Novel selective and sensitive optical chemosensor based on phenylfluorone derivative for detection of Ge(IV) ion in aqueous solution

Article abstract of DOI:10.1016/j.saa.2018.05.063

A water soluble chemosensor for Ge⁴⁺ ion based on fluorone derivative containing 3,4?bis(2?(diethylamino)?2?oxoethoxy)phenyl (R8) has been synthesized. The binding abilities between R8 and 10 equiv. of Na⁺, K⁺, Ca²⁺, Fe²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Al³⁺, Cr³⁺, Fe³⁺ and Ge⁴⁺ ions in 1% v/v EtOH-water (tris-buffer pH 7.0) were studied using UV–vis and fluorescence spectrophotometry. When observed by naked-eyes, the color of R8 changed from yellow-orange to pink and the fluorescent color changed from green to non-fluorescence when complexed with Ge⁴⁺ ion. The spectral analysis showed that UV–vis absorption and fluorescence emission intensity of R8 decreased dramatically when Ge⁴⁺ ion was added comparing with other ions. To explain this behavior, the quantum calculation was performed using the hybrid density functional at B3LYP /LanL2DZ level of theory. The calculated orbital energies indicated that the decreasing of UV–vis absorption and the quenching of fluorescence were due to the complexation induced metal to ligand charge transfer. The association constants (K_a) of R8-Ge⁴⁺ complexes calculated from Benesi–Hildebrand equation was 6.21 × 10⁵ M^?1. The UV–vis detection limit for Ge⁴⁺ was 4.40 × 10^?7 M which was three orders of magnitude lower than those of Al³⁺, Cd²⁺, Cu²⁺ and Na⁺ ion.

Full text of DOI:10.1016/j.saa.2018.05.063

Accepted Manuscript
Novel selective and sensitive optical chemosensor based on
phenylfluorone derivative for detection of Ge(IV) ion in aqueous
solution
Somchai Keawwangchai, Nongnit Morakot, Tasawan
Keawwangchai
PII:
S1386-1425(18)30453-0
doi:10.1016/j.saa.2018.05.063
SAA 16097
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 3 February 2018
Revised date:
Accepted
date:
11 May 2018
1
5 May 2018
Please cite this article as: Somchai Keawwangchai, Nongnit Morakot, Tasawan
Keawwangchai , Novel selective and sensitive optical chemosensor based on
phenylfluorone derivative for detection of Ge(IV) ion in aqueous solution. The address
for the corresponding author was captured as affiliation for all authors. Please check if
appropriate. Saa(2017), doi:10.1016/j.saa.2018.05.063
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
1
Novel selective and sensitive optical chemosensor based on phenylfluorone
derivative for detection of Ge(IV) ion in aqueous solution
Somchai Keawwangchai · Nongnit Morakot · Tasawan Keawwangchai*
Supramolecular Chemistry Research Unit, Department of Chemistry, Faculty of Science, Mahasarakham
University, Maha Sarakham, 44150, Thailand
ABSTRACT
4
+
A water soluble chemosensor for Ge
ion based on fluorone derivative containing
3
,4−bis(2−(diethylamino)−2−oxoethoxy)phenyl (R8) has been synthesized. The binding abilities
+
+
2+
2+
2+
2+
2+
2+
3+
3+
3+
between R8 and 10 equiv. of Na , K , Ca , Fe , Cu , Cd , Hg , Pb , Al , Cr , Fe and
4
+
Ge ions in 1% v/v EtOH-water (tris-buffer pH 7.0) were studied using UV−vis and
fluorescence spectrophotometry. When observed by naked-eyes, the color of R8 changed from
yellow-orange to pink and the fluorescent color changed from green to non-fluorescence when
4
+
complexed with Ge ion. The spectral analysis showed that UV−vis absorption and fluorescence
4
+
emission intensity of R8 decreased dramatically when Ge ion was added comparing with other
ions. To explain this behavior, the quantum calculation was performed using the hybrid density
functional at B3LYP /LanL2DZ level of theory. The calculated orbital energies indicated that the
decreasing of UV-vis absorption and the quenching of fluorescence were due to the
4
+
complexation induced metal to ligand charge transfer. The association constants (K ) of R8-Ge
a
5
-1
complexes calculated from Benesi–Hildebrand equation was 6.21×10 M . The UV-vis detection
4
+
-7
3+
limit for Ge was 4.40×10 M which was three orders of magnitude lower than those of Al ,
2
+
2+
+
Cd , Cu and Na ion.
Keywords: Phenylfluorone · naked-eye · Chemosensor · Germanium(IV) · DFT/LanL2DZ
*
Corresponding author phone/fax: +66 4375 4246, e−mail: k.tasawan@gmail.com (T.
Keawwangchai)

ACCEPTED MANUSCRIPT
2
1
. Introduction
Germanium is an important element that find application in many technological devices
such as in the production of infrared sensing, identification system, phosphors, correction
inhibition in alloys, glass of high refractive index and spiro germanium for cancer therapy, etc.
The world production of germanium products is now increasing, and the level of germanium in
the environment is beginning to rise [1-2]. Therefore, there is a need for specific and precise
determination of germanium in the environment. Several highly sensitive methods have been
developed for the determination of trace amounts of germanium such as mercury-coated glassy
carbon electrode [3], flame atomic absorption spectrometry (FAAS) [4], inductively coupled
plasma-mass spectrometry (ICP-MS) [5], flow injection analysis [6], and atomic emission
spectrometry with inductively coupled plasma (ICP-AES) [7]. Some factors such as initial cost
of the instrument, technical knowledge, consumables and maintenance cost of equipment may
limit the applicability of some method particularly in laboratories in developing countries and for
fieldwork. In this case, the spectrophotometric method is the method of choice due to its
simplicity and relative cheapness.
In recent years, some new reagents called optical chemosensor have been studied as
analytical reagents for the spectrophotometric determination of germanium(IV) ion [8-9] as well
as other metal ions [10-15]. The optical chemosensor consisted of two importance parts: receptor
subunit – a unit responsible for selectivity and sensory subunit – a unit responsible for signaling.
In most cases, receptor subunit and sensory subunit are covalently attached forming
chemosensor. The sensory subunit can be either chromogenic or fluorogenic agents that can be
chosen from various organic fluorescent dye. Among these, phenylfluorone derivatives have
been widely used as analytical reagents in spectrophotometry and fluorescent spectrometry for
the determination of germanium in tea [16], plant material [17], food and fruit [18-19], soil [20],
ores [21] waste and natural waters [22-23]. They provide excellent analytical characteristic in
selectivity, sensitivity and simplicity.
The phenylfluorone consists of phenyl group attached to fluorone molecule at position 9.
The fluorone contains 2,6,7-trihydroxyl-3-ketone-pyranoid ring in its structure which contains
two possible binding sites, namely, an adjacent hydroxyl-keto group at 2- and 3-positions and
adjacent hydroxyls at positions 6 and 7-positions. It was found that different substituents on

ACCEPTED MANUSCRIPT
3
different positions of phenyl group of phenylfluorone will significantly affect the electron cloud
density of the conjugated system and also influence the analytical characteristics of chemosensor
[
24]. While the phenyl group opened the possibility of forming a novel binding site, it increased
the complexity of predicting the preferred binding site of metal ions as well as the analytical
behavior.
The present work focused on the design and synthesis of phenylfluorone−based chromogenic
chemosensor and the potential of selective complexation with metal ion. The design consists of
substituting two hydroxyl hydrogen on phenyl group of phenylfluorone with
(2−(diethylamino)−2−oxoethoxy) to from a new binding site. The binding properties of the
+
+
2+
2+
2+
2+
2+
2+
2+
complexation between sensors and metal ions (Na , K , Ca , Fe , Cu , Zn , Pb , Cd , Hg ,
3
+
3+
3+
4+
Al , Cr , Fe and Ge ) were investigated by UV−Vis and fluorescent spectrophotometry. The
computational calculation has been performed to study the complexation of metal ions. The
geometrical structures, the binding energies and thermodynamic property changes of
+
+
+
2+
2+
2+
2+
2+
2+
2+
3+
complexation between R8 with Na , K , Ag , Ca , Fe , Cu , Zn , Pb , Cd , Hg , Al and
4
+
Ge ions have been calculated using the density functional theory method.
2
. Experiment
2
.1. Reagents
The reagent grade solvents and all materials were purchased form Fluka, BHD, Aldrich, Carlo
Erba, Merck or J.T. Baker and were used without further purification. Commercial grade
solvents such as acetone, dichloromethane, hexane, methanol and ethylacetate were purified by
distillation before use.
2
.2. Apparatus
NMR spectra were recorded using Varian 400 MHz NMR instrument. Matrix Assisted
Laser Desorption Ionization Time of Flight mass spectrometer were determined in acetonitrile by
Bruker Daltonics MALDI−TOF instrument. UV−Vis spectra were obtained using an Agilent
Technologies Cary 60 UV-Vis spectrophotometer at 25°C. Fluorescence spectra were recorded
on Perkin Elmer SL50B fluorescence spectrophotometer with 5.0 nm excitation and emission
slit.

ACCEPTED MANUSCRIPT
4
2
.3. Synthesis of 2,2'-((4-(2,6,7-trihydroxy-3-oxo-3H-xanthen-9-yl)-1,2-
phenylene)bis(oxy))bis(N,N-diethylacetamide), R8
2
,2'−((4−formyl−1,2−phenylene)bis(oxy))bis(N,N−diethylacetamide), 5 (0.839 mg, 2.302 mmol)
was dissolved in 10 mL of 20% ethanol in a 100 mL round-bottom flask. Ten milliliters of
ethanol containing 1.107 g (4.389 mmol) of 1,2,4-triacetoxybenzene and 2 mL of concentrated
hydrochloric acid were added. The solution was refluxed in an oil bath for 2-3 hours. The
formation of product was noticed from the appearance of the red color. The solvent was
evaporated under vacuum. The residue was re-dissolved in ethanol and recrystallized in
EtOH/EtOAc/DCM mixed solvent. The crystal was filtered, washed with EtOH/EtOAc/DCM
mixed solvent and dried in vaccuo. R8 (0.602 g) was obtained as dark red solid in 45% yield.
1
H−NMR spectrum (400 MHz, DMSO-d6, ppm): δ 0.925−0.960 (t, 3H, CH CH , J=14 Hz),
2
3
1
.045−1.075 (t, 6H, CH CH , J=12 Hz), 1.170−1.205 (t, 3H, CH CH , J=14 Hz), 3.201-3,374
2 3 2 3
(
m, 8H, NCH CH , J=69.2 Hz), 4.865 (s, 2H, OCH C=O), 4.987 (s, 2H, OCH C=O), 6.922 (s,
2 3 2 2
2
7
H, fluorone Ar-H), 7.031-7.051 (d, 1H, phenyl Ar-H, J=8 Hz), 7.081 (s, 1H, phenyl Ar-H),
.119-7.140 (d, 1H, phenyl Ar-H, J=8.4 Hz), 7.275 (s, 2H, fluorone Ar-H), ESI-HRMS cal for;
+
[
R8+H] 579.2343 found 579.2345
2
.4. Colorimetric, UV-Vis and fluorescent studies
−
3
A stock solution of 1.0×10 M of various metal ions as their nitrate salts was prepared in
4
+
de-ionized water (except Ge was diluted from 1000 mg/L standard solution in water stabilized
−
3
with HCl pH~1-3). The R8 stock solution (1.0×10 M) was prepared in ethanol.
The working solution of R8 was then prepared by diluting the stock solution to 1.0×10
−
4
M in de-ionized water. For complexation studies with excess metal ions, i.e. 10 equiv., 1.0 mL of
−
3
working standard solution of R8, 1.0 mL of 1.0 M tris-buffer, 1.0 mL of 1.0×10 M of metal
ions were added in 10.0 mL volumetric flask and diluted to the mark with de-ionized water. For
4
+
metal ions other than Ge 100 L of 0.01 M HCl was added before dilution to make solvent
4
+
composition comparable with that of Ge ion.
The determination of association constants was investigated by UV-Vis
spectrophotometric titration. The working solution of R8 1.0 mL and 1.0 M tris-buffer 1.0 mL

ACCEPTED MANUSCRIPT
5
was added in 10.0 mL volumetric flask and diluted to the mark with de-ionized water. The
−
4
1
.0×10 M metal ions were prepared with tris-buffer similar to R8. The metal ions were added
−
5
to a solution of R8 (1.0×10 M) from a micro-burette into 3.0 mL quartz cell with an optical
path length of 1.0 cm. UV-Vis spectral data were recorded after stirring for 30 s.
2
.5. Computational details
The density functional theory (DFT) has been applied to optimize the structures of
+
+
+
2+
phenylfluorone−based chemosensor and its complexes with metal ions i.e., (Na , K , Ag , Ca ,
2
+
2+
2+
2+
2+
2+
3+
4+
Fe , Cu , Zn , Pb , Cd , Hg , Al and Ge ). All DFT calculations have been performed
using the Becke’s three−parameter exchange functional [25] with the Lee−Yang−Parr correlation
functional [26]. The Los Alamos LanL2DZ split−valence basis set [27−29] was used for all
complexation studies. All calculations were performed using GAUSSIAN 09 program [30]. The
density functional theory (B3LYP/ LanL2DZ) calculations was also performed for the electronic
properties calculations of the phenylfluorone derivative and its metal ion complexes analysis.
The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital
(
LUMO) energy gaps have also been investigated at the same level of theory. Thermodynamic
property changes (X) i.e., total energy (E), enthalpy (H) and Gibbs free energy (G)
changes, of complexation in the fully optimized geometry were obtained from equation (1).
X = X(R8/M/waters) – [X(R8) + X(M) + 2X(water)]
(1)
Where X(R8/M/waters), X(R8), X(M) and X(water) are the thermodynamic properties of the
R8/M/waters complex, free chemosensor R8, cation and water molecules, respectively.
In addition, natural bond orbital (NBO) analysis implemented in GAUSSIAN 09 program was
applied through a series of intermolecular interactions under B3LYP/LanL2DZ system to
evaluate the NBO charges
3
. Results and discussion
3
.1. Synthesis
The fluorone signaling unit has an adjacent hydroxyl-keto group at 2- and 3-positions and
adjacent hydroxyls at 6 and 7-positions which capable of complexed with metal ions. In this
work, the new binding site was incorporated at phenyl position 9 in order to improve selectivity.
The new site consist of two N,N−diethyl−2−(4−formylphenoxy)acetamide moieties contain 4

ACCEPTED MANUSCRIPT
6
electron donor oxygen atoms that can be pre-organized to make a cavity for specific size of metal
ion. The precursor benzaldehyde derivative 5 has been synthesized by the procedure form our
previous
work
[31].
The 2,2'-((4-(2,6,7-trihydroxy-3-oxo-3H-xanthen-9-yl)-1,2-
phenylene)bis(oxy)) bis(N,N-diethylacetamide) (R8) has been synthesized according to the
procedure reported by Sano et al. [32] with some modification. The synthetic pathway was
shown in scheme 1. Chemosensor R8 was synthesized by one−pot reaction of 5 and 1,2,4-
triacetoxybenzene in the present of concentrated hydrochloric acid. After purification, R8 was
1
obtained as a dark-red solid and characterized by H-NMR and ESI-HRMS (Fig. S1 and S2).
3
.2. Spectroscopic and selective properties
The color and fluorescent change of 1.0×10 M R8 were tested over a wide range of pH in
-5
aqueous solution which shown in Fig. 1. When pH of the solution increased, the color of R8
changed from yellow to orange to pink in acidic, neutral and basic solution, respectivly. The
-5
absorption spectra of 1.0×10 M R8 at pH 4 and pH 5 show maximum absorption at 487 and
08 nm, respectively (Fig. 2), which were attributable to the univalent cation species and the
5
neutral quinoid species, respectively [33]. At pH 7, 9 and 10, R8 exhibited maximum absorption
at 510 nm. The highest absorption was found at pH 7. The fluorescent color of R8 solution under
UV light at 365 nm also studied. Fluorescent intensity increased with the initial rise in pH,
reached maximum at pH 7, then decreased beyond pH 9. Therefore, pH 7 was chosen for further
studies. To maintain the solution at this pH, 0.1 M tris-solution was added as a buffer.
The optical change of R8 after complexation with metal ions was studied by adding 10 equiv.
+
+
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
of various metal ions such as Na , K , Ca , Fe , Cu , Zn , Pb , Cd , Hg , Al , Cr , Fe
4
+
-5
and Ge ions to the solution of 1.0×10 M R8 in 1% v/v EtOH-water (tris-buffer pH 7). The
photograph of the complex was taken as shown in Fig. 3a. After metal ions were added to the
2
+
3+
solution of R8, the color immediately changes from yellow-orange to pink with Cd , Al and
4
+
2+
3+
Ge . These color change indicate that R8 can serve as “naked-eye” indicator for Cd , Al and
4
+
-5
Ge . The absorption spectra of 1.0×10 M of R8 solutions in 1% v/v EtOH-water (0.1 M tris-
buffer, pH 7) showed the characteristic typical of the phenylfluorone chromophore [34]. The
spectral change of R8 and metals complexation were displayed in Fig. 3b. Chemosensor R8
−
1
−1
showed a maximum absorption center at 510 nm (ε = 66,218 M cm ) and decreased after

ACCEPTED MANUSCRIPT
7
4
+
addition of the metal ion. The maximum decrease in absorption was given by Ge with slightly
red shifted by 19 nm.
The selectivity is an important parameter to evaluate the performance of the chemosensor.
One method for evaluating selectivity was the measurement of competition of foreign metal to
4
+
target metal [35]. The competition selectivity of R8-Ge complex against other metal ions
+
+
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
including Na , K , Ca , Fe , Cu , Zn , Pb , Cd , Hg , Al , Cr and Fe were investigated.
As depicted in Fig. 4 competitive metal ions did not produce significant absorption changes. The
observed relative signal change was less than 10% for all metal ions. These results revealed that
4
+
the recognition of Ge by R8 is not significantly influenced by other metal ions.
The association constant specifies the stability of formation of the complex in solution. It is
also a measure of the strength of the interaction between chemosensor and metal ions. The
4
+
3+
2+
2+
+
association constant of R8 with Ge , Al , Cd , Cu and Na were determined using UV-vis
4
+
spectral titration. Upon increasing the concentration of Ge ion, the absorbance of R8 at 510 nm
4
+
decrease gradually (Fig. 5a). The Benesi–Hildebrand plot of Ge complex was found to be
2
linear with R value 0.997 (Fig. 5b). [36-38] This also implied that stoichiometric ratio between
4
+
R8 and Ge ions was 1:1. The association constant (K ) was calculated from the slope of the
a
5
-1
plot and the K value was found to be 6.21×10 M . The detection limit was calculated on the
a
-7
basis of 3/K and found 4.40×10 M.
+
2+
2+
3+
The spectral change and Benesi–Hildebrand plot of Na , Cd , Cu and Al complexes were
2
shown in Fig. 6 and Fig. S3. The plots were also found to be linear with R value of 0.996, 0.988,
4
2+
4
2+
0
1
.995 and 0.992. The K value was found to be 2.69×10 for R8-Cd , 1.26×10 for R8-Cu ,
a
4
+
4
-1
3+
2+
2+
.66×10 for R8-Na and 2.45×10 M for R8-Al complex. The detection limit of Cd , Cu ,
+
3+
-4
-4
-4
-4
Na and Al were 3.44×10 , 1.97×10 , 9.66×10 and 3.71×10 M, respectively. These results
4
+
clearly show that R8 has potential as a chemosensor for Ge ion.
−
6
The fluorescence behavior of 1.0×10 M R8 in 0.1% v/v EtOH-water (0.1 M tris-buffer, pH
+
+
2+
2+
2+
2+
7
) was studied by adding 10 equiv. of various metal ions such as Na , K , Ca , Fe , Cu , Zn ,
2
+
2+
2+
3+
3+
3+
4+
Pb , Cd , Hg , Al , Cr , Fe and Ge ions to the solution of chemosensor. The emission
spectra (λ at 510 nm) of R8 in the absence and presence of 10 equiv. of various metal ions were
ex
shown in Fig. 7. After excitation at 510 nm, the fluorescence spectra of R8 displayed an
maximum emission at 534 nm corresponding to green fluorescence. The fluorescent intensity

ACCEPTED MANUSCRIPT
8
band center at 534 nm of R8 was decreased after addition of the metal ions which almost
4
+
disappear for R8/Ge ion and fluorescent cannot be observed with naked-eyes.
3
.3. Binding mode and possible binding sites for metal ions
The chemical, the B3LYP/LanL2DZ optimized models and atomic labeling of free R8
are shown in Fig. 8. In the R8 molecule, there are three functional groups that can bind metal
ions, an adjacent hydroxyl-keto group at 2- and 3-positions (OOH), adjacent hydroxyls group at
6
and 7-positions (OHOH) and the oxoethoxy substituents in the benzene ring at position 9
4+
2+
(
OOOO). The optimized structures of R8 and its complexes with Ge and Cd ions in different
binding mode were computed and shown in Fig. 9. The selected bond length, bond angle and
4
+
dihedral angle of R8 and R8-Ge complexed at all possible binding sites were shown in Table
S1 and Table S2. The Gibbs free energy changes (ΔG) also provided the clue to the binding
abilities of binding site. The Gibbs free energy changes of R8 for metal ion complexes in vaccuo
2
+
were calculated and the value were shown under each model in Fig. 9. For Cd , the
complexation of R8 show the lowest energy when bound with metal ions at OOOO position.
2
+
4+
This indicated that OOOO position was preferred for Cd binding site. For Ge the lowest
energy was found when binding with OOH binding site.
4
+
To investigate further, electrostatic density of Ge complexes at all three possible
binding sites of R8 was calculated by using Gaussian 09 program. The molecular electrostatic
potential (MEP) map was generated by using the MOLEKEL 5.4 software [39]. The MEP is a
plot of electrostatic potential mapped onto the constant electron density surface. The red color
surfaces with negative MEP represent the high electron density region. The blue color surfaces
correspond to areas of the lowest electron density. The surfaces with green colors indicate zero
3
potential. The electrostatic potentials (in au) presented over electronic isodensity ρ = 0.05 e/Å
are presented in Fig. 10. The electronic isodensity surfaces of R8 show strong negative charge on
all oxygen atoms of both OOH and the OOOO groups. The minimum and maximum of
4
+
electrostatic potentials are in the ranges of -0.190 to +0.314 for free R8. The Ge complexes at
OOOO, OHOH and OOH binding site are in the ranges of +0.143 to +1.08, +0.140 to +1.22 and
4
+
+
0.164 to + 1.130, respectively. It can be seen that the Ge complexes at OOOO binding site is
the lowest positive electrostatic potential which indicate that this site has higher ligand to metal
charge transfer (LMCT) interaction. To confirm this, the Natural Bond Orbital (NBO) analysis

ACCEPTED MANUSCRIPT
9
also calculated The NBO charge of some atoms are listed in Tables 1. From these data, the NBO
charges of selected atoms of R8 are significantly changed especially at OOOO binding site. The
4
+
NBO charge of Ge are +1.46, + 1.56 and +1.51 for OOOO, OHOH and OOH binding site. The
lowest NBO charge of OOOO site also indicate the highest ligand to metal charge transfer
(
LMCT) interaction.
In order to achieve more effective recognition, receptor and metal ion guests should
exhibit not only interaction complementary but also steric complementary, large contract areas
and multiple interaction sites. There are four oxygen donor atoms at OOOO position which result
in more charge transfer interaction than OOH and OHOH that have only two sites. From ΔG,
NBO, electrostatic potential surfaces result and effective recognition principle, the OOOO
position was selected to optimize structure and calculated complexation properties of R8 with
other metal ions.
3
.4. Geometries and binding energies of R8 and metal ions complexes at OOOO position
The Gibbs free energy changes of R8 for metal ion complexes in vaccuo have been
computed. The computed values of binding energies, binding enthalpies and Gibbs free energies
are listed in Table 2. The binding energies of R8 with metal ions indicated that the binding
occurring via the exothermic processes. The R8 and metal ion binding strengths are in
4
+
3+
2+
2+
2+
2+
2+
decreasing order: R8/Ge >> R8/Al >> R8/Cu ~ R8/Zn > R8/Cd ~ R8/Hg > R8/Pb
2
+
+
+
+
4+
~
R8/Ca >> R8/Ag ~ R8/Na > R8/K . These results indicated that Ge show the most stable
complexed with R8 at oxoethoxy substituted on benzene ring at position 9.
The B3LYP/LanL2DZ optimized structures of R8 and its complexes with metal ions at
oxoethoxy phenyl amide binding are shown in Figs. 11. Two water solvent molecules were
added for completing the octahedral geometry. The selected geometrical parameters of the data
of all optimized structures are listed in Tables 3. The complexations of R8 with metal ions show
the significant change in their structures. In details, the metal ion complexation induces more
symmetrical structure than free chemosensor and the alignment of metal ion depend on the
common metal ion geometry. The presence of two water molecules with 4 oxygen donor atoms
4
+
of binding subunit of R8 results in distorted tetragonal geometry except Ge show distorted
tetrahedral. The average C=O, C−O and C−N bond lengths of free R8 were 1.266, 1.465 and
1
.372 Å, respectively. The average C=O and C−O bond lengths of metal ion complexes were

ACCEPTED MANUSCRIPT
1
0
3
+
longer. Especially for the Al complex showed the longest average C=O and C−O bond lengths
(1.326 and 1.480 Å). The average C−N bond length of metal ion complexes was shorter than free
3
+
chemosensors. The Al complex was the shortest average C−N bond length (1.313 Å). The
dihedral angle between phenyl ring at position 9 and fluorone moiety of the complexes increased
3
+
free chemosensor especially for Al complex. From these data, it was evident that the metal ion
complexation at binding subunit affects not only the bond length within binding subunit itself but
also the electron density within signaling subunit.
3
.5. Electronic properties and partial charge transfer of R8 metal complexes at OOOO position
The electron density of R8 and its metal ion complexes in saturated coordination sphere
complexes were calculated using B3LYP/LanL2DZ level of theory. The NBO charges on the
selected atoms of free R8 and its metal ion complexes are listed in Tables S3. The absolute NBO
charge changed are presented in bar−graph and shown in Fig. 12. From these data, the NBO
charges of selected atoms of oxoethoxy phenyl amide binding subunits and fluorone
4
+
chromophore are significantly changed especially for Ge complex. These results indicate that
the metal ion recognition via ion−dipole interactions induces the charge transfer process from not
only oxoethoxy phenyl amide binding subunits to metal ion but also from fluorone chromophore
subunit.
Electrostatic potential surfaces of R8 and its complexes have been generated. The
3
electrostatic potentials (in au) presented over electronic isodensity ρ = 0.05 e/Å are illustrated in
Fig.S4. The minimum and maximum of electrostatic potentials are presented in the ranges of -
0
.191 to +0.318 for the free form of R8. The electronic isodensity surfaces of the R8 the strongly
negative charge on oxygen atoms of adjacent hydroxyl-keto group and the oxoethoxy
substituents in the benzene ring at position 9 with intense red. All the metal ion complexes
+
3+
4+
(
R8/Na , R8/Al and R8/Ge ) show an increase of the positive charges of as can be seen from
the higher intensity of blue. In the case of metal to ligand charge transfer (MLCT), the
4
+
4+
complexation of Ge ion and R8 shows the highest LMCT which implied that Ge formed the
strongest binding with R8.
The energy level of the corresponding molecular orbitals (MOs), which was first developed
by Weller [40] and have been used in our previous works [41], can provide a clue to the
quenching process from fluorescence emission experiment. According to Weller’s approach the

ACCEPTED MANUSCRIPT
1
1
HOMO−LUMO electron distributions were computed on the total system. The donor orbitals
and acceptor orbitals were distinguished by simply inspecting the orbital distribution diagram.
2
+
The frontier orbital energy level diagrams and electron−transfer paths in R8, R8/Cd and
4
+
R8/Ge complex were chosen to illustrate this process (Fig. 13). First, consider electron transfer
processes in free chemosensor R8 (Fig. 13a). After excitation, the excited electron is able to go
back to ground state. Therefore, free chemosensor is able to exhibit fluorescent. The same is
3
+
4+
true for R8/Al complex (Fig. 13b). For Ge ion, the complexation leads to the transfer of
electron from receptor to fluorophore, the mechanism known as photo-induced electron transfer
(PET) process, which is depicted in Fig. 13c. The picture also shows that after electron transfer
process, the excited electron cannot release fluorescent energy and return to ground state. That is,
4
+
Ge ion cause the quenching in fluorescent emission as well as decreasing in absorption
intensity of R8.
4
. Conclusions
A water soluble and naked-eyes chemosensor for Ge ion base on phenylfluorone
4
+
derivative containing 3,4−bis(2−(diethylamino)−2−oxoethoxy) on phenyl position 9 (R8) has
been synthesized by one−pot reaction of benzaldehyde derivative and 1,2,4-triacetoxybenzene in
the presence of concentrated hydrochloric acid. The binding abilities between R8 and 10 equiv.
+
+
2+
2+
2+
2+
2+
2+
3+
3+
3+
4+
of Na , K , Ca , Fe , Cu , Cd , Hg , Pb , Al , Cr , Fe and Ge ions in 1% v/v EtOH-
water (tris-buffer pH 7) were studied using UV−vis and fluorescence spectrophotometry. The
4+
color of aqueous solution of R8 changed from yellow-orange to pink when complexed with Ge
ion. Both UV−vis absorption and fluorescence emission intensity of R8 decreased dramatically
4
+
when Ge ion was added comparing with other ions. The association constant (K ) calculated by
a
5
4
4
4
4
Benesi–Hildebrand plots were found to be 6.21×10 , 2.69×10 , 1.26×10 , 1.66×10 and 2.45×10
-1
4+
2+
2+
+
3+
-
M for Ge , Cd , Cu , Na and Al complex, respectively. The detection limits were 4.40×10
7
-4
-4
-4
-4
4+
2+
2+
+
3+
,
3.44×10 , 1.97×10 , 9.66×10 and 3.71×10 M for Ge , Cd , Cu , Na and Al ,
respectively. To explain this behavior, the quantum calculation was performed using the hybrid
density functional B3LYP using the Los Alamos LanL2DZ split−valence basis set
(B3LYP/LanL2DZ). The OOOO position was selected to optimized structure and calculated
4
+
complexation properties of R8 with metal ions. The results show that Ge formed the most
stable complexed with R8 at oxoethoxy substituted on phenyl group of phenylfluorone via

ACCEPTED MANUSCRIPT
1
2
ion−dipole interactions. The calculated orbital energies indicated that the decrease of UV-vis
absorption intensity and the quenching of fluorescent emission were due to PET process.
Acknowledgements
The authors gratefully acknowledge the Division of research facilitation and dissemination,
Mahasarakham University, Thailand for financial support of this research and the facility provided by
Supramolecular Chemistry Research Unit, Department of Chemistry, Faculty of Science, Mahasarakham
University.
References
[
[
[
[
[
1] L.S. Keith, O.M. Faroon. N. Maples-Reynnolds, B.A. Fowler, Handbook on the
th
Toxicology of Metals, 4 Edition. London: Academic Press Inc. Ltd. (2015) C37: pp.799-
8
16.
2] L. Zhang, X. Guo, H. Li, Z. Yuan, X. Liu, T. Xu, Separation of trace amounts of Ga and
Ge in aqueous solution using nano-particles micro-column. Talanta 85 (2011) 2463-2469.
DOI: 10.1016/j.talanta.2011.07.096
3] S.Y. Ly, S.S. Song. S.K. Kim, Y.S. Jung, C.H. Lee, Determination of Ge(IV) in rice in a
mercury-coated glassy carbon electrode in the presence of catechol. Food Chem 95 (2006)
3
37-343. DOI: 10.1016/j.foodchem.2005.02.029
4] H. Matusiewicz, M. Krawczyk, Determination of Germanium and Tin and Inorganic Tin
Species by Hydride Generation in Situ Trapping Flame Atomic Absorption Spectrometry.
Anal. Lett. 43 (2010) 2543-2562. DOI: 10.1080/00032711003725631
5] A. Sabarudin, T. Umemura. S. Motomizu, Chitosan functionalized with di-2-
propanolamine: Its application as solid phase extractant for the determination of
germanium in water samples by ICP-MS. Microchem. J. 99 (2011) 34-39. DOI:
1
0.1016/j.microc.2011.03.004
[
[
6] X. Zou, Y. Li, M. Li, B. Zheng, J. Yang, Simultaneous determination of tin, germanium
and molybdenum by diode array detection–flow injection analysis with partial least squares
calibration model. Talanta 62 (2004) 719-725. DOI: 10.1016/j.talanta.2003.09.016
7] N.N. Khomichenko, A.V. Shaverina, A.R. Tsygankova, A.I. Saprykin, ICP-AES analysis
of silicon, germanium, and their oxides. Inorg. Mater. 52 (2016) 1405-1412. DOI:
1
0.1134/S0020168516140077

ACCEPTED MANUSCRIPT
1
3
[
[
8] G. Rosenfeld, Spectrophotometric determination of germanium in biological materials.
Anal. Biochem. 1 (1960) 469-477. DOI: 10.1016/0003-2697(60)90059-2
9] L. Zaijun, Z. Xia, L. Huizen, P. Jiaomai, Development of Spectrophotometric Method for
Determination of Germanium, Rev. Anal. Chem. 26 (2011) 23-42. DOI:
1
0.1515/REVAC.2007.26.1.23
[
[
[
10] Q. Wei, D. Wu, B. Du, Y. Li, C. Duan, Interaction of m-nitrophenylfluorone–Mo(VI)
complex as a probe with human serum albumin: A fluorescence quenching. Spectrochim.
Acta, Part A. 63 (2006), 532-535. DOI: 10.1016/j.saa.2005.05.040
11] Q. Wei, J.Yang, Y. Zhang, G. Chang, B. Du, Determination of antimony(III) in
environmental water samples in microemulsion system by the fluorescence quenching
method, Talanta 58 (2002) 419-426. DOI: 10.1016/S0039-9140(02)00145-5
12] Q. Li, X. Zhao, X. Guan, G. Liu, A novel method of the separation/preconcentration and
determination of trace molybdenum(VI) in water samples using microcrystalline
triphenylmethane loaded with salicyl fluorone, Anal. Chim. Acta. 562 (2006) 44-50. DOI:
1
0.1016/j.aca.2006.01.049
[
13] Q. Chen, Z. Fang, Two sugar-rhodamine “turn-on” fluorescent probes for the selective
3
+
detection of Fe , Spectrochim. Acta, Part A. 193 (2018) 226–234. DOI:
0.1016/j.saa.2017.12.023.
14] C. L. Luke, Photometric Determination of Tin with Phenylfluorone, Anal. Chem. 28 (1956)
276-1279. DOI: 10.1021/ac60116a012
1
[
[
1
15] Y. Jin, Y. Sun, C. Li, C. Yang, A highly selective chemiluminescent probe for the
detectionof chromium(VI), Spectrochim. Acta, Part A. 192 (2018) 82–87. DOI:
1
0.1016/j.saa.2017.10.062
16] Q.-J. Du, W.-B. Chen, Spectrophotometric Determination of Micro Germanium(IV) with
-(4-Carboxylphenylazo)-8-hydroxylquinoline as Colour Reagent, Asian Journal of
[
[
5
Chemistry, 25 (2013) 10373-10375. DOI: 10.14233/ajchem.2013.15510
17] L.A. Ivanitsa, A.Y. Klimkina, T.S. Chmilenko, F.A. Chmilenko, Determination of tin and
germanium with nonylfluorone and polymeric flocculants in plant materials, Vìsnik
Dnìpropetrovs’kogo unìversitetu. Serìâ hìmìâ 24 (2016) 27–35.

ACCEPTED MANUSCRIPT
1
4
[
[
[
18] L. Zaijun, T. Jian, L. Huizhen, Z. Xia, Y. Rui, Determination of trace amounts of
germanium in food and fruit by spectrophotometry with p-methybenzeneazosalicylflurone,
J. Food. Compost. Anal. 20 (2007) 1–6. DOI: 10.1016/j.jfca.2006.04.009
19] L. Zaijun, P. Jiaomai, T. Jan, Spectrophotometric method for determination of germanium
in foods with new color reagent trimethoxylphenylfluorone, Anal. Chim. Acta., 445 (2001)
3
1, 153-159. DOI: 10.1016/S0003-2670(01)01259-4
20] L. Zaijun , Z. Xia, L. Huizhen, Y. Rui, Novel Spectrophotometric Method for
Determination of Trace Germanium in Soils with Methybenzeneazosalicylfluorone using
Ultrasound‐Assisted Leaching, Commun. Soi.l Sc.i Plant. Anal. 39 (2008) 461-474, DOI:
1
0.1080/00103620701826597
[
[
21] E.M. Donaldson, Spectrophotometric determination of germanium in ores, concentrates,
zinc-processing products and related materials with phenylfluorone and
cetyltrimethylammonium bromide after separation by iron collection and heptane
extraction of germanium tetrachloride, Talanta 31 (1984), 997-1004. DOI: 10.1016/0039-
9
140(84)80233-7
22] Z. Xia, L. Zaijun, Y. Rui, L. Huizhen, A novel room temperature ionic liquid extraction
spectrophotometric determination of trace germanium in natural water with
methybenzeneazosalicylfluorone, Anal. Lett. 39(2006) 863-877, DOI:
1
0.1080/00032710600605766
[
[
23] V.G. Amelin, O. I. Abramenkova, Test Determination of Titanium(IV) and
Germanium(IV) in Waste and Natural Waters in the Presence of Each Other, J.Anal.Chem.
6
3(2008) 700–705. DOI: 10.1134/S1061934808070174
24] L. Zaijun, P. Jiaomai, O. Zhongping, Newdeveloptment of the derivative of fluorone as
achromogenic reagent in analytical chemistry, Review in analytical chemistry, 22(2003)
2
57-320. DOI: 10.1515/REVAC.2003.22.2.257
[
[
25] A.D. Becke, Density‐functional thermochemistry. III. The role of exact exchange, J. Chem.
Phys. 98 (1993) 5648−5652. DOI: 10.1063/1.464913
26] C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy formula
into a functional of the electron density, Phys. Rev. B. 37 (1988) 785−789. DOI:
1
0.1103/PhysRevB.37.785

ACCEPTED MANUSCRIPT
1
5
[
[
[
[
27] P.J. Hay, W.R. Wadt, Ab initio effective core potentials for molecular calculations.
Potentials for the transition metal atoms Sc to Hg, J. Chem. Phys. 82 (1985) 270−283.
DOI: 10.1063/1.448799
28] W.R. Wadt, P.J. Hay, Ab initio effective core potentials for molecular calculations.
Potentials for main group elements Na to Bi, J. Chem. Phys. 82 (1985) 284−298. DOI:
1
0.1063/1.448800
29] P.J. Hay, W.R. Wadt, Ab initio effective core potentials for molecular calculations.
Potentials for K to Au including the outermost core orbitals, J. Chem. Phys. 82 (1985)
2
99−310. DOI: 10.1063/1.448975
30] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A.
Jr. Montgomery, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O.
Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui,
A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al–Laham, C.Y. Peng, A. Nanayakkara,
M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople GAUSSIAN 09, Revision A.02, Gaussian Inc, Wallingford CT, (2009).
[
[
[
31] T. Keawwangchai, B. Wanno, N. Morakot, S. Keawwangchai, Optical chemosensors for
Cu(II) ion based on BODIPY derivatives: An experimental and theoretical study, J. Mol.
Model. 19 (2013) 4239-4249. DOI 10.1007/s00894-013-1862-4
32] H. Sano, Studies on Organic Reagents for Inorganic Analysis. IV. Syntheses of New
Phenylfluorone Derivatives and their Reactions with Metal Ions, Bull. Chem. Soc. Jpn. 31
(1958), 974-980. DOI: 10.1246/bcsj.31.974
33] S. Kamino, Y. Kawamae, M. Ijyuin, S. Takada, T. Yamaguchi, M. Doi, Y. Fujita,
Synthesis, Spectral Study and Crystal Structure of a Fluorescein Derivative, p-

ACCEPTED MANUSCRIPT
1
6
Methoxycarbonylphenyl Fluorone, Chem. Pharm. Bull. 57 (2009) 1405-1408. DOI:
1
0.1248/cpb.57.1405
[
[
34] G.K. Patra, R. Chandra, A. Ghorai, K.K. Shrivas, A highly selective benzildihydrazone
2
+
based Schiff base chromogenic chemosensor for rapid detection of Cu in aqueous
solution, Inorg. Chim. Acta. 462 (2017) 315–322. 10.1016/j.ica.2017.04.013
35] H.A. Benesi, J.H. Hildebrand, A Spectrophotometric Investigation of the Interaction of
Iodine with Aromatic Hydrocarbons, J. Am. Chem. Soc. 71(1949) 2703–2707. DOI:
1
0.1021/ja01176a030
[
[
36] C.L. Luke, M.E. Campbell, Photometric Determination of Germanium with
Phenylfluorone, Anal. Chem. 28 (1956) 1273–1276. DOI: 10.1021/ac60116a011
37] H. Kim, B.A. Rao, J.W. Jeong, S. Mallick, S.-M. Kang, J.S. Choi, C.-S. Lee, Y.-A. Son, A
2
+
3+
highly selective dual-channel Cu and Al chemodosimeter in aqueous systems: Sensing
in living cells and microfluidic flows, Sens. Actuators B. Chem. 210 (2015) 173-182. DOI:
1
0.1016/j.snb.2014.12.100
2
+
2+
[
38] V. Tekuri, D.R. Trivedi, A new colorimetric chemosensors for Cu and Cd ions
detection: Application in environmental water samples and analytical method validation,
Anal Chim Acta. 15 (2017),81-93. DOI: 10.1016/j.aca.2017.03.035
[
[
39] U. Varetto, Molekel 5.4, Swiss National Supercomputing Centre, Lugano (Switzerland).
40] A. Weller, Electron-transfer and complex formation in the excited state, Pure Appl Chem.
1
6 (1968) 115−124. DOI: 10.1351/pac196816010115
[
41] T. Keawwangchai, B. Wanno, N. Morakot. Fluorescent sensors based on BODIPY
derivatives for aluminium ion recognition: An experimental and theoretical study, J. Mol.
Model. 19 (2013) 1435-1444. DOI 10.1007/s00894-012-1698-3

ACCEPTED MANUSCRIPT
1
7
4
+
Table 1 Selected NBO charge (in e) analysis of some atoms in complexes of R8 and Ge at
possible binding sites computed at the B3LYP/LanL2DZ level
4
+
Ge binding site
OHOH
Atom
free R8
OOOO
1.4612
OHO
4
+
Ge
No
1.5670
1.5116
-0.3747
-0.3722
-0.7497
-0.9295
-0.4538
-0.6880
-0.6911
-0.5855
-0.5458
-0.6004
-0.5457
N1
N2
O1
O2
O3
O4
O5
O6
O7
O8
O9
-0.5010
-0.5011
-0.6939
-0.5700
-0.5193
-0.7527
-0.7283
-0.5731
-0.6663
-0.5716
-0.6667
-0.4072
-0.4086
-0.5734
-0.2944
-0.4449
-0.6441
-0.6221
-0.5909
-0.8598
-0.5753
-0.8421
-0.3781
-0.3778
-0.6327
-0.4254
-0.5004
-0.8709
-0.8247
-0.5880
-0.5464
-0.5990
-0.5436

ACCEPTED MANUSCRIPT
1
8
C2
C3
0.3293
0.4340
0.3036
0.3033
0.3125
0.3078
0.6944
0.6942
0.4560
0.4425
0.3986
0.4398
0.3019
0.3279
0.7442
0.7407
0.4046
0.4455
0.2724
0.2648
0.5960
0.5741
0.6994
0.6906
0.3869
0.3171
0.3906
0.3505
0.59812
0.57845
0.6995
0.6904
C6
C7
C16
C17
C21
C27
All atoms are on the chemosensor R8 which are defined in Fig 9.
Table 2 The zero point vibrational correction energy (EZPE) and enthalpy (H) and Gibbs free
−
1
energy (G) changes of complexations between chemosensor R8 and metal ions (In kcal mol )
R8 complexes
Ebinding
-92.11
H
-67.01
G
-115.85
+
Na
+
K
-65.88
-40.56
-90.98
-124.34
-287.38
-419.09
-350.46
-338.63
-294.26
-398.91
-808.10
-1561.85
+
Ag
-99.82
-74.82
2
+
Ca
Cu
Cd
-264.03
-401.23
-327.83
-315.28
-272.67
-376.80
-789.04
-1540.39
-239.30
-378.72
-302.82
-289.91
-247.74
-352.18
-765.87
-1516.31
2+
2+
2+
+
+
Hg
2
Pb
Zn
2
3
+
Al
4
+
Ge

ACCEPTED MANUSCRIPT
1
9

ACCEPTED MANUSCRIPT
2
0
Table 3 Selected geometrical data for chemosensor R8 and its metal ions complexes computed at the B3LYP/LANL2DZ level of
theory
+
+
+
2+
2+
2+
2+
2+
2+
3+
4+
Bond length
C20-O6
C21=O7
C26-O8
C27=O9
R8
1.465
1.266
1.464
1.266
1.372
1.372
-
Na
K
Ag
Ca
Cu
Cd
Zn
Hg
Pb
Al
Ge
1.454
1.271
1.454
1.271
1.358
1.358
2.492
2.452
2.494
2.450
1.460
1.272
1.457
1.269
1.359
1.361
2.874
2.725
2.867
2.721
1.465
1.290
1.456
1.276
1.349
1.357
3.132
3.512
2.706
2.266
1.468
1.289
1.467
1.288
1.340
1.340
2.496
2.349
2.501
2.349
1.449
1.287
1.449
1.287
1.344
1.344
2.477
2.066
2.475
2.069
1.422
1.293
1.460
1.292
1.338
1.339
2.416
2.247
2.417
2.246
1.459
1.294
1.458
1.294
1.336
1.336
2.252
2.104
2.259
2.102
1.457
1.295
1.456
1.294
1.339
1.339
1.457
2.314
2.517
2.313
1.461
1.298
1.459
1.296
1.338
1.339
2.605
2.406
2.674
2.468
1.482
1.326
1.478
1.325
1.313
1.313
1.970
1.855
1.968
1.855
1.473
1.312
1.462
1.311
1.326
1.325
3.060
1.950
2.863
1.995
C21-N1
C27-N2
O6-M
O7-M
O8-M
O9-M
-
-
-
dihedral angle
C10-C9-C14-C15
C13-C9-C14-C19
115.941 112.822 113.187 116.505 115.097 111.624 114.979 114.770 114.787 123.167 127.403 122.887
115.109 111.798 112.246 115.405 114.692 109.740 113.753 113.352 113.468 121.245 125.019 119.553

ACCEPTED MANUSCRIPT
2
1
Scheme 1 Synthesis of Phenylfluorone−based chemosensor R8.

ACCEPTED MANUSCRIPT
2
2
-5
Fig. 1. The color and fluorescent change of 1.0×10 M R8 at different pH in aqueous solution.
-5
Fig. 2. The absorption spectra of 1.0×10 M R8 at different pH in aqueous solution.

ACCEPTED MANUSCRIPT
2
3
−
5
−5
Fig. 3. (a) The color changes of 1.010 M R8 and (b) UV−vis spectrum changes of 1.010 M
R8 upon addition of various cations (10 equiv.) in 1% v/v ethanol-water (tris-buffer, pH 7)

ACCEPTED MANUSCRIPT
2
4
−
5
Fig. 4. Competitive selectivity of 1.010 M R8 against various metal ions (50 equiv.) in the
4
+
present of Ge ion (10 equiv.) in 1% v/v ethanol-water (tris-buffer, pH 7)

ACCEPTED MANUSCRIPT
2
5
4
+
Fig. 5. (a) Absorption spectra of R8 after addition of Ge up to 2.5 equiv. in 1% v/v ethanol-water
4
+
(tris-buffer, pH 7) at room temperature; inset: absorbance at 510 nm vs. concentration of Ge
4
+
added. (b) Benesi–Hildebrand plot (absorbance at 510 nm) of R8 with Ge complex.

ACCEPTED MANUSCRIPT
2
6
3
+
+
Fig. 6. Absorption spectra of R8 after addition of (a) Al (b) Na up to 3.5 equiv. in 1% v/v
ethanol-water (tris-buffer, pH 7) at room temperature; inset: Benesi–Hildebrand plot (absorbance at
10 nm).
5
−
6
Fig. 7. Fluorescence spectrum of 1.010 M R8 upon addition of various cations (10 equiv.) in
0
.1% v/v ethanol-water (tris-buffer, pH 7) at room temperature ( = 510 nm) with 5 nm ex and em
ex
4
+
slit; inset: The fluorescent color of free R8 and R8/Ge complex solution under UV light at 365
nm.

ACCEPTED MANUSCRIPT
2
7
4
+
Fig. 8. The B3LYP/LanL2DZ optimized structures of R8 and Ge complexed at OOOO, OHOH
−
1
and OOH possible binding sites. The presented binding free energies in kcal.mol .

ACCEPTED MANUSCRIPT
2
8
Fig. 9. The chemical, optimized models and atomic labeling of chemosensor R8.

ACCEPTED MANUSCRIPT
2
9
4
+
Fig. 10. The electrostatic potentials (in a.u.) of R8 and Ge complexed at OOOO, OHOH and OOH
possible binding sites obtained at B3LYP/LanL2DZ level and presented over electronic isodensity ρ
-3
=
0.05 eÅ .