CH3NH3PbBr3 Perovskite Nanocrystals as Efficient Light-Harvesting Antenna for Fluorescence Resonance Energy Transfer

Article abstract of DOI:10.1002/asia.201601672

Hybrid perovskites have created enormous research interest as a low-cost material for high-performance photovoltaic devices, light-emitting diodes, photodetectors, memory devices and sensors. Perovskite materials in nanocrystal form that display intense luminescence due to the quantum confinement effect were found to be particularly suitable for most of these applications. However, the potential use of perovskite nanocrystals as a light-harvesting antenna for possible applications in artificial photosynthesis systems is not yet explored. In the present work, we study the light-harvesting antenna properties of luminescent methylammonium lead bromide (CH₃NH₃PbBr₃)-based perovskite nanocrystals using fluorescent dyes (rhodamine B, rhodamine 101, and nile red) as energy acceptors. Our studies revealed that CH₃NH₃PbBr₃ nanocrystals are an excellent light-harvesting antenna, and efficient fluorescence resonance energy transfer occurs from the nanocrystals to fluorescent dyes. Further, the energy transfer efficiency is found to be highly dependent on the number of anchoring groups and binding ability of the dyes to the surface of the nanocrystals. These observations may have significant implications for perovskite-based light-harvesting devices and their possible use in artificial photosynthesis systems.

Full text of DOI:10.1002/asia.201601672

CHEMISTRY
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Accepted Article
Title: CH3NH3PbBr3 Perovskite nanocrystals as efficient light
harvesting antenna for fluorescence resonance energy transfer
Authors: Vijayakumar C. Nair, Chinnadurai Muthu, and Anuja Vijayan
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CH3NH3PbBr3 Perovskite nanocrystals as efficient light
harvesting antenna for fluorescence resonance energy transfer
Chinnadurai Muthu,[a, b] Anuja Vijayan[a] and Vijayakumar C. Nair*[a, b]
10]
Abstract: Hybrid perovskites have created enormous research
interest as a low-cost material for high-performance photovoltaic
devices, light-emitting diodes, photodetectors, memories and
sensors. Perovskite materials in nanocrystal form, show intense
luminescence due to quantum confinement effect, were found to be
particularly suitable for most of these applications. However, the
potential use of perovskite nanocrystals as a light harvesting
antenna for possible applications in artificial photosynthesis systems
is not yet explored. In the present work, we study the light harvesting
antenna properties of luminescent methylammonium lead bromide
(CH3NH3PbBr3) based perovskite nanocrystals using fluorescent
dyes (rhodamine B, rhodamine 101 and nile red) as energy
acceptors. Our studies revealed that CH3NH3PbBr3 nanocrystals are
an excellent light harvesting antenna, and efficient fluorescence
resonance energy transfer occurs from the nanocrystals to
fluorescent dyes. Further, the energy transfer efficiency is found to
be highly dependent on the number of anchoring groups and binding
ability of the dyes to the nanocrystals surface. These observations
may have significant implications in the perovskite-based light
harvesting devices and their possible use in artificial photosynthesis
systems.
However, poor stability due to the hygroscopic nature of the
organic salts is still a major concern for practical applications.[11-
13] Reports suggest that the stability of perovskite materials could
be substantially improved by preparing them in nanocrystal form
with alkyl ammonium halides as capping agents.[14-26] Recently,
Pérez-Prieto et al. reported the synthesis of stable perovskite
nanocrystals (PNC) having good emission characteristics, and
its application in electroluminescent devices.[26] Following this
report, several studies done by various groups suggest that
hybrid perovskites in nanocrystal form is suitable for most of the
above mentioned applications.[27-40] In this context, very recently,
we have demonstrated the excellent energy migration properties
of these materials.[28] We have also illustrated the use of PNCs
for memory device applications[29] and as sensors for the
detection of explosives.[40] Nevertheless, the real potential of
PNCs through the optimal utilization of their optical and
electronic properties is yet to be explored.
Photosynthesis, one of the most important and fundamental
natural processes responsible for life on earth, has been
subjected to numerous studies. The key steps in natural
photosynthesis are the solar light energy harvesting via
photoabsorption and funneling of this harvested energy to the
reaction center through energy and electron transfer processes.
Inspired by the natural photosynthesis, chemists have been
attempting to mimic such processes using synthetic materials
consisting of covalent or supramolecular systems.[41-44] Further
interest in this area was evolved due to the research in
advanced materials for optoelectronic devices, where energy-
and electron-transport processes at nanoscale play important
roles.[45,46] For instance, fluorescence resonance energy transfer
Introduction
Organic-inorganic halide perovskites attracted significant
research interest during the last few years mainly due to their
use as photoabsorption layer in photovoltaic devices with high
efficiency.[1-5] These hybrid materials made from abundant and
low-cost compounds has a generic structure of AMX3, where A
is an organic cation, M is a transition metal cation (Pb in most
cases) and X is a halogen anion. They possess the advantages
of both organic (excellent processability and flexibility) and
inorganic (high ordering and electronic mobility) constituents,
which make them suitable for applications such as light emitting
diodes, photodetectors, memories, and sensors in addition to
solar cells.[6-7] The broad range of applications of hybrid
perovskites could be attributed to the high light absorption
coefficient over a wide spectral range, excellent photo- and
electroluminescence, small exciton binding energy, high charge
carrier mobility, and long-range electron/hole diffusion lengths.[8-
(FRET) along donor/acceptor arrays was found to be
a
successful strategy to improve the power conversion efficiency
of photovoltaic devices.[47-50] Though hybrid perovskites find a
wide range of applications, their utility as an efficient light
harvesting antenna system were not explored so far except a
recent report on energy transfer between inorganic PNCs.[51]
In order to use a material as light harvesting antenna, it has
to display two capabilities, viz. excellent light absorption and
efficient energy transfer to the acceptors. In this context,
luminescent PNCs are potential candidates as they exhibit
intense light absorption and good fluorescence quantum yield
due to the quantum confinement effect.[20-22,31] Moreover, they
possess high surface area, which helps them interact effectively
with suitable acceptor dyes through electrostatic forces. As a
proof of concept, herein, we investigate in detail about the light
harvesting antenna properties of perovskite nanocrystals (as
energy donor) using rhodamine dyes (as energy acceptors).
Rhodamine dyes, characterized by excellent photophysical
properties such as high extinction coefficients and good
fluorescence quantum yields, are known to act as efficient
energy acceptors for FRET studies.[52,53] For the present study,
Rhodamine B (RhB) and Rhodamine 101 (Rh101) were used.
The chemical structures of the dyes are shown in Scheme 1.
[a]
C. Muthu, A. Vijayan, Dr. V. C. Nair
Photosciences and Photonics Section
CSIR-National Institute for Interdisciplinary Science and Technology
(NIIST)
Thiruvananthapuram 695 019, India
E-mail: cvijayakumar@niist.res.in
[b]
Academy of Scientific and Innovative Research (AcSIR)
New Delhi 110 001, India
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by transmission electron microscopy (TEM), X-ray diffraction
(XRD), UV-vis absorption and fluorescence spectroscopy. TEM
analysis revealed that the nanocrystals were spherical in shape
with an average diameter of 6.1 nm (Figure 1b). The phase
purity and crystallinity were confirmed by XRD analysis (Figure
S1, ESI). The observed diffraction patterns were corresponding
to the cubic phase with a lattice constant of 5.93 Å.
The absorption and emission spectra of PNCs were
measured in chloroform (Figure 1c). The absorption maximum
corresponding to the excitonic band was observed at 527 nm.
The green emission was sharp (full-width at half maximum: 21
nm) and intense with a maximum at 531 nm. The relatively
smaller Stokes shift (4 nm) implies that the photoluminescence
emission originates nearly completely from the direct exciton
recombination due to the strong quantum confinement
effect.[21,26] In chloroform, the emission quantum yield (f) of the
nanocrystals was found to be 72%. FRET studies were carried
out using the chloroform suspension of the PNCs. One of the
important criteria for donor/acceptor materials to be efficient
FRET pairs is the good spectral overlap between donor
emission and acceptor absorption. This implies the presence of
matching excited energy levels in donor and acceptor species,
which facilitates seamless energy transfer from the excited
donor to the acceptor in the ground state. The emission
spectrum of PNCs showed significant overlap with the high
energy side of the absorption band of rhodamine dyes (Figure
S2, ESI). The spectral overlap was found to be almost similar for
both PNC/RhB and PNC/Rh101 pairs with an overlap integral of
2.98 × 1015 M-1 cm-1 nm4 and 2.53 × 1015 M-1 cm-1 nm4,
respectively. These values are comparable to several quantum
dot/organic dye FRET pairs reported in literature.[54-56]
For the FRET studies, the concentration of the donor was
kept constant (2 mg in 100 mL CHCl3), and the concentration of
the acceptor dyes increased from 0 to 0.6 µM by the successive
addition of 10 L from a 15 M stock solution of the dye to 3 mL
of the donor solution. 425 nm was selected as the excitation
wavelength as the dye absorption was negligible at that
wavelength (Figure S3, ESI). In the absence of the acceptor
dyes, PNCs exhibit intense green emission with an emission
maximum at 531 nm on photoexcitation. On addition of
increasing amounts of RhB (0 – 0.6 µM), the donor emission at
531 nm decreased with a concomitant emission at 576 nm
corresponding to the dye emission (Figure 2a). Donor emission
Scheme 1. Chemical structure of the acceptor dyes used for FRET studies
Results and Discussion
Methylammonium lead bromide (CH3NH3PbBr3) PNCs with
octylammonium bromide as the capping agent were synthesized
as a suspension in toluene.[26] The PNCs consist of lead ions
surrounded by six bromide anions forming an octahedra, and
several of which connected to form
a three-dimensional
structure. The voids formed between the connected octahedras
+
are occupied by the organic cations (CH3NH3 ). The capping
agent present in the reaction mixture interacts with the surface
of the initially formed perovskite nanostructures through
electrostatic forces. This interaction not only prevents the growth
of the perovskite structures to restrict the size in nanometres but
also provides colloidal stability to the nanocrystals. A simplified
schematic representation of a PNC is shown in Figure 1a. Solid
powder of the PNCs having excellent moisture stability was
obtained by the centrifugation of the toluene suspension, which
could be re-dispersed in a variety of solvents such as toluene,
chloroform, tetrahydrofuran etc. The PNCs were characterized
quenching reached
a saturation point when the acceptor
concentration was at 0.6 M. At this concentration, the total
quenching of the donor emission was 50%. On the other hand,
the fluorescence quenching of PNCs was much more efficient in
the presence of Rh101 dye (Figure 2b). About 40% of the PNC
emission was quenched on the first addition (0.05 M) of the dye.
When the dye concentration reached 0.35 M, 91% of the donor
emission was quenched. No further change in the emission
intensity was seen on increasing the acceptor content indicating
a saturation state. Excitation spectra of PNC/dye mixture was
recorded at the dye emission maximum (RhB: 576 nm; Rh101:
606 nm; Figure S6, ESI). The observation of the absorption
features of the PNCs in the excitation spectra confirmed the
FRET process from PNCs to the dyes in both cases.
Figure 1. a) Simplified schematic representation and b) TEM image of the
perovskite nanocrystals. c) UV-vis absorption and emission spectra of the
nanocrystals in chloroform (ex = 425 nm, l = 10 mm).
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Figure 3. Fluorescence decay profiles of perovskite nanocrystals in the
absence and presence of a) RhB (0-0.60 M) and b) Rh101 (0-0.35 M). The
samples were excited with 410 nm laser and the emission decay was probed
at 531 nm.
Figure 2. Steady state emission spectral changes of the perovskite
nanocrystals on addition of increasing amounts of a) RhB and b) Rh101 in
chloroform (ex = 425 nm, l = 10 mm).
The non-radiative nature of the energy transfer process was
confirmed by monitoring the fluorescence decay of PNCs in the
absence and presence of the acceptor dyes (excited at 410 nm,
probed at 531 nm). The PNCs exhibited multi-exponential
fluorescence decay with an average lifetime of 614 ns. The
decay becomes faster on addition of increasing amounts of
acceptor dyes. Such a shortening of the fluorescence lifetime in
the presence of an acceptor indicates non-radiative energy
transfer, and rules out the possibility of the trivial radiative
energy transfer mechanism, i.e., the emission-reabsorption
process.[57] As in the case of fluorescence quenching, shortening
of the lifetime of PNCs was distinctly different in the presence of
RhB and Rh101. It was relatively slower on addition of RhB
(Figure 3a), and at the saturation point (i.e., in the presence 0.60
M of RhB), the fluorescence lifetime of the donor was
decreased to 303 ns. On the other hand, shortening of the donor
lifetime was faster on addition of Rh101 (Figure 3b). It was
decreased to 181 ns in the presence of 0.35 M of Rh101.
Energy transfer efficiency calculated from the lifetime data was
found to be 50% for PNC/RhB, same as that obtained from
fluorescence quenching studies. However, in the case of
PNC/Rh101 pair, the efficiency was found to be 71%, which was
lower than the efficiency calculated from fluorescence quenching
(91%). The fluorescence decay was also monitored at the dye
emission maximum (RhB: 576 nm; Rh101: 606 nm) on excitation
of the PNCs at 410 nm (Figure S7, ESI). The presence of a fast
rise component in the initial time-scale clearly suggests the
formation of the dye excited state through FRET from PNCs.
In order to get a better understanding about the nature of the
quenching process, Stern−Volmer (SV) plot was drawn by
plotting the ratio of the emission intensity of the donor in
absence and presence of the acceptor (I0/I) against the
concentration of the acceptor, [Q]. The linear behaviour of the
SV plot in the case of PNC/RhB (Figure 4a) indicated that the
quenching process is dynamic in nature. The Stern-Volmer
constant (KSV) was determined using the following equation.
[ ]
From the slope of the plot, the KSV was calculated as 1.83 × 106
M-1. Interestingly, the SV plot of PNC/Rh101 showed a non-
linear behavior with an upward curvature (Figure 4b). The
positive deviation from linearity implies the presence of both
static and dynamic components in the fluorescence quenching
process.[57-59] The following adjusted Sern-Volmer equation was
used to separate the dynamic (KD) and static (KS) quenching
components.
[ ]
[ ]
KD was and KS was determined using the following equations
[ ]
[ ]
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where,  and 0 are the lifetime of PNC in the presence and
absence of the dyes, respectively. The corresponding plots are
shown in Figure S8, ESI. The dynamic and static quenching
constants were calculated as 7.30 × 106 M-1 and 6.57 × 106 M-1,
respectively. The presence of both components in the quenching
process explains the discrepancy in energy transfer efficiency of
PNC/Rh101 pair obtained from fluorescence and lifetime studies.
In static quenching, the lifetime of the donor does not decrease
in the presence of the acceptor. However, fluorescence intensity
decreases due to the formation of a non-fluorescent complex in
the ground state. So the difference of 20% in the energy transfer
efficiency could be attributed to the contribution of static
quenching.
The above observations clearly imply that the FRET
efficiency of the PNCs is significantly higher in the presence of
Rh101 than that of RhB. It must be noted that the major
difference between RhB and Rh101 is that the former has only
one binding site, the quarternary ammonium group (the
carboxylic acid group remain unionized in relatively non-polar
solvent like chloroform). On the other hand, the latter is a zwitter
ion or an inner salt with two binding sites, the quarternary
ammonium and carboxylate groups. As a result, it could be
assumed that the electrostatic interaction between PNCs and
RhB would be weak, whereas, that of PNCs and Rh101 would
be strong. To confirm this aspect, UV-vis absorption and
emission spectra of the mixtures were measured in chloroform.
Interestingly, both dyes showed red-shift in the absorption and
Figure 4. Relative changes in the emission intensity of perovskite
nanocrystals as function of the concentration of a) RhB and b) Rh101.
(Solvent: chloroform, ex = 425 nm, l = 10 mm).
Figure 5. Absorption spectra of a) RhB, c) Rh101 and the emission spectra of b) RhB, d) Rh101 in the absence (red) and presence (green) of perovskite
nanocrystals. (ex = 425 nm; Conc. RhB: 0.60 M and Rh101: 0.35 M).
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Figure 6. a) Chemical structure of nile red b) fluorescence emission spectra of PNC, nile red and their mixture (ex = 425 nm) and c) fluorescence decay profile of
perovskite nanocrystals in the absence and presence of nile red. The samples were excited with 410 nm laser and the emission decay was probed at 531 nm.
emission maximum in the presence of PNCs. This indicates that
the dye molecules are interacting with the PNC surface through
electrostatic forces, which changes the electron distribution of
the dyes resulting in red-shift in the absorption and emission
maximum.[54,57] However, the red-shift was marginal for RhB;
only 0.2 nm in the absorption maximum (Figure 5a), and of 6 nm
in the emission maximum (Figure 5b). On the other hand,
remarkable red-shift was observed for Rh-101; absorption
maximum shifted by 7 nm (Figure 5c) and emission maximum
shifted by 16 nm (Figure 5d). Such a shift in the absorption and
emission maximum not only confirms a strong electrostatic
interaction but also reiterates the contribution of static
component in the fluorescence quenching of PNCs due to the
close proximity of Rh101. Further evidence for the effect of
with the PNCs. Compared to rhodamines, better spectral overlap
was found between the emission of PNCs and absorption of NR
dye due to the complete overlap between PNC emission and
dye absorption, (Figure S2c), and the pair exhibited an overlap
integral of 4.04 × 1015 M-1 cm-1 nm4. Subsequently, FRET
studies were carried out by adding NR dye in chloroform to the
PNCs dispersed in chloroform (Figure 6b). On excitation of the
mixture at 425 nm no quenching was observed for the donor
emission at 531 nm. Nevertheless, an emission peak
corresponding to the NR emission was observed at 600 nm.
However, the emission intensity of the NR emission was less
compared to the emission on the direct excitation of the dye.
These observations indicate that FRET is absent in PNC/NR
pair and the observation of dye emission on excitation at 425 nm,
where the dye has negligible absorption, could be due to simple
1
binding groups was obtained from H NMR and FT-IR studies of
the dyes in the absence and presence of PNCs (Figure S9-S13,
ESI). The NMR spectra revealed that the protons of Rh101 close
to amine and carboxyl groups were significantly shifted in the
presence of PNCs indicating their close proximity to the surface
of PNCs. But only negligible shifts were seen in the NMR
spectra of RhB indicating a weak interaction with PNCs. FT-IR
analysis reiterated this observation; the keto group in Rh101
was shifted by 17 cm-1, whereas, only 6 cm-1 shift was seen in
the case of RhB in the presence of PNCs.
It must also be noted that about 49% enhancement was
observed for RhB emission on FRET when compared to that of
the direct excitation of the dye, whereas, this enhancement was
about 90% for Rh101. This implies that FRET from PNCs is a
more efficient pathway for the excitation of the dyes than that of
direct excitation. Moreover, better enhancement for Rh101
reiterates the FRET efficiency is higher in PNC/Rh101 mixture.
No change in the absorption characteristics of PNCs was
observed in the presence of dyes indicating that the dye binding
does not affect its electronic properties (Figure S4, ESI) of the
nanocrystals. The morphological features such as the size and
shape of the PNCs were also not altered on dye binding as
observed from the TEM images of the mixed samples (Figure
S14, ESI).
Figure 7. Schematic representation of the emission properties and FRET
process between perovskite nanocrystals and various dye molecules.
emission – reabsorption process (photons emitted by PNCs
absorbed by NR dyes resulting its emission). This was reiterated
by the comparison of the fluorescence lifetime profile of PNC
alone and PNC/NR mixture (Figure 6c). As shown in the figure,
noticeable changes were absent in the lifetime decay profile of
the PNCs in the presence of NR. The emission and FRET
properties of PNCs in the absence and presence of
RhB/Rh101/NR is summarized in Figure 7
To further confirm the role of anchoring group, FRET studies
were carried out under identical conditions with nile red (NR;
Figure 6a), which is spectroscopically similar to rhodamines but
do not possess any anchoring groups to interact electrostatically
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The same procedure was followed for the synthesis of octylammonium
bromide using 1 g of octylamine (7.7 mM, 1 equivalent) and 2.1 ml of
30% HBr (7.7 mM, 1 equivalent) in glacial acetic acid. Yield: 98%; 1H
NMR (500 MHz, CDCl3, TMS) δ (ppm): 0.87-0.89 (t, 3H), 1.26-1.32 (m,
8H), 1.37-1.43 (p, 2H), 1.78-1.84 (p, 2H), 3.00-3.07 (M, 2H), 7.96 (s, 3H);
13C NMR (125 MHz, D2O) δ (ppm): 13.34, 21.94, 25.50, 26.64, 28.09,
28.14, 30.97, 39.51.
Conclusions
In summary, the application of perovskite nanocrystals as light
harvesting antennae for efficient fluorescence resonance energy
transfer processes were illustrated by using methylammonium
lead bromide nanocrystals as donor and rhodamine dyes (RhB
and Rh101) as acceptors. The interaction between the
nanocrystals and dyes are electrostatic in nature, and as a result,
the binding ability of the dye molecules on the nanocrystal
surface plays a key role on FRET efficiency. Excellent light
harvesting properties and high FRET efficiencies makes
luminescent perovskite nanocrystals a good candidate as the
light absorber in artificial photosynthesis systems.
Synthesis of hybrid perovskite nanocrystals: The CH3NH3PbBr3
perovskite nanocrystals with octylammonium bromide as the capping
agent were synthesized as a suspension in toluene using a procedure
reported by Perez-Prieto and co-workers.[26] Briefly, 2 ml of octadecene
was heated to 80 C, and octylammonium bromide (16.8 mg, 0.08 mmol)
was added to this solution. Subsequently methylammonium bromide
(13.2 mg, 0.12 mmol dissolved in 100 µL of DMF) and lead (II) bromide
(36.7 mg, 0.1 mmol dissolved in 200µL of DMF) were added. A yellow
dispersion was formed and the nanocrystals were immediately
precipitated by addition of acetone. It was then centrifuged at 7000 rpm
for 10 minutes, supernatant solution decanted and the residual
nanocrystals were dispersed in toluene.
Experimental Section
Chemicals: Lead bromide (99.999%, Sigma Aldrich), methylamine (40%
w/w in water, Alfa aesar), hydrobromic acid (33% in glacial acetic acid,
Sigma Aldrich), octylamine (99%, Sigma Aldrich), oleic acid (99%, Sigma
Aldrich), 1-octadecene (95%, Sigma Aldrich), rhodamine B (95%, Sigma
Aldrich), rhodamine 101 (95%, Sigma Aldrich), nile red (Sigma Aldrich),
acetone (99% Spectrochem), chloroform (99%, Spectrochem) and
toluene (99%,Spectrochem) were used without any further purification.
Photophysical measurements: All the energy transfer studies were
carried out in chloroform. Typically, 2.0 mg of perovskite nanocrystals
was uniformly dispersed in 100 ml of chloroform by sonication. The dyes
were prepared in micro molar concentration (15 µM). 10 µL of dye
solution was added to the perovskite dispersion (3 mL) for each
measurement.
Characterization: 1H and 13C NMR spectra were recorded on a 500 MHz
Bruker Avance DPX Spectrometer. Electronic absorption spectra were
recorded on a Shimadzu UV-2600 UV-vis spectrophotometer and the
The fluorescence quantum yield of perovskite nanocrystals was
measured by the relative method using fluorescein dissolved in 0.1 M
NaOH as the standard dye (Φ = 0.95). The quantum yield of the
perovskite nanocrystals was calculated using the following equation.
emission
spectra
were
recorded
on
a
SPEX-Fluourolog
Spectrofluorimeter. Optical properties in solution were measured by
using a quartz cuvette with 1 cm path length. For emission studies, right
angle geometry was used. X-ray diffraction studies were carried out on
powdered samples with Xeuss Simultaneous 2D WAXs/SAXs using Cu-K
α radiation (λ = 1.5418Å). TEM measurements were carried out using
FEI-TECNAI T30, with EDAX at accelerating voltage of 300 KV. Samples
for TEM analysis were prepared by drop casting perovskite nanocrystals
dispersed in chloroform onto a carbon coated copper grid at the required
concentrations at ambient conditions. The solvent was removed under
vacuum. TEM images were obtained without staining. The lifetime
studies were carried out using an IBH FluoroCube time correlated pico
second single photon counting (TCSPC) system. Samples were excited
using a pulsed diode laser (˂100 ps pulse duration) at a sample emission
wavelength of 410 nm (NanoLED-11) with a repetition rate of 250 KHz.
(1)
Where As and Au are the absorbance of standard (dye) and unknown
(PNC) respectively. Fs and Fu are the areas under the fluorescence
spectrum of the standard and unknown. ns and nu are the refractive
indices of the solvent used for standard and sample, respectively.
The overlapping integral that describes the degree of spectral overlap
between the donor emission and acceptor absorption was calculated
using the following formula
∫
(2)
Synthesis of precursors
∫
Synthesis of Methyl- and Octylammonium Bromides: The precursors,
methylammonium bromide (CH3NH3Br) and octylammonium bromide
(C8H17NH3Br), were synthesized by reaction of the corresponding amine
in water/HBr, using reported procedures.[60] Briefly, for the synthesis of
methylammonium bromide, 2.5 ml of 40% methylamine in water (32.2
mM, 1 equivalent) was taken in the round bottom flask, and 8.67 ml of
30% HBr (32.2 mM, 1 equivalent) in glacial acetic acid was added to this
at 0 C. Then the reaction mixture was stirred for about 2 hours, followed
by the addition of diethyl ether for the precipitation of methyl ammonium
bromide. It was then filtered, washed several times with diethyl ether, and
dried under vacuum for overnight. Yield: 98%; 1H NMR (500 MHz, DMSO,
TMS) δ (ppm): 2.34-2.38 (q, 3H), 7.65 (s, 3H); 13C NMR (125 MHz, D2O)
δ (ppm): 24.69.
where FD ( is the fluorescence intensity of the perovskite nanocrystals
in the wavelength range of to d (dimensionless unit) and is the
molar extinction coefficient of the dye molecules (M-1cm-1) at the
wavelength λ.
The efficiency of the energy transfer was calculated from the following
equation.
(3)
 and 0 are the fluorescence intensities of the donor in the presence and
absence of the acceptor dyes.
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[24] S. Gonzalez-Carrero, R. E. Galian and J. Perez-Prieto, J. Mater. Chem.
A 2015, 3, 9187-9193.
Acknowledgements
[25] A. Swarnkar, R. Chulliyil, V. K. Ravi, M. Irfanullah, A. Chowdhury and A.
Nag, Angew. Chem. Int. Ed. 2015, 54, 15424-15428.
This work was financially supported by DST Ramanujan
Fellowship
(SR/S2/RJN-133/2012),
DST-SERI
project
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The
potential
use
of
hybrid
Chinnadurai Muthu,[a, b] Anuja Vijayan [a]
and Vijayakumar C. Nair*[a, b]
perovskites as an efficient light
harvesting antenna for fluorescence
resonance energy transfer (FRET)
process is described. This is
Page No. – Page No.
demonstrated
hybrid perovskite
(CH3NH3PbBr3, PNP) as energy donor
and rhodamine dyes such as
rhodamine B (RhB) and rhodamine
101 (Rh101) as energy acceptors.
using
luminescent
nanoparticles
CH3NH3PbBr3 Perovskite
nanocrystals as efficient light
harvesting antenna for fluorescence
resonance energy transfer
For internal use, please do not delete. Submitted_Manuscript
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