12

Accepted Manuscript

Substitutional group dependent colori/fluorimetric sensing of Mn2+, Fe3+ and

Zn2+ ions by simple Schiff base chemosensor

P.S. Hariharan, Savarimuthu Philip Anthony

PII: S1386-1425(14)01558-3
DOI: http://dx.doi.org/10.1016/j.saa.2014.10.061
Reference: SAA 12876

To appear in: Spectrochimica Acta Part A: Molecular and Biomo-

lecular Spectroscopy

Received Date: 24 June 2014

Revised Date: 10 October 2014
Accepted Date: 15 October 2014

Please cite this article as: P.S. Hariharan, S.P. Anthony, Substitutional group dependent colori/fluorimetric sensing
of Mn2+, Fe3+ and Zn2+ ions by simple Schiff base chemosensor, Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.10.061

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.
 1

Substitutional group dependent colori/fluorimetric sensing of Mn2+, Fe3+ and

Zn2+ ions by simple Schiff base chemosensor

P. S. Hariharan and Savarimuthu Philip Anthony*

School of Chemical & Biotechnology, SASTRA University, Thanjavur-613401, Tamil

Nadu, India. Fax: +914362264120; Tel: +914362264101; E-mail:

philip@biotech.sastra.edu

Abstract: Schiff base is one of the easiest synthesizable chemosensor and exhibit

strong coordination with metal ions; the property that has been vastly exploited for

metal ions sensing. Simple Schiff base chemosensors (1a-d and 2a-d) were

synthesized and demonstrated substitutional group dependent colorimetric sensing of

metal ions. Chemosensor without (1a, 2a) and OCH3 substitution (1b, 2b) did not

show any significant colour change for metal ions. However, a highly selective

colorimetric change (colourless to pink) for Mn2+ ions (10-6 M) was observed with

diethylamine substituted 1c, 2c. Hydroxyl substitution (1d, 2d) leads to selective

colorimetric sensing (colourless to orange) of Fe3+ ions (10-6 M). PVA thin films of

2c/2d were fabricated and demonstrated selective colorimetric sensing of Mn2+ and

Fe3+ ions. The practical applicability of the synthesized chemosensors were also

demonstrated by performing selective colorimetric sensing of Mn2+ and Fe3+ ions in

real samples such as tap, ground, pond and river water. Effect of substitution on the

fluorescence selectivity of Zn2+ has also been investigated.

Keywords: Fluorescence sensor, Colorimetric sensor, Zn2+ sensor, Mn2+ sensor, Fe3+

sensor.
 2

1. Introduction

Selective detection and screening of heavy transition metal ions (HTM) is highly

important because of their strong influence in chemical, biological and environmental

process [1,2]. Among the various approaches developed, molecular chemosensors that

show optical (both colorimetric and fluorescence) responses upon selective binding

with metal ions have received great interest since these methods are cost-effective,

rapid, real time-monitoring and facile [3,4]. The ease of synthesis coupled with

synthetic tailorability, good biological activities, strong photophysical properties and

metal coordination ability has made Schiff bases as one of the most widely explored

molecular chemosensors for selective sensing of metal ions [5-7]. Particularly, Salen,

a tetradentate [OˆNˆNˆO] chelating bis-Schiff base, based ligands and its metal

complexes have been exploited for various potential applications in many fields

including catalysts [8], DNA cleavage [9], optical materials [10], magnetic materials

[11] and sensors [6-7]. For example, the excellent luminescent properties and good

thermal stabilities of Zn(II) [12], B(III) [13], Al(III) [14], and Pt(II) [15] based Salen

complexes have been successfully used as emitters in fabricating organic light-

emitting diodes (OLEDs). Salen type ligands have also been widely used as

fluorescence chemosensors for selective detection of various cations, such as Zn2+

[6a-d], Mg2+ [6g], Cu2+ [32,37,42], Al3+ [6h] and Pt2+ [7e]. However, there are only a

few reports on the selective colorimetric as well as multiple metal ions sensing by

simple Salen ligand [16].

Salen chemosensors that are known to have strong binding affinities with

metal ions often showed strong fluorescence enhancement via chelation enhanced

fluorescence mechanism for metal ions such as Zn2+, Cd2+ and Al3+ [17]. However,

the chemosensor should show strong preference with metal ions of interest to exhibit
 3

the high selectivity in presence of other metal cations. The preferential coordination

of organic ligands with metal ions are strongly influenced by the structure,

substituents, solvent and temperature [18]. Hence a subtle change in the structure of

Salen chemosensor might affect the affinity of metal ions that could modify the

selectivity or sensing of metal ions.

Herein, we report the effect of substitutional group in the Schiff base

chemosensors (Scheme 1) on the optical sensing (colorimetric and fluorescence) of

metal ions. Chemosensors, 1a-d and 2a-d, exhibited selective turn-on fluorescence for

Zn2+ ions (15 to 80 fold fluorescence enhancement). Interestingly, highly selective

colorimetric sensing for Mn2+ ions (colourless to pink) was observed with

diethylamino substituted chemosensor, 1c and 2c. 1d and 2d, a hydroxyl group

substituted chemosensor, showed selective colorimetric sensing of Fe3+ ions. The

practical utility of 2c and 2d for selective colorimetric sensing of Mn2+ and Fe3+ has

also been demonstrated from different water samples.

2. Experimental Sections

2.1. Materials

Ethylene diamine, (±)-trans-1,2-Diaminocyclohexane (99 %), salicylaldehyde,

2-hydroxy-5-methoxy benzaldehyde, 2-hydroxy-5-diethylamino benzaldehyde and 2,

4-dihydroxy benzaldehyde was obtained from sigma-Aldrich. Poly vinyl alcohol

(PVA, M. W. 125000) was obtained from SD Fine chemicals, India. The solvents

were obtained from Merck India. All chemicals are used as received. The metal ion

solutions used for the colorimetric and fluorescence sensor experiments were prepared

by preparing 10-3 M stock solution in Mill-Q water. The chemosensors were dissolved

in dimethyl formamide (DMF). The sensing experiment was repeated three times to

confirm the reproducibility of the method. Absorption and fluorescence spectra were
 4

recorded using Perking Elmer Lambda 1050 and Jasco fluorescence spectrometer-FP-

8200 instruments. Elemental analyses were measured with a Perkin-Elmer 2400 II

CHN analyzer.

2.2. General synthesis of 1a-d and 2a-d

Aldehyde (2.2mmol, salicylaldehyde or 4-methoxysalicylaldehyde, 4-

diethylamino-2-hydroxy benzaldehyde or 2, 4-dihydroxy benzaldehyde) was

dissolved in ethanol (30 ml) and stirred at room temperature. To this solution, either

ethylene diamine (1mmol) or trans-1,2-diaminocyclohexane (1mmol) was added

drop-wise under stirring. The immediate appearance of yellow colour indicates the

formation of Schiff bases. The solution was allowed to stir for another 6 h at room

temperature that produced yellow to light yellow coloured precipitates. The formed

precipitate was filtered off, washed with ethanol and dried under vacuum.

1a: Yield = 85 %. m.p. 122 °C. 1H NMR (CDCl3) δ 13.25 (s, 2H (OH), 8.37 (s, 2H

(imine H)), 7.31-7.34 (d, 2H), 7.23-7.26 (d, 2H), 6.95-6.97 (d, 2H), 6.85-6.90 (t, 2H),
13
3.95 (s, 4H). C NMR (CDCl3) δ 166.51, 161.01, 132.41, 131.50, 118.70, 118.64,

116.96, 59.75. C16H16N2O2 (268.31): calcd. C 71.62, H 6.01, N 10.44; found C 71.27,

H 6.31, N 10.37.

2a: Yield = 80 %. m.p. 112 °C. 1H NMR (CDCl3) δ 13.37 (s, 2H (OH)), 8.28 (s, 2H

(imine H)), 7.23-7.28 (t, 2H), 7.15-7.18 (d, 2H), 6.89-6.92 (d, 2H), 6.81-6.84 (t, 2H),
13
3.29-3.35 (m, 2H), 1.88-1.98 (m, 4H), 1.46-1.52 (m, 4H). C NMR (CDCl3) δ

164.71, 160.96, 132.17, 131.48, 118.65, 118.60, 116.77, 72.63, 33.10, 24.18.

C20H22N2O2 (322.17): calcd. C 74.51, H 6.88, N 8.69; found C 74.46, H 6.94, N 8.31.

1b: Yield = 80 %. m.p. 154 °C. δ 13.72 (s, 2H (OH)), 8.18 (s, 2H (imine H)), 7.06-
13
7.08 (d, 2H), 6.35-6.41 (m, 4H), 3.83 (s, 4H), 3.78 (s, 6H). C NMR (CDCl3) δ
 5

165.42, 164.76, 163.53, 132.74, 112.31, 106.43, 101.14, 58.75, 55.34. C18H20N2O4

(328.36): calcd. C 65.84, H 6.14, N 8.53; found C 65.46, H 6.24, N 8.45.

2b: Yield = 80 %. m.p. 108 °C. 1H NMR (CDCl3) δ 13.83, (s, 2H (OH)), 8.08 (s, 2H),

6.97-7.00 (d, 2H), 6.28-6.35 (m, 4H), 3.75 (s, 6H), 3.20-3.23 (m, 2H), 1.84-1.92 (m,

4H), 1.40-1.46 (m, 4H). 13C NMR (CDCl3) δ 164.96, 163.73, 163.43, 132.77, 112.22,

106.22, 101.09, 71.56, 55.31, 33.07, 24.23. C22H26N2O4 (382.45): calcd. C 69.09, H

6.85, N 7.32; found C 69.46, H 6.74, N 7.18.

1c: Yield = 80 %. m.p. 131 °C. 1H NMR (CDCl3) δ 13.55 (s, 2H (OH)), 8.20 (s, 2H

(imine H)), 7.04-7.07 (d, 2H), 6.14-6.17 (d, 4H), 3.71 (s, 4H), 3.31-3.37 (q, 8H), 1.05-
13
1.10 (t, 12H). C NMR (CDCl3) δ 164.85, 164.79, 150.92, 133.00, 107.78, 102.78,

97.25, 57.56, 43.73, 12.53. C24H34N4O2 (410.55): calcd. C 70.21, H 8.35, N 13.65;

found C 70.46, H 8.14, N 13.31.

2c: Yield = 80 %. m.p. 195 °C. 1H NMR (CDCl3 ) δ 13.18 (s, 2H (OH)), 7.92 (s, 2H

(imine H)), 6.86-6.89 (d, 2H), 6.01-6.07 (m, 4H), 3.28-3.35 (q, 8H), 3.13-3.16 (m,
13
2H), 1.80-1.95 (m, 4H), 1.37-1.57 (m, 4H), 1.11-1.16 (t, 12H). C NMR (CDCl3) δ

166.17, 162.71, 151.43, 133.08, 108.25, 102.91, 98.14, 70.75, 44.44, 33.25, 24.35,

12.72. C28H40N4O2 (464.64): calcd. C 72.38, H 8.68, N 12.06; found C 72.41, H 8.65,

N 12.13.

1d: Yield = 80 %. m.p. 250 °C (decomp.). 1H NMR (CDCl3) δ 13.58-13.64 (b, 4H,

OH)), 8.35 (s, 2H (imine H)), 7.14-7.17 (d, 2H), 6.24-6.28 (d, 2H), 6.16-6.17 (d, 2H),
13
3.77 (s, 4H). C NMR (CDCl3) δ 165.78, 164.52, 161.87, 133.33, 111.11, 106.90,

102.53, 57.67. C16H16N2O4 (300.31): calcd. C 63.99, H 5.37, N 9.33; found C 63.59,

H 5.74, N 9.22.

2d: Yield = 80 %. m.p. 264 °C (decomp.). 1H NMR (CDCl3) δ 13.51-13.54 (b, 4H

(OH)), 8.17 (s, 2H (imine H)), 6.98-7.01 (d, 2H), 6.17-6.20 (d, 2H), 6.11-6.12 (d, 2H),
 6

13
3.20-3.23 (m, 2H), 1.76-1.87 (m, 4H), 1.37-1.58 (m, 4H). C NMR (CDCl3) δ

163.74, 161.51, 132.90, 110.99, 106.78, 102.40, 70.71, 32.68, 23.77. C20H22N2O4

(354.40): calcd. C 67.78, H 6.26, N 7.90; found C 67.56, H 6.04, N 7.63.

3. Results and discussion

The synthesis of Schiff base chemosensor (1a-d and 2a-d) is quite

straightforward reaction that involves the condensation of diamine and an aldehyde

precursor in ethanol solution at room temperature (Scheme-S1). Although, the

synthetic protocol as well as some of the chemosensor (1a, 2a) has already been

known [19], the optical sensing properties have never been investigated thoroughly.

Particularly, 1c,d and 2c,d are newly synthesized which showed substitutional group

dependent colorimetric sensing of Mn2+ and Fe3+ ions. 1a-d and 2a-d were

characterized by elemental analysis, 1H and 13C-NMR. The selective optical responses

(both fluorescence as well as colorimetric sensing) of 1a-d and 2a-d were explored by

adding various metal ions dissolved in water.

Figure 1 shows the absorption spectra of 1a-d and 2a-d in DMF. 1a-d and 2a-d

exhibited intense absorption in the range of 300-350 nm that are assigned to π-π*

transition involving molecular orbitals particularly localized on the C=N group and

benzene ring. The low intensity absorption around 380 nm is assigned to n-π*

transition involving molecular orbitals of the C=N chromophore and benzene ring

[20]. The absorption spectra of 1a and 2a with different metal ions are shown in figure

S1. The metal interaction especially transition metal ions (Cr3+, Mn2+, Fe3+, Co 2+, Ni2+

and Cu 2+) with 1a and 2a red shifts the absorption λmax (350-420 nm). Even though

Fe3+ addition to 1a and 2a produced very weak absorption at longer wavelength (475

nm), visible colour was not able to observe. 1b and 2b also exhibited a similar
 7

absorption change without producing any naked eye detectable colour change for any

particular metal ions (Fig. S2).

Interestingly 1c and 2c showed a selective colorimetric change (colourless to

pink colour) upon the addition of Mn2+ ions (Fig. 2). Although Co2+, Ni2+ and Cr3+

addition exhibited colourless to light yellow colour formation, only Mn2+ produced

distinctly different colour. Mn2+ is one of the essential trace elements for several

endogenous anti-oxidant enzymes [21]. The absorption studies of 1c/2c showed the

emergence of two new peaks with Mn2+; a strong absorption at 415 nm and a clear

low intense broad peak around 520 nm. The intensity of π-π* transition band (320-

340 nm) was reduced by addition of Mn2+. The red shift of n-π* transition band from

380 nm to 415 nm is due to the coordination of Mn2+ with imine nitrogen. The metal

coordination with imine nitrogen is known to increase the electron withdrawing

ability of C=N group [8a]. The broad low intense band at 520 nm could be assigned to

ligand to metal charge transfer (LMCT) [22]. The absorption titration showed clear

spectral changes for 1c and 2c (red shifted n-π* transition at 415 nm and LMCT at

520 nm) with the addition of Mn2+ ions (Fig. 3a, S3a). A clear reduction of absorption

intensity at 340 nm and emergence of new absorption at 415 and 520 nm could be

observed with the first addition of Mn2+ (0.1 equivalent) to 1c/2c. The intensity of

new absorption peaks was increased linearly up to the addition of 1 equivalent of

Mn2+ at µM concentration (Fig. 3a, S3a inset). The concentration dependent studies

further suggest the 5 µM detection limit of Mn2+ by 1c/2c. This suggests the

formation of 1:1 coordination complexes between Mn2+ and 1c/2c. The exact

coordination complex structure could not be established since the attempted single

crystal growth was not successful. However, the structure could be similar to the

famous Jacobson catalysts that are also 1:1 coordination complex of Mn2+ with bis-
 8

Schiff base tetradendate ligands [23]. The selectivity studies of 1c and 2c indicates

that other metal ions except Fe3+ and Co2+ had negligible interference on the

selectivity of Mn2+ (Fig. 3b, S3b). Mn2+ additions into 1c and 2c in presence Fe3+ and

Co2+ showed only slight enhancement absorption at 415 nm and suggest that both

metal ions are competitively coordinated with 1c and 2c. It is noted that addition of

Mn2+ to 2c in presence of Cd2+ exhibited strong enhancement in the absorption at 415

nm compared with Mn2+-2c. The reason for the strong absorption is not clear right

now, however, it could be due to the hetero-metallic complexes formation. Recently,

we have reported strong enhancement of fluorescence with triphenylamine based

Schiff bases upon addition of Zn2+ followed by Cd2+ and vice versa [24]. Absorption

peak at 415 nm was chosen for selectivity analysis since it was a distinct and strong

absorption with Mn2+.

1d and 2d in which hydroxyl group was substituted instead of diethylamine

exhibited selective colorimetric sensing of Fe3+ (Fig. 4). Fe3+ is the most abundant

transition-metal ion in humans and other mammals, and it plays important roles in

various biological systems [25]. The deficiency of Fe3+ leads to anemia, liver and

kidney damages, diabetes, and heart diseases [26]. Addition of Fe3+ ions into 1d and

2d selectively produced orange colour solution (Fig. 4). Mn2+, Co2+, Cr3+ and Ni2+

showed only light yellow colour with 1d and 2d. The absorption measurement of 1d

and 2d with Fe3+ showed broad low intense LMCT band at 480 nm that could be

responsible for the orange colour. Other metal ions only showed enhancement of n-π*

transition around 400 nm. The concentration dependent studies again clearly showed

the linear enhancement of n-π* and LMCT band intensity with each addition of Fe3+

at µM concentration (Fig. 5a, S4a). The titration studies further suggested the

formation of 1:1.5 coordination complexes between Fe3+ and 1d/2d (Fig. 5a, S4a
 9

inset). 1d/2d chemosensor can detect Fe3+ ions up to 2 µM. The interference studies

indicate the high selectivity of Fe3+ in presence of other metal ions (Fig. 5b, S4b). In

an effort to fabricate sensor devices, PVA thin films of 2c and 2d was fabricated by

mixing methanol solution of chemosensor (1 ml, 10 -4 M) into aqueous solution of

PVA (1 wt%). The solution was stirred together for 1 h then it was drop coated on the

glass plate. The air dried thin film of PVA-2c and PVA-2d was dipped (1 min) into

aqueous metal ions solution of Mn2+ and Fe3+ (10-6 M), respectively. The Mn2+ ion

dipping and Fe3+ dipping clearly showed naked eye detectable pink colour and orange

colour change, respectively (Fig. 6). The reproducibility of the approach was

confirmed by repeating the experiment three times. Polymer-chemosensor film

prepared one week before also showed similar results and suggest the good stability

of the thin film. The practical applicability of the 2c and 2d chemosensor for sensing

Mn2+ and Fe3+ ions in different water samples (tap, ground, pond and river water)

have also been demonstrated (Fig. S5). Several chemosensors have been reported for

selective colorimetric sensing of Fe3+ (Table 1, 27), however, 1d/2d offered the

advantage of easy synthesis and high selectivity compared to reported molecules.

Mn2+ colorimetric sensors were mostly developed based on noble metal nanoparticles

such as silver (Ag) and gold nanoparticles (AuNPs) and molecular chemosensor for

Mn2+ was rarely reported [28].

Schiff base chemosensors were often exhibited selective turn-on fluorescence

for Zn2+ compared to other metal ions including Cd 2+ [6b,c,d,15b]. The coordination

of Zn2+ with imine nitrogen of Schiff bases that restricts the free rotation of C=N bond

and rigidify the fluorophore that is responsible for the strong fluorescence

enhancement [29]. However, transition metal ions such as Fe3+, Cu2+, Co 2+, Ni2+ and

Mn2+ usually forms strong and preferential coordination with Schiff bases and
 10

quenches the fluorescence due to the paramagnetic nature of metal ions. Hence these

metal ions might strongly affect the selectivity of Schiff base chemosensor. 1a-d and

2a-d chemosensors that differ by simple substitutional group offered an opportunity to

study the structure-property relationship on the fluorescence sensing and selectivity.

1a-d and 2a-d showed selective turn-on fluorescence for Zn2+ ions (Fig. 7a,

S6-8). Zn2+ addition exhibited almost 15 to 80 fold enhancements of fluorescence.

The fluorescence λmax of 1a-d and 2a-d with Zn2+ ions varied from 419 to 448 nm.

Among the eight chemosensors, 1b and 2b showed fluorescence enhancement for

Cd2+ ions also (20 fold, λmax = 418 nm) but the intensity was slightly lesser compared

with Zn2+ ion (30 fold, λmax = 418 nm). The fluorescence titration studies showed the

steady enhancement of fluorescence intensity by the addition of Zn2+ ions (10 -6 M,

Fig. 7b). The fluorescence enhancement was saturated by the addition of one

equivalent of Zn2+ and suggests the formation of 1:1 coordination complexes between

Zn2+ and chemosensors.

Although all chemosensor showed selective fluorescence sensing of only Zn2+,

they displayed different selectivity depend on the substitutional group. 1a and 2a did

not show any fluorescence turn-on with Zn2+ in presence of Co2+ (Fig. 8a, S9). Zn2+

addition showed only weak turn-on fluorescence was observed in presence of Mn2+

and Ni2+ metal ions. 1b,c and 2b,c selectivity was strongly affected by the presence

many transition metal ions such as Cr3+, Mn2+, Fe3+, Co 2+, Ni2+ and Cu2+ (Fig. 8b, 9a,

S9, S10). However, hydroxyl group substituted chemosensor 1d and 2d showed better

selectivity for Zn2+ in presence of other metal cations (Fig. 9b, S10) except Fe3+. It is

noted that 1d and 2d showed selective colorimetric changes for Fe3+ ions. Cr3+, Mn2+,

Hg2+ and Pb2+ did not show any significant influence on the fluorescence turn-on.

Although Co2+, Ni2+ and Cu 2+ metal ions presence exerted some influence, Zn2+
 11

addition showed considerable turn-on fluorescence intensity. Hence, the selectivity of

1a and 2a without any substitution on the phenyl ring was strongly influenced by

Co2+, Mn2+ and Ni2+. Electron donor group, methoxy and diethyl amino, substitution

(1b-c and 2b-c) lead to stronger and preferential coordination with many transition

metal ions (Cr3+, Mn2+, Fe3+, Co 2+, Ni2+ and Cu 2+. But a hydroxyl group substituted 1d

and 2d showed high selectivities in presence of other metal cations.

4. Conclusion

Naked-eye detectable colorimetric sensing of biologically important Mn2+ and

Fe3+ at ppm level was demonstrated by changing the substitutional group of simple

Schiff base chemosensors. A highly selective Mn2+ colorimetric sensing (colourless to

pink) was observed with 1c and 2c. Whereas hydroxyl group substituted chemosensor

1d and 2d showed selective colorimetric sensing of Fe3+ ions (colourless to orange).

The interference studies revealed the high selectivity for Mn2+ and Fe3+ by 1c/2c and

1d/2d, respectively. Thin films of PVA with chemosensor have been fabricated and

demonstrated the selective colorimetric sensing Mn2+/Fe3+ ions in water. The practical

applications of 2c/2d for selective sensing of Mn2+/Fe3+ in real samples such as tap,

ground, pond and river water have also been demonstrated. Substitutional group

dependent fluorescence selectivity for Zn2+ in presence of other metal ions has also

been demonstrated.

Acknowledgments

Financial supports from DST, New Delhi, India (DST Fast Track Scheme No.

SR/FT/CS-03/2011 (G), SASTRA University (TRR Scheme) and instrumentation

facility under CRF facility, SASTRA University are acknowledged with gratitude.

References
 12

[1] S. J. Lippard, J. M. Berg, Principles of Bioinorganic Chemistry; University

Science Books: Mill Valley, CA, (1994).

[2] a R. A. Bissel, A. P. De Silva, H. Q. N. Gunaratne, P. L. M. Lynch, G. E. M.

Maguire, C. P. McCoy, K. R. A. S. Sandanayake, Fluorescent (PET

(photoinduced electron transfer) sensors. Top. Curr. Chem., 168 (1993) 223-

264.

b R. Bergonzi, L. Fabbrizzi,M. Licchelli, C.Mangano, Molecular switches of

fluorescence operating through metal centred redox couples, Coord. Chem.

Rev., 170 (1998) 31-46.

[3] a P. D. Beer, P. A. Gale, Anion Recognition and Sensing: The State of the Art

and Future Perspectives. Angew. Chem., Int. Ed. 40 (2001) 486-516.

b K. Hanaoka, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, Selective

Detection of Zinc Ions with Novel Luminescent Lanthanide Probes. Angew.

Chem., Int. Ed. 42 (2003) 2996-2999.

c L. Gai, H. Chen, B. Zou, H. Lu, G. Lai, Z. Li, Z. Shen, Chem. Commun. 48

(2012) 10721-10723.

d X. Cheng, S. Li, H. Jia, A. Zhong, C. Zhong, J. Feng, J. Qin, Z. Li,

Fluorescent and Colorimetric Probes for Mercury(II): Tunable Structures of

Electron Donor and π-Conjugated Bridge. Chem. Eur. J. 18 (2012) 1691-1699.

e E. L. Que, D. W. Domaille, C. J. Chang, Metals in Neurobiology: Probing

Their Chemistry and Biology with Molecular Imaging, Chem. Rev. 108

(2008) 1517-1549.

f E. Galbraith, T. D. James, Boron based anion receptors as sensors, Chem. Soc.

Rev. 39 (2010) 3831-3842.

 13

g Z. C. Xu, J. Yoon, D. R. Spring, Fluorescent chemosensors for Zn2+. Chem.

Soc. Rev. 39 (2010) 1996-2006.

h C. McDonagh, C. S. Burke, B. D. MacCraith, Optical Chemical Sensors.

Chem. Rev. 108 (2008) 400-422.

[4] a N. Kaur, S. Kumar, Colorimetric metal ion sensors. Tetrahedron 67 (2011)

9233-9264.

b V. Kumar Guptaa, A. K. Singh, M. R. Ganjali, P. Norouzi, F. Faridbod, N.

Mergu, Comparative study of colorimetric sensors based on newly synthesized

Schiff bases. Sens. Actuators B: Chem. 182 (2013) 642-651.

c J. Cheng, K. Wei, X. Ma, X. Zhou, H. Xiang, Synthesis and Photophysical

Properties of Colorful Salen-Type Schiff Bases, J. Phys. Chem. C 117 (2013)

16552-16563.

d S. P. Anthony, Polymorph-dependent solid-state fluorescence and selective

metal-ion-sensor properties of 2-(2-hydroxyphenyl)-4(3H)-quinazolinone.

Chem. Asian J. 7 (2012) 374-379.

e P. S. Hariharan, A. Sivasubramanian, S. P. Anthony, Off-on Fluorescent

Sensor from On-off Sensor: Exploiting Silver Nanoparticles Influence on the

Organic Fluorophore Fluorescence. J. Fluoresc., 24 (2014) 319-327.

[5] Y. Xu, J. Meng, L. Meng, Y. Dong, Y. Cheng, C. Zhu, A Highly Selective

Fluorescence-Based Polymer Sensor Incorporating an (R,R)-Salen Moiety for

Zn2+ Detection. Chem. Eur. J. 16 (2010) 12898-12903.

[6] a H. Y. Shrivastava, B. U. Nair, A fluorescence-based assay for nanogram

quantification of proteins using a protein binding ligand. Anal. Bioanal. Chem.

375 (2003) 169-174.

 14

b Y. Zhou, H. N. Kim, J. Yoon, A selective ‘Off–On’ fluorescent sensor for

Zn2+ based on hydrazone–pyrene derivative and its application for imaging of

intracellular Zn2+. J. Bioorg. Med. Chem. Lett. 20 (2010) 125-128.

c W. H. Wu, J. F. Sun, S. M. Ji, W. T. Wu, J. Z. Zhao, H. M. Guo, Tuning the

emissive triplet excited states of platinum(II) Schiff base complexes

with pyrene, and application for luminescent oxygen sensing and triplet–

triplet-annihilation based upconversions. Dalton Trans. 40 (2011) 11550-

11561.

d Y. Dong, J. F. Li, X. X. Jiang, F. Y. Song, Y. X. Cheng, C. J. Zhu,

Na+ Triggered Fluorescence Sensors for Mg2+ Detection Based on a Coumarin

Salen Moiety. Org. Lett. 13 (2011) 2252-2255.

e C. Gou, S. H. Qin, H. Q. Wu, Y. Wang, J. Luo, X. Y. A. Liu, A highly

selective chemosensor for Cu2+ and Al3+ in two different ways based on

Salicylaldehyde Schiff. Inorg. Chem. Commun. 14 (2011) 1622-1625.

f V. K. Gupta, A. K. Singh, N. Mergu, Antipyrine based Schiff bases as Turn-

on Fluorescent sensors for Al(III) ion, Electrochimi. Acta 117 (2014) 405–

412.

g V. K. Gupta, A. K. Singh, S. Mehtab, B. Gupta, A cobalt(II)-selective PVC

membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-

diaminotoluene, Anal. Chim. Acta, 566 (2006) 5-10.

[7] a I. P. Oliveri, S. Di Bella, Sensitive Fluorescent Detection and Lewis Basicity

of Aliphatic Amines. J. Phys. Chem. A 115 (2011) 14325-14330.

b I. P. Oliveri, S. Di Bella, Highly sensitive fluorescent probe for detection of

alkaloids. Tetrahedron 67 (2011) 9446-9449.

 15

c Y. Feng, J. H. Cheng, L. Zhou, X. G. Zhou, H. F. Xiang, Ratiometric optical

oxygen sensing: a review in respect of material design. Analyst 137 (2012)

4885-4901.

d L. Zhou, Y. Feng, J. H. Cheng, N. Sun, X. G. Zhou, H. F. Xiang, Simple,

selective, and sensitive colorimetric and ratiometric fluorescence/

phosphorescence probes for platinum(II) based on Salen-type Schiff bases.

RSC Adv. 2 (2012) 10529-10536.

e S. M. Borisov, R. Saf, R. Fischer, I. Klimant, Synthesis and Properties of New

Phosphorescent Red Light-Excitable Platinum(II) and Palladium(II)

Complexes with Schiff Bases for Oxygen Sensing and Triplet–Triplet

Annihilation-Based Upconversion. Inorg. Chem. 52 (2013) 1206-1216.

[8] a M. J. O’Donnell, The Enantioselective Synthesis of α-Amino Acids by Phase-

Transfer Catalysis with Achiral Schiff Base Esters. Acc. Chem. Res. 37 (2004)

506-517.

b K. C. Gupta, A. K. Sutar, The Enantioselective Synthesis of α-Amino Acids

by Phase-Transfer Catalysis with Achiral Schiff Base Esters. Coord. Chem.

Rev. 252 (2008) 1420-1450.

c L. Canali, D. C. Sherrington, Utilisation of homogeneous and supported chiral

metal(salen) complexes in asymmetric catalysis. Chem. Soc. Rev. 28 (1999)

85-93.

[9] P. G. Cozzi, Metal–Salen Schiff base complexes in catalysis: practical aspects.

Chem. Soc. Rev. 33 (2004) 410-421.

[10] a P. G. Lacroix, Second-Order Optical Nonlinearities in Coordination

Chemistry: The Case of Bis(salicylaldiminato)metal Schiff Base Complexes.

Eur. J. Inorg. Chem. (2001) 339-348.

 16

b E. Hadjoudis, I. M. Mavridis, Photochromism and thermochromism of Schiff

bases in the solid state: structural aspects. Chem. Soc. Rev. 33 (2004) 579-

588.

[11] H. Miyasaka, A. Saitoh, S. Abe, Magnetic assemblies based on Mn(III) salen

analogues. Coord. Chem. Rev. 251 (2007) 2622-2664.

[12] a G. Yu, Y. Q. Liu, Y. R. Song, X. Wu, D. B. Zhu, A new blue light-emitting

material. Synth. Met. 117 (2001) 211-214.

b K. H. Chang, C. C. Huang, Y. H. Liu, Y. H. Hu, P. T. Chou, Y. C. Lin,

Synthesis of photo-luminescent Zn(II) Schiff base complexes and its

derivative containing Pd(II) moiety, Dalton Trans. (2004) 1731-1738.

[13] a Q. F. Hou, L. Y. Zhao, H. Y. Zhang, Y. Wang, S. M. Jiang, Synthesis and

luminescent properties of two Schiff-base boron complexes, J. Lumin. 126

(2007) 447-451.

b Y. Zhou, J. W. Kim, M. J. Kim, W. J. Son, S. J. Han, H. N. Kim, S. Han, Y.

Kim, C. Lee, S. J. Kim, D. H. Kim, J. J. Kim, J. Yoon, Novel Bi-Nuclear

Boron Complex with Pyrene Ligand: Red-Light Emitting as well as Electron

Transporting Material in Organic Light-Emitting Diodes, Org. Lett. 12 (2010)

1272-1275.

c Y. Zhou, J. W. Kim, R. Nandhakumar, M. J. Kim, E. Cho, Y. S. Kim, Y. H.

Jang, C. Lee, S. Han, K. M. Kim, J. J. Kim, J. Yoon, Novel binaphthyl-

containing bi-nuclear boron complex with low concentration quenching effect

for efficient organic light-emitting diodes, Chem. Commun. 46 (2010) 6512-

6514.

[14] a K. Y. Hwang, M. H. Lee, H. Jang, Y. Sung, J. S. Lee, S. H. Kim, Y. Do,

 17

Aluminium–salen luminophores as new hole-blocking materials for

phosphorescent OLEDs, Dalton Trans. (2008) 1818-1820.

b J. O. Huh, M. H. Lee, H.Jang, K. Y. Hwang, J. S. Lee, S. H. Kim, Y. Do,

A Novel Solution-Processible Heterodinuclear AlIII/IrIII Complex for

Host−Dopant Assembly OLEDs, Inorg. Chem. 47 (2008) 6566-6568.

c K. Y. Hwang, H. Kim, Y. S. Lee, M. H. Lee, Y. Do, Synthesis and Properties

of Salen–Aluminum Complexes as a Novel Class of Color-Tunable

Luminophores, Chem. Eur. J. 15 (2009) 6478-6487.

[15] a C. M. Che, S. C. Chan, H. F. Xiang, M. C. W. Chan, Y. Liu, Y. Wang,

Tetradentate Schiff base platinum(II) complexes as new class of

phosphorescent materials for high-efficiency and white-light

electroluminescent devices, Chem. Commun. (2004) 1484-1485.

b H. F. Xiang, S. C. Chan, K. K. Y. Wu, C. M. Che, P. T. Lai, High-efficiency

red electrophosphorescence based on neutral bis(pyrrole)-diimine platinum(II)

complex, Chem. Commun. (2005) 1408-1410.

c J. Zhang, F. C. Zhao, X. J. Zhu, W. K. Wong, D. G. Ma, W. Y. Wong, New

phosphorescent platinum(II) Schiff base complexes for PHOLED applications,

J. Mater. Chem. 22 (2012) 16448−16457.

[16] a D. Udhayakumari, S. Saravanamoorthy, M. Ashok and S. Velmathi, Simple

imine linked colorimetric and fluorescent receptor for sensing Zn2+ ions in

aqueous medium based on inhibition of ESIPT mechanism, Tetrahedron Lett.

52 (2011) 4631-4635.

b S. C. Wang, G. W. Men, L. Y. Zhao, Q. F. Hou, S. M. Jiang, Binaphthyl-

derived salicylidene Schiff base for dual-channel sensing of Cu, Zn cations

 18

and integrated molecular logic gates, Sens. Actuators B: Chem. 145 (2010)

826-831.

c J. Cheng, Y. Zhang, X. Ma, X. Zhou, H. Xiang, Colorimetric and fluorescent

pH and Cu2+ probes induced by photoisomerization of a maleonitrile-based

Salen ligand, Chem. Commun., 49 (2013) 11791-11793.

[17] X. Qian, Y. Xiao, Y. Xu, X. Guo, J. Qiana and W. Zhu, “Alive” dyes as

fluorescent sensors: fluorophore, mechanism, receptorand images in

living cells, Chem. Commun. 46 (2010) 6418-6436.

[18] a W. L. Leong, J. J. Vittal, One-Dimensional Coordination Polymers:

Complexity and Diversity in Structures, Properties, and Applications,

Chem. Rev. 111 (2011) 688-764.

b C.-P. Li, M. Du, Role of solvents in coordination supramolecular systems,

Chem. Commun. 47 (2011) 5958-5972.

c S. P. Anthony, T. P. Radhakrishnan, Coordination Polymers of Cu(I) with a

Chiral Push−Pull Ligand:  Hierarchical Network Structures and Second

Harmonic Generation, Crystal Growth & Design 4 (2004) 1223-1227.

[19] a H. Diehl, C. C. Hach, "Bis(N,N'-Disalicylalethylenediamine)-µ-

Aquodicobalt(II)". Inorg. Synth. 3 (1950) 196–201.

b S. M. Devidas, S. H. Quadri, S. A. Kamble, F. M. Syed, D. Y. Vyavhare,

Novel One-Pot Synthesis of Schiff Base Compounds Derived From Different

Diamine & Aromatic Aldehyde Catalyzed by P2O5/SiO2 Under Free-Solvent

Condition at Room Temperature, J. Chem. Pharm. Res., 3 (2011) 489-495.

[20] a L. Zhou, P. Y. Cai, Y. Feng, J. H. Cheng, H. F. Xiang, J. Liu, D. Wu, X. G.

Zhou, Synthesis and photophysical properties of water-soluble sulfonato-

 19

Salen-type Schiff bases and their applications of fluorescence sensors for

Cu2+ in water and living cells, Anal. Chim. Acta 735 (2012) 96-106.

b J. H. Cheng, K. Y. Wei, X. F. Ma, X. G. Zhou, H. F. Xiang, Synthesis and

Photophysical Properties of Colorful Salen-Type Schiff Bases, J. Phys. Chem.

C 2013, 117, 16552-16563.

[21] R. C.G. Martin, Y. Li, Q. Liu, N. S. Jensen, D. F. Barker, M. A. Doll, D. W.

Hein, Manganese Superoxide Dismutase V16A Single-Nucleotide

Polymorphism in the Mitochondrial Targeting Sequence Is Associated with

Reduced Enzymatic Activity in Cryopreserved Human Hepatocytes, DNA

Cell Biol. 28 (2009) 3-7.

[22] C. B. Black, B. Andrioletti, A. C. Try, C. Ruiperez, J. L. Sessler,

Dipyrrolylquinoxalines:  Efficient Sensors for Fluoride Anion in Organic

Solution, J. Am. Chem. Soc. 121 (1999) 10438-10439.

[23] T. P. Yoon, E. N. Jacobsen, Privileged Chiral Catalysts, Science, 299 (2003)

1691-1693.

[24] P.S.Hariharan, S. P. Anthony, Selective turn-on fluorescence for Zn2+ and

Zn2+ + Cd2+ metal ions by single Schiff base chemosensor, Analytica Chimica

Acta, 848 (2014) 74-79.

[25] J.J.R. Fausto da Silva, R.J.P. Williams, The Biological Chemistry of the

Elements, Oxford University, New York, (1992).

[26] C. Brugnara, Iron deficiency and erythropoiesis: new diagnostic approaches.

Clin. Chem. 49 (2003) 1573-1578.

[27] a H. J. Jung, N. Singh, D. Y. Lee, D. O. Jang, Single sensor for multiple

analytes: chromogenic detection of I- and fluorescent detection of Fe3+,

Tetrahedron Letters 51 (2010) 3962–3965.

 20

b K. P. Nandrea, A. L. Puyad, S. V. Bhosale, S. V. Bhosale, A novel donor-

acceptor receptor for selective detection of Pb(2+) and Fe(3+) ions, Talanta 130

(2014) 103–107.

c T.-B. Wei, P. Zhang, B.-B. Shi, P. Chen, Q. Lin, J. Liu, Y.-M. Zhang, A

highly selective chemosensor for colorimetric detection of Fe3+ and

fluorescence turn-on response of Zn2+, Dyes and Pigments 97 (2013) 297-302.

d D. Wei, Y. Sun, J. Yin, G. Wei, Y. Du, Design and application of Fe3+ probe

for “naked-eye” colorimetric detection in fully aqueous system, Sensors and

Actuators B 160 (2011) 1316– 1321.

e S. Devaraj, Y.-K Tsui, C.-Y. Chiang, Y.-P. Yen, A new dual functional

sensor: Highly selective colorimetric chemosensor for Fe3+ and fluorescent

sensor for Mg2+, Spectrochimica Acta Part A, 96 (2012) 594–599

[28] a Y. Zhou, H. Zhao, C. Li, P. He, W. Peng, L. Yuan, L. Zeng, Y. He,

Colorimetric detection of Mn2+ using silver nanoparticles co-functionalized

with 4-mercaptobenzoic acid and melamine as a probe, Talanta 97 (2012)

331–335.

b Y.-X. Gao, J.-W. Xin, Z.-Y. Shen, W. Pan, X. Li, A.-G. Wu, A new rapid

colorimetric detection method of Mn2+ based on tripolyphosphate modified

silver nanoparticles, Sensors and Actuators B 181 (2013) 288– 293.

[29] J.-S. Wu, W.-M. Liu, X.-Q. Zhuang, F. Wang, P.-F. Wang, S.-L. Tao, X.-H.

Zhang, S.-K. Wu, S.-T. Lee, Fluorescence Turn On of Coumarin Derivatives

by Metal Cations:  A New Signaling Mechanism Based on C=N

Isomerization, Org. Lett. 9 (2007) 33-36.

 21

Figure Caption

Scheme 1. Molecular structures of Schiff base chemosensors.

Figure 1. Absorption spectra of chemosensors in DMF.

Figure 2. Digital and absorption spectra of chemosensors (10 -6 M) (a, b) 1c and

(c, d) 2c with different metal ions (10-3 M).

Figure 3. (a) Absorption change of 2c Vs Mn2+ concentration (10-6 M) and (b)

interference studies of other metal ions (10-3 M) on the selectivity of

Mn2+.

Figure 4. Digital and absorption spectra of chemosensors with different metal

ions (a, b) 1d and (c, d) 2d.

Figure 5. (a) Absorption change of 2d Vs Fe3+ concentration (10-6 M) and (b)

interference studies of other metal ions (10-3 M) on the selectivity of

Fe3+.

Figure 6. Digital image of PVA-chemosensor colour change with Mn2+ and Fe3+.

Figure 7. (a) Fluorescence spectra of 1a with different metal ions and (b) change

of fluorescence Vs concentration of Zn2+ (λex = 340 nm).

Figure 8. (a) 1a and (b) 1b selectivity of Zn2+ in presence of other metal cations.

(black bar = 1a and 1b with different metal ions (10 -3 M) and red bar =

after the addition of Zn2+ (10-6 M)).

Figure 9. (a) 1c and (b) 1d selectivity of Zn2+ in presence of other metal cations

(black bar = 1a and 1b with different metal ions (10 -3 M) and red bar =

after the addition of Zn2+ (10-6 M)).

Table 1. Structure of some of the previously reported colorimetric chemosensor

for Fe3+ ions.

 22

Table 1

Compound
OH

structure N
O
N

HO
HO O
N OH N
OH

N
N
N OH O O OH
N
HO
OH

S S CH3

Reference 27a 27b 27c 27d 27e

 23

Scheme 1

Figure 1
 24

Figure 2
 25

Figure 3
 26

Figure 4
 27

Figure 5
 28

Figure 6

Figure 7
 29

Figure 8
 30

Figure 9
 31

Schiff base based Colori/fluorimetric chemosensor for sensing Mn2+, Fe3+ and
Zn2+ ions: Effect of structural change on the selectivity of metal ions

Schiff base based chemosensor exhibited substitutional group dependent

fluoro/colorimetric sensing of metal ions and selectivity.
 32

Highlights

• Simple Schiff base colorimetric sensor for Mn2+ and Fe3+ ions.

• Role of substitutional group on colorimetric detection of Mn2+/Fe3+.

• Sensing of Mn2+/Fe3+ using PVA chemosensor composite film.

• Fluorescence sensing of Zn2+ ions and substitutional group dependent

selectivity.