 2.42×10-2 µB ((MBA)2PbI4)
>
1.17×10-2 µB
((FMBA)2PbI4), where µB is the Bohr magneton, and the trend is
in good agreement with our experimental results. It is worth to
note that this kind of estimation in magnetic transition dipole
moment make an assumption in the incident angle (q) between
magnetic and electric transition dipole to be 0 degree, making the
results hard to be compared with different material systems.
In order to investigate whether the observed variation in CD and
CPL intensities of chiral HOIPs could be ascribed to the intrinsic
property of the chiral components, rotatory strength of the R-form
chiral molecules were estimated using time-dependent density
functional theory (TD-DFT) method at B3LYP/LANL2DZ level of
theory (see Table S7 in Supporting Information).[20b, 27] However,
the calculated rotatory strength of chiral molecule seems erratic
(Table S7) and shows no apparent correspondence with the gPL
of HOIPs. As illustrated in Figure S33a, the observed gPL of
HOIPs seems irrelevant to the rotatory strength of the organic
ligands, suggesting that the chiroptical properties of the HOIPs
cannot be directly deduced from the optical property of chiral
organic molecules. In other words, the contribution of the achiral
inorganic layer cannot be ignored.
substituents. As the atomic number increases from 1 (for H) to 53
(for I), we expect to observe a more pronounced effect of L on Mif,
⇀
which should lead to a higher rotatory strength. However, plotting
the maxima gPL versus atomic number, atomic weight, or
polarizability does not result in a conclusive argument, suggesting
that the theory developed for the discrete molecular system needs
to be modified for application in materials (Figure S33b-d).
As the optoelectronic properties of a material are strongly
associated with the packing of its molecular units in the solid-state,
we hypothesize that the chiroptical properties of HOIPs may also
be derived from the structural variations of HOIPs. The first
structure-property relationship identified is the d-spacing effect on
the gPL value obtained from CPL spectra. As illustrated in Figure
4a (or see Figure S27 in Supporting Information for a plot using
CD intensity), the rotatory strength (i.e. g value) of chiral HOIPs
declines as the d-spacing enlarged. While the smaller CD
intensity of (FMBA)2PbI4 compared to (MBA)2PbI4 can be
rationalized by the larger d-spacing of the former, a more
pronounced trend is identified in the Cl, Br, and I-series. The
observed gPL value is reversely proportional to the third power of
d-spacing within the (ClMBA)2PbI4, (BrMBA)2PbI4, and
As expressed in eq. (2), the theoretical rotatory strength of a
system is a product of the electric transition dipole moment and
the magnetic transition dipole moment. According to the
derivations summarized in the supporting information, the electric
dipole matrix is associated with the difference of the electron
ꢁ
(IMBA)2PbI4 series, indicating a smaller ꢀ(Mag. dipole) of HOIP with
a larger d-spacing.
However, the abrupt increase in gPL value from (FMBA)2PbI4 to
(ClMBA)2PbI4 cannot be explained by the d-spacing differences.
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10.1002/anie.202107239
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RESEARCH ARTICLE
organic cations and perovskite films are provided. Also, the
corresponding characteristic analysis and computer calculation
are included.
Thus, in addition to d-spacing, there should be another structural
factor that strongly affects the Mif of HOIPs. As the d-spacing is a
measure of the distance between inorganic layers, the relative
orientation involving chiral organic cations cannot be derived from
the PXRD patterns of the HOIP thin film. Therefore, single crystals
of (FMBA)2PbI4 and (ClMBA)2PbI4 were obtained, and their
structural differences are scrutinized. The most obvious structural
difference observed in (ClMBA)2PbI4 is the alignment of the chiral
ammonium ion with the inorganic layer through the interaction of
the para-chlorine atom and the axial iodine of the [PbI4]2- layer
with a C-Cl-I angle of around 173o (Figure 4b). However, the
related C-F-I angle of 132o (similar to C-H-I angle of 134o in
(MBA)2PbI4 as demonstrated in Figure S16) significantly deviates
from linearity, implying the lack of halogen-halogen interaction in
(FMBA)2PbI4 (Figure 4c). Such interaction would help fix the
relative orientation of chiral molecules,[28] leading to a more
regular structure and a stronger overall angular momentum for the
whole material.
Acknowledgements
This research was supported by the Ministry of Science and
Technology of Taiwan (MOST-109-2124-M-002-011; MOST-109-
2639-M-002-001-ASP).
Conflict of interest
The authors declare no conflict of interest.
Keywords: Chiral • Perovskite • Rotatory strength • Circular
ꢁ
In short, our results indicate that the ꢀ(Mag. dipole) term of the
dichroism • Circular polarized luminescence
rotatory strength of HOIPs could be harnessed by interplaying the
d-spacing and the halogen-halogen interaction. As the d-spacing
enlargement from H to I leads the reduced rotatory strength in
HOIPs, the introduction of heavy atom at the para-position of the
phenyl group of MBA is in favor of halogen-halogen interaction.
Eventually, these offsetting effects lead to the optimal CD and
CPL intensity with chlorine substitution, rendering the rotatory
strength and hence trend of circular dichroism intensity of the title
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Conclusion
In summary, we have explored the chiroptical properties of a
series of chiral HOIPs by incorporating chiral ammonium cations
with different para-substituent at the phenyl ring of MBA. Varying
the para-substituent from hydrogen to halogen atoms leads to
markedly modulation in the CD and CPL intensities. The Cl-
substituted HOIPs exhibit the strongest CD intensity among the
chiral organic cations investigated, whereas the F-substituted
ones feature the weakest CD response. The observed CD
intensity is found to be generally associated with the d-spacing of
HOIPs, where the increase in d-spacing will lead to a decrease in
rotatory strength. However, the strong halogen-halogen
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enhanced rotational strength. As a result, the Cl-substituted
HOIPs with the optimal angular momentum and d-spacing exhibit
the highest magnetic transition dipole and display the highest
rotational strength among the fabricated HOIPs. Thus, the
modulation of the magnetic transition dipoles of HOIPs can be
utilized for further designing the spintronic devices with high-
performance chiroptical properties.
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Associated Content
Supporting Information. The supporting information is available
free of charge via the Internet. Synthetic methods for chiral
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Through incorporating Cl-substituted chiral organic cations, chiroptical properties of 2D chiral perovskite
can be significantly enhanced. The observed CD and CPL intensities are found to be associated with the
d-spacing of HOIPs and the strength of the halogen-halogen interaction within the system. These findings
can be utilized for further development of spintronic devices with high-performance chiroptical properties.
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