1H and 13C NMR spectra of commercial rhodamine ester derivatives

Article abstract of DOI:10.1002/1097-458X(200006)38:6<475::AID-MRC662>3.0.CO;2-X

Ethyl and methyl esters of commercial rhodamines B, 19, 101 and 110 and propyl and butyl esters of commercial rhodamine B were synthesized and isolated with different counterions (yields 70-98%). The ¹H and ¹³C NMR spectral data for these compounds were fully assigned by a combination of one-and two-dimensional experiments. The Fourier transform IR and UV-visible spectra were also recorded and the main bands were identified. Copyright

Full text of DOI:10.1002/1097-458X(200006)38:6<475::AID-MRC662>3.0.CO;2-X

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2000; 38: 475–478
Reference Data
1H and 13C NMR spectra of commercial rhodamine
ester derivatives
was concentrated and the esters were converted into bromide, iodide or
perchlorate salts by treatment with an excess of a 14% aqueous solution
of potassium iodide, potassium bromide or sodium perchlorate. The ratio
between the aqueous and alcoholic solution was kept around 1 : 2. The
resulting precipitated dye was filtered off or in some cases the resulting
oleum was decanted off, to yield after drying the respective ester in high
yield in most cases. No attempts were made to obtain higher yields.
All the reactions were monitored by thin-layer chromatography
(TLC) on aluminium sheets precoated with Merck silica gel 60 F254
(0.25 mm) using n-butanol–water–ethanol (9 : 3 : 1) acidified with 1%
acetic acid as the eluent of several systems tested, this proved to be the
only one capable of separating successfully the rhodamine acid from
its ester.
S. S. Ramos,1 A. F. Vilhena,1 L. Santos2 and
1
∗
P. Almeida
1
Departamento de Qu´ımica e Unidade de I & D de Materiais
Teˆxteis e Papeleiros, Universidade da Beira Interior, 6200-053
Covilha˜, Portugal
2
Instituto Nacional de Engenharia e Tecnologia Industrial
IBQTA, Laborato´ rio de Qu´ımica Anal´ıtica e de S´ıntese LAQAS,
Estrada do Pac¸o do Lumiar, 1649-038 Lisboa, Portugal
Spectra
Received 11 November 1999; accepted 14 January 2000
IR spectra was recorded on a Mattson 5000-FTS Fourier transform (FT)
IR spectrophotometer and UV–visible (Vis) spectra were obtained with
a Perkin-Elmer Lambda 6 instrument.
ABSTRACT: Ethyl and methyl esters of commercial rhodamines B, 19,
101 and 110 and propyl and butyl esters of commercial rhodamine
B were synthesized and isolated with different counterions (yields
70–98%). The 1H and 13C NMR spectral data for these compounds
were fully assigned by a combination of one- and two-dimensional
experiments. The Fourier transform IR and UV–visible spectra were
1H and 13C NMR spectra were recorded with a General Electric QE-
PLUS-300 spectrometer equipped with NICOLET and NUTS software.
All chemical shifts were determined on the υ scale relative to internal
TMS (D0.00 ppm) for the 1H and to CDCl3 (D77.7 ppm) for the 13C
spectra. The spectra were recorded from solutions of a given dye in
CDCl3 or CDCl3 containing a drop of DMSO-d6.
also recorded and the main bands were identified. Copyright
John Wiley & Sons, Ltd.
2000
1H NMR and COSY spectra were recorded at room temperature at
300.15 MHz in a 5 mm probe with a 90° pulse width of 12.5 µs and
a relaxation delay of 1.0 µs. COSY spectra were processed using a
sinusoidal multiplication in both dimensions and recorded in magnitude
mode. The final data matrix was symmetrized after multiplication with
a sine window function. Typically 256 FIDs were recorded in t1 of size
1024 and eight scans each.
1
KEYWORDS: NMR; H NMR; 13C NMR; rhodamine esters
INTRODUCTION
The rhodamines1 are xanthene derivatives of alkylated m-aminophenols.
This class of dye shows typically strong fluorescence due to the ring
closure by the oxygen atom at the 2,20-position of the related parent
diphenylmethine dyes. Without such a bridge very little or no fluoresce
is observed. Therefore, some of the most important applications of this
class of dye are based on this high fluorescence yield .ꢀF ½ 0.7/, the
short lifetime of the S1 state (ꢁF Ä 10 ns), the little intersystem crossing
to triplet states, the strong absorption of the pumping radiation and
the high photochemical stability. For instance, rhodamine 6G (the ethyl
ester of rhodamine B) was used in one of the first two dye lasers and
it is still the dye most frequently used for dye lasers. Rhodamines can
also be applied in the textile industry to mordanted cotton and to silk.
Recently, other important new applications of rhodamines in the acid
or ester form were reported, such as their use as probes and indicators2
and as dyes for medical and biological applications.3
Table 1. Structures and yields of rhodamine esters
Starting Rhoda-
rhoda-
mine
mine
ester
Yield
(%)
The present work of rhodamine esterifications with low molecular
weight alcohols yielded models for cellulose binding, which constitutes
an alternative to the use of reactive isothiocyanate rhodamines.4
R1
R2
R3
Et
R4
R5
X
B
1
2
Me
Me
Me
Et
Et
Et
n-Pr
n-Pr
n-Pr
n-Bu
n-Bu
n-Bu
H
H
H
H
H
H
H
H
H
H
H
H
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
H
H
H
H
H
H
H
H
H
H
H
H
ClO4
I
Br
ClO4
I
Br
ClO4
I
Br
ClO4
I
Br
83
79
94
95
96
91
93
95
76
90
70
72
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
3
4
5
6
7
8
9
10
11
12
EXPERIMENTAL
Materials
The starting rhodamines were purchased from Aldrich and used as
received. The alcohols used were of analytical-reagent grade.
The esterification of rhodamines having carboxylic groups was car-
ried out under Fischer conditions. Typically, the rhodamine was dis-
solved in a minimum volume of the appropriate alcohol solution con-
taining 3% of sulphuric acid and the resulting solution was then heated
with stirring at 50 °C for 1–6 days, until total conversion to the respec-
tive ester was achieved. The resulting still highly fluorescent solution
19
116
110
101
13
14
Me
Et
Me
Me
H
H
Et
Et
H
H
ClO4
ClO4
98
97
15
16
Me
Et
H
H
H
H
Me
Me
H
H
ClO4
ClO4
70
95
17
18
Me
Et
H
H
H
H
H
H
H
H
ClO4
ClO4
98
98
* Correspondence to: P. Almeida, Departamento de Qu´ımica e Unidade de I &
D de Materiais Teˆxteis e Papeleiros, Universidade da Beira Interior, 6200-053
Covilha˜, Portugal; e-mail: pjsa@alpha2.ubi.pt
19
20
Me
Et
—.CH2/3 — —.CH2/3 — ClO4
—.CH2/3 — —.CH2/3 — ClO4
97
75
Contract/grant sponsor: JNICT.
Copyright 2000 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2000; 38: 475–478

476
Reference Data
4096 ð 256 blocks of data. Compounds were dissolved in CDCl3 or
CDCl3 containing a drop of DMSO-d6
Table 2. UV–Vis and IR spectral data for rhodamine
esters
a
Rhodamine ester
IR .cmꢀ1
/
UV–Vis,ꢂmax .nm/b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1082, 1593, 1728
1076, 1587, 1722
1076, 1589, 1722
1074, 1589, 1709
1093, 1589, 1714
1077, 1591, 1715
1074, 1589, 1709
1074, 1591, 1707
1091, 1590, 1715
1072, 1583, 1707
1077, 1590, 1716
1076, 1591, 1717
1091, 1608, 1721, 3402
1084, 1606, 1710, 3396
1092, 1642, 1720, 3325
1078, 1606, 1712, 3329
1084, 1595, 1712, 3157
1094, 1608, 1720, 3306
1085, 1595, 1720
556
556
556
556
556
556
556
556
556
556
556
557
529
530
525
528
511
512
578
577
RESULTS AND DISCUSSION
The structure, numbering scheme and yields obtained for the different
rhodamine esters are presented in Table 1. The UV–Vis and FTIR
spectra data are given in Table 2 and the 1H and 13C NMR spectral
data in Tables 3 and 4 and Tables 5 and 6, respectively.
Generally, the UV–Vis spectra show a 10–15 nm bathochromic shift
with respect to the acid rhodamine.
The IR spectra of all esters of the different rhodamines dis-
play typically three strong bands at 1072–1094, 1583–1597 and
1707–1728 cmꢀ1, which are characteristic of C—O, C C and C
axial deformation modes, respectively.
O
The 30/80 protons and the 40/50 protons, responsible for two doublets
and two triplets, respectively, were distinguished by the effect of the
substituted ester and diphenylmethine on the different positions of the
ring known from the literature5 together with the observation of the roof
effect. These attributions were confirmed by one- and multiple-bond
homo- and heteronuclear correlation experiments.
Typical values of the ortho and meta coupling constants were
observed in the ester substituted phenylmethine ring, with values of
7.5–8.0 Hz and 1.0–1.5 Hz, respectively. The 1–2/7–8 ortho con-
stants and 2–4/5–7 meta constants observed for the diphenylmethine
rings also present typical values of coupling constants of 9.0–9.5 and
2.0–2.5 Hz, respectively.
1099, 1597, 1714
a KBr disc.
b EtOH–1% DMF.
Noteworthy is the stronger concentration dependence of the proton
signals close to nitrogen with a relative 4,5-proton deshielding and 2,7-
proton shielding as the concentration of the sample decreases, leading
to an overall better resolution of the spectra.
13C NMR spectra were recorded at room temperature at 75.6 MHz, a
pulse width for a 90° pulse of 20.0 µs, a relaxation delay of 1.0 µs and
broadband proton decoupling.
Short- and long-distance heteronuclear correlations were made using
HETCOR and COLOC type experiments, respectively, at room tem-
perature. These spectra were obtained as matrices of 4096 ð 128 and
The almost identical chemical shifts of C-40 and C-60 were assigned
by long-range correlation. As expected, the chemical shift of the ester
carbonyl appears to the lowest field, ca 165 ppm.
The 19 and 20 saturated ring proton and carbon chemical shifts
were unequivocally assigned by a combination of direct and long-range
Table 3. 1H NMR aromatic spectral data for rhodamine esters [CDCl3; υ (ppm), J (Hz)]
H-1,8
d
H-2,7
dd
H-4,5
d
H-30
dd
H-40
dt
H-50
dt
H-60
dd
Rhodamine
ester
(9.0–9.5) (9.0–9.5; 2.0–2.5) (2.0–2.5) (7.5–8.0; 1.0–1.5) (7.5–8.0; 1.0–1.5) (7.5–8.0; 1.0–1.5) (7.5–8.0; 1.0–1.5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17a
18a
19
20
7.06
7.03
7.00
7.09
7.11
7.10
7.08
7.08
7.09
7.08
7.09
7.10
6.80 (s)
6.74 (s)
6.94
6.95
6.75
6.85
6.86
6.86
6.90
6.93
6.94
6.86
6.84
6.93
6.88
6.91
6.94
—
6.89
6.77
6.74
6.87
6.84
6.83
6.88
6.82
6.85
6.83
6.81
6.87
6.88 (s)
6.79 (s)
6.67
6.66
6.65
6.53
—
8.30
8.27
8.24
8.30
8.32
8.31
8.29
8.30
8.30
8.29
8.29
8.28
8.32
8.37
8.28
8.28
8.06
7.94
8.31
8.26
7.75
7.72
7.69
7.75
7.77
7.75
7.72
7.74
7.75
7.74
7.75
7.75
7.77
7.79
7.73
7.73
7.53
7.42
7.75
7.70
7.82
7.80
7.77
7.82
7.85
7.83
7.81
7.81
7.82
7.81
7.83
7.82
7.83
7.82
7.80
7.79
7.59
7.47
7.81
7.78
7.32
7.29
7.25
7.31
7.34
7.31
7.32
7.31
7.31
7.32
7.32
7.31
7.29
7.29
7.29
7.29
7.09
6.97
7.25
7.26
6.84
6.85
6.64
6.52
—
6.62
6.54 (s)
6.55 (s)
—
—
a CDCl3 C 1 drop of DMSO.
Copyright 2000 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2000; 38: 475–478

477
Reference Data
Table 4. 1H NMR aliphatic spectral data of substituents of rhodamine esters [CDCl3, υ (ppm), J (Hz)]
Rhodamine ester
R1
R2
R3
R4
1.33, t, 7.0; 3.62; q, 7.0
1.30, t, 7.0; 3.61, q, 7.0
1.27, t, 7.0; 3.59, q, 7.0
1.33, t, 7.0; 3.64, q, 7.0
1.36, t, 7.0; 3.68, q, 7.0
1.34, t, 7.0; 3.67, q, 7.0
1.35, t, 7.0; 3.63, q, 7.0
R5
1
2
3
4
5
6
7
3.69, s
3.65, s
3.62, s
—
—
—
—
—
—
—
—
—
—
1.07, t, 7.0; 4.07, q, 7.0
1.10, t, 7.0; 4.10, q, 7.0
1.09, t, 7.0; 4.08, q, 7.0
0.78, t, 7.0; 1.47, sext., 7.0;
3.98, t, 6.5
—
—
—
8
9
0.78, t, 7.5; 1.47, sext., 7.0;
3.98, t, 6.5
0.79, t, 7.0; 1.45, sext., 7.0;
3.99 t, 6.5
0.80, t, 7.5; 1.14, sext., 7.5;
1.40, qt, 7.0; 4.01, t, 7.0
0.80, t, 7.5; 1.16, sext., 7.5;
1.42, qt, 7.5; 4.02, t, 7.5
0.81, t, 7.5; 1.16, sext., 7.5;
1.40, qt, 7.0; 4.02, t, 6.5
3.65, s
1.00, t, 7.0; 4.05, q, 7.0
3.65, s
1.01, t, 7.0; 4.03, q, 7.0
3.42, s
0.75, t, 7.0; 3.69, q, 7.0
3.70, s
—
—
—
—
—
1.32, t, 7.0; 3.63, q, 7.0
1.33, t, 7.0; 3.68, q, 7.0
1.33, t, 7.0; 3.63, q, 7.0
1.34, t, 7.0; 3.66, q, 7.0
1.34, t, 7.0; 3.66, q, 7.0
—
—
—
—
—
10
11
12
13
14
15
2.22, s
2.20, s
—
—
—
5.43, sl
5.20, sl
1.43, t, 7.0; 3.56, q, 7.0
1.43, t, 7.0; 3.53, q, 7.0
—
—
—
—
—
—
NH not detectable
NH not detectable
3.04, s
3.04, s
16
17a
18a
19
4.17, sl
4.99, sl
—
3.54, t, 6.9 [NCH2.CH2/2];
3.06, t, 6.0 [N.CH2/2CH2];
2.13, qt, 6.0 .NCH2CH2CH2/
3.55, t, 6.0 [NCH2.CH2/2];
3.05, t, 6.0 [N.CH2/2CH2];
2.12, qt, 6.0 .NCH2CH2CH2/
3.50, t, 6.0 [NCH2.CH2/2];
2.68, t, 6.0 [N.CH2/2CH2];
1.98, qt, 6.0 .NCH2CH2CH2/
3.49, t, 6.0 [NCH2.CH2/2];
2.66, t, 6.0 [N.CH2/2CH2];
1.97, qt, 6.0 .NCH2CH2CH2/
20
1.07, t, 7.0; 4.08, q, 7.0
a CDCl3 C 1 drop of DMSO.
Table 5. 13C NMR spectral data for Rhodamine esters 1–10 [CDCl3; υ (ppm)]
1
2
3
4
5
6
7
8
9
10
C-1/8
C-2/7
C-3/6
C-4/5
C-4a/5a
C-8a/9a
C-9
131.3
114.9
154.9
97.4
131.2
114.4
155.8
96.6
131.1
114.3
155.7
96.4
131.2
114.5
155.4
97.0
131.2
114.2
155.4
96.3
131.2
114.3
155.4
96.3
130.3
114.3
155.7
96.8
131.2
114.1
155.5
96.3
131.2
114.3
155.4
96.5
131.2
114.2
155.5
96.3
157.5
114.5
158.8
133.4
129.7
131.3
130.2
133.1
130.5
165.5
157.9
113.7
158.9
133.5
130.3
131.3
130.3
132.9
130.3
165.3
157.8
113.6
158.7
133.5
130.2
131.1
130.1
132.8
130.1
165.2
157.7
114.1
158.9
133.2
130.3
131.1
130.1
132.7
130.2
164.9
157.6
113.5
158.9
133.3
130.3
131.4
130.1
133.0
130.1
165.0
157.6
113.5
158.9
133.3
130.3
131.2
130.0
132.9
130.1
164.9
157.9
113.9
158.9
133.3
130.6
130.2
130.1
132.7
130.1
165.1
157.7
113.5
158.8
133.3
130.2
131.3
130.1
132.9
130.3
165.1
157.7
113.6
158.8
133.4
130.3
131.2
130.1
132.9
130.3
165.1
157.7
113.4
158.7
133.3
130.2
131.2
130.1
132.9
130.3
165.2
65.5
C-10
C-20
C-30
C-40
C-50
C-60
C
O
67.1
21.6
9.9
67.1
21.6
10.1
67.2
21.6
10.2
61.3
13.6
61.5
13.8
61.4
13.8
30.3
19.0
13.5
OR1
55.0
52.3
52.2
NR3
NR4
46.7
12.4
46.2
12.7
46.0
12.6
46.2
12.4
46.2
12.7
46.2
12.6
46.1
12.4
46.0
12.5
46.2
12.6
46.0
12.5
Copyright 2000 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2000; 38: 475–478

478
Reference Data
Table 6. 13C NMR spectral data for rhodamine esters 11–20 [CDCl3; υ (ppm)]
11
12
13
14
15
16
17a
18a
19
20
C-1/8
C-2/7
C-3/6
C-4/5
C-4a/5a
C-8a/9a
C-9
131.2
114.5
155.8
96.6
131.2
114.4
155.4
96.9
128.9
126.7
154.8
95.6
156.9
115.0
157.8
133.8
129.7
131.3
130.1
133.1
130.4
162.2
128.7
125.6
156.2
93.9
157.3
113.7
158.0
133.6
130.5
131.1
130.0
132.5
130.1
164.9
131.1
117.2
158.1
94.8
158.4
113.6
159.0
133.7
129.8
130.0
130.2
132.8
130.2
165.4
131.1
116.9
158.1
94.6
158.5
113.6
158.9
133.4
130.1
129.9
130.1
132.6
130.2
164.8
131.1
117.3
158.0
98.1
159.3
113.7
159.3
133.5
130.2
130.9
129.9
132.4
130.0
165.1
131.1
117.4
157.8
97.8
159.3
113.5
159.3
133.6
130.4
130.8
129.8
133.3
129.9
165.6
125.7
123.6
151.0
105.1
152.0
112.7
155.9
132.8
129.6
129.9
130.0
131.1
130.3
164.1
125.9
123.8
151.3
105.5
152.2
113.1
155.8
134.5
130.5
131.0
129.9
132.8
130.7
165.3
157.8
113.7
158.9
133.2
130.2
131.2
130.2
132.7
130.2
165.0
65.3
157.6
113.7
158.7
133.2
130.7
131.3
130.1
132.9
130.3
165.1
65.4
C-10
C-20
C-30
C-40
C-50
C-60
C
O
30.3
18.8
30.3
18.9
61.2
13.4
61.3
13.6
61.0
13.3
61.4
13.9
OR1
52.2
52.2
52.0
52.4
13.2
—
46.2
12.6
13.5
—
46.2
12.5
R2
17.3
39.8
13.4
17.1
38.6
13.6
—
30.0
—
—
30.0
—
—
—
—
—
—
—
50.8b
20.4c
27.5d
50.3b
19.5c
19.8d
51.0b
20.7c
27.7d
50.6b
19.8c
20.0d
NR3
NR4
R5
NR3
—
NR3
—
NR3
—
NR3
—
NR3
—
NR3
—
—
—
—
—
a CDCl3 C 1 drop of DMSO.
b NCH2CH2CH2.
c NCH2CH2CH2.
d NCH2CH2CH2.
heteronuclear correlation, starting from the H-1/H-8 cross peak and the
methylene signal in the benzylic position of R2.
REFERENCES
The assignment of proton signals of the different aliphatic groups
(R1, R2, R3, R4 and R5) was easily and unambiguously achieved
by the analysis of the multiplicity and relative integration of the
signals and by the shielding effect known from literature data.5 The
assignment of the related carbon was mainly achieved based on typical
υc data5 and by the observation of the strong signals of the N-alkyl
groups of the weaker ester group signal(s). These assignments were
also confirmed by homo- and heteronuclear one- and multiple-bond
correlation experiments.
1. Zollinger H. Color Chemistry. Syntheses, Properties and Applications
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Acknowledgement
Thanks are due to JNICT, Lisbon, for funding of the Project PRAXIS
XXI/2/2.1/QUI/22/94.
Copyright 2000 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2000; 38: 475–478