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H.L. Noh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 239 (2020) 118457
1.0 × 10−4 M), it showed marked color change to light blue with
ultra-fast detection speed (b1.0 s) with ambient stability over 10 days,
as shown in Fig. 9a and Fig. S4. In addition, we also investigated H2S de-
tection properties of solid SQ1 by using SQ1-dyed fabric as shown in
Fig. 9b. SQ1-dyed fabric were prepared by dipping polyethylene tere-
phthalate (PET) textile into SQ1 solution. After drying, the dyed fabric
were exposed to a H2S gas with a total flow rate of 1000 sccm (dry
air:H2S (1000 ppm) = 1:1) in the chamber. Noticeable color change
from blue to colorless was clearly observed. Rapid and naked-eye-
based colorimetric H2S sensing capability of SQ1 in solid states suggest
the potential applicability to cheap, simple but very effective practical
H2S sensors such as optical solid chemosensors. The color change was
measured by applying the commonly used Commission Internationale
de L'Eclairage (CIE) Lab standard among various color quantifications.
The changes in the CIE L*, a*, b*, and chroma (C) values, and the hue
angle (H), are shown in Table 1. The three coordinates of the CIE Lab
represent the lightness of the color (L* = 0 yields black and L* = 100 in-
dicates diffuse white; specular white may be higher), its position be-
tween red/magenta and green (a*, negative values indicate green,
while positive values indicate magenta), and its position between yel-
low and blue (b*, negative values indicate blue and positive values indi-
cate yellow). From the coordinate values, the color change (ΔEab) was
calculated using equation given as follows:
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2
2
ΔEab ¼ ðΔLꢁÞ þ ðΔaꢁÞ þ ðΔbꢁÞ
In general, when the color change value is 5 or higher, observers can
recognize two distinctive colors [16]. The dyed fabric exhibited a color
difference value of 6.69, indicating that before and after gas exposure,
the color of the fabric is perceptible.
4. Conclusion
In summary, we synthesized squarylium-based chromogenic H2S
chemosensors (SQ1, SQ2, and SQ3), systemically characterized the de-
tection performances, and elucidated the sensing mechanism. SQ1 ex-
hibited naked-eye-discernable and rapid colorimetric changes when
exposed to H2S with detection limit of 7.2 ppb. SQ1 featured high selec-
tivity for H2S detection over other relevant anions and nucleophiles. In
addition to the solution environment, versatile detection capability of
H2S in solid state such as SQ1-coated silica and SQ1-dyed fabric suggests
the simple, low-cost, and practical applications of SQ1 to the effective
H2S chemosensors.
CRediT authorship contribution statement
Ha Lim Noh: Investigation. Byeong M. Oh: Investigation. Young Ki
Park: Investigation. Hye W. Chun: Investigation. Junyeop Lee: Investi-
gation. Jae Keon Kim: Investigation. Jian Zheng: Investigation.
Daewoong Jung: Formal analysis, Writing - review & editing. Woosung
Lee: Formal analysis, Writing - review & editing. Jong H. Kim: Concep-
tualization, Methodology, Supervision, Writing - original draft.
Fig. 8. (a) UV–Vis absorption spectrum changes in response to various anion analytes,
(b) comparison of absorption ratio for various anions in SQ1 (A and A0 are the
absorbance in the presence and the absence of anions at 649 nm, respectively), and
(c) photographs showing selective colorimetric change of SQ1 in response to the various
anions.
of SQ1 to different analytes. As shown in Fig. 8, when 1 equivalent of dif-
ferent anions were added into SQ1 solution, addition of H2S only exhib-
ited naked-eye-discernable color change by UV–Vis spectral changes
while addition of other anions did not have significant effect on the ab-
sorption spectrum and color changes of SQ1 solution. Furthermore,
upon addition of different nucleophiles (sodium sulfide (Na2S),
thiophenol (PhSH), and glutathione (GSH)) to SQ1 solution, color
changes was observed from Na2S due to the H2S generation and PhSH
addition, as shown in Fig. S3.
Finally, in order to demonstrate the practical application of SQ1 for
H2S detection, we investigated their detection capability in solid state
and in dyed fabric. Solution of SQ1 (20 ml, 5.0 × 10−4 M) was added
to silica (230–400 mesh, 3 g, white), stirred for 1 min, and dried to pre-
pare blue silica. When the SQ1-silica was exposed to H2S (2 ml,
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgement
This work was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded by
the Ministry of Education (NRF-2018R1D1A1B07047645). This study
was also supported by a grant from Priority Research Centers Program
(2019R1A6A1A11051471) funded by the NRF. This study has been