Synthesis of novel chalcone derivatives and their stabilization effect of spiropyran in PMMA films

Article abstract of DOI:10.1016/j.cclet.2011.04.001

Three novel bis-chalcone derivatives with different alkyldioxy spacers were synthesized and dispersed into polymethyl methacrylate (PMMA) chloroform solution with 6-nitro-1′-ethyl-3′,3′-dimethylspiro-2H-1- benzopyran-2,2′-indoline (ESP) to prepare photoch

Full text of DOI:10.1016/j.cclet.2011.04.001

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1025–1028
www.elsevier.com/locate/cclet
Synthesis of novel chalcone derivatives and their stabilization effect
of spiropyran in PMMA films
Zheng Kai Si, Qing Zhang, Min Zhao Xue, Yuan Yuan Zhu,
*
Liang Ming, Qiao Rong Sheng, Yan Gang Liu
School of Chemistry and Chemical Engineering, Shanghai Jiaotong University, Shanghai 200240, China
Received 23 November 2010
Abstract
Three novel bis-chalcone derivatives with different alkyldioxy spacers were synthesized and dispersed into polymethyl
methacrylate (PMMA) chloroform solution with 6-nitro-10-ethyl-30,30-dimethylspiro-2H-1-benzopyran-2,20-indoline (ESP) to
prepare photochromic PMMA films in a facile way. After irradiation with 365 nm UV light, the photocrosslinking reaction
between chalcone units was proved to retard the decolorization of merocyanine form of the photochromic spiropyran effectively, as
results of the steric hindrance produced by photocycloaddition of chalcone groups. It has been found that the bis-chalcone molecule
with the shortest spacer has the most effective stabilizing effect on retardation of decoloration of spiropyran.
# 2011 Yan Gang Liu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Photochromism; Chalcone; Spiropyran; Photocycloaddition; Stabilization effect
Spiropyran derivatives, as one of the most well known class of organic photochromic compounds, have
attracted much attention for several decades due to their potential application in fields of optical switch,
rewritable data storage and biological labeling [1–3]. Nevertheless, the poor stability of the colored merocyanine
form of spiropyran usually restricts its practical applications [4]. Extensive study has been carried out to improve
the durability of photochromic property. For example, Oda [5] examined the protecting effect of spiropyran by
amphoteric counter-ionic complexes against the decolorization reaction on cellulose. Lin [6] and Tork et al. [7]
studied the photo-chromic characters of spiropyran in different polymer matrices. However, spiropyran
derivatives still remain on the way to be practical devices.
It is known that, photocrosslinking reaction between a, b-unsaturated carbonyl groups (named chalcone or
cinnamoyl units) obeys the [2p + 2p] mechanism [8]. Choi [4,9] found that after the introduction of
photocrosslinkable moieties into photochromic polymers in the main chain and the side chain, the photocycloaddition
can control the free volume surrounding merocyanine moiety and then retard the relaxation. While such work involved
a much more complicated synthesis and polymerization process, which therefore limited its application.
Herein, we report the synthesis of three novel chalcone derivatives of 1,2-di(20-benzoyl-4-styryloxy)ethane
(BSOE), 1,4-di(20-benzoyl-4-styryloxy)butane (BSOB), 1,6-di(20-benzoyl-4-styryloxy)hexane (BSOH) with the
* Corresponding author.
E-mail address: ygliu@sjtu.edu.cn (Y.G. Liu).
1001-8417/$ – see front matter # 2011 Yan Gang Liu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.04.001

1026
[(Scheme_1)TD$FIG]
Z.K. Si et al. / Chinese Chemical Letters 22 (2011) 1025–1028
O
O
O
K2CO3, DMF
OH + Br-(CH2)n-Br
O
(CH2)n O
o
80
C
n= 2, BSOE; 4, BSOB; 6, BSOH.
Scheme 1. Synthesis procedure of bis-chalcone derivatives.
[(Scheme_2)TD$FIG]
O
O
O
O
UV: 365 nm
+
O
O
O
O
Scheme 2. Photocycloaddition reaction of bis-chalcone derivatives during 365 nm UV light irradiation.
structure of two chalcone moieties connected by different alkyldioxy spacer chains. We also prepared photochromic
films in a facile way by dispersing ESP with the bis-chalcone derivatives into PMMA/CHCl3 solution, then studied the
photochromic properties of the films after being irradiated with 365 nm UV light. The novel chalcone derivatives
would retard the transformation of merocyanine to the form of spiropyran and improved the stability via
photocrosslinking of chalcone groups.
ESP was synthesized as the similar method described in Ref. [10]. 4-Hydroxychalcone was prepared according
to the method of Rehab [11]. The general preparation of BSOE, BSOB and BSOH was illustrated in Scheme 1. The
1
structures of the compounds were confirmed with H NMR, MS and elemental analysis [12]. Photoreactive films
were prepared by spin-coating the dissolved chalcone derivatives, ESP and PMMA in chloroform according to the
proportion of 0.05 mmol/0.05 mmol/0.1 g onto quartz plates.
The photoreactions in solid PMMA films were monitored by UV–vis spectra at the relevant characteristic
absorption wavelength as shown in Fig. 1(a). The maximum absorbance at 339 nm attributed to chalcone groups
successively decreased with the exposure to UV light, as the result of the [2p + 2p] photocycloaddition of the double
bonds of chalcone groups. While the colored merocyanine form of spiropyran showed maximum absorbance at
581 nm and the absorption intensity of the chromophore increased gradually with the irradiation time increasing.
Therefore, it is obvious that the photocrosslinking reaction between chalcone units (Scheme 2) and photochromic
transformation of spiropyran in the films proceeded coincidently with the irradiation of 365 nm UV light.
FTIR spectra and 1H NMR were also helpful to observe the photoreaction of chalcone groups. The FTIR spectra
were recorded with the samples before and after UV irradiation. As shown in Fig. 1(b), significant changes in the
[(Fig._1)TD$FIG]
0 (Sec)
5
15
30
60
100
150
210
300
a
b
70
60
50
40
30
20
1.0
0.8
0.6
0.4
0.2
0.0
After
1659
1598
Before
300
400
500
600
700
1700
1600
1500
Wavenumber (cm-1)
Wavelength (nm)
Fig. 1. Spectral changes of BSOB/ESP/PMMA film irradiated with UV light: (a) UV–vis spectra and (b) infrared spectra.

[(Fig._2)TD$FIG]
Z.K. Si et al. / Chinese Chemical Letters 22 (2011) 1025–1028
6.78
1027
6.58
6.9 6.8 6.7 6.6 6.5
4.80
4.31
4.50
4.8 4.6 4.4 4.2
(ppm)
10
9
8
7
6
5
4
3
2
1
0
Fig. 2. 1H NMR of BSOB/PMMA film in CDCl3 after irradiation with 365 nm UV light.
[(Fig._3)TD$FIG]
ESP
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.0
-0.1
-0.2
BSOH
BSOB
BSOE
0
400
800
1200
Time (s)
0
1500
3000
4500
6000
7500
Time (s)
Fig. 3. Change of absorbance at 581 nm during dark decolorization and the decay rate constant. ESP: ESP/PMMA film k (sꢀ1): 2.01 ꢁ 10ꢀ4; BSOH:
BSOH/ESP/PMMA film, k (sꢀ1): 1.35 ꢁ 10ꢀ4; BSOB: BSOB/ESP/PMMA film, k (sꢀ1): 1.04 ꢁ 10ꢀ4; BSOE: BSOE/ESP/PMMA film, k (sꢀ1):
9.24 ꢁ 10ꢀ5
.
spectra occurred indeed. The intensities of stretching vibration of the double bond at 1598 cmꢀ1 and the unsaturated
ketone carbonyl at 1659 cmꢀ1 in chalcone moiety decreased significantly with UV irradiation. In 1H NMR spectra of
BSOB/PMMA film (Fig. 2), new chemical shifts of 6.78, 6.58, 4.80, 4.50 and 4.31 [13], which were due to the
hydrogen atoms in oxyalkyl substituted benzene and cyclobutane, appeared after UV irradiation and were all
consistent with the literature [14] Thus, the occurrence of the [2p + 2p] photocrosslinking between chalcone moieties
1
could be confirmed by H NMR, UV–vis and FTIR spectral analysis.
The stabilization effect of the chalcone derivatives on merocyanine ring closure reaction was carried out by
monitoring the absorption change at lmax during dark decolorization of the colored merocyanine in PMMA films
which were irradiated with the 365 nm UV light for 15 min. The results in Fig. 3 showed that the film’s decolorized
rates doped with chalcone derivatives were much slower than that of sample ESP after UV irradiation. It could be
explained that photocrosslinking between chalcone moieties could reduce the distance between PMMA polymer
chains and confine the transformation from the colored trans-merocyanine to spiropyran, then stabilize the
merocyanine structure in solid films effectively.
It should be noted that the films contained three chalcone derivatives exhibited different decay rates (Fig. 3).
Sample BSOE had the lowest decolorized rate while sample BSOH had the fastest one which was induced by the
length of spacer chains between chalcone units. After UV irradiation the photocrosslinked polymer of BSOE with
shortest spacer was most rigid which results in the smallest free volume between polymer chains. While the
photoproduct of BSOH, containing a six CH2 soft chain between the chalcone moieties, might be looser than the

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Z.K. Si et al. / Chinese Chemical Letters 22 (2011) 1025–1028
photoproduct of BSOE and the photochromic reaction could occur easily. Sample BSOB had a moderate soft spacer
and decay rate compared to the other samples, which confirmed that the photocrosslinking between chalcone moieties
reduced free volume surrounding merocyanine and then stabilized the colored structure.
In conclusion, three novel bis-chalcone derivatives had been synthesized. Photochromic PMMA films doped with
ESP and bis-chalcone derivatives were prepared via a facile method and the photochemical reactions were investigated
under irradiation of UV light. It had been found that photocrosslinking between chalcone units stabilized the
decolorization behavior of merocyanine effectively resulting from the steric hindrance produced by photocycloaddi-
tion, while the shortest soft chain containing bis-chalcone BSOE was the most effective one among the three
derivatives. These facilely prepared photochromic films might be used in low cost data storage.
Acknowledgments
We are grateful for the financial support from the National High Technology Research and Development Program
of China (No. 2005AA320030) and SJTU-Aeronautics Industry Joint Program (No. 0304). We thank Dr Dongqing Wu
for discussions.
References
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[12] BSOE: 1H NMR (400 MHz, CDCl3): d 8.01 (d, 4H, J = 6.8 Hz), 7.79 (d, 2H, J = 15.6 Hz), 7.62 (d, 4H, J = 8.8 Hz), 7.58 (t, 2H, J = 7.2 Hz),
7.50 (t, 4H, J = 7.2 Hz), 7.43 (d, 2H, J = 15.6 Hz); 7.00 (d, 4H, J = 8.8 Hz), 4.40 (s, 4H); LC–MS: m/z 474.0 ([M+]). Anal. Calcd. for C32H26O4:
C, 80.99; H, 5.52. Found: C, 81.01; H, 5.48. BSOB: 1H NMR (400 MHz, CDCl3): d 8.01 (d, 4H, J = 7.2 Hz), 7.79 (d, 2H, J = 15.6 Hz), 7.60 (d,
4H, J = 8.8 Hz), 7.56 (t, 2H, J = 7.6 Hz), 7.50 (t, 4H, J = 7.6 Hz), 7.42 (d, 2H, J = 15.6 Hz), 6.93 (d, 4H, J = 8.8 Hz), 4.09 (t, 4H, J = 5.6 Hz),
2.02 (m, 4H, J = 2.8 Hz); LC-MS: m/z 502.2 ([M+]). Anal. Calcd. for C34H30O4: C, 81.25; H, 6.02. Found: C, 81.28; H, 6.00. BSOH: 1H NMR
(400 MHz, CDCl3): d 8.01 (d, 4H, J = 7.2 Hz), 7.79 (d, 2H, J = 15.6 Hz), 7.60 (d, 4H, J = 8.8 Hz), 7.57 (t, 2H, J = 7.6 Hz), 7.50 (t, 4H,
J = 7.6 Hz), 7.41 (d, 2H, J = 15.6 Hz), 6.93 (d, 4H, J = 8.8 Hz), 4.02 (t, 4H, J = 6.4 Hz), 1.85 (m, 4H, J = 6.4 Hz), 1.58 (m, 4H, J = 3.6 Hz);
LC–MS: m/z 530.1 ([M+]). Anal. Calcd. for C36H34O4: C, 81.48; H, 6.46. Found: C, 81.51; H 6.42.
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J = 6.4 Hz), 4.50 (d, J = 6.4 Hz), 4.31 (d, J = 6.4 Hz).
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