Complete 1H and 13C NMR spectral assignment of symmetric and asymmetric bis-spiropyran derivatives

Article abstract of DOI:10.1002/mrc.1640

¹H and ¹³C NMR spectra of symmetric and asymmetric bis-spiropyrans, Series 1-3, were completely assigned. Especially, the ¹H assignment of asymmetric spiropyrans was achieved by utilizing ¹H-¹H COSY and nOe experiments. All of the carbons in the dye molecules were investigated through a combination of heteronuclear 2D-shift correlation spectroscopy (HETCOR), together with an attached proton test (APT). Copyright

Full text of DOI:10.1002/mrc.1640

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2005; 43: 873–876
Published online 22 July 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1640
Spectral Assignments and Reference Data
or carbonyl group.6 Since two merocyanine chromorphores in the
Complete 1H and 13C NMR spectral
assignment of symmetric and asymmetric
bis-spiropyran derivatives
dimeric spiropyran systems are linked, either directly or through a
linking group, the two merocyanine chromorphores are expected to
overlap, and hence induce a bathochromic shift of their maximum
wavelengths. For studying this connection, the detailed 1H and
13C NMR spectroscopic data of those bis-spiropyrans prepared
symmetric (Series 1–2) and asymmetric (Series 3) were examined,
whose chemical structures are shown in Scheme 2.
Sam-Rok Keum,1∗ Hyo-Jung Roh,1 Yoon-Ki Choi,1
Soon-Sung Lim,2 Sung-Hoon Kim3 and Kwangnak Koh4
These symmetric and asymmetric BSPs are the potent key
materials for the synthesis of bent-shaped (banana shaped) liquid
crystals,8 in the cases when X and Y are long alkyl-chained linkages,
as in Scheme 3.
1
Department of New Material Chemistry, Korea University, Jochiwon
339-700, Korea
2
Silver Biotechnology Research Center, Hallym University, Chunchon
200-702, Korea
3
Department of Dyeing and Finishing, Kyungpook National University,
RESULTS AND DISCUSSION
Daegu 702-701, Korea
Department of Pharmacy, Pusan National University, Pusan 609-735,
4
Symmetric bis-spiropyrans (Series 1–2) were generally synthesized
by the reaction of 5,50-substituted bis-salicylaldehyde and Fischer
base (FB) derivatives, in a 1 : 2.5 mole ratio. The asymmetric bis-
spiropyrans (Series 3) were prepared by a two-step reaction, using
two differently substituted Fischer bases. As a representative exam-
ple, bis-spiropyranyl sulfides were synthesized by the reaction
of 5,50-thiobis(3-nitrosalicylaldehyde) and Fischer base derivatives
in a 1 : 2.5 mole ratio. For the synthesis of the doubly formy-
lated bis-salicylaldehyde, 4,40-thiobisphenol in toluene was reacted
with SnCl4/tributylamine under N2, followed by reaction with
paraformaldehyde. The formylation of 4,40-thiobisphenol gave the
monoformylated product, hydroxyphenylsulfanyl salicylaldehyde
as the major product and the doubly formylated bis-salicylaldehyde
as a minor product.
Korea
Received 18 March 2005; accepted 9 June 2005
1H and 13C NMR spectra of symmetric and asymmetric
bis-spiropyrans, Series 1-3, were completely assigned.
Especially, the 1H assignment of asymmetric spiropyrans
was achieved by utilizing 1H–1H COSY and nOe
experiments. All of the carbons in the dye molecules were
investigated through a combination of heteronuclear 2D-
shift correlation spectroscopy (HETCOR), together with
an attached proton test (APT). Copyright  2005 John
Wiley & Sons, Ltd.
The symbols, melting points (mp) and other characteristics of
the symmetric (Series 1–2) and asymmetric (Series 3) bis-spiropyrans
examined are summarized in Table 1.
KEYWORDS: NMR; 1H NMR; 13C NMR; 2DNMR; APT; symmetric
bis-spiropyrans; asymmetric bis-spiropyrans
1H NMR assignment of the symmetric and asymmetric bis-
spiropyrans (Series 1–3) were very straightforward, as found from
the known chemical shifts and coupling constants of the mono-
spiropyrans.9 The proton NMR spectral data of bis-spiropyrans
(Series 1), bis(8-nitrospiropyranyl) sulfides (Series 2) and asym-
metric bis-spiropyran (Series 3) in DMSO are given in Table 2.
The proton NMR spectra of these materials showed N–Me
peaks at 2.61–2.67 ppm, with the exception of compound SP-ASP
(2.72–2.75 ppm, measured in CDCl3ꢁ. Two geminal methyl groups
(prochiral center, C30) appeared at 1.08–1.12 and 1.20–1.24 ppm for
the 9-methyl and 8-methyl groups, respectively, with the exception
of compound SP-ASP (1.19 and 1.31–1.34 ppm, measured in CDCl3ꢁ.
From the nOe experimental study of the gem-dimethyl peaks of the
bis-spiropyran systems, the relative stereochemistry of the indolino
gem-dimethyl groups can be assigned, as in mono-spiropyrans.8 By
analyzing the nOe enhancement study, the protons of the SP unit 1,
such as H-3, H-4, H-80, H- 90 and H-100, etc. could not be differen-
tiated from the protons of the SP unit 2, such as H-300, H-400, H-8000,
H-9000 and H-10000, etc. The olefinic protons appeared as pairs of dou-
blets at 5.73–5.80 and 6.90–7.08 ppm for H3 and H4, respectively.
Their peaks had large coupling constants, J D 10.1–10.2 Hz, for both
olefinic protons, with the H3 and H4 signals very characteristic of
bis-spiropyran systems, as in mono-SP.9
INTRODUCTION
Thermo- and photochromic indolinobenzospiropyran dyes have
recently become important in connection with the rapid development
of information recording systems, such as high-density optical
data storage, optical switching, displays and nonlinear optics.1,2
Structurally, spiropyran dyes consist of two ꢀ systems linked by a
tetrahedral spiro carbon. They form a colored metastable state on
heating or irradiation with UV light, while the reverse process is
induced spontaneously or by visible light and heat. The metastable
state is called photomerocyanine, as it resembles the structure of
merocyanine dyes (MC). The process is shown in Scheme 1.
Since the stability of the spiropyran structure, as well as the
ultimate absorption associated with the merocyanine chromophore,
is strongly dependent on the substituents present, it is of interest
to investigate the influence of structural changes of the parent
spiropyran. Structural modification of spiropyrans has thus been an
active areaof research. Amajoreffortof thislaboratory has been in the
structural modification of spiropyrans for special functionalties.3–7
Previously, our laboratory reported synthesis and solvatokinetic
studies of symmetric and asymmetric bis-indolinospirobenzopyrans
(BSPs), which contain two spiropyran moieties connected at C-
6, either directly or through a connecting group, such as a thio-
These results were corroborated by the 1H–1H COSY plot of
SP-ASP, which showed cross peaks for H-3,300 and H-4,400, H-7000 and
H-6000, H- 70 and H-60, H-8,800 and H-7,700, and for H- 50 and H-60.
From the heteronuclear 2D-shift correlation spectrum
(HETCOR)10 forthe preparedSP-ASP, adirect 13C–1H correlation for
SP-ASP could be established. The 12 carbons in each unit of bis-SPs
were coupled with 12 previously assigned protons. These carbons
were C-3, 4, 5, 7, 8, 40, 50, 60, 70, 80, 90 and 100 in each unit. These carbons
have now been assigned, and are summarized in Tables 3 and 4.
Geminal methyl peaks are shown at 25–26 and 19.8–20.6 ppm
for C-80 and C-90, respectively. Interestingly, the pro-R methyl carbon
(C80) resonates at a lower frequency than that of the pro-S methyl
carbon (C90). In fact, it has been reported9 that for the S-epimer of
6-nitrospirobenzopyran the pro-R methyl group (H90) resonates at
1.24 ppm, while the pro-S methyl group (H80) appears at 1.37 ppm in
their 1H NMR spectra. To assign the residual six quaternary aromatic
carbons, use was made of substituent-induced shift increments for
C-2, 20, 4a, 6, 8a, 30, 30a, 50 and 70a from the benzene and coupled
X
hn
N+
N
O
X
∆/hn
−O
SP
MC
Photochromism of spiropyrans
Scheme 1
ŁCorrespondence to: Sam-Rok Keum, Department of New Material Chemistry
Korea University, Jochiwon 339-700 South Korea. E-mail: keum@korea.ac.kr
Contract/grant sponsor: Korea Science and Engineering Foundation;
Contract/grant number: R01-2003-000-10248-0.
Copyright  2005 John Wiley & Sons, Ltd.

874
Spectral Assignments and Reference Data
Series 1: G = − and X = Y
Series 2: G = S or CO and X = Y
Series 3: G = − and X ≠ Y
X = H, Cl, NHCOR
Y = H, Cl, NHCOR
Z = −, ΝΟ2
SP unit 2
9′ 8′
4′
3
x
Z
5
7
7″
10′′′
N
6′
O
G
O
N
6′′′
10′
5″
Z
Y
3″
8′′′
4′′′
9′′′
SP unit 1
Structures of bis-spiropyrans
Scheme 2
Table 1. Symbols and characterization of the bis-spiropyrans examined
Substituents
Melting
Symbolsa
G
X and Y
Z
point (mp)
Yield
Color
Noteb
Series 1
Series 2
Bis-SP
–
–
H
H
H
260–262
280–282
221–224
240c
248c
231c
87
75
62
94
91
76
77
82
82
87
79
Yellow
White
Green
Green
Green
Blue
–
–
Bis-CSP
Cl
Bis-ASP
–
NHCOMe
H
–
TBis-NSP
TBis-CNSP
TBis-ANSP
CbBis-SP
CbBis-CSP
SP-ASP
S
H
NO2
NO2
NO2
H
P,T
P,T
P,T
–
S
Cl
NHCOPh
H
S
CO
CO
–
139
White
White
Violet
Yellow
Yellow
Green
Cl
H
155
–
Series 3
H and NHCOMe
H and Cl
Cl and HCOMe
H
121
–
SP-CSP
–
H
239
–
CSP-ASP
–
H
129
–
a T- and Cbbis-SP denote thio- and carbonylated bis-spiropyran, and A- and C-, NSP, amido-, chloro- and nitrospiropyran, respectively.
b P and T denote photochromic and thermochromic dyes, respectively.
c Literature data obtained from Ref. 6(d).
Commercially available Fluka grade Fischer base (1,3,3-trimethyl-2-
methyleneindoline) was nitrated with H2SO4/HNO3, and then
reduced with stannous chloride dihydrate and conc. HCl. ASP
was obtained from the reaction of alkyl- or arylamido-Fischer base
(RCONH-FB) with an equimolecular amount of salicylaldehyde.
Samples for the 1H,13C NMR determination were prepared
as 1 M solutions in either CHCl3-d or DMSO-d6, as mentioned
elsewhere.
G
Merocyanine
Merocyanine
Vent-shaped-liquid crystalline molecules
Scheme 3
spectra. For calculation of the chemical shifts of these carbons, by
comparison of the substituted benzenes, the increment method10
was employed. The calculated values of the above carbons were 104,
119, 132, 153, 51, 138.7, 123 and 146.7 ppm for C-2, 20, 4a, 6, 8a, 30,
30a, 50 and 70a, respectively. The calculated values were reasonably
close to the experimental chemical shifts. Both the values of the
calculated and experimental chemical shifts deviated by no more
than 1%. Because of the ambiguity of the chemical shift of C-4a,
the attached proton test spectra (APT)11 of SP-ASP were used. The
chemical shifts of C-60 and C-4a were too close to be separated in the
HETCOR spectrum, whereas they were well separated in the APT
spectrum. Tables 3 and 4 summarize the13C NMR chemical shifts for
the symmetric (Series 1–2) and asymmetric bis-spiropyrans (Series
3) examined.
NMR spectra
The one- and two-dimensional 1H and 13C NMR spectra were
recorded with a Varian Mercury 300 NMR spectrometer, operating
at 300.07 MHz for the 1H and 75.46 MHz for the 13C resonances,
respectively. The samples used were 0.1 M solutions in DMSO-d6
for both the 1H and 13C, prepared in 5 mm NMR tubes at 298 K.
The 1H and 13C chemical shifts were referred to SiMe4 in CDCl3 as
an internal standard, or to the residual solvent signal in DMSO-d6
(1H D 2.50 ppm and 13C D 39.52 ppm). The digital resolutions of the
1H and 13C NMR spectra were 0.25 and 0.6 Hz per point, respectively.
The narrower spectral region of special interest was also measured,
but with a smaller spectral width and greater digital resolution
(down to 0.2 Hz). The following techniques were used: proton-noise
decoupling, APT, 1H–1H COSY and 1H–13C HETCOR. The 1H–1H
COSY spectra were obtained in the magnitude mode, with 1024
points in the F2 dimension and 256 increments in the F1 dimension.
Each increment was obtained with 16 scans, a spectral width of
4500 Hz and a relaxation delay of 1 s. The resolutions were 5.4 and
10.7 Hz per point in the F1 and F2 dimensions, respectively. The
1H–13C HETCOR spectra were measured with the one-bond C–H
EXPERIMENTAL
Materials
Symmetric (Series 1–2) and asymmetric bis-spiropyrans (Series 3)
were prepared according to the previously described methods.6
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2005; 43: 873–876

875
Spectral Assignments and Reference Data
Table 2. 1H-NMR data for the bis-spirobenzopyrans in DMSO-d6
Series 1
Series 2
Series 3a
SP-ASb,c
Protons
Bis-SP
Bis-CSP
Bis-ASPb
TBis-NSPb
TBis-CNSPb
CbBis-CSb
SP-CSP
CbSP-ASPb
H-40,4000
H- 50
7.11
6.77
7.13
6.56
1.11
1.22
2.66
5.80
7.06
7.43
7.32
6.71
10.2
8.4
7.17
–
7.30
–
7.07
6.85
7.17
6.54
1.19
1.38
2.75
5.91
6.88
7.29
7.68
–
7.01
–
7.01
–
7.09, 7.17
6.77
7.09, 7.28
6.86
7.15, 7.28
–
H-60,6000
H-70,7000
H-80,8000
H-90,9000
H-100,10000
H-3,300
H-4,400
H-5,500
H-7,700
H-8,800
7.15
6.59
1.12
1.24
2.67
5.80
7.08
7.45
7.35
6.74
10.2
8.5
7.23
6.49
1.08
1.20
2.63
5.80
7.05
7.42
7.31
6.72
10.2
8.4
7.12
6.44
1.19
1.33
2.72
5.89
6.88
7.29
7.68
–
7.13
6.45
1.15
1.28
2.72
5.74
6.95
7.59
7.62
6.76
10.3
8.2
7.11, 7.13
6.56
7.17
7.11, 7.25
6.55, 6.48
1.09
6.54, 6.46
1.19
1.10
1.21
1.31, 1.34
2.72, 2.75
5.73, 5.71
6.90
1.20, 1.19
2.63, 2.61
5.77
2.64
5.79, 5.80
7.06, 7.07
7.44, 7.43
7.31, 7.34
6.71, 6.72
10.2
7.05, 7.03
7.42
7.19
7.24
7.31, 7.29
6.71
6.76, 6.74
10.1
J(3-H,4-H)
J(7-H,8-H)
10.4
–
10.4
–
10.1
8.4
8.1
8.4
a Numbers are unduplicated, if chemical shifts of SP units 1 and 2 are coincident.
b Protons of aceto- and amide groups resonate at 1.98–2.15 and 9.67 ppm, respectively.
c Data in CDCl3.
Table 3. 13C-NMR data for the symmetric bis-spirobenzopyrans (series 1–2) in CHCl3 ꢀ d, including data for a mono-spiropyran for comparison
Series 1
Bis-ASPb
Series 2
Carbons
Mono-SPa
Bis-SPb
TBis-SP
TBis-NSP
TBis-CNSP
CbBis-SP
CbBis-CSP
C-2,20
C-30
C-3’a
C-40
C-50
C-60
C-70
C-70a
C-80
C-90
C-100
C-3
106.5
51.92
136.0
n/a
104.1
51.38
136.3
121.5
118.9
127.5
106.8
147.8
25.69
19.88
28.58
119.6
129.4
118.8
124.6
132.0
127.4
114.7
153.1
104.3
51.42
136.4
114.3
131.6
118.9
106.5
144.0
25.62
19.84
28.75
119.5
129.4
118.8
124.6
131.9
127.4
114.7
153.1
104.9
52.23
137.0
121.9
119.6
128.0
107.2
148.5
26.27
20.57
29.34
120.5
129.4
120.0
130.1
126.8
133.4
116.4
154.4
107.3
52.32
137.4
121.4
120.0
127.8
107.1
147.3
26.00
20.02
28.87
122.5
127.9
122.7
133.9
125.1
128.1
135.8
148.1
107.2
52.34
137.7
121.9
124.6
127.5
108.1
145.9
25.82
19.79
28.98
122.0
128.2
122.5
134.0
125.4
128.2
137.4
147.9
105.3
51.9
105.8
52.44
138.8
122.5
124.5
127.8
108.2
147.1
26.11
20.28
29.40
120.1
129.8
118.8
129.5
130.7
133.0
115.0
158.2
136.4
121.5
119.4
127.7
106.9
147.9
25.9
131.7
118.9
106.8
144.1
25.67
19.68
28.70
121.3
128.4
120.6
125.8
140.5
122.9
115.4
159.4
20.00
28.86
120.1
129.1
118.4
129.0
130.1
132.4
114.6
158.0
C-4
C-4a
C-5
C-6
C-7
C-8
C-8a
a Data of 50-acetamido-6-nitro SP for comparison from Ref. 6(a).
b Data in DMSO-d6.
coupling value set to 140 Hz, using 2048 points in the F2 dimensions
and 256 increments in the F1 dimension, with a relaxation delay of
1 s. The spectral width was 20 000 Hz in the F2 and 4500 Hz in the F1
dimensions. The resulting resolution was 19.53 Hz per point in the
F2 and 17.6 Hz per point in the F1 dimensions. All two-dimensional
experiments were performed by standard pulse sequences, using
the Mercury Data System software Version VNMR 6.1B. For proton
decoupling, Waltz 16 modulation was used.
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2005; 43: 873–876

876
Spectral Assignments and Reference Data
13
Table 4.
C-NMR data for asymmetric bis-spirobenzopyrans (Series 3) in DMSO-d6
SP unit 1
SP unit 2
SP-ASPa
Carbons
SP-CSP
SP-ASPa
CSP-ASP
Carbons
SP-CSP
CSP-ASP
C-2,20
C-30
C-30a
C-40
C-50
C-60
C-70
C-70a
C-80
C-90
C-100
C-3
104.1
51.40
136.3
121.5
119.0
127.5
106.8
147.9
25.70
19.89
28.60
119.2
129.4
118.9
124.6
131.9
127.5
114.7
153.1
104.3
51.71
136.7
121.5
119.1
127.6
106.7
148.2
25.85
20.16
28.92
119.7
129.4
118.9
124.7
132.7
127.9
115.2
153.5
104.1
51.51
138.7
121.9
122.5
127.0
108.0
146.7
25.26
19.54
28.60
119.5
129.4
118.7
124.6
132.1
127.5
114.7
152.9
C-200,2000
C-3000
C-3000a
C-4000
C-5000
C-6000
C-7000
C-7000a
C-8000
C-9000
C-10000
C-300
C-400
C-400a
C-500
C-600
C-700
104.1
51.56
138.7
122.0
122.5
127.1
108.1
146.8
25.31
19.59
28.65
119.7
129.7
118.7
124.7
132.1
127.5
114.7
152.9
104.5
51.80
137.4
115.6
129.8
120.4
106.6
145.5
25.71
20.06
29.07
119.5
129.5
118.8
124.7
132.6
127.8
115.2
153.6
104.3
51.42
136.4
114.3
131.6
118.9
106.5
143.9
25.60
19.83
28.73
119.1
129.6
118.8
124.6
131.8
127.4
114.7
153.1
C-4
C-4a
C-5
C-6
C-7
C-8
C-800
C-800a
C-8a
a Data in CDCl3.
6. (a) Keum SR, Hur MS, Kazmaier PM, Buncel E Can. J. Chem. 1991;
69: 1940; (b) Keum SR, Lim SS, Min BH Bull. Korean Chem. Soc.
1995; 16: 1; (c) Keum SR, Choi YK, Lee MJ, Kim SH Dyes Pigments
2001; 50(3): 171; (d) Keum SR, Ku BS, Kim SE, Choi YK, Kim SH,
Koh KN. Bull. Korean Chem. Soc. 2004; 25(9): 1361.
Acknowledgments
This work has been supported by Grant No. R01-2003-000-10248-
0 from the Basic Research Program of the Korea Science and
Engineering Foundation (S.R.K.).
7. (a) Swansberg S, Choi YK, Keum SR, Lee MJ, Buncel E,
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Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2005; 43: 873–876