Adjustment of the solid fluorescence of a chalcone derivative through controlling steric hindrance

Article abstract of DOI:10.1039/c7ra09122b

We designed and synthesized a chalcone derivative, ANPEO, which exhibits weak emission in the solution state but high fluorescence efficiency in the solid state (66%) because ANPEO shows a coplanar conformation with a dihedral angle 1.58° and a loose pattern with a mean interlayer distance of approximately 4.21 ?.

Full text of DOI:10.1039/c7ra09122b

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Adjustment of the solid fluorescence of a chalcone
derivative through controlling steric hindrance†
Cite this: RSC Adv., 2017, 7, 46354
a
c
Jie Liu,b Junkuo Gao,
Rong Lua and Fang Liua
*
Liang Zhang,
Received 17th August 2017
Accepted 22nd September 2017
We designed and synthesized a chalcone derivative, ANPEO, which exhibits weak emission in the solution
state but high fluorescence efficiency in the solid state (66%) because ANPEO shows a coplanar
conformation with a dihedral angle 1.58ꢀ and a loose pattern with a mean interlayer distance of
approximately 4.21 A˚.
DOI: 10.1039/c7ra09122b
rsc.li/rsc-advances
Many well-known traditional luminogenic materials, such as, delocalization of electronic charge distribution and overlapping
polyaromatic hydrocarbons, dicyanomethylene-4H-pyran, and p orbitals.13 Furthermore, as a family of traditional luminogenic
coumarin derivatives, oen possess strong emissions in their materials, chalcone and its derivatives oen possess strong
solution states; however, their luminescence emissions are emissions in the solution state but their luminescence are
always quenched in solutions with high concentrations and in always quenched in high-concentration solutions or/and solid
the solid state.1 The main cause for quenching is the intense states.14 However, their optical properties are easily controlled
intermolecular p–p stacking interaction between the aromatic by introducing electron donor or acceptor groups to aromatic
rings of adjoining luminophores, thereby leading to decay or rings. In view of the considerable importance and adjustable
relaxation back to the ground state from the excited state of the structure of chalcone and its derivatives, designing and
luminophore via non-radiative channels. Quenching limits synthesizing a chalcone that can emit strong uorescence in
practical applications, thus, researchers have made numerous solid state is possible.
efforts to design and synthesize new luminogenic materials that
Herein, we successfully designed and synthesized two chal-
show low uorescence efficiencies in the solution state but their cone derivatives, 3-(2-(allyloxy)naphthalen-1-yl)-1-phenylprop-2-
uorescence efficiencies increase with the increase of concen- en-1-one (abbreviated as ANPEO) and 1-phenyl-3-(2-((4-
tration and they can emit strong uorescence in their solid vinylbenzyl)oxy)naphthalen-1-yl)prop-2-en-1-one (abbreviated
states.2–10 Such luminogenic materials are focused on propeller- as VBNPEO), with similar structures and different steric
like luminogens, such as hexaphenylsilole and tetraphenyle- hindrances (allyl for ANPEO and 4-vinylbenzyl for VBNPEO).
thenes. Recently, Tang et al. have designed and synthesized ANPEO exhibits weak emission in its solution state but high
a coumarin derivative (9,10,11,12,13,14-hexahydro-6H-5-oxa- uorescence efficiency in its solid state. Moreover, VBNPEO
7a,10a-diazacyclohepta[no]tetraphene-6,7(8H)-dione)
that exhibits weak uorescence in both solution and solid states.
exhibits high uorescence efficiency in its solid state due to its Single-crystal X-ray diffraction (SCXRD) data of ANPEO and
intrinsic structural exibility and nonplanarity.11 Motivated by VBNPEO (from chloroform/ethanol) were collected and
their successful case, we modied traditional luminogenic analyzed to further understand the relationships between the
materials to achieve strong emissions in the solid state.
uorescence properties and molecular structures of ANPEO and
Chalcone and its derivatives have displayed numerous VBNPEO.
applications in biological chemistry activities.12 As a member of
The synthetic procedure for preparing ANPEO and VBNPEO
the p-conjugated system, the optical properties of chalcone and is displayed in Scheme 1. Considering the inuence of steric
its derivatives, including nonlinear optical and uorescence hindrance, we synthesized two new intermediate compounds,
property, have received considerable attention owing to the 2-(allyloxy)-1-naphthaldehyde (abbreviated as AN) and 2-((4-
vinylbenzyl)oxy)-1-naphthaldehyde (abbreviated as VBN), with
different steric hindrances by introducing allyl and 4-vinyl-
aSchool of Material Science and Engineering, Yancheng Institute of Technology,
Yancheng 224051, Jiangsu, China. E-mail: zhangliang@ycit.edu.cn
bState Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, P. R.
China
benzyl into 2-hydroxy-1-naphthaldehyde. ANPEO and VBNPEO
were further synthesized through an aldol condensation reac-
tion between AN/VBN and acetophenone. ANPEO and VBNPEO
were fully characterized and conrmed by 1H and 13C NMR
spectroscopy, mass spectrometry, and SCXRD.
cCollege of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou, 310018,
China
The absorption spectra of ANPEO and VBNPEO in different
polar solvents are shown in Fig. 1 and S7,† respectively. As
exhibited in Fig. 1, the absorption spectrum of ANPEO in
† Electronic supplementary information (ESI) available. CCDC 1564717 and
1564718. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c7ra09122b
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THF/water mixture to investigate this phenomenon. When
water (fw ¼ 10%) was added to the ANPEO THF solution (Fig. 2),
the emission wavelength was blue-shied from 520 nm to
488 nm and photoluminescence (PL) intensity increased.
However, the emission wavelength was red-shied from 488 nm
to 518 nm as the water fraction changed from 20% to 80%. The
PL intensity increased as the water fraction increased from 20%
to 60%, but slightly decreased when the water fraction further
increased from 60% to 80%. When the water fraction increased
to 90%, the emission wavelength was blue-shied to 470 nm
and PL intensity further increased. The different behaviors of
ANPEO in THF/water mixture solution was caused by the
different aggregation states of ANPEO in the THF/water mixture
solution, as conrmed by scanning electron microscopy. As
shown in Fig. S10,† the aggregating states of ANPEO in THF/
water mixture solution from 20% to 40%, from 50% to 60%,
and from 70% to 80% are similar. The different aggregating
states suggest that ANPEO exhibits different morphologies,
leading to different uorescence behaviors. The emission
behavior of VBNPEO in THF/water mixture was similar to that of
ANPEO (Fig. S11 and S12†). We further investigated the emis-
sion spectra of ANPEO and VBNPEO in the solid state. As dis-
played in Fig. 3, solid ANPEO emits a strong green light at lmax
514 nm with its uorescence quantum yield as high as 66%.
However, solid VBNPEO exhibited almost no uorescence
(Fig. S13†).
Scheme 1 Synthesis of ANPEO and VBNPEO. (i) potassium carbonate,
allyl bromide or 4-vinylbenzyl chloride; (ii) 98% concentrated sulfuric
acid, acetic acid, acetophenone.
SCXRD data of ANPEO and VBNPEO (from chloroform/
ethanol, CCDC: 1564717 for ANPEO and 1564718 for
VBNPEO†) were collected and analyzed to further understand
the relationships between molecular structures and uores-
cence properties of ANPEO and VBNPEO. To demonstrate the
coplanarity of the molecules, two benzene rings (named as
a and b, Fig. 4) were chosen as the basic planes and the
Fig. 1 UV-vis absorption spectra of ANPEO.
toluene (a weak polar solvent) shows two prominent bands at
lmax 335 and 374 nm, which can be ascribed to a localized
aromatic p–p* transition and charge transfer, respectively.
When the polarity of the solvent increased, a slight charge
transfer was observed. The absorption wavelength at lmax
374 nm was red-shied to 375 nm to 376 nm to 380 nm when
the solvent changed from toluene to chloroform to tetrahydro-
furan (THF) to N,N-dimethylformamide (DMF). The absorption
behavior of VBNPEO was similar to that of ANPEO. Compared
with the absorption spectrum of ANPEO in toluene solution, the
absorption spectrum of VBNPEO in toluene solution was only
red-shied by ꢁ2 nm. Moreover, the emission spectra of ANPEO
and VBNPEO were investigated in different solvents. Unlike
other chalcone derivatives,14 ANPEO and VBNPEO exhibited
almost no uorescence in common solvents, such as toluene
and chloroform (Fig. S8 and S9†). To conrm these phenom-
enon, the uorescence quantum yields of ANPEO and VBNPEO
were also determined in different solvents using quinine
bisulfate (54.6% in 0.1 N H2SO4) as a standard. Subsquently, the
uorescence quantum yields of ANPEO and VBNPEO were
much less than 1% in different solvents. The emission spectra
Fig. 2 Emission spectra of ANPEO in the THF/water mixtures (4 ꢂ
of ANPEO and VBNPEO in the aggregation state were studied in 10ꢃ4 mol Lꢃ1). Photographs were taken under 365 nm UV light.
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the motion of a chemical bond is strong, which leads to decay or
relaxation back to the ground state from the excited state of the
luminophore via non-radiative channels. Furthermore,
although ANPEO showed a coplanar conformation in solid
state, the molecules were arranged in a loose pattern with
˚
a mean interlayer distance of approximately 4.21 A, indicating
no p–p intermolecular interactions between the p-plane of the
neighboring molecules, leading to the high-uorescence
quantum yield of ANPEO. The molecules of VBNPEO arranged
in a more loose pattern with a mean interlayer distance of
˚
approximately 4.81 A, due to high steric hindrance of vinyl-
benzyl group.
To gain a clear understanding of the relationships between
molecular structure, electronic structure, and uorescence
property of ANPEO and VBNPEO. The ground-state geometry of
ANPEO and VBNPEO were optimized via the hybrid density
functional theory (B3LYP) with 6-31G* basis set using the
Gaussian 03 program package. As shown in Fig. S14a and b,†
the highest occupied molecular orbital (HOMO) of ANPEO is a p
orbital and the electron density is spread to chalcone and
naphthalene groups, while the lowest unoccupied molecular
orbital (LUMO) is of p* character and is distributed on the
whole molecule except allyloxy group. Thus, there is no obvious
change in the electron density of allyloxy group. The electron
density of VBNPEO is similar to that of ANPEO. The electron
density of vinylbenzyl group is also no obvious change, sug-
gesting that allyloxy and vinylbenzyl group exhibit little effect on
the electronic structure. As shown in Fig. S14c and f,† the
coplanarity of ANPEO and VBNPEO are poor at ground-state
with dihedral angles of 87.17ꢀ and 39.66ꢀ, respectively. The
low planarity indicates a small p-electron delocalization,
leading to a weak uorescence of ANPEO and VBNPEO in
Fig. 3 Emission spectrum of solid ANPEO (inset: excitation wave-
length 325–365 nm, exposure time 200 ms).
corresponding dihedral angles between the two planes were
1.58ꢀ for ANPEO and 32.33ꢀ for VBNPEO, suggesting that
ANPEO exhibits better coplanarity than VBNPEO. Generally,
molecules with high coplanar conformation will benet for
uorescence efficiency because of the bigger p-electron delo-
calization.15 Subsequently, allyloxy group (low steric hindrance)
is little effect on ANPEO which shows a planar conformation,
while vinylbenzyl group (high steric hindrance) causes VBNPEO
to exhibit a distorted conformation rather than a planar
conformation. The weak uorescence of ANPEO and VBNPEO in
solution may be due to two reasons: (1) ANPEO and VBNPEO
exhibit low planarity with small p-electron delocalization; (2)
Fig. 4 Crystal structures, the related dihedral angles, and the molecular stacking patterns and relative mean distances of ANPEO (a–c) and
VBNPEO (d–f) interlayers.
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solution. However, ANPEO exhibits high planarity at solid state
from Fig. 4, while VBNPEO still displays poor planarity at solid
state from Fig. 4, leading to a high uorescence of ANPEO at
solid state.
6 (a) H. Naito, Y. Morisaki and Y. Chujo, Angew. Chem., Int. Ed.,
2015, 54, 5084; (b) H. Naito, K. Nishino, Y. Morisaki,
K. Tanaka and Y. Chujo, Angew. Chem., Int. Ed., 2017, 56, 254.
7 (a) Z. Mao, Z. Yang, Y. Mu, Y. Zhang, Y. F. Wang, Z. Chi,
C. C. Lo, S. Liu, A. Lien and J. Xu, Angew. Chem., Int. Ed.,
2015, 54, 6270; (b) Z. Chi, X. Zhang, B. Xu, X. Zhou, C. Ma,
Y. Zhang, S. Liu and J. Xu, Chem. Soc. Rev., 2012, 41, 3878.
8 (a) R. Li, S. Xiao, Y. Li, Q. Lin, R. Zhang, J. Zhao, C. Yang,
K. Zou, D. Li and T. Yi, Chem. Sci., 2014, 5, 3922; (b)
C.-M. Chou, S. Nobusue, S. Saito, D. Inoue, D. Hashizume
and S. Yamaguchi, Chem. Sci., 2015, 6, 2354; (c) A. Shao,
Y. Xie, S. Zhu, Z. Guo, S. Zhu, J. Guo, P. Shi, T. D. James,
H. Tian and W. H. Zhu, Angew. Chem., Int. Ed., 2015, 54,
7275; (d) H. Lu, Y. Zheng, X. Zhao, L. Wang, S. Ma, X. Han,
B. Xu, W. Tian and H. Gao, Angew. Chem., Int. Ed., 2016,
55, 155.
We successfully designed and synthesized two chalcone
derivatives, ANPEO and VBNPEO, with similar structures and
different steric hindrances (allyl for ANPEO and 4-vinylbenzyl
for VBNPEO). ANPEO exhibits weak emission in the solution
state but high uorescence efficiency in the solid state (66%).
Moreover, VBNPEO shows weak uorescence in both solution
and solid states. On the basis of single-crystal structural anal-
ysis, ANPEO exhibits a coplanar conformation with a dihedral
angle as low as 1.58ꢀ, which is different from that of VBNPEO,
with a dihedral angle as high as 32.33ꢀ. Furthermore, the
ANPEO molecules are arranged in a loose pattern with a mean
˚
interlayer distance of approximately 4.21 A, indicating no p–p
intermolecular interaction between the p-plane of the neigh-
boring molecules. Our results strongly suggest that the solid
9 J. Seo, J. W. Chung, J. E. Kwon and S. Y. Park, Chem. Sci.,
2014, 5, 4845.
uorescence of chalcone derivatives can be tunable by 10 (a) Y. Q. Dong, J. W. Lam and B. Z. Tang, J. Phys. Chem. Lett.,
controlling steric hindrance.
2015, 6, 3429; (b) J. Qian, Z. Zhu, A. Qin, W. Qin, L. Chu,
F. Cai, H. Zhang, Q. Wu, R. Hu, B. Z. Tang and S. He, Adv.
Mater., 2015, 27, 2332.
Conflicts of interest
11 F. Bu, R. Duan, Y. Xie, Y. Yi, Q. Peng, R. Hu, A. Qin, Z. Zhao
and B. Z. Tang, Angew. Chem., Int. Ed., 2015, 54, 14492.
12 (a) S. Satbhaiya and O. P. Chourasia, RSC Adv., 2015, 5,
84810; (b) W. Lin, L. Yuan, Z. Cao, Y. Feng and L. Long,
Chem.–Eur. J., 2009, 15, 5096; (c) Z. Nowakowska, Eur. J.
Med. Chem., 2007, 42, 125; (d) G.-J. Kim, K. Lee, H. Kwon
and H.-J. Kim, Org. Lett., 2011, 13, 2799.
13 (a) E. D. D'Silva, D. Narayan Rao, R. Philip, R. J. Butcher,
Rajnikant and S. M. Dharmaprakash, J. Phys. Chem. Solids,
2011, 72, 824; (b) T. Chandra Shekhara Shetty,
There are no conicts to declare.
Notes and references
1 (a) Q. Xu, C. H. Heo, G. Kim, H. W. Lee, H. M. Kim and
J. Yoon, Angew. Chem., Int. Ed., 2015, 54, 4890; (b) Z. Guo,
W. Zhu and H. Tian, Chem. Commun., 2012, 48, 6073; (c)
J. J. Shie, Y. C. Liu, Y. M. Lee, C. Lim, J. M. Fang and
C. H. Wong, J. Am. Chem. Soc., 2014, 136, 9953; (d)
Q. Zhang, H. Kuwabara, W. J. Potscavage Jr, S. Huang,
Y. Hatae, T. Shibata and C. Adachi, J. Am. Chem. Soc., 2014,
136, 18070; (e) P.-Y. Gu, J. Gao, Q. Zhang, G. Liu, F. Zhou,
Q.-F. Xu and J.-M. Lu, J. Mater. Chem. C, 2014, 2, 1539; (f)
J. Xiao, Y. Divayana, Q. Zhang, H. M. Doung, H. Zhang,
F. Boey, X. W. Sun and F. Wudl, J. Mater. Chem., 2010, 20,
8167.
S.
Raghavendra,
C.
S.
Chidan
Kumar
and
S. M. Dharmaprakash, Opt. Laser Technol., 2016, 77, 23; (c)
P. S. Patil, S. R. Maidur, S. V. Rao and
S. M. Dharmaprakash, Opt. Laser Technol., 2016, 81, 70; (d)
C. Shekhara Shetty, S. Raghavendra, C. S. Chidan Kumar
and S. M. Dharmaprakash, Appl. Phys. B, 2016, 122; (e)
˜
L. M. G. Abegao, R. D. Fonseca, F. A. Santos, G. B. Souza,
2 (a) Z. Xie, C. Chen, S. Xu, J. Li, Y. Zhang, S. Liu, J. Xu and
Z. Chi, Angew. Chem., Int. Ed., 2015, 54, 7181; (b) T. Yu,
D. Ou, Z. Yang, Q. Huang, Z. Mao, J. Chen, Y. Zhang,
S. Liu, J. Xu, M. R. Bryce and Z. Chi, Chem. Sci., 2017, 8, 1163.
3 (a) J. Yang, L. Li, Y. Yu, Z. Ren, Q. Peng, S. Ye, Q. Li and Z. Li,
Mater. Chem. Front., 2017, 1, 91; (b) C. Wang, B. Xu, M. Li,
Z. Chi, Y. Xie, Q. Li and Z. Li, Mater. Horiz., 2016, 3, 220.
4 (a) S. Sekiguchi, K. Kondo, Y. Sei, M. Akita and M. Yoshizawa,
Angew. Chem., Int. Ed., 2016, 55, 6906; (b) M. Yamashina,
M. M. Sartin, Y. Sei, M. Akita, S. Takeuchi, T. Tahara and
M. Yoshizawa, J. Am. Chem. Soc., 2015, 137, 9266.
A. L. B. S. Barreiros, M. L. Barreiros, M. A. R. C. Alencar,
C. R. Mendonça, D. L. Silva, L. De Boni and J. J. Rodrigues,
Chem. Phys. Lett., 2016, 648, 91.
14 (a) E. Yang, C. Ruzie, M. Krayer, J. R. Diers,
D. M. Niedzwiedzki, C. Kirmaier, J. S. Lindsey, D. F. Bocian
and D. Holten, Photochem. Photobiol., 2013, 89, 586; (b)
Q. Zhou, P. Gu, Y. Zhang, N. Li, Q. Xu, Y. Zhang and J. Lu,
Chin. J. Chem., 2014, 32, 573; (c) K. G. Komarova,
S. N. Sakipov, V. G. Plotnikov and M. V. Almov, J. Lumin.,
2015, 164, 57.
15 (a) Y. Cheng, Y. Qi, Y. Tang, C. Zheng, Y. Wan, W. Huang and
R. Chen, J. Phys. Chem. Lett., 2016, 7, 3609; (b) T. J. Fauvell,
T. Zheng, N. E. Jackson, M. A. Ratner, L. Yu and
L. X. Chen, Chem. Mater., 2016, 28, 2814.
5 (a) B. Xu, J. He, Y. Dong, F. Chen, W. Yu and W. Tian, Chem.
Commun., 2011, 47, 6602; (b) J. Zhang, J. Chen, B. Xu,
L. Wang, S. Ma, Y. Dong, B. Li, L. Ye and W. Tian, Chem.
Commun., 2013, 49, 3878.
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