Induced chain alignment, efficient energy transfer, and enhanced light emission in functional poly acetylene-perovskite hybrids

Article abstract of DOI:10.1021/ma051616h

The hybridization of functional polyacetylenes with lead bromide perovskite was investigated. It was observed that the perovskite induces the nonmesogenic polyactylene chains to align like liquid crystals within the inorganic layers. It was shown that pho

Full text of DOI:10.1021/ma051616h

Macromolecules 2005, 38, 8127-8130
8127
Induced Chain Alignment, Efficient Energy
Transfer, and Enhanced Light Emission in
Functional Polyacetylene-Perovskite
Hybrids
Jianli Hua,† Zhen Li,† Jacky W. Y. Lam,†
Haipeng Xu,‡ Jingzhi Sun,‡ Yuping Dong,†
Yongqiang Dong,†,‡ Anjun Qin,† Wangzhang Yuan,‡
Hongzheng Chen,‡ Mang Wang,‡ and
Ben Zhong Tang*,†,‡
Department of Chemistry, The Hong Kong University of
Science & Technology, Clear Water Bay, Kowloon,
Hong Kong, China, and Department of Polymer Science and
Engineering, Zhejiang University, Hangzhou 310027, China
Received July 23, 2005
Hybridization of organic and inorganic species at the
molecular level has attracted much interest among
scientists because it offers the potential of combining
the best parts of the two classes of materials in a single
molecular composite as well as creating new properties
arising from the molecular interactions between the two
kinds of building blocks. One promising group of organic-
inorganic hybrids is the self-assembled multilayers of
organic cations and inorganic anions, where the layers
of organic ammonium salt alternate with the layers of
corner-sharing metal halide octahedra.1,2 Most of the
organic moieties used in the construction of ammonium
salt-metal halide perovskites have been nonfunctional
groups such as alkyl chains that play a secondary role
of merely helping to improve the processability of the
hybrids.1-3
Figure 1. IR spectra of (A) polyimide P2(9), (B) polyamine
P3(9), (C) polysalt P4(9), and (D) hybrid H5(9).
Scheme 1. Syntheses of Poly(1-phenyl-1-alkyne)
Ammonium Salt-Lead Bromide Perovskite Hybrids
Hybridization of π-conjugated macromolecules with
perovskites may generate new materials with novel
properties. This possibility has been explored but met
with only limited success. For example, Mitzi et al. have
integrated R,ω-diaminated oligothiophenes into lead
halide perovskites.4 The light-emitting diodes fabricated
from the oligothiophene-perovskite hybrids exhibited
maximum power efficiency and external quantum ef-
ficiency of 0.1 lm/W and 0.1%, respectively.4 A possible
reason for the poor device performance is the efficient
intersystem crossing in the oligothiophene system.
Polyacetylenes have traditionally been regarded as
poor emitters, but our recent work has proven that the
polymers can be excellent luminophors with photolu-
minescence (PL) quantum yields (ΦPL) up to unity,
provided that appropriate substituents or pendants are
appended to the polyene backbone.5 In this work, we
hybridized a group of emissive polyacetylenes with lead
bromide perovskites. In this communication, we dem-
onstrate how the molecular hybrids benefit from syn-
ergistic interplay between organic and inorganic com-
ponents: the soluble polymers endow the hybrids with
solubility or processability, while the perovskite layers
induce the polymer chains to luminesce more efficiently.
The synthetic routes to the polyacetylene-lead bro-
mide hybrids [H5(m); m ) 3, 9] are depicted in Scheme
1. ω-Chloro-1-phenyl-1-alkynes 1(m) are prepared by
palladium-catalyzed coupling of ω-chloro-1-alkynes with
iodobenzene,6 which are converted to 2(m) by the
reaction with potassium phthalimide. The monomers
are isolated in high yields and characterized by spec-
troscopic methods, from which satisfactory analysis data
are obtained [see Supporting Information (SI) for de-
tails]. The polymerizations of 2(m) are effected by
WCl6-Ph4Sn in toluene at 60 °C, giving yellow powdery
poly“imides” P2(m) in good yields. The phthalimido
group of P2(m) is hydrolyzed by hydrazine, producing
poly“amines” P3(m) in high yields (>89%). Treatment
of P3(m) with aqueous HBr gives rise to poly“salts”
P4(m), the complexation of which with lead bromide
results in the formation of the polyacetylene-perovskite
hybrids in >83% yields.
The hybrids are soluble in common polar solvents
such as DMF, DMSO, and water. They are thermally
stable, losing little of their weight when heated to ∼350
°C under nitrogen (e.g., SI, Figure S1). Their molecular
structures are characterized spectroscopically. An IR
spectrum of H5(9) is shown in Figure 1 as an example,
with those of P2(9)-P4(9) given in the same figure for
comparison. Two bands arising from stretching vibra-
† The Hong Kong University of Science & Technology.
‡ Zhejiang University.
* To whom correspondence should be addressed: Ph +852-2358-
7375; Fax +852-2358-1594; e-mail tangbenz@ust.hk.
10.1021/ma051616h CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/08/2005

8128 Communications to the Editor
Macromolecules, Vol. 38, No. 20, 2005
confirming that the hydrolysis has proceeded to comple-
tion. The spectrum of P3(9) is broad and structureless,
possibly because the polymer chains have aggregated
via hydrogen bonding of their amino pendnats. The
resonance peaks of P4(9) and H5(9) are sharper and
better resolved due to the blockage of the H-bonding
channel as well as their good solubility in the polar
solvent. New peaks are found at δ ∼ 8 in the spectra of
P4(9) and H5(9), which are assignable to the resonances
of the protons of their ammonium ions (NH3+).7
The polyacetylene backbone of polysalt P4(9) absorbs
at ∼340 nm (Figure 3A).5,9 Upon hybridization with lead
bromide, a new peak appears at 397 nm in the spectrum
of H5(9). To identify the origin of this peak, we prepared
1
a “model hybrid” (C4H9NH3)2PbBr4 and measured its
absorption spectrum. The model hybrid absorbs at 404
nm, verifying that the peak of H5(9) at 397 nm is
associated with exciton absorption of its lead bromide
perovskite component.10
While P4(9) is amorphous, its hybrid H5(9) displays
reflection peaks at low 2θ angles of 4.1° and 7.7° (Figure
4). The d-spacing associated with the reflection at 2θ )
Figure 2. 1H NMR spectra of solutions of (A) monomer 2(9),
(B) polyimide P2(9), (C) polyamine P3(9), (D) polysalt P4(9),
and (E) hybrid H5(9) in chloroform-d (A-C) or DMSO-d6 (D,
E). The solvent and water peaks are marked with asterisks.
tions of phthalimido group of polyimide P2(9) appear
at 1773 and 1713 cm-1 (Figure 1A),7 which disappear
after P2(9) has been subjeted to hydrolysis deprotection.
In the spectrum of the hydrolysis product or polyamine
P3(9), new absorption bands associated with stretching
and bending vibrations of amine group are observed at
3379 and 1573 cm-1, respectively. The ammonium ion
of polysalt P4(9) absorbs at 3000 and 1615 cm-1.7 The
absorption bands of the ammonium ion of hybrid H5(9)
are observed in a similar spectral region (Figure 1D).8
Figure 4. X-ray diffraction patterns of the thin solid films of
polysalt P4(9) and hybrid H5(9) spin-coated on quartz sub-
strates.
1
Figure 2 shows H NMR spectra of the solutions of
monomer 2(9), polymers P2(9)-P4(9), and hybrid H5(9)
in chloroform-d or DMSO-d6. The protons of ethyn-
ylphenyl (≡CC6H5) and propargyl groups (≡CCH2) of the
monomer resonate at δ 7.37-7.25 and 2.39, respectively.
The resonances upfield shift when the ethynylphenyl
and propargyl groups of 2(9) are transformed to styryl
(dCC6H5) and allyl groups (dCCH2)7 of P2(9) by the
W-catalyzed acetylene polymerization. The peaks are
broadened due to the rigid nature of the polyene
backbone.5,9 There are no peaks of phthalimido protons
[C6H4(CO)2] in the spectrum of P3(9) (Figure 2C),
4.1° is 21.5 Å, close to the molecular length of the repeat
unit of the polymer chain in its fully extended confor-
mation. The model hybrid (C4H9NH3)2PbBr4 shows an
intense reflection peak at 2θ ) 6.4°. The broad refelction
peak of H5(9) at 2θ ) 7.7° is probably a combination of
the reflection of the perovskite layer and the secondary
refelction of the polymer chain. The XRD pattern of the
hybrid is similar to those of the liquid crystalline
polyacetylenes developed in our laboratories5,9,11 al-
Figure 3. (A) Absorption spectra of thin solid films of polysalt P4(9), hybrid H5(9), and model hybrid compound (BuNH3)2PbBr4.
(B) Emission spectra of solutions of P2(9)-P4(9), H5(9), and poly(1-phenyl-1-octyne) (PPO) in THF. Polymer concentration: 0.05
mM; excitation wavelength (nm): 330 [P2(9)-P4(9) and H5(9)], 355 (PPO).

Macromolecules, Vol. 38, No. 20, 2005
Communications to the Editor 8129
though the polymer in H5(9) carries no mesogenic units.
The long-range order of the polymer chains thus must
have been induced by the perovskite when they are
intercalated into the lead bromide layers.
Acknowledgment. This work was partly supported
by the Research Grants Council of Hong Kong (603505,
603304, 664903, 6085/62P, and 6121/01P) and the
National Science Foundation of China (N_HKUST-
606_03). B.Z.T. thanks the support from the Cao Guang-
biao Foundation of the Zhejiang University.
The PL peaks of the solid films of polyamine P3(9)
and model hybrid (C4H9NH3)2PbBr4 are located at 458
and 433 nm, respectively (SI, Figure S2). The PL
spectrum of hybrid H5(9) peaks at 466 nm with no
shoulder at 433 nm, indicating that an efficient energy
transfer has taken place in the polyacetylene-perovs-
kite hybrid. The violet light of 433 nm emitted from the
perovskite framework has been absorbed by or trans-
ferred to the polyacetylene chains, the radiative decay
of whose singlet excited state leads to the blue light
emission at 466 nm.
Supporting Information Available: Synthesis and char-
acterization details for 2(m), P2(m)-P4(m), and H5(m); TGA
thermograms of P2(9)-P4(9) and H5(m) and PL spectra of the
films of P3(9), H5(9), and (BuNH3)2PbBr2. This material is
available free of charge via the Internet at http://pubs.acs.org.
References and Notes
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Figure 3B. Using 9,10-diphenylanthracene as stan-
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longer spacer (m ) 9) discussed above. Their ΦPL values
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forming, and thermally stable. The provskite induces
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liquid crystals within the inorganic layers. Photoenergy
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to the polyacetylene chains, and the chain interactions
are supressed by the segregation of the polymer chains
in separate perovskite layers. The energy transfer and
chain separation both help enhance the light emission
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first successful example of constructing a conjugated
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MA051616H