Synthesis of a Novel Disperse Reactive Dye Involving a Versatile Bridge Group for the Sustainable Coloration of Natural Fibers in Supercritical Carbon Dioxide

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Figure 1. FT-IR spectra of A) the precursor and B) the anthraquinone-type disperse reactive dye.

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Adv. Sci. 2018, 1801368
O
O
HN
N
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N
Cl
Cl
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Figure 3. 
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C NMR spectra of the anthraquinone-type disperse reactive dye measured in DMSO-d
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O
HN
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N
Cl
Cl
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Figure 2. 
1
H NMR spectra of the anthraquinone disperse reactive dye.

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1801368 (7 of 14)
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2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.advancedscience.com
the final product by employing the condensa-
tion reaction between the reactants according 
to the proposed reaction route of step 2 in 
Scheme 1.
Furthermore, Figure 3 shows the 
13
C NMR 
spectra for the final product of the synthe-
sized disperse reactive dye. All the C-(1-14)
carbon atoms from the anthraquinone back-
bone ring were detected, with chemical shifts 
(
δ) ranging from 185.26 to 113.66 ppm. 
Moreover, the C-(17-22) carbon atoms from 
the benzene ring of the versatile bridge were 
also observed with chemical shifts (
δ) from 
151.31 to 116.37 ppm. The C-15 and C-16 
carbon atoms from the ethyl chain of the 
bridge group were also detected at chemical 
shifts (
δ) of 39.75 and 49.69 ppm, respec-
tively. Additionally, the characteristic carbons 
of C-(23-25) from the S-triazine ring were 
detected with chemical shifts (
δ) at 170.65 
and 170.46 ppm. Therefore, these results fur-
ther demonstrate that the expected carbon 
backbone structure was successfully achieved 
for the disperse reactive dye, according to the 
designed chemical structure and synthesis 
route in Scheme 1.
2.2.3. UV–Vis Absorption Spectral Analysis 
of the Dye Precursor and Its Final Product
UV–vis absorption spectral analysis was also 
performed to investigate the color charac-
teristics of the synthesized disperse reac-
tive dye and its precursor in the solvents of 
dimethylsulfoxide (DMSO), DMF, ethanol, 
dichloromethane, and n-hexane with dye con-
centrations of 1.0 
× 10
−4
–1.5 
× 10
−4
mol L
−1
. 
The obtained results are shown in Figure 4 
and Table 2.
Figure 4A shows that the synthesized dye 
precursor and its disperse reactive dye both 
presented a characteristic single absorption 
peak with good shape and high intensity at 
a visible wavelength range of 375.0–600.0 nm 
in dichloromethane. Moreover, a maximum 
absorption wavelength (
λ
max
) of the dye pre-
cursor at 502.0 nm was detected, and a slight 
shift in this maximum to 495.0 nm in the 
final disperse reactive dye product was also determined. Obvi-
ously, an inductive effect occurred to lead to the wavelength 
shift due to the bonding of the electron-withdrawing reactive 
group of dichloro-S-triazine onto the dye precursor system, as 
well as the effect of increased steric hindrance from the bound 
reactive group on the coplanarity of the dye.
Table 2 shows the solvation effects of different solvents with 
various polarities on the chromophoric matrix and the color 
characteristics of the synthesized disperse reactive dye. Evi-
dent solvation effects from the solvents were observed on the 
conjugated system of the synthesized anthraquinone dye: a sig-
nificant hypsochromic shift in the maximum absorption wave-
length (
λ
max
) from 504 to 481 nm was observed with decreasing 
polarity, from DMSO to the nonpolar solvent n-hexane. These 
observations clearly indicate that the achieved disperse reac-
tive dye involving an anthraquinone chromophoric matrix 
and the designed versatile bridge group tends to interact more 
closely with the polar solvents, which simultaneously affects 
the electronic cloud density of the dye conjugation system. The-
oretically, strong polar solvents, such as DMSO or DMF, which 
Adv. Sci. 2018, 1801368
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Absorbance
Wavelength (nm) 
(A) 
Absorbance
Wavelength (nm)