Preparation and optical characteristics of layered perovskite-type lead-bromide-incorporated azobenzene chromophores

Article abstract of DOI:10.1016/j.jssc.2012.11.009

Lead bromide-based layered perovskite powders with azobenzene derivatives were prepared by a homogeneous precipitation method. From the diffuse reflectance (DR) and photoluminescence (PL) spectra of the hybrid powder materials, the present hybrids exhibit

Full text of DOI:10.1016/j.jssc.2012.11.009

Journal of Solid State Chemistry 198 (2013) 452–458
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Journal of Solid State Chemistry
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Preparation and optical characteristics of layered perovskite-type
lead-bromide-incorporated azobenzene chromophores
Ryo Sasai n, Hisashi Shinomura
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, F3-3(250), Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Lead bromide-based layered perovskite powders with azobenzene derivatives were prepared by a
homogeneous precipitation method. From the diffuse reflectance (DR) and photoluminescence (PL)
spectra of the hybrid powder materials, the present hybrids exhibited sharp absorption and PL peaks
originating from excitons produced in the PbBr24ꢀ layer. When the present hybrid powder was
irradiated with UV light at 350 nm, the absorption band from the trans-azobenzene chromophore,
observed around 350 nm, decreased, while the absorption band from the cis-azobenzene chromophore,
observed around 450 nm, increased. These results indicate that azobenzene chromophores in the
present hybrid materials exhibit reversible photoisomerization. Moreover, it was found that the PL
intensity from the exciton also varied due to photoisomerization of the azobenzene chromophores in
the present hybrid. Thus, for the first time we succeeded in preparing the azobenzene derivative lead-
bromide-based layered perovskite with photochromism before and after UV light irradiation.
& 2012 Elsevier Inc. All rights reserved.
Received 27 July 2012
Received in revised form
6 November 2012
Accepted 11 November 2012
Available online 22 November 2012
Keywords:
Lead bromide-based layered perovskite
Azobenzene derivatives
Photoisomerization
Inorganic/organic hybrid materials
Photoluminescence
1. Introduction
types of hybrid systems can be controlled by using selected
functional organic ammonium as cations.
Metal halide-based layered perovskites with chemical formu-
las such as (R-NH3)2MX4 (R-NH3: organic ammonium such as
alkylammonium; M: Pb, Sn, Ge, and so on; and X: Cl, Br, and I) is
well known as one of the natural two-dimensional (2D) super-
lattice compounds [1–16]. A strong quantum-confinement effect
appears in the 2D semiconductor layer, and then a stable exciton
with a large binding energy of several hundred meV is formed. As
a result, metal halide-based layered perovskites exhibit attractive
optical properties such as photoluminescence (PL), electrolumi-
nescence (EL), and nonlinear optical effects originating from these
excitons. In earlier studies, halide-based layered perovskites that
used simple alkyl ammonium molecules as organic ammonium
ions were investigated [4,6,14]. In this hybrid system, organic
ammonium plays only the role of an insulating barrier layer.
Recently, various halide-based layered perovskite materials with
not only simple alkylammonium cations but also with various
functional organic ammonium ions such as chromophores, poly-
It is well known that the azobenzene chromophores exhibit
reversible photoisomerization from trans- to cis- forms, enabling
the optical and electronic properties of azobenzene chromophores
to be significantly varied by the same photoisomerization process.
Thus, the photoswitching of various properties and functions by
the photoisomerization of azobenzene chromophores has been
attempted by many researchers [18–23]. Halide-based layered
perovskites with azobenzene chromophores have also been
investigated, and a photoinduced energy transfer from the
trans-azobenzene chromophore to a lead halide semiconductor
layer was reported [8,16,17]. However, photoisomerization of
azobenzene chromophores and changes to the optical and/or
electronic properties of a metal halide semiconductor layer by
photoisomerization is yet to be achieved. In this study, we
attempted to synthesize a lead-bromide-based layered perovs-
kite, which is a typical compounds, with azobenzene ammonium
derivatives, and the spectroscopic characteristics of the synthe-
sized hybrid powder was investigated both before and after UV
and/or visible light irradiation.
mers, and compounds with
p-conjugated systems have been
reported [2,3,10,15,16]. In these reported hybrid systems, unique
optical, electronic, and magnetic properties could be observed.
These experimental facts indicate that the properties of these
2. Experimental
2.1. Materials
n Corresponding author. Present address: Department of Physics and Materials
Science, Interdisciplinary Graduate School of Science and Engineering, Shimane
University, 1060, Nishikawatsu-cho, Matue 690-8504, Japan.
Lead(II) bromide (Kojundo Chemical Laboratory Co., Ltd.),
E-mail address: rsasai@riko.shimane-u.ac.jp (R. Sasai).
4-(phenylazo)phenol (Sigma-Aldrich Co. LLC.), n-dibromoalkane
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2012.11.009

R. Sasai, H. Shinomura / Journal of Solid State Chemistry 198 (2013) 452–458
453
(TCI), and potassium phthalimide and hydrobromic acid (Nacalai
Tesque) were all used without further purification. Hydrazine
monohydrate, silver nitrate aqueous solution, N,N-dimethylfor-
mamide (DMF), and sodium hydroxide were purchased from
Kishida Chemical Co., Ltd. and also used without further purifica-
tion. All other solvents were reagent grade.
hydrazine monohydrate (400 mmol) was added to 160 cc of a
tetrahydrofuran (THF)/ethanol (EtOH) mixed solution (80/20, v/v),
and then this mixture was heated at 353 K for 3 h. After removing
the white precipitate (phthalic salt), the product was extracted by
chloroform. After dehydrating the chloroform solution by MgSO4,
impurities were removed from the concentrated filtrate by
diethylether. Compound C as an orange powder was collected
by concentrating the obtained filtrate [n¼2: yield¼99.7%,
2.2. Synthesis of azobenzene derivatives
1H NMR (500 MHz, CDCl3)
d 7.92 (d, 2H), 7.88 (d, 2H), 7.50
(t, 2H), 7.44 (t, 1H), 7.03 (d, 2H), 4.09 (t, 2H), 3.13 (t, 2H), 1.53
The azobenzene derivatives (compound D) used in this study
were synthesized according to Scheme 1. Compound A: 4-
(phenylazo)phonol (30 mmol) and 1,n-dibromoalkane (60 mmol,
carbon number: n¼2, 4, 6) were added to 30 cc of a 1 mol/dm3
NaOH aqueous solution, and then this mixture was refluxed with
vigorous stirring overnight. After confirming a neutral pH, the
products were extracted by chloroform. After dehydrating the
chloroform solution by MgSO4, compound A as a yellow powder
was obtained by evaporating the solvent [n¼2: yield¼76.0%,
(br, 2H). n¼4: yield¼68.4%, 1H NMR (500 MHz, CDCl3)
d 7.91
(td, 2H), 7.87 (td, 2H), 7.50 (tt, 2H), 7.43 (tt, 1H), 7.00 (td, 2H),
4.07 (t, 2H), 2.80 (t, 2H), 1.88 (quint, 2H), 1.65 (quint, 2H), 1.52
(br, 2H). n¼6: yield¼70.0%)]. Compound D: compound
C
(2 mmol) was added to 100 cc of diethylether under N2 atmo-
sphere. Hydrobromic acid (2.4 mmol of 47%) was dropped to the
mixed solution in an ice bath, producing an orange precipitate.
Filtrated compound D as an ocher powder was obtained by a
small amount of acetone [n¼2: yield¼99.1%, 1H NMR (500 MHz,
1H NMR (500 MHz, CDCl3)
d 7.93 (td, 2H), 7.88 (td, 2H), 7.51
DMS-d6)
d 7.97 (br, 3H), 7.93 (d, 2H), 7.85 (d, 2H), 7.60–7.52
(t, 2H), 7.45 (t, 1H), 7.03 (td, 2H), 4.38 (tt, 2H), 3.68 (tt, 2H). n¼4:
yield¼38.2%, 1H NMR (500MHz, CDCl3)
d
7.92 (td, 2H), 7.88
(m, 3H), 7.20 (d, 2H), 4.29 (t, 2H), 3.29 (t, 2H) n¼4: yield¼83.6%,
1H NMR (500 MHz, DMS-d6)
d
7.90 (td, 2H), 7.84 (td, 2H), 7.68
(td, 2H), 7.50 (tt, 2H), 7.44 (tt, 1H), 7.00 (td, 2H), 4.09 (t, 2H), 3.51
(br, 3H), 7.58 (tt, 3H), 7.53 (tt, 1H), 7.14 (td, 2H), 4.12 (t, 2H), 2.88
(t, 2H), 2.31–2.08 (m, 2H), 2.02–1.97 (m, 2H). n¼6: yield¼56.4%,
1H NMR (500 MHz, CDCl3)
d 7.91 (td, 2H), 7.87 (td, 2H), 7.50
(sext, 2H), 1.82 (quint, 2H), 1.72 (quint, 2H). n¼6: yield¼36.6%,
1H NMR (500 MHz, DMS-d6)
d 7.89 (td, 2H), 7.84 (td, 2H), 7.63
(tt, 2H), 7.43 (tt, 1H), 7.00 (td, 2H), 4.05 (t, 2H), 3.44 (t, 2H), 1.92
(quint, 2H), 1.85 (quint, 2H), 1.54 (quint, 4H)]. Compound B:
compound A (15 mmol) and potassium phthalimide (18 mmol)
was added to 200 cc of a DMF, and then this mixture was heated
at 363 K for 3 h. After evaporating the solvent, the product was
extracted by hot water and chloroform, and then the product was
rinsed with hot water until bromide ions could no longer be
observed by the AgNO3 method. After dehydrating the chloroform
solution by MgSO4, compound B as an orange powder was
obtained by evaporating the solvent [n¼2: yield¼97.6%,
(br, 3H), 7.58 (tt, 3H), 7.52 (tt, 1H), 7.13 (td, 2H), 4.10 (t, 2H), 2.80
(sext, 2H), 1.77 (quint, 2H), 1.57 (quint, 2H), 1.46 (quint, 2H), 1.39
(quint, 2H)]. Hereafter, synthesized azobenzene derivatives are
abbreviated as AzoCnAþBrꢀ (n¼2, 4, 6).
2.3. Preparation of layered perovskite compounds with lead (II)
bromide and azobenzene derivatives
1H NMR (500 MHz, DMSO-d6)
d
7.90–7.84 (m, 6H), 7.75–7.72
AzoCnAþBrꢀ (0.10 mmol) and lead(II) bromide (0.05 mmol)
were completely dissolved in 0.3 cc of DMF. After irradiating this
DMF solution with near UV light (450 nm) for 10 min, precipitates
were produced by adding sufficient quantities of acetone to this
DMF solution under light shielding. These precipitates were
collected by filtration, and then dried under reduced pressure at
room temperature. Hereafter, obtained hybrid powders are abbre-
viated as PbBr–AzoCnA (n¼2, 4, 6).
(m, 2H), 7.49 (tt, 2H), 7.43 (tt, 1H), 6.99 (td, 2H), 4.32 (t, 2H), 4.16
(t, 2H). n¼4: yield¼98.5%, 1H NMR (500 MHz, DMSO-d6)
d 7.91–
7.84 (m, 5H), 7.71 (sext, 2H), 7.50 (tt, 2H), 7.43 (tt, 1H), 6.98
(td, 2H), 4.09 (t, 2H), 3.79 (t, 2H), 1.96–1.85 (m, 4H). n¼6:
yield¼98.8%, 1H NMR (500 MHz, DMSO-d6)
d 7.91–7.84 (m, 6H),
7.71 (q, 2H), 7.50 (t, 2H), 6.98 (d, 2H), 4.03 (t, 2H), 3.71 (t, 2H),
1.82 (quint, 2H)]. Compound C: compound B (8 mmol) and
Scheme 1. Synthesis routes of AzoCnA (n¼2, 4, and 6).

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2.4. Photoirradiation of PbBr–AzoCnA powders
3. Results and discussion
To investigate the occurrence of photoisomerization of AzoCnA
incorporated in PbBr–AzoCnA hybrids, photoirradiation of PbBr–
AzoCnA powder was performed at room temperature. A Xe lamp
(300 W: MAX-303, Asahi Spectra Co., Ltd.) was used as the light
source. To adjust the wavelength for photoirradiation, band-pass
filters for UV irradiation (35079 nm) and visible irradiation
(45079 nm) were used.
3.1. Preparation of PbBr–AzoCnA hybrid powder
The composition formula of PbBr–AzoCnA hybrid powders
calculated from ICP-AES, SEM–EDS, and CHN elemental analysis
agreed with the ideal composition formula of PbBr–AzoCnA
hybrids, (Ph–NQN–Ph–O–(CH2)n–NH3)PbBr4 (Ph: phenyl group,
n¼2, 4, 6). XRD patterns of all the hybrid powders are shown in
Fig. 1. All the hybrid powders exhibited diffraction peaks from the
001 plane, and thus it is found that all the hybrid powders
possessed a layered structure. Plate crystals could be observed
in the SEM images of all the synthesized hybrid powders
(cf. photographs in Fig. 1). These results indicate that PbBr–AzoCnA
hybrid materials we wanted to synthesize could be prepared.
2.5. Characterization
X-ray diffraction (XRD) measurements of PbBr–AzoCnA before
and after photoirradiation were performed by powder diffract-
In Table 1, both the basal spacing value, d, and the tilt angle,
y,
ometer with Ni-filtered Cu
Ka radiation (50 kV, 100 mA:
of the major axis of the incorporated AzoCnA molecule against the
RINT-2500, RIGAKU). The diffuse reflection (DR) spectra of
PbBr–AzoCnA before and after photoirradiation were measured
by a V-670 UV–vis spectrophotometer (JASCO, reference sam-
ple: MgO powder). The photoluminescence (PL) spectra of
PbBr–AzoCnA before and after photoirradiation were measured
by FP-6600 fluorophotometer (JASCO) attached to a powder
sample holder at an excitation wavelength lex of 350 nm at
room temperature under ambient conditions. Images of PbBr–
AzoCnA powders were captured by a scanning electron micro-
scope (SEM) (JSM-T20, JEOL Ltd.). To identify the chemical
situation of the Pb and Br atoms in the inorganic layer before
and after photoirradiation, X-ray photoelectron spectroscopy
(XPS) was carried out on an ESCA-3300 (Shimadzu) equipped
normal line of the PbBr4 layer are shown. Here,
calculated by using the following equation:
y
values were
ꢀ
ꢁ
dꢀ2dPbꢀBr
2L
y
¼ cosꢀ1
ð1Þ
where dPbꢀBr is the thickness of the PbBr layer (0.30 nm) and L is
length of the major axis of the AzoCnA molecule with an all-trans
methylene group. The d values increased with an increase in the n
value. However, the
y value, which was about 591, did not depend
on the n value. These facts indicate that synthesized PbBr–AzoCnA
hybrid crystals possess the same crystal structure, even when the
chain length of the methylene group is varied. Fig. 2 shows the
XPS spectra of the (a) Pb 4f and (b) Br 3d orbits of the PbBr–
AzoCnA hybrid powders. The position and shape of the peaks
originating from the Pb 4f and Br 3d orbits did not change.
with Al K
a radiation. Infrared spectra of PbBr–AzoCnA before
and after photoirradiation were measured by the KBr pellet
method (FT-IR 6100, JASCO).
The composition formula of PbBr–AzoCnA was determined
from the following data: (1) the content of Pb in PbBr–AzoCnA
was determined by inductively coupled plasma-atomic elec-
tron spectroscopy (ICP-AES: Perkin-Elmer); (2) the abundance
molar ratio of Br/Pb in PbBr–AzoCnA was evaluated by
scanning electron microscopy–energy dispersive spectroscopy
(SEM–EDS: JSM-T20, JEOL Ltd.); (3) the amount of carbon,
hydrogen, and nitrogen in PbBr–AzoCnA was evaluated by a
CHN corder (MTA-620, Yanaco).
Table 1
Basal spacing value, d, and tilt angle,
rated AzoCnA molecules.
y, of incorpo-
n
d (nm)
y
(deg.)
2
4
6
2.30
2.61
2.88
58.6
57.8
57.6
Fig. 1. XRD patterns and SEM images of PbBr–AzoCnA materials [n¼2 (a), 4 (b), and 6 (c)].

R. Sasai, H. Shinomura / Journal of Solid State Chemistry 198 (2013) 452–458
455
Fig. 3. Schematic model structure of PbBr–AzoCnA hybrid material.
Fig. 2. XPS spectra of Pb 4f (top) and Br 3d (bottom) of PbBr–AzoCnA materials
[n¼2 (a), 4 (b), 6 (c), and (C16H33NH3)2PbBr4 (d)].
Fig. 4. Photoabsorption and photoluminescence spectra of PbBr–AzoCnA powder
(solid lines) and dissolved in DMF solution (broken line) [n¼2 (a), 4 (b), and 6 (c)].
Moreover, the position and shape of the peaks was the same as
that of the (C16H33NH3)2PbBr4 hybrid powder, which is a typical
hybrid compound. Thus, it is found that the crystal structure of
the synthesized PbBr–AzoCnA hybrids is the same as that of the
(C16H33NH3)2PbBr4 hybrid. The peak originating from the Br 3d
orbit was asymmetrical. This is caused by a distortion of the
octahedron of PbBr24ꢀ, as reported in previous paper [14]. Thus,
we suggest the schematic structure model of PbBr–AzoCnA
crystals shown in Fig. 3.
hybrid compounds will also be produced. Although a mixed DMF
solution of PbBr2 and AzoCnAþBrꢀ does not show the emission,
PbBr–AzoCnA hybrid powders showed a remarkable and sharp PL
peak with a small Stokes shift. Thus, it is found that synthesized
PbBr–AzoCnA hybrid powders have an objective layered perovs-
kite crystal structure and exhibit PL from excitons produced in the
PbBr24ꢀ layer. Moreover, the absorption peak from the azobenzene
group observed around 350 nm did not vary upon hybridization
of PbBr2 with AzoCnAþBrꢀ. This fact indicates that AzoCnAþ
cations have no intermolecular interaction in the interlayer space
of PbBr–AzoCnA hybrids. Thus, it can be predicted that AzoCnAþ
cations in the synthesized PbBr–AzoCnA hybrid powders exhibit a
photoisomerization reaction from the trans- form to the cis- form
under UV irradiation.
3.2. Spectroscopic properties of PbBr–AzoCnA hybrid powder
Fig. 4 shows the DR and PL spectra of the PbBr–AzoCnA hybrid
powders. A new peak or shoulder was observed at around 400 nm
in the DR spectra of the PbBr–AzoCnA hybrid powders. Because
this peak or shoulder was not observed in the mixed DMF
solution of PbBr2 and AzoCnAþBrꢀ, it is found that this new peak
or shoulder appeared by the formation of the hybrid compounds
of PbBr2 with AzoCnAþBrꢀ. Such a peak can also be observed in
the DR spectrum of the (C16H33NH3)2PbBr4 hybrid powder, and it
is well known that this absorption peak is due to the production
of excitons in the PbBr24ꢀ octahedral layer. Thus, it can be
expected that excitons in the PbBr24ꢀ layer of the PbBr–AzoCnA
3.3. Photoisomerization from trans- to cis-AzoCnA chromophores
in PbBr–AzoCnA hybrid powder
Fig. 5 shows the DR spectra of PbBr–AzoCnA hybrid powders
before and after UV light irradiation. An absorption peak around
350 nm from the trans- form of AzoCnA in all the PbBr–AzoCnA

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R. Sasai, H. Shinomura / Journal of Solid State Chemistry 198 (2013) 452–458
hybrids decreased by UV light irradiation, and then the absorption
peak around 450 nm from the cis- form of AzoCnA appeared and
increased. That is, AzoCnA chromophores incorporated in the
PbBr24ꢀ layer structure exhibited photoisomerization from trans-
to cis- forms under UV light irradiation. Estimating the photo-
isomerization rate (X) from the trans- to the cis- forms is
determined from the following equation:
trans
ir
At0rans
At0ransꢀA
X ¼
ꢁ 100
ð2Þ
trans
ir
where At0rans and A
are the absorbance at 350 nm before and
after UV irradiation, respectively. The values of X for PbBr–
AzoC2A, PbBr–AzoC4A, and PbBr–AzoC6A were 33%, 32%, and
34%, respectively, and thus were almost same. This fact indicates
that the synthesized PbBr–AzoCnA has nearly equal vacant space
and can accommodate cis- forms of AzoCnA in its interlayer space.
Therefore, we succeeded in synthesizing PbBr24ꢀ-based layered
perovskite compounds incorporating AzoCnA chromophores,
which, for the first time show a reversible photoisomerization
reaction.
Fig. 5. DR spectra of PbBr–AzoCnA materials [n¼2 (a), 4 (b), and 6 (c)] before UV
irradiation (solid lines), after UV irradiation (broken lines), and after visible
irradiation to UV-irradiated samples (circles). (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this
article.)
Fig. 6 shows the PL spectra of the PbBr–AzoCnA hybrid powder
before and after UV light irradiation. The intensity of the PL peak
observed around 410 nm decreased under UV light irradiation,
regardless of the value of n. The PL spectra of PbBr–C16A did not
vary by UV light irradiation. Thus, it is found that this decrease in
the intensity of the PL peak is caused by photoisomerization from
the trans- to the cis- forms of AzoCnA chromophores incorporated
in the interlayer space of the PbBr24ꢀ-based layered perovskite
compound. Moreover, XRD patterns, FT-IR spectra, morphologies,
and XPS spectra of the PbBr–AzoCnA hybrid powders did not
change. Fig. 7 shows a structural model of the PbBr–AzoCnA
hybrids before and after UV light irradiation as suggested from
these experimental results. Thus, the reason why the PL changed
by UV light irradiation may have been caused by re-absorption or
energy transfer from excitons produced in the PbBr24ꢀ layers to
the cis-AzoCnA chromophores. If the reason for reduction of PL
intensity by UV light irradiation was re-absorption, then the PL
quenching rate is independent of the D values, but if the reason
for the reduction was energy transfer, then the PL quenching rate
depends on the D values. In Fig. 8, the quenching rates of PL
intensity from excitons produced in the PbBr24ꢀ layers are plotted
against distance between the PbBr24ꢀ layer and the AzoCnA
chromophore, D, which shows that PL intensity depends on
D value, i.e., PL intensity decreases with an increase in D value.
Thus, it is found that this PL quenching can be caused by the
energy transfer from excitons produced in the PbBr24ꢀ layer to the
cis-AzoCnA chromophore.
Fig. 6. PL spectra of PbBr–AzoCnA materials [n¼2 (a), 4 (b), and 6 (c)] before UV
irradiation (solid lines), after UV irradiation (broken lines), and after visible
irradiation to UV-irradiated samples (circles). (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this
article.)
Fig. 7. Schematic model structures of PbBr–AzoCnA hybrid materials before and after UV irradiation.

R. Sasai, H. Shinomura / Journal of Solid State Chemistry 198 (2013) 452–458
457
Fig. 8. Dependence of PL quenching rate on D values.
3.4. Iteration photoisomerization reaction of AzoCnA chromophores
in PbBr–AzoCnA hybrid powders
In Fig. 9, the intensity of the Kubelka–Munk (KM) function
value at the absorption peak of the trans- and cis- forms of
AzoCnA (a) and the PL peak (b) are plotted as functions of
iteration number, m. The photo-absorption change of trans-
AzoCnA observed around 350 nm under both UV and visible light
irradiation, which originated from the p–p* phototransition, was
fully reversible regardless of the value of n. However, the KM
intensity of cis-AzoCnA observed at around 450 nm under both
UV and visible light irradiation, which originated from the n–p*
phototransition, gradually increased with an increase in m value.
This difference of photoisomerization behavior between trans-
and cis-AzoCnA was abnormal because the photoisomerization
behavior of both trans- and cis-azobenzenes are generally in
accord in a dilute solution. Thus, the increase in photoabsorption
from the n–p* phototransition cannot be explained by an increase
Fig. 9. KM values (a) and PL intensity (b) of PbBr–AzoCnA hybrid materials as a
function of iteration number, m, of UV and visible light irradiation.
in the number of cis-AzoCnA chromophores. Moreover, the PL
intensity of the PbBr–AzoCnA hybrids also decreased with an
increase in m value, although the PL intensity was somewhat
restored. These results indicate that PL quenching would be
caused by the energy transfer from excitons produced in the
materials could be recognized as one of the several photoswitch-
able PL materials, although a way to control the increase in
PbBr24ꢀ layer to the n–
phores in PbBr–AzoCnA hybrids. The mechanism of the photo-
absorption from the n– * phototransition of AzoCnA is still
unclear, although the self-assembled structure of AzoCnA chro-
mophores in PbBr–AzoCnA hybrids is considered to be one of the
reasons of this behavior.
p
* phototransition of AzoCnA chromo-
probability of an n–p* phototransition is required.
p
Acknowledgments
This work is partly supported by the Research Promotion
Foundation of Nagoya University. Authors are grateful to Prof.
K. Takase (College of Science and Technology, Nihon University)
for fruitful discussions of PL data. The synchrotron-radiation
X-ray diffraction experiments for checking the crystallinity of
the PbBr–AzoCnA hybrid powder were performed at the BL02B2
in the SPring-8 with approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (Program no. 2010A1287).
4. Conclusions
In this study, we succeeded in synthesizing hybrid solid
materials of AzoCnA chromophores (n¼2, 4, 6) with PbBr42ꢀ
-
based perovskite layers, in which for the first time the AzoCnA
chromophores exhibited reversible photoisomerization from
trans- and cis- forms. Moreover, the PL intensity of this hybrid
material responded to UV and visible light irradiation. Mean-
while, we found abnormal photoisomerization behavior of the
AzoCnA chromophores in the PbBr–AzoCnA hybrids, i.e., an
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