Targeted Synthesis of Trimeric Organic-Bromoplumbate Hybrids That Display Intrinsic, Highly Stokes-Shifted, Broadband Emission

Article abstract of DOI:10.1021/acs.chemmater.9b03925

Zero-dimensional (0D) hybrid organic-inorganic lead halides have been shown to display efficient broadband photoluminescence and are, therefore, of significant interest for artificial lighting applications. However, work that investigates the formability of the materials as a function of templating organic cation structure is rare. This severely limits our ability to rationally design new materials displaying specific structural and photophysical properties. With the goal of accessing rare 0D trimeric bromoplumbates, we have systematically varied templating N-alkylpyridinium cations and examined their impact upon inorganic lattice structure. Whereas comparatively short and flexible N-alkyl substituents (ethyl, 2-hydroxyethyl, and pentyl) yield one-dimensional (1D) inorganic chains, more rigid substituents (benzyl, acetamidyl, and cyanomethyl) afford hybrids composed of lead bromide face-sharing trimers (i.e., [Pb3Br12]6-). Of the rigid substituents studied, benzyl groups were found to enforce the highest level of distortion of the [PbBr6]4- octahedra that comprise their trimeric structures. Upon exposure to ultraviolet (UV) light, N-benzylpyridinium lead bromide (1)6[Pb3Br12] exhibits a broadband emission, centered at 571 nm, which spans from 400 to 800 nm. More specifically, it displays a large Stokes shift of ca. 1.39 eV and a full width at half-maximum of ca. 146 nm. This broadband emission decays with a comparatively long lifetime of 426 ns at room temperature, which increases to 5.8 μs at 77 K. The reduced size and dimensionality of its inorganic lattice also result in a photoluminescence quantum yield (of at least 10%) that is approximately one order of magnitude higher than that of its 1D congeners. Mechanistically, broadband emission in (1)6[Pb3Br12] is believed to originate from triplet excited state(s) obtained from excited-state structural reorganization of the [Pb3Br12]6- moiety.

Full text of DOI:10.1021/acs.chemmater.9b03925

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Article
Targeted synthesis of trimeric organic-bromoplumbate hybrids
that display intrinsic, highly Stokes-shifted, broadband emission
Benny Febriansyah, Chong Shern Daniel Neo, David Giovanni, Shivani Srivastava, Yulia Lekina, Teck
Ming Koh, Yongxin Li, Ze Xiang Shen, Mark Asta, Tze Chien Sum, Nripan Mathews, and Jason England
Chem. Mater., Just Accepted Manuscript • Publication Date (Web): 01 May 2020
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Chemistry of Materials
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Targeted synthesis of trimeric organic-bromoplumbate hybrids that
display intrinsic, highly Stokes-shifted, broadband emission
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Benny Febriansyah,a,b,c Chong Shern Daniel Neo,a David Giovanni,d Shivani Srivastava,e Yulia Lekina,d
Teck Ming Koh,b Yongxin Li,a Ze Xiang Shen,d Mark Asta,e Tze Chien Sum,d Nripan Mathewsb,f,* and
Jason England.a,*
aDivision of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological
University, 21 Nanyang Link, Singapore 637371.
bEnergy Research Institute at Nanyang Technological University (ERI@N), Research Techno Plaza, X-Frontier Block Level
5, 50 Nanyang Drive, Singapore 637553.
cInterdisciplinary Graduate School (IGS), Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
dDivision of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological Universi-
ty, 21 Nanyang Link, Singapore 63737.
eDepartment of Materials Science and Engineering, University of California, Berkeley, California 94720, United States
fSchool of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
ABSTRACT: Zero-dimensional (0D) hybrid organic-inorganic lead halides have been shown to display efficient broadband photo-
luminescence and are, therefore, of significant interest for artificial lighting applications. However, work that investigates the form-
ability of the materials as a function of templating organic cation structure are rare. This severely limits our ability to rationally
design new materials displaying specific structural and photophysical properties. With the goal of accessing rare 0D trimeric bro-
moplumbates, we have systematically varied templating N-alkylpyridinium cations and examined their impact upon inorganic lat-
tice structure. Whereas comparatively short and flexible N-alkyl substituents (ethyl, 2-hydroxyethyl, and pentyl) yield one-
dimensional (1D) inorganic chains, more rigid substituents (benzyl, acetamidyl, and cyanomethyl) afford hybrids composed of
lead-bromide face-sharing trimers ([Pb3Br12]6-). Of the rigid substituents studied, benzyl groups were found to enforce the highest
level of distortion of the [PbBr6]4- octahedra that comprise their trimeric structures. Upon exposure to ultra-violet (UV) light, N-
benzylpyridinium lead-bromide (1)6[Pb3Br12] exhibits a broadband emission, centered at 571 nm, which spans from 400 to 800 nm.
More specifically, it displays a large Stokes shift of ca. 1.39 eV and a full width at half maximum (FWHM) of ca. 146 nm. This
broadband emission decays with a comparatively long lifetime of 426 ns at room temperature, which increases to 5.8 µs at 77 K.
The reduced size and dimensionality of its inorganic lattice also results in a photoluminescence quantum yield (at least 10 %) that is
approximately one order magnitude higher than that of its 1D congeners. Mechanistically, broadband emission in (1)6[Pb3Br12] is
believed to originate from triplet excited state(s) obtained from excited-state structural reorganization of the [Pb3Br12]6- moiety.
INTRODUCTION
wavelengths.10-15 Such properties render the low-dimensional
materials promising phosphors for artificial illumination.
In recent years, organic-inorganic metal halide hybrids have
been intensively investigated due to the exceptional versatility
of their structural and optoelectronic properties.1-3 When ap-
propriate organic and inorganic components are chosen, the
connectivity of their constituent metal halide polyhedra can be
tuned to provide three- (3D), two- (2D), one- (1D), or zero-
dimensional (0D) anionic inorganic architectures.4-9 Such
structural variety implies that there is a vast parameter space
available for exploration of novel structures that may exhibit
new and useful features. For example, lowering the dimen-
sionality of the inorganic lattice leads to more localized elec-
tronic states and, consequently, narrower conduction and va-
lence bands. This promotes self-trapping of excitons and
yields stronger exciton emission. As a result, unlike the nar-
row, weakly Stokes-shifted emission bands, typically, ob-
served in 3D metal halide hybrids, 2D, 1D and 0D materials
have been shown capable of displaying efficient and heavily
Structurally, 2D metal halide hybrids can be viewed as be-
ing derived from their 3D counterparts by slicing the inorganic
lattice along either the (100), (110), or (111) crystallographic
16
planes.1-3, These 2D structures are typically templated by
long, narrow organic cations containing primary ammonium
functionality, which permit efficient packing and exhibit
strong H-bonding interactions with the inorganic lattice.1-3, 16
Although early observations of broadband emission in 2D
perovskites were limited to comparatively rare corrugated
(110)-oriented structures,17-18 the more common (100) variants
were also later shown to exhibit similar broad PL features,
albeit with a strong dependence on temperature.19-20 The phys-
ical origin of the broadband emission in these materials has
been attributed to transient self-trapping of excitons in the
inorganic lattice, which relax radiatively (to the ground state)
from a broad and structurally distorted excited state.14,
21-22
Stokes-shifted luminescence, at
a
wide range of
Although organic-inorganic metal halides are often considered
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to be similar to inorganic semiconductors, with extended band 2D perovskites with different interoctahedral connectivity that
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structures, it has been suggested that exciton self-trapping in
these materials involves excited state structural reorganization
(distortion and/or bond breaking).23-24 This results in conver-
sion of delocalized excitons to localized excitons. Alternative-
ly, it has been proposed that permanent color centers, such as
positive and negative ion vacancies, and atoms in interstitial
sites, are responsible for the observed exciton trapping and
luminescence processes.25
endow the materials with favorable white-light emitting be-
havior.47 The unifying theme across these studies is the use of
cyclic cations, such as pyridiniums, with appended alkyl sub-
stituents, which are straightforward to structurally vary and
prepare.
Utilizing the aforementioned cyclic ammonium cation mo-
tifs, we sought to access comparatively rare trimeric bromo-
plumbate compounds. To this end,
a series of N-
Meanwhile, inclusion of organic cations containing sterical-
ly hindered charge centers can lead to 1D structures, in which
the metal-halide octahedra arrange in chains via different con-
nectivity modes (face-, corner-, or edge-sharing).1-3, 6 In addi-
tion, 0D hybrids consisting of discrete molecular mono- or
oligometallate structures can be obtained with organic cations
possessing rigid and/or bulky substituents.1-4 As a consequence
of pronounced structural distortion upon photoexcitation, these
alkylpyridinium salts were prepared and used to template for-
mation of new low dimensional organic-inorganic lead bro-
mide hybrids (1 – 6; Fig. 1). Based upon literature
precedent,46, 48-49 it was anticipated that inclusion of flexible
and short N-alkyl substituents, such as ethyl (4), pentyl (5) and
2-hydroxyethyl (6), would result in assembly of 1D inorganic
chains. The coulombic interactions between the pyridinium
rings and inorganic lattice, in such systems, cause the former
to orientate parallel to the latter. These interactions are distinct
from those that dominate in 2D perovskites, where H-bonding
interactions associated with the ammonium functionality of
the cations are a controlling factor.2, 16, 50 By extension, it was
postulated that relatively rigid N-alkyl substituents, such as
benzyl (1), acetamidyl (2) and cyanomethyl (3), would in-
crease the effective steric impact of the organic cation and,
thereby, cause a further reduction of the dimensionality of the
bromoplumbate. This proved to be true and allowed synthesis
of a handful of rare trimeric bromoplumbates. We performed
detailed studies of the optical properties of one of them,
(1)6[Pb3Br12], and found that it displays heavily Stokes-shifted,
broadband emission that is more efficient than it’s 1D ana-
logues.
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materials typically display broadband emissions with large
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Stokes shifts.7-8,
Furthermore, owing to abundant exciton
self-trapping states and enhanced electron-phonon coupling in
their organic-inorganic ‘host-guest’ lattices, highly efficient
PL has been demonstrated for 1D and 0D hybrid materials.11-12,
27-32 In particular, broadband emission with photoluminescence
quantum efficiencies (PLQE) of up to 10 – 20 % have been
reported for 1D hybrids. Further reducing the dimensionality
to 0D clusters was shown to allow for further improvement of
the PLQE to near unity values.
As might be inferred from the aforementioned reports, the
efficiency of PL emission from metal halide hybrids is highly
sensitive to dimensionality of the inorganic lattice and the
nature of the templating cations. Thus, any work that contrib-
utes to our understanding of the molecular design criteria re-
quired for successful formation of 0D structures, which dis-
play broadband emission of superior efficiency, is of signifi-
cant value. Unfortunately, despite the plethora of reports de-
tailing 1D and 0D metal-halide hybrids templated by organic
cations of diverse architectures, including those based around
36-39
hydrocarbon-,11, 33-35 heteroatom-endowed linear aliphatic,
cyclic aliphatic,7, 26, 40-41 and aromatic moieties,31-32, 42-43 sys-
tematic studies of the impact of cation structure upon inorgan-
Figure 1. The N-alkylpyridinium cations used in this work.
ic lattice structure and PL properties are still relatively
38, 44
scarce.35,
Instead, the overwhelming majority of works
EXPERIMENTAL METHODS
involve the use of largely, unrelated organic cations, which
make structural analysis difficult. As a result, our ability to
rationally dictate the dimensionality of the materials through
the modification of organic cations is limited and accessing
materials with specific inorganic lattice fine structure is rather
hit-and-miss.
Chemicals. Lead(II) bromide (99.999%), Lead(II) chloride
(99.999%), Lead(II) iodide (99.999%), bromoethane (≥99%),
1-bromopentane (98%), 2-bromoethanol (95%), and 2-
bromoacetamide (98%) were obtained from Sigma Aldrich,
while pyridine (anhydrous, 99.5+%), α-bromotoluene (99%),
2-bromo-acetonitrile (96%), and α-chlorotoluene (99%) were
purchased from Alfa Aesar. Unless otherwise stated, all rea-
gents were used without purification.
Our group is interested in investigating the impact of sys-
tematic variation of templating organic cation upon the struc-
ture of self-assembled low-dimensionality lead halide inorgan-
ic lattices, and its concomitant influence upon their photophys-
ical properties. For instance, we have shown that appending
hydrogen bonding functionalities to viologens can induce their
dimerization and endow the resulting 1D materials with pho-
toconductivity.45 In addition, we reported the role of primary
Synthesis. The following general procedure was used to
synthesize the N-alkylpyridinium bromide salts: a round bot-
tom flask was charged with pyridine (1 equiv) and 1.1 equiv of
the requisite bromoalkyl reagent. Acetonitrile was added and
resulting mixture was stirred at reflux, under an argon atmos-
phere, for 1 – 2.5 days. The course of the reaction was moni-
+
ammonium groups (-NH3 ) as a prerequisite for formation of
2D lead-halide perovskites.46 Neutral (i.e. uncharged) H-bond
donor functional groups, such as hydroxyl, carboxyl, and car-
bonamide were, on the other hand, found to result in formation
of 1D structures. We further demonstrated that slight modifi-
cation in organic cation structure would lead to formation of
1
tored using H NMR spectroscopy and, upon completion, it
was allowed to cool to room temperature. The precipitate ob-
tained was isolated by filtration, washed thoroughly with di-
ethyl ether, and dried in vacuo to give the desired products.
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Chemistry of Materials
1-(benzyl)pyridin-1-ium bromide, (1)Br. Isolated as a
brown solid (1.37 g; 90% yield). H NMR (400 MHz, DMSO-
d6): δ 9.36 (d, 2 H, ArH), 8.65 (dd, 1 H, ArH), 8.20 (dd, 2 H,
ArH), 7.60 (dd, 2 H, ArH), 7.41 (m, 3 H, ArH), 6.00 (s, 2 H,
CH2). 13C{1H} NMR (100 MHz, DMSO-d6): δ 146.0, 144.8,
134.3, 129.3, 129.2, 128.8, 128.4, 63.0.
X-ray crystallography. Crystals were mounted on a
Bruker X8 Quest CPAD area detector diffractometer and data
was collected using a IμS 3.0 Microfocus Mo-Kα radiation
source (λ = 0.71073 Å), at cryogenic temperatures (100 K).
Data reduction and absorption corrections were performed
using the SAINT and SADABS software packages, respective-
ly.51 All structures were solved by direct methods and refined
by full-matrix least squares procedures on F2, using the Bruker
SHELXTL-2014 software package.52-53 Non-hydrogen atoms
were anisotropically refined, after which hydrogen atoms were
introduced at calculated positions and the data was further
refined. The graphical illustrations of crystal structures used
throughout the main paper and supporting information were
created using the program VESTA.54
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1-(acetamidyl)pyridin-1-ium bromide, (2)Br. Isolated as
a white solid (1.11 g; 91% yield). 1H NMR (400 MHz,
DMSO-d6): δ 8.97 (d, 2 H, ArH), 8.65 (dd, 1 H, ArH), 8.18
(dd, 2 H, ArH), 8.02 (s, 1 H, C(O)NH2), 7.69 (s, 1 H,
C(O)NH2), 5.41 (s, 2 H, CH2). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 166.0, 146.2, 146.0, 127.4, 61.5.
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1-(cyanomethyl)pyridin-1-ium bromide, (3)Br. Isolated
1
as a white solid (0.78 g; 83% yield). H NMR (400 MHz,
Powder X-ray diffraction. Powder X-ray diffraction
measurements were conducted using a Bruker AXS D8
ADVANCE system containing a Cu K radiation source ( =
1.5418 Å). The XRD spectra were recorded with an incident
angle of 5, a step size of 0.05, and a delay time of 1s for
each step.
DMSO-d6): δ 9.16 (d, 2 H, ArH), 8.71 (dd, 1 H, ArH), 8.23
(dd, 2 H, ArH), 5.99 (s, 2 H, CH2). 13C{1H} NMR (100 MHz,
DMSO-d6): δ 147.6, 145.5, 128.6, 114.3, 47.7.
1-(ethyl)pyridin-1-ium bromide, (4)Br. Isolated as a
1
white solid (1.25 g; 84% yield). H NMR (400 MHz, DMSO-
d6): δ 9.28 (d, 2 H, ArH), 8.63 (dd, 1 H, ArH), 8.17 (dd, 2 H,
ArH), 4.72 (q, 2 H, CH2), 1.52 (t, 3 H, CH3). 13C{1H} NMR
(100 MHz, DMSO-d6): δ 146.0, 145.2, 128.6, 56.8, 16.9.
Density Functional Theory (DFT) Calculations. First-
principles DFT calculations were performed to investigate the
electronic structure of the compound (1)6[Pb3Br12]. Calcula-
tions considered a 495-atom unit cell with atomic positions
taken from the refined experimental structure, without further
optimization. DFT calculations were performed using version
5.4.4 of the Vienna Ab initio Simulation Package (VASP),55
employing the Perdew-Burke-Ernzerhof (PBE) Generalized
Gradient Approximation (GGA)56 exchange-correlation func-
tional, with explicit inclusion of spin-orbit-coupling terms
employing the approach implemented in VASP. The electron-
ion interactions were described with the projector-augmented-
wave (PAW)57 method as implemented in VASP.58 PAW po-
tentials labeled “PAW_PBE C 08Apr2002”, “PAW_PBE N
08Apr2002”, “PAW_PBE H 15Jun2001”, “PAW_PBE Pb
08Apr2002”, and “PAW_PBE Br 06Sep2000” were employed
for C, N, H, Pb and Br, respectively. A plane wave cutoff en-
ergy of 440 eV was used for the expansion of wavefunctions.
For Density of States (DOS) calculations, the tetrahedron
method with Blöchl corrections59 was used and the Brillouin
zone was sampled on a kpoint mesh of 2 × 2 × 2. The elec-
tronic band structure was evaluated along the special k-point
paths in the Brilllouin zone.
1-(pentyl)pyridin-1-ium bromide, (5)Br. Isolated as a
yellow solid (1.22 g; 91% yield). 1H NMR (400 MHz, DMSO-
d6): δ 9.20 (d, 2 H, ArH), 8.63 (dd, 1 H, ArH), 8.18 (dd, 2 H,
ArH), 4.66 (t, 2 H, CH2), 1.92 (m, 2 H, CH2), 1.33 (m, 4 H,
CH2), 0.85 (t, 3 H, CH3). 13C{1H} NMR (100 MHz, DMSO-
d6): δ 145.5, 144.7, 127.9, 60.2, 30.4, 27.2, 21.4, 13.5.
1-(2-hydroxyethyl)pyridin-1-ium
bromide,
(6)Br.
1
Isolated as a brown solid (0.94 g; 88% yield). H NMR (400
MHz, DMSO-d6): δ 9.09 (d, 2 H, ArH), 8.63 (dd, 1 H, ArH),
8.17 (dd, 2 H, ArH), 4.73 (t, 2 H, CH2), 3.86 (t, 2 H, CH2).
13C{1H} NMR (100 MHz, DMSO-d6): δ 145.7, 145.2, 127.7,
63.1, 60.0.
1-benzylpyridin-1-ium chloride, (1)Cl. Isolated as pale
1
yellow oil (1.12 g; 85% yield). H NMR (400 MHz, DMSO-
d6): δ 9.29 (d, 2 H, ArH), 8.63 (dd, 1 H, ArH), 8.19 (dd, 2 H,
ArH), 7.59–7.40 (m, 5 H, ArH), 5.91 (s, 2 H, CH2). 13C{1H}
NMR (100 MHz, DMSO-d6): δ 146.0, 144.9, 134.3, 129.4,
129.2, 128.8, 128.5, 63.2.
1-benzylpyridin-1-ium iodide, (1)I. Isolated as brown sol-
1
id (1.17 g; 83% yield). H NMR (400 MHz, DMSO-d6): δ
9.20 (d, 2 H, ArH), 8.64 (dd, 1 H, ArH), 8.19 (dd, 2 H, ArH),
7.58–7.38 (m, 5 H, ArH), 5.88 (s, 2 H, CH2). 13C{1H} NMR
(100 MHz, DMSO-d6): δ 146.0, 144.8, 134.3, 129.4, 129.2,
128.8, 128.5, 63.3.
UV-vis spectroscopy. UV-vis spectra of polycrystalline
samples were collected using a Shimadzu UV-3600 UV-VIS-
NIR Spectrophotometer, with BaSO4 as the 100% reflectance
reference. The measurements were conducted over a 300 –
800 nm wavelength range, in the diffuse reflectance mode,
using an integrating sphere, and a scanning resolution of 0.5
nm s-1. Relative absorbance was obtained from Kubel-
ka−Munk transformation of the reflectance spectra: α/S = (1 −
R)2(2R)-1, where R is the reflectance, and α and S are the ab-
sorption and scattering coefficients, respectively.
Crystal growth. In general, vials were charged with con-
centrated solutions (~0.25 – 0.33 M) composed of stoichio-
metric amounts of PbBr2 and N-alkylpyridinium halide salt
dissolved in dimethyl sulfoxide (DMSO), after which the anti-
solvent acetone was introduced by the vapor diffusion method,
under ambient conditions. The single crystals, which formed
within 2 – 7 days (~37-72% yield based on Pb content), were
either used in X-ray crystallographic studies or isolated and
dried in vacuo for further characterization.
Steady-state, time-resolved, temperature- and power-
dependent photoluminescence (PL) spectroscopies. Sam-
ples were photoexcited with 325 nm femtosecond laser pulses,
generated using an optical parametric amplifier (OPA, Coher-
ent OPerA Solo). The OPA was powered by a Coherent
LIBRA laser, with a fundamental wavelength of 800 nm and
output pulse-width of ~50 fs, at a repetition rate of 1 kHz. The
PL signal was collected using a lens pair and sent to a spec-
trometer (Princeton Instrument, SP-2500 series), where it was
1
Nuclear Magnetic Resonance (NMR) spectroscopy. H
and 13C{1H} NMR spectra of organic compounds were record-
ed in DMSO-d6 solution using a Bruker AV400 spectrometer.
Chemical shift values (ppm) are referenced against residual
protic solvent peaks.
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Figure 2. Single crystal X-ray structures of the 1D lead bromide hybrids a) 4[PbBr3], b) 5[PbBr3] and c) 6[PbBr3]. Dark gray,
brown, gray, blue and red spheroids represent Pb, Br, C, N and O atoms, respectively. H atoms are omitted for clarity. Thermal
ellipsoids are shown at 50% probability.
detected by a CCD camera (Pixis-400) or a streak camera (Op-
tronis) in steady-state and TRPL measurements, respectively.
The power-dependent measurements were obtained in this
configuration by changing the excitation power in the range of
2.5 – 40 µW, using a set of variable density filters. For tem-
perature-dependent studies, the samples were mounted onto a
liquid nitrogen-cooled Janis st-300 cryostat, adjusted to the
optical plane of the inverted microscope, and measured within
the temperature range 77 – 293 K.
C-H···Br intermolecular interactions between the bromoplum-
bate chains and pyridinium cations, the main driving force for
crystal packing is likely to be Coulombic interactions. This
notion is supported by the tendency of the pyridinium rings to
align parallel to the inorganic lattices, which minimizes sepa-
ration of the opposing charges of these two components. Fur-
thermore, the structures of 5[PbBr3] and 6[PbBr3] (Figs. 2b
and 2c), whose cations contain pentyl and 2-hydroxyethyl
substituents, respectively, show similar properties. This sug-
gests that long-chain linear N-alkyl substituents and those with
neutral H-bond donor functionality, do not interfere with self-
assembly of the 1D Pb-Br polymeric chains.
Photoluminescence quantum yield. Samples were photo-
excited with 325 nm femtosecond laser pulses, generated us-
ing an optical parametric amplifier (OPA, Coherent OPerA
Solo). The OPA was powered by a Coherent LIBRA laser,
with a fundamental wavelength of 800 nm and output pulse-
width of ~50 fs, at a repetition rate of 1 kHz and 2.5 µW.
Table 1. List of selected bond lengths (Å) from the single
crystal X-ray structures of (1)6[Pb3Br12], (2)6[Pb3Br12],
(3)6[Pb3Br12], 4[PbBr3], 5[PbBr3], and 6[PbBr3].
Raman spectroscopy. Raman scattering measurements
were performed using a WITec alpha 300RAS confocal Ra-
man microscope. An Acton spectrometer with a diffraction
grating of 1800 grooves mm-1 (1.3 cm−1 resolution) and a
thermoelectrically cooled Andor CCD detector were used to
collect data. To avoid absorption by the samples, which could
lead to photoluminescence and degradation, the 633 nm (red)
line from a He−Ne gas laser with a power of 5 mW was cho-
sen, while the laser spot area was ~1 μm2. The backscattered
Raman signal passed through two 633 nm BragGrate Notch
Filters (BNF). Measurements at 80 K were conducted under a
nitrogen gas flow cryostat.
β
Pb−(μ2-Br) α
Pb−Brt
Pb−Pb
Compounds
(1)6[Pb3Br12]
(2)6[Pb3Br12]
(3)6[Pb3Br12]
4[PbBr3]
3.0016(4),
3.1665(5)
2.9219(5)
3.9345(5)
3.0583(4),
3.2722(6)
2.8764(4)
3.8458(5)
2.9746(16) -
3.2225(17)
2.8423(17) -
2.9678(16)
3.8143(10) -
3.9365(10)
2.8185(12) -
3.3633(12)
3.9456(16)
5[PbBr3]
2.9895(8) -
3.3423(11)
2.7861(8)
3.9797(5)
RESULTS AND DISCUSSION
6[PbBr3]
2.8874(9) -
3.2526(12)
3.8667(7) -
3.9275(7)
X-ray crystal structures of the N-alkylpyridinium-templated
compounds containing 1D bromoplumbate chains and trimeric
bromoplumbates are shown in Figures 2 and 3, respectively.
(Selected bond lengths are provided in Table 1, and more ex-
tensive lists of structural parameters, plus crystallographic and
refinement data, are provided in the Supporting Information.)
As anticipated, employing flexible N-alkyl substituents leads
to formation of 1D polymeric chains of the monomer [PbBr3]-.
This is exemplified by the cation N-ethylpyridinium (4), where
the 1D chains in 4[PbBr3] (Figure 2a) are built from face-
sharing of its constituent [PbBr6]4- octahedra. The coordination
sphere of Pb is distorted, with large differences between the
lengths of Pb–Br bonds (ranging from 2.8185(13) to
3.3633(13) Å) mutually trans to one another along two of the
three molecular axes. Despite the potential existence of several
αbridging Pb−Br bond lengths. βTerminal Pb−Br bond lengths.
In contrast, distinct bromoplumbate architectures are ob-
tained with the more rigid substituents of 1, 2, and 3 (Figure
3), using the same crystallization conditions. More specifical-
ly, the resulting hybrids (1)6[Pb3Br12], (2)6[Pb3Br12] and
(3)6[Pb3Br12] are comprised of discrete molecular [Pb3Br12]6-
trimers that are separated by, and appear at regular intervals in,
a matrix of organic countercations. Such inorganic motifs are
very rare, relative to 1D and 2D hybrids, and are distinct from
the more common 0D compounds composed of monomeric
halides.7, 12, 26-27 In fact, we are aware of only four compounds
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b)
a)
c)
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Figure 3. Single crystal X-ray structures of trimeric lead-bromide hybrids a) (1)6[Pb3Br12], b) (2)6[Pb3Br12] and c) (3)6[Pb3Br12].
Dark gray, brown, gray, blue, red, and yellow spheroids represent Pb, Br, C, N, O and S atoms, respectively. H atoms are omitted
for clarity. Thermal ellipsoids are shown at 50% probability.
60-62
containing trimeric Pb-Br units.5,
The major difference
weakening of the Pb−Br bonds and an increase in Pb−Br bond
lengths, while the latter reflects a decrease of the overall ri-
gidity of bonding. These results are consistent with their X-ray
crystal structures, wherein (1)6[Pb3Br12] contains six terminal-
ly-bound halides in each of their trimeric inorganic compo-
nents, while 4[PbBr3] has none (i.e., all are bridging). The
peaks below 100 cm-1, contributed by vibrations involving
scissoring modes of Pb−Br−Pb and Br−Pb−Br, differ as well.
However, precise assignment of these features is not straight-
forward due to the large number of overlapping vibrational
modes in this region. As such, exact assignments would re-
quire a combination of calculations and measurements at low
temperatures.
between cations 1 – 3 and 4 – 6, used in this study, is that the
N-alkyl substituents in the former group contain sp or sp2 hy-
bridized C atoms. This endows them with a degree of rigidity
that inhibits ideal packing around the inorganic octahedra and,
thereby, prevents assembly of infinite 1D [PbBr3]- chains.
The trimers are built from monomeric lead bromide octahe-
dra that link to one another in a face-sharing fashion. As such,
all 6 bromide ions in the central [PbBr6]4- octahedra are bridg-
ing (μ2-Br-), whereas the outer [PbBr6]4- octahedra have 3 ter-
minally bound ions (Brt-) and 3 that bridge to the central Pb
ion. Consistent with expectations, the Pb-Brt bonds are gener-
ally shorter than the Pb−(μ2-Br) bonds (Table 1; for more
complete data, see the tables in the Supporting Information).
For instance, in (1)6[Pb3Br12] the former are 2.9219(5) Å long,
whereas the latter vary from 3.0016(4) − 3.1665(5) Å. Fur-
thermore, the Pb−(μ2-Br) distances in the trimers are, on the
whole, longer than those in the 1D chains templated by 4+, 5+
and 6+. Notably, there is deviation in the average Pb−Pb dis-
tances amongst the three trimers, with those of (1)6[Pb3Br12]
and (2)6[Pb3Br12] being the longest and shortest, respectively,
at 3.9345(5) and 3.8458(5) Å. Although there is some overlap
in their ranges, the Pb-Pb separations in the 1D chains are
generally longer than those in the bromoplumbate trimers
(Table 1).
Overall, the bulky N-benzylpyridium cations in
(1)6[Pb3Br12] impose greater structural distortion of their con-
stituent [PbBr6]4- octahedra than the cations that template the
other trimeric structures, (2)6[Pb3Br12] and (3)6[Pb3Br12] (Ta-
ble 2). The degree of intra-octahedral distortion is assessed via
the parameters octahedral elongation (λoct), octahedral angle
variance (σ2oct), and octahedral bond length distortion (∆oct),23,
64 which are calculated using the following equations:
ퟔ
ퟐ
ퟏ
ퟔ
풅풊
풐풄풕
=
∑ [
]
(ퟏ)
풅ퟎ
풊=ퟏ
ퟏퟐ
ퟏ
ퟐ
훔ퟐ
∆
=
∑ 풊 − ퟗퟎ
풊=ퟏ
(ퟐ)
Interestingly, the tendency to form inorganic trimers, rather
than 1D structures, is also influenced by the identity of the
halide. Whereas replacement of the bromide ions in
(1)6[Pb3Br12] with chloride provides the isostructural, trimer-
containing compound (1)6[Pb3Cl12], combination of PbI2 with
(1)I affords the 1D iodoplumbate 1[PbI3] (Figure S1). The
larger Pb-halide voids formed by the bigger iodide anions are,
presumably, better able to accommodate close packing with
the N-benzylpyridinium cation.
(
)
풐풄풕
ퟏퟏ
ퟔ
ퟐ
ퟏ
ퟔ
풅풊 − 풅풎
=
∑ [
]
(ퟑ)
풐풄풕
풅풎
풊=ퟏ
where di corresponds to Pb–Br bond length, d0 to center-to-
vertex distance of a regular octahedron of the same volume, dm
to average bond length, and i to individual Br–Pb–Br angle.
λoct and σ2 provide a quantitative measure of octahedral dis-
oct
The breaking of 1D bromoplumbate chains into trimeric
units is readily apparent in single crystal, low-frequency Ra-
man measurements (Figure S2). Based upon a close similarity
to vibrations (at 142 cm-1) in published 1D bromoplumbate
compounds possessing face-sharing linkages,6, 63 the vibration
in 4[PbBr3] at 143 cm-1 can be assigned as symmetric stretch-
ing of comparatively strong Pb−Br bonds. In (1)6[Pb3Br12],
this Raman mode shifts to lower energy (132 cm-1) and de-
creases in intensity by a factor of 3. The former indicates
tortion independent of the effective size of the octahedron,
with larger values equating to greater distortion.
It was previously reported, and is generally accepted, that
the tendency of 2D bromoplumbate perovskites to demonstrate
broadband photoluminescence increases with increasing dis-
tortion of their constituent lead bromide octahedra.6, 65 Thus, it
is noteworthy that the levels of intra-octahedral structural dis-
tortion displayed by (1)6[Pb3Br12] – (3)6[Pb3Br12] are very
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Figure 4 a) Room temperature UV-vis diffuse reflectance spectrum (DRS), transformed using the Kubelka-Munk (K-M) function,
and photoluminescence (PL, λex = 350 nm) spectrum of (1)6[Pb3Br12]. b) Chromaticity coordinates for the PL emission of
(1)6[Pb3Br12]. c) Laser fluence-dependent integrated PL intensity of (1)6[Pb3Br12], recorded at 293 K in the range 8 – 143 μJ /cm2,
plus a linear fit of the data. d) Time-resolved PL spectra of (1)6[Pb3Br12], recorded at an emission wavelength of 570 nm, at temper-
atures of 77 and 293 K.
large, even relative to broadband-emitting 2D perovskites.65-67
This is a direct consequence of the very different coordination
spheres of the “central” and two “terminal” lead ions that
comprise the trimers. More specifically, the terminal [PbBr6]4-
octahedra contain 3 terminally-bound Br- ions and a further
three that μ2-bridge in a facial fashion to a central Pb2+ ion. By
extension, the central Pb2+ ions are coordinated only to bridg-
ing Br- ions. The inherently lower symmetry of the coordina-
tion sphere of the terminal Pb2+ ions, combined with the sig-
nificant difference between the bond lengths and angles to μ2-
bridging Br- ions versus terminally-bound Br- ions, results in
the aforementioned large deviations from ideal octahedral
symmetry. Consistent with our expectations, all of the trimeric
hybrids reported herein were found to exhibit broadband emis-
sion (Figure S3). Of these, we elected to study the optical
properties of the compound displaying the largest intra-
octahedral distortions, (1)6[Pb3Br12], in greater detail.
broad, with a maxima at 571 nm, an emission width of ca. 1.45
eV, and a full width at half maximum (FWHM) of ca. 146 nm
(Figure 4a). Relative to its absorption onset, the observed PL
exhibits a large Stokes shift of ca. 1.39 eV.
Table 2. Distortion parameters derived from the single crystal
X-ray structures of the trimeric bromoplumbates (1)6[Pb3Br12],
(2)6[Pb3Br12], and (3)6[Pb3Br12]α
λoct
(avg)
σ2
(avg)
∆
oct (×10-4)d
oct
Compound
b
c
(1)6[Pb3Br12]
(2)6[Pb3Br12]
(3)6[Pb3Br12]
1.0120
1.0058
1.0114
39.07
13.04
31.93
10.79
27.66
21.93
αAveraged distortion parameters are given because the unit
cells of (1)6[Pb3Br12], (2)6[Pb3Br12] and (3)6[Pb3Br12] contain
two, two, and three geometrically distinct octahedra, respec-
Single crystals of (1)6[Pb3Br12] appear colorless and trans-
parent under ambient light, which is indicative of little-to-no
light absorption in the visible region and a large HOMO-
LUMO energy gap. Consistent with this, its pseudo-absorption
spectrum, converted from diffuse-reflectance measurements
using the Kubelka−Munk function, shows an absorption band
with a maxima of 318 nm (Figure 4a). Upon photoexcitation
by ≤ 375 nm UV light, (1)6[Pb3Br12] exhibits strong photolu-
minescence (PL) at room temperature. The emission band is
b
tively. Further details are provided in the SI. Octahedral elon-
c
d
gation. Octahedral angle variance. Octahedral bond length
distortion.
A similar PL feature was also observed in ball-milled pow-
der samples of (1)6[Pb3Br12] (Figure S4), which indicates that
differences in particle size and defects do not significantly
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affect the emission. Purity of the bulk (1)6[Pb3Br12] was con-
the 1-butyl-1-methylpyrrolidinium cation, (bmpy)6[Pb3Br12],70
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firmed using powder X-ray diffraction, shown in Figure S5,
where the obtained pattern exhibits a near perfect match with
the simulated XRD pattern. The observed broadband emission
corresponds to “warm” white-light, with a correlated colour
temperature (CCT) of 3667 K, Commission Internationale de
l'Eclairage (CIE) chromaticity coordinate (0.43; 0.50), and
colour rendering index (CRI) of 64 (Figures 4b), making it
suitable for indoor illumination.
which was shown to exhibit two emission peaks, at 501 and
564 nm, with respective decay lifetimes of 18 and 44 μs, at 77
K. To explain this phenomenon, the presence of two co-
existing excited-state energy minima, accessed with different
energy barriers, was proposed. The origin of the difference
between the PL behaviour of (1)6[Pb3Br12] and other Pb-Br
trimers is not clear at this stage, and the in-depth photophysics
investigations that would be required to elucidate the mecha-
nism of emission are beyond the scope of the current work.
However, we suspect that it stems from different structural
distortions in the photoexcited state(s) that are themselves the
result of differences in the supramolecular interactions be-
tween the inorganic clusters and the accompanying templating
organic cations.
The PLQE of (1)6[Pb3Br12] was determined to be at least 10
% (Figure S6), which is similar to that reported for other tri-
meric bromoplumbates.29 As a frame of reference, the proto-
typical 1D compound 4[PbBr3] exhibits a PLQE of ca. 1.0 %,
which is of a similar magnitude to values reported for other
1D lead-bromide hybrids (0.4 – 0.6 %).6, 44 Thus, although the
1D materials templated by 4 – 6 also exhibit broadband emis-
sion (Figure S7), moving to a 0D trimer can yield a ten-fold
enhancement of PLQE. This is a straightforward consequence
of increased quantum-confinement and illustrates why a de-
crease in dimensionality is advantageous.
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Identical PL features were obtained for (1)6[Pb3Br12] when
excitation wavelengths shorter than 375 nm were used (Figure
S8). Such invariance suggests that the broadband emission is
an intrinsic feature of this material. In addition, photolumines-
cence excitation (PLE) spectra probing the emission band over
the range 450 – 700 nm retain the same shape and features
(Figure S9). This implies that the entirety of the observed
emission originates from a common set of excited states.
Moreover, the PLE spectra exhibit similar onsets of ca. 390–
400 nm as the UV-vis data, which further evidences the intrin-
sic origin of the broadband PL. This conclusion is also sup-
ported by power-dependent continuous-wave PL measure-
ments. If the emission arose from permanent defects, PL
would be expected to saturate as these traps become filled.
Instead, PL intensity is found to increase linearly with fluence
from 8 to 143 μJ cm-2 at 293 K (Figures 4c and S10), with no
signs of saturation. Also, no blue-shift of PL spectra was ob-
served with increasing excitation fluence, ruling out the possi-
bility of it being deep-trap emission.
The luminescent decay of (1)6[Pb3Br12] at room temperature
was recorded and, as shown in Figure 4d, monoexponential
fitting of its broadband emission gives a comparatively long
lifetime of approximately 426 ns. Additionally, no significant
variation of PL lifetime is seen across different emission
wavelengths (Figure S11). Decrease of the temperature to 77
K results in an increase the luminescent decay lifetime to
around 5.8 µs (also by single-exponential fitting). This is simi-
lar to observations reported for 0D organic-inorganic metal
halide hybrids that have emissions from excitons localized in
individual metal halide clusters.26-27, 68 In particular, the afore-
mentioned behavior of (1)6[Pb3Br12] is indicative of emission
originating from a triplet excited state(s), similar to the phos-
phorescence commonly associated with heavy metal complex-
es.69
Figure 5. a) Density Functional Theory (DFT) calculated elec-
tronic band structure and density of states (DOS) plots for
(1)6[Pb3Br12]. The computational methodology employed is
described above. b) Schematic depiction of the proposed
mechanism of broadband emission in (1)6[Pb3Br12]. The
straight and curved arrows represent optical transitions and
excited state rearrangement, respectively.
Upon lowering the temperature to 77 K, the emission spec-
trum of (1)6[Pb3Br12] becomes progressively narrower and
shifts slightly to higher energy (Figures S12 and 13). This,
presumably, reflects reduced thermal population of higher
vibrational states at low temperatures. Interestingly, we did not
observe additional bands appearing in the PL spectrum within
the temperature range of 77 – 293 K. This is in contrast to the
previously reported trimeric Pb-Br compound templated by
Modelling the temperature dependence (77 – 293 K) of the
integrated PL intensity and decay lifetime of (1)6[Pb3Br12]
with the Self-Trapped Exciton (STE) Model, which is normal-
ly applied to typical semiconducting materials, yields good fits
71
(Figures S14 and S15).43, However, unlike hybrid metal
halide systems of higher dimensionalities,14, 21 (1)6[Pb3Br12] is
not an extended solid; it is comprised of discrete molecular
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entities. Consistent with this, its DFT calculated electronic kHz repetition rate) for approximately six hours, under ambi-
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structure exhibits nearly dispersionless “bands” (Figure 5a).
This implies that the photogenerated excitons would be very
much localized in the individual bromoplumbate clusters, as
they are spacially isolated from one another and have no ap-
preciable electronic coupling. As such, the highly Stokes shift-
ed broadband emission observed in (1)6[Pb3Br12] can be as-
sumed to a result of structural reorganization of the photoex-
cited trimers.72-75
ent conditions (RH = 70 %, RT), (1)6[Pb3Br12] was able to
retain around 90% of its initial PL intensity (Figure 6b).
These measurements indicate relatively good stability. We
attribute this to the presence of the bulky N-benzylpyridinium
cations, which acts as a protective “matrix” or “host” for the
“guest” [Pb3Br12]6- moieties.
A further question is whether the observed PL behaviour is
a consequence of energy/charge transfer from the Pb-Br tri-
mers to the organic countercations, with broadband emission
from the latter. Accordingly, the UV-vis DRS of (1)Br was
recorded (Figure S17), and it was found to exhibit an ex-
tremely weak feature at similar energies to the broadband
emission of (1)6[Pb3Br12]. Furthermore, the DFT calculations
yielded two sets of largely cation-based bands (Figure S18), at
1.36-1.68 and 2.24-2.59 eV above the Fermi level, intermedi-
ate between the Pb and Br dominated highest occupied molec-
ular orbitals (HOMOs) and lowest unoccupied molecular or-
bitals (LUMOs), which are respectively within 0.5 eV of the
Fermi level and approximately 3 – 3.5 eV above the Fermi
level. However, given the spatial separation of the organic and
inorganic components, which results in the majority of Pb 6s
and Br 4p contributions to the HOMOs being from within the
same trimer, there is likely to be significant barriers to energy
transfer between them. Considering this and the relatively high
intensity and long lifetimes of broadband emission of
(1)6[Pb3Br12], we favour retention of the exciton within the
[Pb3Br12]6- moiety. Analogous (and well-evidenced) conclu-
sions were drawn for the 0D tetraphenylphosphonium-
templated chloroantimonate (Ph4P)2[SbCl5], which displays
similar broadband white light emission properties.12 DFT cal-
culations for this compound similarly gave organic cation-
based LUMOs, but they also showed that the excited triplet
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-
state of the SbCl5 moiety was substantially stabilized and the
calculated emission from this state was in excellent agreement
with experiment.
A schematic depiction of our proposed broadband emission
mechanism is provided in Figure 5b. Upon photon absorption,
the [Pb3Br12]6- species are initially excited to a high energy
singlet excited state. Subsequently, there is ultrafast excited
state structural reorganization and intersystem crossing to
lower energy triplet excited state(s), from which the highly
Stokes-shifted broadband emission occurs. This general mech-
anism has been demonstrated (and is widely accepted) for
heavy atom-containing metal complexes and molecules,71-72, 74-
75 and has been recently proposed for similar 0D Pb-, Sn-, Ge-,
and Sb-based hybrids.7, 12, 68 Although it has not yet been con-
firmed that a triplet exciton can be accessed and stabilized by
the Pb-Br trimers of (1)6[Pb3Br12], its relatively long emission
lifetime (Figure 4d) is consistent with this assumption. Future
studies may clarify these points.
Figure 6. a) Photoluminescence (PL, λex = 350 nm) spectra of
(1)6[Pb3Br12] recorded fresh and after storage for 3 and 6
months under ambient conditions (room temperature (RT) and
relative humidity (RH) = 70 %). b) Normalized PL intensity of
(1)6[Pb3Br12] under constant illumination, using an excitation
wavelength of 350 nm and a laser fluence of ~5 μJ cm-2, under
ambient conditions (RT and RH = 70 %).
CONCLUSIONS
In summary, we set out to selectively induce formation of
trimeric bromoplumbates by engineering the molecular struc-
ture of templating pyridinium cations. This was successfully
achieved through incorporation of comparatively rigid benzyl,
acetamidyl, and cyanomethyl substituents, which contain sp2
or sp hybridized C atoms. The resulting “0D” [Pb3Br12]6- tri-
mers are very rare and we aware of only four examples having
been published prior to this study. As such, we have almost
doubled the number known. Of the three trimers detailed here-
in, the N-benzylpyridinium containing compound (1)6[Pb3Br12]
exhibits the most severe distortions of the constituent lead-
bromide octahedra (i.e., coordination spheres). It’s highly con-
fined inorganic lattice and strong intra-octahedral distortions
result in PL emission that is efficient (at least 10% PLQE),
One of the most important factors for assessing the applica-
bility of a material for practical lighting applications, is its
stability upon storage and exposure to light, under ambient
conditions. Accordingly, we measured the PL spectrum of
(1)6[Pb3Br12] after storage in air, with a relative humidity (RH)
of 70 %, at room temperature (RT) for 3 and 6 months. As
shown in Figure 6a, virtually no change in PL emission shape
and position was observed. In addition, upon continuous exci-
tation by 350 nm wavelength light (5 μJ cm-2 fluence, at a 1
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relative to its 1D congeners, ultra-broad (ca. 146 nm), and
highly Stokes-shifted (1.39 eV). Mechanistically, the broad-
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8
9
band emission is deduced to proceed via excited-state structur-
al reorganization of the inorganic [Pb3Br12]6- to an emissive
triplet state(s). Further studies are required to confirm this
assertion and exclude the possibility of energy/charge transfer
to (and emission from) the organic cation. Regardless, our
work demonstrates deliberate tailoring of the Pb-halide lattice
structure at a molecular level in order to induce desirable pho-
tophysical properties. This represents a rare example of ration-
al design of the microscopic structure of haloplumbates, and
the cation-inorganic lattice structure correlations elucidated
herein can be used to inform future engineering of p-block
metal halide materials possessing specific motifs and dimen-
sionalities.
REFERENCES
1. Manser, J. S.; Christians, J. A.; Kamat, P. V., Intriguing Optoe-
lectronic Properties of Metal Halide Perovskites. Chem. Rev.
2016, 116 (21), 12956–13008.
2. Saparov, B.; Mitzi, D. B., Organic-Inorganic Perovskites: Struc-
tural Versatility for Functional Materials Design. Chem. Rev.
2016, 116 (7), 4558–4596.
3. Lin, H.; Zhou, C.; Tian, Y.; Siegrist, T.; Ma, B., Low-
Dimensional Organometal Halide Perovskites. ACS Energy Lett.
2017, 3 (1), 54–62.
4. Mercier, N.; Louvain, N.; Bi, W., Structural diversity and retro-
crystal engineering analysis of iodometalate hybrids.
CrystEngComm 2009, 11 (5).
5. Smith, M. D.; Watson, B. L.; Dauskardt, R. H.; Karunadasa, H.
I., Broadband Emission with a Massive Stokes Shift from Sul-
fonium Pb–Br Hybrids. Chem. Mater. 2017, 29 (17), 7083–
7087.
6. Mao, L.; Guo, P.; Kepenekian, M.; Hadar, I.; Katan, C.; Even, J.;
Schaller, R. D.; Stoumpos, C. C.; Kanatzidis, M. G., Structural
Diversity in White-Light-Emitting Hybrid Lead Bromide Perov-
skites. J. Am. Chem. Soc. 2018, 140 (40), 13078–13088.
7. Morad, V.; Shynkarenko, Y.; Yakunin, S.; Brumberg, A.; Schal-
ler, R. D.; Kovalenko, M. V., Disphenoidal Zero-Dimensional
Lead, Tin, and Germanium Halides: Highly Emissive Singlet
and Triplet Self-Trapped Excitons and X-ray Scintillation. J.
Am. Chem. Soc. 2019, 141 (25), 9764–9768.
8. Yangui, A.; Roccanova, R.; Wu, Y.; Du, M.-H.; Saparov, B.,
Highly Efficient Broad-Band Luminescence Involving Organic
and Inorganic Molecules in a Zero-Dimensional Hybrid Lead
Chloride. J. Phys. Chem. C 2019, 123 (36), 22470–22477.
9. Han, Y.; Li, Y.; Wang, Y.; Cao, G.; Yue, S.; Zhang, L.; Cui, B.
B.; Chen, Q., From Distortion to Disconnection: Linear Alkyl
Diammonium Cations Tune Structure and Photoluminescence of
Lead Bromide Perovskites. Adv. Opt. Mater. 2020, 8, 1902051.
10. Wu, X.; Trinh, M. T.; Niesner, D.; Zhu, H.; Norman, Z.; Owen,
J. S.; Yaffe, O.; Kudisch, B. J.; Zhu, X. Y., Trap states in lead
iodide perovskites. J. Am. Chem. Soc. 2015, 137 (5), 2089–2096.
11. Yuan, Z.; Zhou, C.; Tian, Y.; Shu, Y.; Messier, J.; Wang, J. C.;
van de Burgt, L. J.; Kountouriotis, K.; Xin, Y.; Holt, E.; Schan-
ze, K.; Clark, R.; Siegrist, T.; Ma, B., One-dimensional organic
lead halide perovskites with efficient bluish white-light emis-
sion. Nat. Commun. 2017, 8.
12. Zhou, C.; Worku, M.; Neu, J.; Lin, H.; Tian, Y.; Lee, S.; Zhou,
Y.; Han, D.; Chen, S.; Hao, A.; Djurovich, P. I.; Siegrist, T.; Du,
M.-H.; Ma, B., Facile Preparation of Light Emitting Organic
Metal Halide Crystals with Near-Unity Quantum Efficiency.
Chem. Mater. 2018, 30 (7), 2374–2378.
13. Zhou, C.; Tian, Y.; Yuan, Z.; Lin, H.; Chen, B.; Clark, R.;
Dilbeck, T.; Zhou, Y.; Hurley, J.; Neu, J.; Besara, T.; Siegrist,
T.; Djurovich, P.; Ma, B., Highly Efficient Broadband Yellow
Phosphor Based on Zero-Dimensional Tin Mixed-Halide Perov-
skite. ACS Appl. Mater. Interfaces 2017, 9 (51), 44579–44583.
14. Smith, M. D.; Karunadasa, H. I., White-Light Emission from
Layered Halide Perovskites. Acc. Chem. Res. 2018, 51 (3), 619–
627.
15. Gautier, R.; Massuyeau, F.; Galnon, G.; Paris, M., Lead Halide
Post-Perovskite-Type Chains for High-Efficiency White-Light
Emission. Adv. Mater. 2019, 31 (14), e1807383.
16. Cheng, Z.; Lin, J., Layered organic–inorganic hybrid perov-
skites: structure, optical properties, film preparation, patterning
and templating engineering. CrystEngComm 2010, 12 (10).
17. Dohner, E. R.; Hoke, E. T.; Karunadasa, H. I., Self-assembly of
broadband white-light emitters. J. Am. Chem. Soc. 2014, 136 (5),
1718–1721.
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11
12
13
14
15
16
17
18
19
20
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ASSOCIATED CONTENT
Supporting Information
Crystal structures of hybrid lead-iodide perovskites (cif files).
Experimental procedures, materials synthesis, additional photo-
physics spectra, band structure, Density of States plots and crys-
tallographic data (pdf).
The Supporting Information is available free of charge on the
ACS Publications website.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jengland@ntu.edu.sg.
*Email: nripan@ntu.edu.sg.
Notes
The authors declare no competing financial interest. CIF data for
associated crystal structures have been deposited in the Cam-
bridge Crystallographic Data Centre under deposition numbers
CCDC 1915772-1915779.
ACKNOWLEDGMENT
JE thanks NTU for funding (M4081442). NM, KTM, BF would
like to acknowledge the funding from the Singapore National
Research Foundation through the Singapore–Berkeley Research
Initiative for Sustainable Energy (SinBeRISE) CREATE Program,
Office of Naval Research Global (ONRG-NICOP-N62909-17-1-
2155), and the Competitive Research Program: NRF–CRP14–
2014–03. TCS and DG acknowledge the support from the Minis-
try of Education Tier
2 grants MOE2017-T2-1-001 and
MOE2017-T2-2-002 and from the Singapore National Research
Foundation through the NRF Investigatorship (NRF-NRFI-2018-
04). The efforts of S.S. and M.A., associated with the DFT calcu-
lations, were funded by the U.S. Department of Energy, Office of
Science, Office of Basic Energy Sciences, Materials Sciences and
Engineering Division under Contract No. DE-AC02-05-CH11231
(Materials Project program KC23MP). The computations made
use of resources at the National Energy Research Scientific Com-
puting Center (NERSC), a U.S. Department of Energy Office of
Science User Facility operated under Contract No. DE-AC02-
05CH11231.
18. Dohner, E. R.; Jaffe, A.; Bradshaw, L. R.; Karunadasa, H. I.,
Intrinsic White-Light Emission from Layered Hybrid Perov-
skites. J. Am. Chem. Soc. 2014, 136 (38), 13154–13157.
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Chemistry of Materials
Page 10 of 12
19. Neogi, I.; Bruno, A.; Bahulayan, D.; Goh, T. W.; Ghosh, B.;
Acentric Hybrid Perovskite Single Crystals NH(CH3)3SnX3 (X =
Ganguly, R.; Cortecchia, D.; Sum, T. C.; Soci, C.; Mathews, N.;
Mhaisalkar, S. G., Broadband-Emitting 2 D Hybrid Organic-
Cl, Br). Chem. Mater. 2016, 28 (19), 6968–6974.
35. Jalilian, E.; Lidin, S., Size matters—sometimes. The
[CuxIy](y−x)−(NR4)+(y−x) systems. CrystEngComm 2011, 13 (19).
36. You et al., An organic-inorganic perovskite ferroelectric with
large piezoelectric response. Science 2017, 357, 306–309.
37. Hua, X. N.; Liao, W. Q.; Tang, Y. Y.; Li, P. F.; Shi, P. P.; Zhao,
D.; Xiong, R. G., A Room-Temperature Hybrid Lead Iodide
Perovskite Ferroelectric. J. Am. Chem. Soc. 2018, 140 (38),
12296–12302.
38. Bakthavatsalam, R.; Haris, M. P. U.; Shaikh, S. R.; Lohar, A.;
Mohanty, A.; Moghe, D.; Sharma, S.; Biswas, C.; Raavi, S. S.
K.; Gonnade, R. G.; Kundu, J., Ligand Structure Directed Di-
mensionality Reduction (2D →1D) in Lead Bromide Perovskite.
J. Phys. Chem. C 2019, 124 (3), 1888–1897.
39. Mousdis, G. A.; Ganotopoulos, N.-M.; Barkaoui, H.; Abid, Y.;
Psycharis, V.; Savvidou, A.; Raptopoulou, C. P., One-
Dimensional Organic-Inorganic Hybrid Materials Based on An-
timony. Eur. J. Inorg. Chem. 2017, 2017 (28), 3401–3408.
40. Li, S. L.; Zhang, F. Q.; Zhang, X. M., An organic-ligand-free
thermochromic luminescent cuprous iodide trinuclear cluster:
evidence for cluster centered emission and configuration distor-
tion with temperature. Chem. Commun. 2015, 51 (38), 8062–
8065.
41. Goforth, A. M.; Smith, M. D.; Peterson, L.; zur Loye, H-C.,
Preparation and Characterization of Novel Inorganic−Organic
Hybrid Materials Containing Rare, Mixed-Halide Anions of
Bismuth(III) Inorg. Chem. 2004, 43 (22), 7042–7049.
42. Bi, W.; Leblanc, N.; Mercier, N.; Auban-Senzier, P.; Pasquier,
C., Thermally Induced Bi(III) Lone Pair Stereoactivity: Ferroe-
lectric Phase Transition and Semiconducting Properties of
(MV)BiBr5(MV= methylviologen). Chem. Mater. 2009, 21 (18),
4099–4101.
43. Jung, M.-H., Broadband white light emission from one-
dimensional zigzag edge-sharing perovskite. New J. Chem.
2020, 44 (1), 171–180.
44. Cui, B. B.; Han, Y.; Huang, B.; Zhao, Y.; Wu, X.; Liu, L.; Cao,
G.; Du, Q.; Liu, N.; Zou, W.; Sun, M.; Wang, L.; Liu, X.; Wang,
J.; Zhou, H.; Chen, Q., Locally collective hydrogen bonding iso-
lates lead octahedra for white emission improvement. Nat.
Commun. 2019, 10 (1), 5190.
45. Febriansyah, B.; Koh, T. M.; John, R. A.; Ganguly, R.; Li, Y.;
Bruno, A.; Mhaisalkar, S. G.; England, J., Inducing Panchro-
matic Absorption and Photoconductivity in Polycrystalline Mo-
lecular 1D Lead-Iodide Perovskites through π-Stacked Vio-
logens. Chem. Mater. 2018, 30 (17), 5827–5830.
46. Febriansyah, B.; Lekina, Y.; Ghosh, B.; Harikesh, P. C.; Koh, T.
M.; Li, Y.; Shen, Z.; Mathews, N.; England, J., Molecular Engi-
neering of Pure 2D Lead-Iodide Perovskite Solar Absorbers
Displaying Reduced Band Gaps and Dielectric Confinement.
ChemSusChem 2020, 13, doi: 10.1002/cssc.202000028.
47. Febriansyah, B.; Giovanni, D.; Ramesh, S.; Koh, T. M.; Li, Y.;
Sum, T. C.; Mathews, N.; England, J., Inducing formation of a
corrugated, white-light emitting 2D lead-bromide perovskite via
subtle changes in templating cation. J. Mater. Chem. C 2020, 8
(3), 889–893.
1
2
3
4
5
6
7
8
Inorganic
Perovskite
Based
on
Cyclohexane-
bis(methylamonium) Cation. ChemSusChem 2017, 10 (19),
3765–3772.
20. Hu, H.; Morris, S. A.; Qiao, X.; Zhao, D.; Salim, T.; Chen, B.;
Chia, E. E. M.; Lam, Y. M., Molecular engineering of two-
dimensional hybrid perovskites with broadband emission for
white light-emitting diodes. J. Mater. Chem. C 2018, 6 (38),
10301–10307.
21. Cortecchia, D.; Yin, J.; Petrozza, A.; Soci, C., White light emis-
sion in low-dimensional perovskites. J. Mater. Chem. C 2019, 7
(17), 4956–4969.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22. Williams, R. T.; Song, K. S., The Self-Trapped Exciton. J. Phys.
Chem. Solids 1990, 51, 679–716.
23. Cortecchia, D.; Neutzner, S.; Srimath Kandada, A. R.; Mosconi,
E.; Meggiolaro, D.; De Angelis, F.; Soci, C.; Petrozza, A.,
Broadband Emission in Two-Dimensional Hybrid Perovskites:
The Role of Structural Deformation. J. Am. Chem. Soc. 2016,
139 (1), 39–42.
24. Cortecchia, D.; Yin, J.; Bruno, A.; Lo, S.-Z. A.; Gurzadyan, G.
G.; Mhaisalkar, S.; Brédas, J.-L.; Soci, C., Polaron self-
localization in white-light emitting hybrid perovskites. J. Mater.
Chem. C 2017, 5 (11), 2771–2780.
25. Booker, E. P.; Thomas, T. H.; Quarti, C.; Stanton, M. R.; Dash-
wood, C. D.; Gillett, A. J.; Richter, J. M.; Pearson, A. J.; Davis,
N.; Sirringhaus, H.; Price, M. B.; Greenham, N. C.; Beljonne,
D.; Dutton, S. E.; Deschler, F., Formation of Long-Lived Color
Centers for Broadband Visible Light Emission in Low-
Dimensional Layered Perovskites. J. Am. Chem. Soc. 2017, 139
(51), 18632–18639.
26. Zhou, C.; Lin, H.; Shi, H.; Tian, Y.; Pak, C.; Shatruk, M.; Zhou,
Y.; Djurovich, P.; Du, M.-H.; Ma, B., A Zero-Dimensional Or-
ganic Seesaw-Shaped Tin Bromide with Highly Efficient
Strongly Stokes-Shifted Deep-Red Emission. Angew. Chem. Int.
Ed. 2018, 57 (4), 1021–1024.
27. Zhou, C.; Lin, H.; Tian, Y.; Yuan, Z.; Clark, R.; Chen, B.; van
de Burgt, L. J.; Wang, J. C.; Zhou, Y.; Hanson, K.; Meisner, Q.
J.; Neu, J.; Besara, T.; Siegrist, T.; Lambers, E.; Djurovich, P.;
Ma, B., Luminescent zero-dimensional organic metal halide hy-
brids with near-unity quantum efficiency. Chem. Sci. 2018, 9
(3), 586–593.
28. Li, M.; Zhou, J.; Zhou, G.; Molokeev, M. S.; Zhao, J.; Morad,
V.; Kovalenko, M. V.; Xia, Z., Hybrid Metal Halides with Mul-
tiple Photoluminescence Centers. Angew. Chem. Int. Ed. 2019,
58 (51), 18670–18675.
29. Lin, H.; Zhou, C.; Neu, J.; Zhou, Y.; Han, D.; Chen, S.; Worku,
M.; Chaaban, M.; Lee, S.; Berkwits, E.; Siegrist, T.; Du, M. H.;
Ma, B., Bulk Assembly of Corrugated 1D Metal Halides with
Broadband Yellow Emission. Adv. Opt. Mater. 2019, 7 (6),
1801474.
30. Yuan, H.; Massuyeau, F.; Gautier, N.; Kama, A. B.; Faulques,
E.; Chen, F.; Shen, Q.; Zhang, L.; Paris, M.; Gautier, R., Doped
Lead Halide White Phosphors for Very High Efficiency and Ul-
tra-High Color Rendering. Angew. Chem. Int. Ed. 2020, 59 (7),
2802–2807.
48. Duan, H. B.; Yu, S. S.; Liu, S. X.; Zhang, H., An inorganic-
organic hybrid crystal with a two-step dielectric response and
thermochromic luminescence. Dalton Trans. 2017, 46 (7), 2220–
2227.
49. Duan, H. B.; Yu, S. S.; Tong, Y. B.; Zhou, H.; Ren, X. M., Two
in one: switchable ion conductivity and white light emission in-
tegrated in an iodoplumbate-based twin chain hybrid crystal.
Dalton Trans. 2016, 45 (11), 4810–4818.
50. Mitzi, D. B., Templating and structural engineering in organic–
inorganic perovskites. J. Chem. Soc., Dalton Trans. 2001, 1, 1–
12.
51. SAINT and SADABS; Bruker AXS Inc.: Madison, WI, (2007).
52. Sheldrick, G. M. SHELXL-97, Program for crystal structure
31. Zhang, Y.-L.; Wang, G.-B., Large-Size crystal based on rare
earth-free Cu(I) hybrid trigger yellow light with high emissive
quantum yields. J. Mol. Struct. 2019, 1183, 241–245.
32. Yangui, A.; Roccanova, R.; McWhorter, T. M.; Wu, Y.; Du, M.-
H.; Saparov, B., Hybrid Organic–Inorganic Halides
(C5H7N2)2MBr4 (M = Hg, Zn) with High Color Rendering Index
and High-Efficiency White-Light Emission. Chem. Mater. 2019,
31 (8), 2983–2991.
33. Jiang, C.; Zhong, N.; Luo, C.; Lin, H.; Zhang, Y.; Peng, H.;
Duan, C. G., (Diisopropylammonium)2MnBr4: a multifunctional
ferroelectric with efficient green-emission and excellent gas
sensing properties. Chem. Commun. 2017, 53 (44), 5954–5957.
34. Dang, Y.; Zhong, C.; Zhang, G.; Ju, D.; Wang, L.; Xia, S.; Xia,
H.; Tao, X., Crystallographic Investigations into Properties of
refinement; Göttingen, 1997.
ACS Paragon Plus Environment

Page 11 of 12
Chemistry of Materials
53. Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
phenanthroline: Implications for Excited-State Structural Distor-
tion. Inorg. Chem., 1998, 37, 2285–2290
2008, 64, 112–122.
1
2
3
4
5
6
7
8
54. Momma, K.; Izumi, F., An Integrated Three-Dimensional Visu-
alization System VESTA Using wxWidgets. Commission on
Crystallogr. Comput. 2006, 7, 106–119.
55. Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab
initio Total-energy Calculations Using a Plane-wave Basis Set
Phys. Rev. B 1996, 54, 11169–11186.
56. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient
Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–
3868.
57. Blochl, P. E., Projector augmented-wave method. Phys. Rev. B
1994, 50 (24), 17953–17979.
58. Kresse, G. and Joubert, D., From ultrasoft pseudopotentials to
the projector augmented-wave method. Phys. Rev. B 1999, 59
(3), 1758–1775.
59. Blochl, P. E.; Jepsen, O.; Andersen, O. K., Improved tetrahedron
method for Brillouin-zone integrations. Phys. Rev. B 1994, 49
(23), 16223–16233
60. Thirumurugan, A.; Rao, C. N. R., Supramolecular Organization
in Lead Bromide Salts of Imidazolium-Based Ionic Liquids.
Cryst. Growth Des. 2008, 8, 1640–1644.
73. Shaw, G. B.; Grant, C. D.; Shirota, H.; Castner, E. W.; Meyer,
G. J.; Chen, L. X., Ultrafast structural rearrangements in the
MLCT excited state for copper(I) bis-phenanthrolines in solu-
tion. J. Am. Chem. Soc., 2007, 129, 2147–2160.
74. Mel’nikov, M. Y.; Weinstein, J. A., Structural reorganization in
the excited state of transition metal complexes. High Energy
Chem. 2008, 42 (4), 287–289.
75. Zhou, C.; Tian, Y.; Yuan, Z.; Han, M.; Wang, J.; Zhu, L.;
Tameh, M. S.; Huang, C.; Ma, B., Precise Design of Phospho-
rescent Molecular Butterflies with Tunable Photoinduced Struc-
tural Change and Dual Emission. Angew. Chem. Int. Ed. 2015,
54 (33), 9591–9595.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61. Pan, J.; Sun, A.-H.; Han, S.-D.; Wei, L.; Li, J.-H.; Wang, G.-M.,
Low-Dimensional Lead(II) Halides with In Situ Generated Tri-
pyridine-Derivatives as Countercations: Synthesis, Structures
and Properties. J. Clust. Sci. 2017, 28 (5), 2669–2679.
62. Zhou, J.; Li, M.; Ning, L.; Zhang, R.; Molokeev, M. S.; Zhao, J.;
Yang, S.; Han, K.; Xia, Z., Broad-Band Emission in a Zero-
Dimensional Hybrid Organic [PbBr6] Trimer with Intrinsic Va-
cancies. J. Phys. Chem. Lett. 2019, 10 (6), 1337–1341.
63. Niemann, R. G.; Kontos, A. G.; Palles, D.; Kamitsos, E. I.;
Kaltzoglou, A.; Brivio, F.; Falaras, P.; Cameron, P. J., Halogen
+
Effects on Ordering and Bonding of CH3NH3 in CH3NH3PbX3
(X = Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic
Study. J. Phys. Chem. C 2016, 120 (5), 2509–2519.
64. Robinson, K.; Gibbs, G. V.; Ribbe, P. H., Quadratic Elongation:
a Quantitative Measure of Distortion in Coordination Polyhe-
dral. Science 1971, 172, 567–570.
65. Mao, L.; Wu, Y.; Stoumpos, C. C.; Wasielewski, M. R.; Kanat-
zidis, M. G., White-Light Emission and Structural Distortion in
New Corrugated Two-Dimensional Lead Bromide Perovskites.
J. Am. Chem. Soc. 2017, 139 (14), 5210–5215.
66. Wang, S.; Yao, Y.; Kong, J.; Zhao, S.; Sun, Z.; Wu, Z.; Li, L.;
Luo, J., Highly efficient white-light emission in a polar two-
dimensional hybrid perovskite. Chem. Commun. 2018, 54 (32),
4053–4056.
67. Neogi, I.; Bruno, A.; Bahulayan, D.; Goh, T. W.; Ghosh, B.;
Ganguly, R.; Cortecchia, D.; Sum, T. C.; Soci, C.; Mathews, N.;
Mhaisalkar, S. G., Broadband-Emitting 2ꢀD Hybrid Organic-
Inorganic
Perovskite
Based
on
Cyclohexane-
bis(methylamonium) Cation. ChemSusChem 2017, 10 (19),
3765–3772.
68. Zhou, C.; Lin, H.; Worku, M.; Neu, J.; Zhou, Y.; Tian, Y.; Lee,
S.; Djurovich, P.; Siegrist, T.; Ma, B., Blue Emitting Single
Crystalline Assembly of Metal Halide Clusters. J. Am. Chem.
Soc. 2018, 140 (41), 13181-13184.
69. Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley,
S.; Thompson, M. E.; Forrest, S. R., Nature, 1998, 395, 151–
154.
70. Lee, S.; Zhou, C.; Neu, J.; Beery, D.; Arcidiacono, A.; Chaaban,
M.; Lin, H.; Gaiser, A.; Chen, B.; Albrecht-Schmitt, T. E.;
Siegrist, T.; Ma, B., Bulk Assemblies of Lead Bromide Trimer
Clusters with Geometry-Dependent Photophysical Properties.
Chem. Mater. 2019, 32 (1), 374–380.
71. Chong, W. K.; Giovanni, D.; Sum, T. C., Excitonics in 2D Per-
ovskites. In Halide Perovskites: Photovoltaics, Light Emitting
Devices, and Beyond; Sum, T. C., Mathews, N.; Wiley-VCH
Verlag GmbH & Co. KGaA: Weinheim, 2019; 55–79.
72. Miller, M. T.; Gantzel, P. K.; Karpishin, T. B., Structures of the
Copper(I) and Copper(II) Complexes of 2,9-Diphenyl-1,10-
ACS Paragon Plus Environment

Chemistry of Materials
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2
3
4
5
6
7
8
9
10
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13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
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