Ruthenium-based phosphorescent probe for selective and naked-eye detection of cyanide in aqueous media

Article abstract of DOI:10.1016/j.dyepig.2020.108196

A simple molecular phosphorescent Ru(II) probe P1 has been synthesized by the reaction of 5-aldehyde-2,2′-bipyridine with ruthenium(II) chlorides under mild conditions. The probe upon interaction with different cation and anion showed high selectivity and sensitivity for cyanide ion (CN^?) through phosphorescence “turn-on” response in aqueous solution (60% water) with a detection limit of 0.75 μM. The significant phosphorescence enhancement (~ 30-fold) is attributed to the nucleophilic addition of cyanide ion to the aldehyde groups of the ruthenium complex in 3 : 1 stoichiometry, in which a naked-eye sensitive orange red color of solution changed to a yellow. The generation of cyanohydrin species through nucleophilic addition has been confirmed by ¹H NMR, FT-IR and mass spectra. Based on the color change of the solution, a visual colorimetric strip was prepared, which also showed good detection performance on cyanide ion with quick response time. The prominent efficiency of the Ru(II) probe proved the potential possibility of application in biosystems relating with cyanide ion.

Full text of DOI:10.1016/j.dyepig.2020.108196

Journal Pre-proof
Ruthenium-based phosphorescent probe for selective and naked-eye detection of
cyanide in aqueous media
Jing-Wei Zhu, Hui-Dan Ou, Niwei Xu, Wei Deng, Zi-Jian Yao
PII:
S0143-7208(19)32565-3
DOI:
https://doi.org/10.1016/j.dyepig.2020.108196
DYPI 108196
Reference:
To appear in: Dyes and Pigments
Received Date: 6 December 2019
Revised Date: 8 January 2020
Accepted Date: 8 January 2020
Please cite this article as: Zhu J-W, Ou H-D, Xu N, Deng W, Yao Z-J, Ruthenium-based phosphorescent
probe for selective and naked-eye detection of cyanide in aqueous media, Dyes and Pigments (2020),
doi: https://doi.org/10.1016/j.dyepig.2020.108196.
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CRediT author statement
Jing-Wei Zhu: Ph.D student, Conceptualization, Methodology and Writing original draft;
Hui-Dan Ou: Ph.D student, Methodology and Characterization;
Ni-Wei Xu, Methodology, Characterization and Writing-Review and Editing;
Wei Deng, Co-supervision;
Zi-Jian Yao, Supervision, Conceptualization, Methodology, Writing-Review and Editing.

Ruthenium-based phosphorescent probe for selective and naked-eye
detection of cyanide in aqueous media
Jing-Wei Zhu,a Hui-Dan Ou,a Niwei Xu,c Wei Deng,*a Zi-Jian Yao*a, b
a School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai,
201418, China.
b
State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha
410082, China
c Hunan Traditional Chinese Medical College, Zhuzhou, 412012, China
Corresponding author: Email: zjyao@sit.edu.cn; Tel: +86-21-60877231, Fax: +86-21-60873335.
(Graphical Abstract)
The ruthenium probe exhibits highly selective and sensitive for CN– recognition in aqueous
solution (60 % water) with a detection limit of 0.75 µM. Changes in the color of the solution were
clearly observed with the naked eye. Based on the color change of the solution, a strip was prepared
and showed good detection performance CN– ion and quick response time.

Ruthenium-based phosphorescent probe for selective and naked-eye
detection of cyanide in aqueous media
Jing-Wei Zhu,a Hui-Dan Ou,a Niwei Xu,c Wei Deng,*a Zi-Jian Yao*a, b
a School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai,
201418, China.
b
State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha
410082, China
c Hunan Traditional Chinese Medical College, Zhuzhou, 412012, China
Corresponding author: Email: zjyao@sit.edu.cn; Tel: +86-21-60877231, Fax: +86-21-60873335.
Abstract: A simple molecular phosphorescent Ru(II) probe P1 has been synthesized by the reaction
of 5-aldehyde-2,2′-bipyridine with ruthenium(II) chlorides under mild conditions. The probe upon
interaction with different cation and anion showed high selectivity and sensitivity for cyanide ion
(CN‒) through phosphorescence “turn-on” response in aqueous solution (60 % water) with a
detection limit of 0.75 µM. The significant phosphorescence enhancement (∼ 30-fold) is attributed
to the nucleophilic addition of cyanide ion to the aldehyde groups of the ruthenium complex in 3 : 1
stoichiometry, in which a naked-eye sensitive orange red color of solution changed to a yellow. The
1
generation of cyanohydrin species through nucleophilic addition has been confirmed by H NMR,
FT-IR and mass spectra. Based on the color change of the solution, a visual colorimetric strip was
prepared, which also showed good detection performance on cyanide ion with quick response time.
The prominent efficiency of the Ru(II) probe proved the potential possibility of application in
biosystems relating with cyanide ion.
Keywords: Ruthenium complex, cyanide, probe, aqueous media.

Introduction
Cyanide ion (CN‒) as an extremely toxic inorganic anion is harmful to the environment and
human health.1 However, its wide range of application, particularly in gold mining, electroplating,
and various chemical industries, leads to unavoidable environmental spills [1, 2]. It is inevitable that
some cyanide ion will leak into domestic water along with industrial waste-water. The maximum
concentration of cyanide in drinking water published by the world health organization is 1.9 µM [3].
Due to the irreplaceability of cyanide in industrial production, it is necessary to use a simple and
intuitive method to selectively detect the cyanide content. So far, various types of colorimetric and
fluorescent receptors have been considered as excellent sensor materials for cyanide ions, and
reactive fluorescent probes are becoming a hot research direction due to their advantages of
selectivity, sensitivity, rapid and intuitive detection [4‒6].
Ruthenium(II) polypyridy complexes of 2,2′-bipyridine(bpy) [7‒10] and related ligands [11‒13]
have interesting photophysical, photochemical, and electrochemical properties that make them
attractive for development of luminescent sensors [14, 15], dye-sensitized solar cells [16‒19],
photoinduced switches [20‒23], and photoactive devices [24‒27]. The phosphorescent ruthenium(II)
polypyridine complexes as chemosensors [28, 29] has recently attracted tremendous interest owing
to their favorable photophysical properties, such as visible excitation wavelengths, large Stoke
shifts, relatively long excited state lifetimes, suitable redox properties for electrochemiluminescence,
and high stability in aqueous media compared with those of pure organic luminophores. Recently, a
huge number of chromogenic and luminescent receptors / probes based on ruthenium(II)
polypyridine complexes has been synthesized for the selective and sensitive sensing of metal
cations [30, 31], anions [32‒34], molecular oxygen [35‒37], and biologically relevant molecules
[38‒40].

The cyanide has a strong affinity for electron-deficient carbonyl units capable of forming
cyanohydrins, thus the interferences from acetate and fluoride can be minimized by designing a
novel chemosensor particularly for cyanide [41‒46]. Herein, we report the synthesis of a
remarkable bipyridine based colorimetric probe P1 (Scheme 1), and its application towards cyanide
ion (CN‒) detection. The interaction of the designed ruthenium(II) complex with cyanide ion was
researched by UV-vis absorption, photoluminescence (PL), FT-IR, and 1H-NMR spectroscopy. The
effect of water content in the solvent on phosphorescence, the expansion of the contrast ion species
and the feasibility study as a colorimetric test paper also have been performed to prove whether the
probe has the possibility of practical application.
Results and discussion
Synthesis of phosphorescent Ru(II) probe P1. The ligand 5-aldehyde-2,2'-bipyridine L was
prepared by direct reactions from 2-(tributylstannyl)pyridine and 6-bromo-3-pyridinecarbaldehyde
under N2 atmosphere according to the reported procedures (Scheme 1) [47‒49]. The color of the
turbid liquid changes rapidly from yellow to black after reaching the set temperature. The ligand
was obtained in high yields as white or light yellow solids. With the ligands in hand, the reactivity
of L1 with ruthenium trichloride was investigated in the presence of ethanol and water as the
solution. The black-colored solution mixture gradually became clear red solution as the reaction
went on. The target product tris (5-aldehyde-2,2'-bipyridyl) Ru (II) hexafluorophosphate was
collected in an appropriate manner at room temperature as an air-stable dark red solid. The product
is soluble in acetone, acetonitrile and DMSO, slightly soluble in CH2Cl2, but insoluble in non-polar
solvents such as diethyl ether and hexane. The Ligand acts as a chelate through the N,
1
N-coordination mode of the product which is supported by FT-IR and H NMR spectroscopy. P1

was fully characterized by various spectroscopic techniques.
Scheme 1. Synthesis of P1. For a detailed synthetic procedure, see the Experimental section.
Crystal Structure of P1. To unambiguously elucidate the molecular structure of the P1, we
dissolved the P1 in acetonitrile, and then slowly diffused into the ether solution to obtain a single
crystal suitable for the P1 suitable for single crystal diffraction analysis. Compounds P1 were found
to crystallize in the triclinic space group P 1. Its single crystal structure is shown in Fig. 1. Selected
geometric data are given in supporting information. The structures revealed that the ruthenium
centers adopt a similar octahedral geometry through tridentate coordination of three bipyridines
ligand (Fig. 1). The distances of Ru‒N bonds in the complex are 2.1(4) Å (Ru–N(1)), 2.1(4) Å (Ru–
N(2)), 2.0 (4) Å (Ru–N(3)), 2.1(4) Å (Ru–N(4)), 2.1(4) Å (Ru–N(5)) and 2.1(5) Å (Ru–N(6)) are
within the range of known values for the bond in similar ruthenium complexes [50]. The bond
lengths of C(11)–O(1), C(22)–O(2) and C(33)–O(3) are 1.2(8) Å, 1.2 (9) Å, and 1.2 (12) Å,
respectively, which are also consistent with previous reports [66]. The angels of N–Ru–N are
78.9(17)° (N(1)–Ru–N(2)), 78.7(19)° (N(3)–Ru–N(4)), 78.2(2)° (N(6)–Ru–N(5)). The dihedral
angle between different bipyridines has been calculated are 84.8° (N(2)–C(1)–N(1) and N(4)–
C(12)–N(3)), 80.5° (N(4)–C(12)–N(3) and N(6)–C(23)–N(5)) and 85.8° (N(2)–C(1)–N(1) and
N(6)–C(23)–N(5)).

Fig. 1. Molecule structure of the ruthenium compound P1 (thermal ellipsoids were drawn at the 30%
probability level). All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ru–N(1), 2.057(4); Ru–N(2), 2.065(4); Ru–N(3), 2.045(4); Ru–N(4), 2.059(4); Ru–N(5),
2.063(4); Ru–N(6), 2.062(5); N(1)–C(1), 1.338(7); N(2)–C(6), 1.361(7); N(3)–C(16), 1.355(7);
N(4)–C(17), 1.330(8); N(5)–C(23), 1.333(9); O(1)–C(11), 1.202(9); O(2)–C(22), 1.206(8); C(33)–
O(3), 1.229(12); N(6)–C(28), 1.375(8); N(1)–Ru–N(2), 78.94(17); N(3)–Ru–N(4), 78.77(19);
N(6)–Ru–N(5), 78.2(2); C(1)–N(1)–C(5), 118.7(5); C(12)–N(3)–C(16), 118.6(5); C(23)–N(5)–
C(27), 119.3(6).
UV–vis spectrum analysis of P1. UV‒vis spectrum of P1 in CH3CN displays sharp bands at
approximately 300 nm assigned to intraligand (IL) π−π* transitions. Additionally, the broad metal‒
to‒ligand charge‒transfer (MLCT) absorption is observed in the 425‒550 nm range consisting of
two or more MLCT bands (Fig. 2a) [51‒54]. The ability of the newly developed P1 to act as a
chemosensor for different anions (3.0 equiv.) has been examined by UV-vis absorption and
photoluminescence spectroscopy in CH3CN solution at room temperature. The UV-vis spectrum of
P1 display significant absorption changes exclusively in the presence of CN– (Fig. 2). Upon
addition of 3.0 equiv. of CN– to an acetonitrile solution of P1 and the absorption maximum
dramatically blue shifted from 475 to 375 nm (∆λ = 30 nm). A prominent orange to yellow color

change was observed (inset of Fig. 2b). In contrast, no significant changes of λmax and the color
–
2‒
3‒
were observed in the presence of other anions, such as AcO–, Br–, Cl–, ClO4 , CN‒, CO3 , PO4 ,
2‒
+
SO4 , OH‒, Et-S‒, Ph-S‒, Ph-NH2, Ca2+, Na+, CN‒, K+, NH4 , F‒ and Zn2+ (Fig.3). The reaction of
an aldehyde group attached to the 5‒position of the N-coordinating pyridyl moiety of the ligand
with CN‒ is selective through the above observations. UV-vis titration experiments have been
implemented to understand more about the reasons for the color change. The incremental addition
of CN‒ (0.0−3.0 equiv.) to the CH3CN solution of P1 (20 µM) at room temperature reveals a
gradual decrease of LLCT peak at 310 nm and the absorption maximum gradually blue shifted from
450‒500 nm to 420‒470 nm (∆λ = 30 nm) (Fig.2) [55]. The different colors before and after
addition of CN‒ ions could be easily distinguished by the naked eye (inset of Fig. 2b).
Fig. 2. (a) UV-vis spectrum of P1 (20 µM); (b) P1 solution is added to the equivalent of CN‒ (0.3 eq
/ time) UV titration image (inset: left: P1, right: P1 + 3.0 eq. CN–).

Fig. 3. UV-vis spectra of P1 (20 µM) in the presence of 3.0 equiv. of various ions: (a) AcO–, Br–,
–
2–
3–
2–
+
Cl–, ClO4 , CN–, CO3 , PO4 , SO4 , OH–, Et-S‒, Ph-S‒, Ph-NH2, F‒; (b) Ca2+, Na+, CN–, K+, NH4 ,
Zn2+) in CH3CN.
Fluorescence spectroscopic analysis of P1. P1 phosphorescence emission spectrum show a red‒
shifted, weak band at 700 nm compared with the phosphorescence spectrum of
[Ru(bpy-CHO)3](PF6)2 (λmax = 612 nm) [56]. This is due to the strong electron-absorbing effect of –
CHO in P1. The titration of P1 (λex = 460 nm) shows the gradual disappearance of the PL band at
700 nm with increasing amounts of CN− ion and the appearance of the new band at 618 nm. This
phenomenon occurs because the addition of CN‒ reduces the strong electron absorption of the
aldehyde groups, thereby enhancing the phosphorescence and causing blue shift (∆λ = 100 nm) (Fig.
4a). The phosphorescence emission intensity of the P1 + CN− adduct at 618 nm is plotted against
the mole fraction of CN− at a constant total concentration (20 µM). The maximum emission
intensity was reached when the mole fraction of CN− was 0.74. These results clearly indicate a 1:3
binding stoichiometry of P1 with CN− (Fig. 4b).

Fig. 4. (a) P1 solution is added to the equivalent of CN– (0.3 eq / time) phosphorescence titration
(illustration left: P1, right: P1 + 3CN–). (b) Job’s plots of P1 + CN− adduct complexes. The
phosphorescence emission intensity is plotted against mole fraction of CN−, at a constant total
concentration of 20.0 µM in CH3CN.
Reaction time of the ruthenium probe. Encouraged by the good detection of ruthenium complex
with CN‒, we turned our attention on the effect of reaction time. The results were optimized shown
in Fig.5. It was obvious that the PL intensity increased gradually upon addition of CN‒ from 20 s
and reached a maximum at about 120 s, which indicated the probe could rapidly respond to CN‒.
Fig. 5. Reaction time course of PL intensity of probe (20 µM) after adding 3.0 equiv. CN‒ in
CH3CN at 298K (λex =618 nm).

Selectivity of the probe for CN‒ detection. Most of the ions used in literature for comparison are
only anions, therefore, it is necessary to add cations to the contrast ions because there are not only
anions in the domestic water. To evaluate the specificity of sensor towards CN‒, various ions were
examined in parallel under the same conditions. No remarkable PL intensity enhancement was
observed upon addition of other potentially competing anions (3.0 equiv.) to a 20 µM solution of P1
in the absence of cyanide (Fig. 6). Reversely, adding 3.0 equivalent CN‒ into P1 in the presence of
excessive anions evoke phosphorescence intensity enhancement. It is noteworthy to mention that
−
anions such as ClO4 and F− that are well-known to compete in the detection of CN− are found to
not interfere in the developed chemosensor system (Fig. 7). P1 has much higher selectivity for CN‒
than the other ions examined here. This unique property enabled CN‒ to be detected directly by the
naked eye over other species. Therefore, P1 may be considered as a highly selective probe for CN‒.
–
Fig. 6. PL spectra of P1 solution with different ions (λ = 460 nm). (a) AcO–, Br–, Cl–, ClO4 , CN–,
2–
3–
2
+
CO3 , PO4 , SO4 –, OH–, Et-S‒, Ph-S‒, Ph-NH2, F–; (b) Ca2+, Na+, CN–, K+, NH4 , Zn2+.

Fig. 7. Behavior of P1 toward CN‒ and other anions as measured by PL in acetonitrile solution (1:
Ca2+, 2: Na+, 3: K+, 4: NH4 , 5: Zn2+, 6: AcO‒, 7: Br‒, 8: Cl‒, 9: ClO4 , 10: CO3 , 11: PO4 , 12:
+
‒
2‒
3‒
SO4 , 13: OH‒, 14: Et-S‒, 15: Ph-S‒, 16: Ph-NH2, 17: F‒, 18:CN‒).
2‒
Effect of the water content. For practical use of the P1, PL titrations were carried out in CH3CN /
H2O solution (60 / 40, 30 / 70 and 20 / 80 v/v) and compared with the emission properties in pure
acetonitrile solution (Fig. 8). However, a maximum of ~ 7.5 equiv. CN‒ is required to complete the
reaction in 80% aqueous solution (CH3CN / H2O 20 / 80) that unlike the pure acetonitrile solution
titration process. On the other hand, in 70% aqueous acetonitrile (CH3CN / H2O 30 / 70), the
reaction requires a minimum of 4.5 equiv. of CN−. In the case of 60% aqueous acetonitrile (CH3CN
/ H2O 40 / 60) a minimum of 3.0 equiv. of CN− is required for completing the reaction, which is
similar to that of pure CH3CN. This study demonstrates that the presence of water in the solution
has a large effect on the reactivity of cyanide with P1 in aqueous solution. This result is also
consistent with the conclusions of the previously reported cyanide probes that the strong hydration
of CN− in aqueous solution reduces its nucleophilicity. Further, the phosphorescence titration data
of different water contents were plotted, and it was found that pure acetonitrile and 60% aqueous

acetonitrile solution were basically the same in the growth trend under the same conditions. The
phosphorescence growth trend of other water contents is slower than that of pure acetonitrile
especially 80% water acetonitrile solution(CH3CN / H2O 20 / 80), which requires not only up to 7.5
equiv. of CN‒ to achieve the phosphorescence intensity of pure acetonitrile solution but also a much
lower growth trend. Therefore, it can be concluded from these studies that P1 is selective and
sensitive to CN‒ in aqueous solution (60% water), which makes P1 possible as a probe for detecting
CN‒ in practical applications.
Fig. 8. Titration image of P1 in different aqueous solutions. (a) CH3CN / H2O (50 / 50); (b) CH3CN
/ H2O (40 / 60); (c) CH3CN / H2O (30 / 70); (d) P1 titrated in different water content solutions
phosphorescence growth trend.

The determination limit was detected CN‒ in the Solution State. The detection limit is one of the
important criteria to judge the performance of the probe. Recently, the detection limit of both pure
organic fluorescent probes and organic metal fluorescent probes in the detection of related ions is
getting lower and lower. In table 1, the detection limits of pure organic phosphorescence and
organometallic fluorescent probes with certain representativeness in detecting CN– in recent years
are listed. The detection limits in the table are large and small but the overall trend shows a decrease.
The detection limit of P1 for CN– was calculated based on the phosphorescence titration data
according to a reported method [57]. Under optimal conditions, calibration graphs for the
determination of CN– were constructed. The decreased phosphorescence intensity of the system
showed a good linear relationship (r = 0.991), as shown in Fig. 9. The limit of detection (LOD) was
calculated to be 0.75 µM on the basis of S / N = 3, which is far lower than the permissible limit (1.9
mM) set by the WHO
Table 1. Detection limit of cyanide for different types of probes
Compound
RuL1-CuL2 [58]
L [59]
Solvent
LOD /µM
DMF / H2O (5 / 5)
CH3CN / H2O (6 / 4)
H2O
1.20
0.50
0.28
0.67
0.88
0.46
3.60
0.75
3 [60]
THF
Probe 1 [61]
GSB [62]
3TBN [63]
S1 [64]
DMSO / H2O (9 / 1)
DMSO / H2O (9 / 1)
MeOH / H2O (5 / 5)
CH3CN / H2O (6 / 4)
P1

Fig. 9. P1 (20 µM) as a probe for calibration of CN– luminescence detection
Preparation of Filter Paper Test Strips. Motivated by the favorable features of P1 as a potential
probe for CN− in solution, we have prepared luminescent test strips using P1 for the detection of
CN− anions by contact mode. The ordinary filter paper (1.8cm × 2.0 cm) was immersed in P1
solution (20 µM) for 5 minutes and then removed to dry naturally. A series of CN‒ solution of
different concentrations (5000–0.5 µM) was configured and 2 µL was dropped on the filter paper
and data were collected, all of which was shown in Fig. 10. Small spots of CN– solution of different
concentrations were generated on the test strip impregnated with P1. The color of the test strip with
concentration of a drop of 50 µM could still be clearly observed to change from orange to pale
yellow by naked eyes. When excited with 365nm, the test strip with the drop of CN– solution
showed red fluorescent spots, even though the concentration was 5 µM. The test results demonstrate
the practical utility of the P1 impregnated test strips for the instant on-site visualization of trace
amounts of cyanide ions present in solution by the naked eye and the 365 nm [65].

Fig. 10. Plot of the emission intensity at (a) visable light and (b) 365 nm of the test strips against
concentration of added CN– in acetonitrile (1: blank, 2: 5000 µM, 3: 500 µM, 4: 50 µM, 5: 5 µM, 6:
0.5 µM, The same below).
Confirmation of the generation of cyanohydrins. The formation of cyanohydrin was further
1
confirmed by H NMR and FT-IR spectroscopy. Nuclear magnetic profiling of the reaction of
aldehyde groups with cyanide ions is well described in many articles. Khatua [55] studied the
change of aldehyde group and CN– binding by nuclear magnetic titration. It narrated the change of
proton peak in the reaction between aldehyde group and CN– and proposed that the early
disappearance of aldehyde matrix hydrogen is due to the possibility of hydration. Fig. 11 shows
during the addition of P1 with 3.0 equiv of CN− the intensity of the sharp singlet at δ 9.96 ppm
corresponding to the aldehyde protons immediate disappearance and upfield shifts are noted for the
formylated pyridyl ring protons of the ligand. All of the ligand proton hydrogen signals besides the
cyanohydrin protons move toward the upfield [66]. In addition, results obtained from ESI-HRMS
1
spectra were consistent with that of H NMR spectra. The corresponding characteristic peaks of
cyanohydrins were found in the mass spectra of P1 with CN– in different molar ratios (P1 : CN– =
1:1; 1:2; 1:3; respectively) (Fig.S9‒S11 in ESI).

Scheme 2. Cyanide detection by P1 based on cyanohydrins formation.
Fig. 11. Partial 1H NMR spectra show the changes of P1 and P1 + 3.0 eq. CN– in d6‒DMSO at room
temperature.
The FT-IR spectrum clearly indicates the appearance of the cyanogen group stretching frequency
(~ 2170 cm-1) and disappearance of the carbonyl frequency of stretching (~ 1700 cm-1) of the
1
aldehyde group in P1. On the basis of the results from H NMR chemical shifts, mass spectra and
FT-IR spectroscopy, the most plausible mechanism for the formation of the cyanide adducts
(cyanohydrin) was proposed. The strong electron-deficient properties of the –CHO group in P1
make it susceptible to nucleophilic attack by CN–, while the carbonyl group is attacked by the
formation of cyanohydrin, a very stable adduct that makes the reaction completely irreversible [67,
68].

Conclusions
In summary, a new ruthenium complex (P1) has been prepared to detect cyanide based on a
cyanohydrin chemodosimeter reaction. The immediate color change from orange-red to yellow and
orange luminescence can be observed by the naked eye after CN− addition. The probe upon
interaction with different cation and anion showed high selectivity and sensitivity for CN– through
phosphorescence “turn-on” response in aqueous solution (60 % water) with a detection limit of 0.75
µM. Phosphorescent test strips have been fabricated and utilized for the detection of micromole
levels of cyanide in mixed aqueous solution. Finally, the formation of cyanohydrin has been further
corroborated by 1H NMR, FT-IR and mass spectral studies.
Experimental Section
All manipulations were performed under an atmosphere of nitrogen using standard Schlenk
1
techniques. Chemicals were used as commercial products without further purification. H NMR
(500 MHz) spectra were recorded with a Bruker DMX–500 spectrometer. Elemental analysis was
performed on an Elementar vario EL III analyzer. IR (KBr) spectra were recorded with the Nicolet
FT-IR spectrophotometer.
The P1 solution used in phosphorescence titration and UV–vis titration is composed of specpure
acetonitrile as the solvent, and the anion and cation solutions are used as the solvent of acetonitrile :
water (60 / 40), the corresponding salts are used as the solute. To reduce the interference of the
anion and cation solvents, the concentration of all anions and cations is 100 µM, and The
concentration of the transparent solution of P1 is 20 µM. Waiting for 3 minutes after each equal
amount of ion solution is added to make the data accurate and the excitation wavelength is λ= 460
nm.

Synthesis of 5-aldehyde-2, 2'-bipyridine(CHO-bpy) L1. Pd(PPh3)2Cl2 (52.0 mg, 0.08 mmol),
PPh3 (38.5mg, 0.15 mmol), 2-(tributylstannylpyridine) (552.2 mg, 1.50 mmol),
6-bromo-3-pyridinecarbaldehyde (329.0 mg, 1.77 mmol) and toluene (20.0 mL) were added to an
oven-dried Schlenk flask. The resulting mixture was stirred for 72 h under N2 atomsphere. Then the
recation mixture was cooled to room temperature and the solvent was removed under reduced
pressure. The obtained solid was dissolved in CH2Cl2 (25.0 mL) and washed with a saturated
NH4Cl solution (15.0 mL). The aqueous phase was extracted with CH2Cl2. The organic layers were
combined, the solvent was removed under reduced pressure and the crude product was purified by
silica gel column chromatography (EA / PE = 3 / 7) to give L1 as a white solid. Yield: 47 % (130.0
o
1
mg), mp: 223 C (76 mmHg), IR (KBr): 1699, 1584, 1553, 1445, 1250, 1034, 846 cm‒1. H NMR
(500 MHz, CDCl3): δ 10.17 (1H, s), 9.13 (1H, s), 8.73 (1H, d, J = 3.9 Hz), 8.61 (1H, d, J = 8.2 Hz),
8.51 (1H, d, J = 7.9 Hz), 8.29 (1H, dd, J = 8.2, 3.5 Hz), 7.87 (1H, t, J = 7.0 Hz), 7.42–7.36 (1H, m),
13C NMR (125 MHz, CDCl3): δ 190.9, 160.8, 154.7, 151.8, 149.5, 137.5, 137.2, 131.2, 125.0, 122.4,
121.5 ppm, HRMS calcd [M+H]+: m/z 185.0715; found: 185.0712, Elemental analysis calcd (%) for
C11H8N2O: C 71.73, H 4.38, N 15.21; found: C 71.65, H 4.40, N 15.30. 1H and 13C NMR data are in
agreement with those published [69].
Synthesis of [Ru(CHO-bpy)3](PF6)2 P1. 64.4 mg of L1 (0.35 mmol) in 15 mL of EtOH was added
to a solution of RuCl3 (20.7 mg, 0.10 mmol) in 20 mL of EtOH / H2O (3 / 1). The reaction mixture
was refluxed for 24 h, and then cooled to room temperature. After the solvent was evaporated, the
residue was dissolved in a small amount of water, and then the aqueous solution was washed with
CH2Cl2. A saturated solution of NH4PF6 was added to yield red precipitate of the product, which
was further purified by neutral aluminum oxide column chromatography with CH2Cl2 / MeOH (10 /
1) as eluent. The target Ru(II) complex P1 was isolated as a red solid. Yield: 54 % (53.0 mg), mp:

o
1
469 C (76 mmHg), IR (KBr): 1761, 1623, 1583, 1423, 1295, 810 cm‒1, H NMR (500 MHz,
d6-DMSO) δ 9.89 (3H, dd, J = 5.0, 2.5 Hz), 9.03 (3H, s), 8.97 (3H, s), 8.56 (3H, t, J = 5.0 Hz), 8.16
(6H, dd, J = 5.0, 2.5 Hz), 7.83 (3H, dd, J = 5.0, 2.5 Hz), 7.61 (3H, s), 13C NMR (125 MHz,
d6-DMSO): δ 190.9, 160.9, 156.2, 151.5, 149.3, 138.8, 133.6, 129.3, 126.4, 126.2, 125.1 ppm,
HRMS calcd [M‒PF6]+: m/z 799.0595; found: 799.0587, Elemental analysis calcd (%) for
C33H24F12N6O3P2Ru: C 42.01, H 2.56, N 8.91; Found: C 42.15, H 2.47, N 8.78.
X-ray Crystallography. Diffraction data of P1 were collected on a Bruker Smart APEX CCD
diffractometer with graphite-monochromated MoKa radiation (λ = 0.71073 Å). All the data were
collected at room temperature, and the structures were solved by direct methods and subsequently
refined on F2 by using full-matrix least-squares techniques (SHELXL). SADABS absorption
corrections were applied to the data, all non–hydrogen atoms were refined anisotropically, and
hydrogen atoms were located at calculated positions. All calculations were performed using the
Bruker program Smart.
Supporting Information
1
Electronic supplementary information (ESI) available: H NMR spectra of ligand and ruthenium
complex; FT-IR spectra of complex. CCDC 1956947 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif.
Conflicts of Interest
The authors declare no competing financial interests.
Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21601125), the
Chenguang Scholar of Shanghai Municipal Education Commission (No. 16CG64), the Shanghai
Gaofeng & Gaoyuan Project for University Academic Program Development, and the Industry
Catalysis Funding of Shanghai Institute of Technology (CHJJ-2).
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Supporting formation
Ruthenium-based phosphorescent probe for selective and naked-eye
detection of cyanide in aqueous media
Jing-Wei Zhu,a Hui-Dan Ou,a Niwei Xu,c Wei Deng,*a Zi-Jian Yao*a, b
a School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai,
201418, China.
b
State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha
410082, China
c Hunan Traditional Chinese Medical College, Zhuzhou, 412012, China
Corresponding author: Email: zjyao@sit.edu.cn; Tel: +86-21-60877231, Fax: +86-21-60873335.