Multi-step synthesis, photophysical and physicochemical investigation of novel pyrazoline a heterocyclic D- π -A chromophore as a fluorescent chemosensor for the detection of Fe3+ metal ion

Journal Pre-proof Multi-step synthesis, photophysical and physicochemical investigation of novel pyrazoline a heterocyclic D- π -A chromophore as a fluorescent chemosensor for the 3+ detection of Fe metal ion Salman A. Khan PII:

S0022-2860(20)30409-9

DOI:

https://doi.org/10.1016/j.molstruc.2020.128084

Reference:

MOLSTR 128084

To appear in:

Journal of Molecular Structure

Received Date: 27 January 2020 Revised Date:

9 March 2020

Accepted Date: 15 March 2020

Please cite this article as: S.A. Khan, Multi-step synthesis, photophysical and physicochemical investigation of novel pyrazoline a heterocyclic D- π -A chromophore as a fluorescent chemosensor 3+ for the detection of Fe metal ion, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/ j.molstruc.2020.128084. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier B.V.

I have done all the experimental and writing work of this manuscript with myself.

Dr. Salman A Khan Associate Professor Department of Chemistry, King Abdulaziz University, Jeddah Saudi Arabia

Multi-step synthesis, photophysical and physicochemical investigation of novel pyrazoline a heterocyclic D- π -A chromophore as a fluorescent chemosensor for the detection of Fe3+ metal ion Salman A Khan,* Department of Chemistry, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589, Saudi Arabia *Correspondence Author e-mail adders: [email protected] (S. A. Khan)

500 450

Dye 2+ Cu 2+ Sr 2+ Sn 2+ Cd 2+ Co 3+ Cr 2+ Zn 2+ Mn 3+ Al 3+ Fe

350 300 250 200 150 100 50 0

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Wavelength (nm)

600

500 0.0 eq

400 Emission Intensity

Emission Intensity

400

300 9.0 eq.

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100

650

0

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Wavelength (nm)

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Multi-step synthesis, photophysical and physicochemical investigation of novel pyrazoline a heterocyclic D- π -A chromophore as a fluorescent chemosensor for the detection of Fe3+ metal ion Salman A. Khan,* Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia Correspondence Author e-mail: [email protected] (S. A. Khan) Abstract: The title compound has been 2-(1-(benzo[d]thiazol-2-yl)-5-(3,4-dimethoxyphenyl)-4,5-dihydro1H-pyrazol-3-yl)phenol (BTDP) synthesized by reaction of (E)-3-(3,4-dimethoxyphenyl)-1-(2hydroxyphenyl)prop-2-en-1-one (DMPO)

with 2-Hydrazinylbenzo[d]thiazole. DMPO was

synthesized

1-(2

by

the

reaction

of

hydroxyphenyl)ethan-1-one

with

3,4-

dimethoxybenzaldehyde. Structure of compound has been confirmed by the elemental analysis and spectroscopic techniques (FT-IR, 1H-NMR and

13

C-NMR). Photophysical properties of the

BTDP such as absorption, emission, stokes shift, transition dipole moments and fluorescence quantum yield have been studied in various solvents of different polarity and chromophore demonstrated positive solvatochromism. The chromophore undergoes micellization in two different micelles and its can be used as probe to determine the critical micelle concentration of surfactant such as CTAB and SDS.

In addition, Pyrazoline derivative used as fluorescent

chemosensor for metal ion selectively based on fluorometric detraction and pyrazoline displayed as on-off fluorescence chemosensor for the determination of Fe3+ ion in solution. Hildebrand, Stern-Volmer and job’s plot method has described quenching behavior of chromophore with Fe3+ ion. Keywords: Pyrazoline; Photophysical; Stokes shift; CMC; Metal ion.

1

1. Introduction Five membered heterocyclic compounds with special reference of nitrogen containing compounds such as pyrrole, pyrazole and pyrazoline are biologically active compounds [1]. Pyrazoline is one of the most importance heterocyclic containing with two adjacent nitrogen atoms and one endocyclic double bond. Pyrazolines have been used in the various filed of medicinal chemistry such as antibacterial [2], anticancer [3], antitumor, anti-HIV, antiinflammatory and many other activities [4, 5]. Nowadays pyrazolines systems, as biomolecules have attracted more attention due to their interesting pharmacological properties. Pyrazoline heterocyclic usually gives the blue fluorescence in the solution stage with high fluorescence quantum yield due to having the intramolecular charge transfer character. Due to their highly fluorescence properties, they are widely used in the field of material science such as hole transfer material [6], organic light emitting

diodes [7], dye synthesized solar sell [8],

electroluminescence and optical limiting [9]. Pyrazoline heterocyclic ring used as acceptor when electron donor group such as N-CH3, OH, OCH3 containing with long π- bond conjugated system are joint with the pyrazoline ring the whole molecule is known as donor (D) –π-Acceptor (A) chromophore. Donor group containing with long pi bond conjugation pyrazoline might be enhanced the fluorescence of the molecule due the intramolacular charge transfer from donor group to the pyrazoline ring. Photophysical and physical chemical properties such as absorption, emission, stokes shift, transition dipole moments, oscillator strength and fluorescence quantum yield are very important parameters of the compound with the help of these parameters we can identify physical behavior of the chromophore [10]. Fluorescent chemosensor for numerous analyses have been paid much consideration by analysis because of its sooner analytical time and prospective cost [11]. Fluorescent chemosensor have a number of pluses as well as ease of

2

detection, sensitivity and low cast techniques as compare to other. A number of organic compounds such as chalcone, Schiff base, imidazole, pyridine and quinolone have been used as fluorescent chemosensors for the detection of metal ions [12-16]. Iron is the fourth greatest copious element in the world, is one of the most important element for human bodies which is danger in our body either overdose or deficiency. Its play various important role in human bodies such as oxygen transportation in form of oxyhemoglobin. In particular, iron ion in blood can promote the formation of red blood proteins and the lack of iron can lead to anemia. However excess iron contents may also impair biological systems because its redox active from catalyzes the generation of highly reactive oxygen species, which involves in kinds of diseases including Parkinson syndrome Alzheimer’s disease and cancer [17]. Therefore, the development of selective and sensitive fluorescent chemosensor for iron has enticed consideration and numerous fluorescence molecular structures have been designed for the sensing of iron by chelation. [18,19]. Due to important of the iron in present paper myself design and synthesized hydroxyl pyrazoline by the multistep reaction with photophysical and physicochemical properties and it’s used as fluorescent chemosensor for the detection of Fe3+ ion. 2. Experimental 2.1.Chemicals and reagents All the chemicals 3,4-dimethyoxy benzaldehyde, 2-hydroxy acetophenone, sodium hydroxide, 1phenyl thiourea were purchased from Acros Organic. All the other chemical and solvents were used for this experiment were analytical grade and used as received. The stock solution of the pyrazoline (BTDP) was prepared in DMF, CTAB, SDS and ten different metal salts were prepared in double distilled water.

2-Hydrazinyl benzothiazole and chalcone have been

synthesized in pervious paper [20] (Scheme 1). 3

2.2.Equipment Silica gel 60 F254 coted thin-layer chromatography (TLC) plate was used to conformed the purity of the synthesized compound. The melting points of the newly synthesize pyrazoline compound was on a Stuart Scientific Co. Ltd melting point apparatus. FTIR measurement of the pyrazoline derivative was recorded with Perkin-Elmer 100 FT-IR spectrometer. Proton and carbon NMR spectra of the pyrazoline compound was recorded at 600/ 125 MHz on Bruker AVANCE in DMSO-d6 as deuterated solvent. The UV-vis absorbance and emission spectra of the pyrazoline derivative were recorded with Shimadzu UV-16550PCUV/VIS spectrophotometer and Shimadzu RF 5301 PC spectrofluorophotometer. 2.3. Synthesis

of

2-(1-(benzo[d]thiazol-2-yl)-5-(3,4-dimethoxyphenyl)-4,5-dihydro-1H-

pyrazol-3-yl)phenol (BTDP) A mixture of hydroxyl chalcone and 2-hydrazinyl benzothiazole was dissolved in 15 ml EtOH then NaOH was added to the reaction mixture and refluxed for 5 h. The improvement of the reaction was monitored by the TLC. When reaction was completed the reaction mixture allowed cool at room temperature. The precipitate formed was filtered off washed with cooled EtOH and water and then dried to give pyrazoline (BTDP) [21]. Brown Crystal: % yields: 78.56%; IR : 3428 (O-H), 3029 (C-Hst), 2965 (C-Hst), 1629 (C=N), 1591 (C=C), 1434 (C-N), 1224 (C-S); 1HNMR (600MHz, DMSO-d6, ppm) `: 11.16 (s, 1H, OH), 8.06 (d, 1H, CHAromatic, J = 7.2 Hz), 7.92 (dd, 1H, CHAromatic, J = 6.8 Hz), 7.81( dd, 1H, CHAromatic, J = 4.2 Hz), 7.68 (d, 1H, CHAromatic, J = 7.2Hz), 7.53 (d, 1H, CHBenzothiazole, J = 6.8Hz), 7.41 (dd, 1H, CHBenzothiazole, J = 3.4 Hz), 7.36 (s, 1H, CHAromatic) 7.08 (dd, 1H, CHBenzothiazole, J = 4.2 Hz), 6.93 (d, 1H, CHBenzothiazole, J = 6.8Hz), 5.73 (dd, CHX, JXA = 5.2 , JXB

4

= 5.6 Hz), 4.45 (dd, CHA, JAB = 6.8, JAX = 6.8 Hz), 3.46 (dd, CHB, JBA = 4.0, JBX = 4.0 Hz), 3.95 (s, 3H, OCH3), 3.91 (s, 3H, OCH3).

13

C-NMR (125 MHz, DMSO-d6): 164.23 (C=N,

benzothiazolyl), 153.68 (C=N, pyrazoline ring), 144.32 (C-N), 135.92, 135.17, 134.19, 133.83, 131.21, 130.63, 128.24, 126.10, 125.81, 124.36, 123.67, 122.18, 121.78, 119.23, (C-Aromatic), Anal. Calc. for C24H21N3S: C, 66.80, H, 4.91, N, 9.74. Found: C, 66.72, H, 4.88, N, 9.68. 3. Result and discussion 3.1.Chemistry: Bezothiazole pyrazoline was obtained by the reaction of chalcone with 2-hydrazinobenzothiazole in EtOH in the presence of catalytic amount of NaOH at reflex (Scheme 2). The formation of the pyrazoline ring due the nucleophilic substitution reaction. The structure of the pyrazoline derivative was assigned by analysis of the spectral data including IR, 1H-NMR,

13

C-NMR, and

purity of the compound was confirmed by the elemental analysis. The IR spectra of the pyrazoline exhibited absorption peak at 3029 cm-1 for aromatic stretching 2965 cm-1 for C-H stretching in ethyl group, 1629 cm-1 for C=N stretching in benzothiazole 1591 cm-1 for C=C, 1542 cm-1 for C=N stretching for pyrazoline ring, 1434 cm-1 for C-N stretching and 1224 for C-S stretching. The structure of the compound further conformed by the 1H-NMR and

13

C-NMR

spectra. The protons attached to the C-4 and C-5 carbon atoms of the five membered ring gave ABX spin system.1H-NMR spectra showed tree doublet at δ 5.73, 4.45 and 3.46 of the proton Hx, Ha and Hb as shown in Scheme 1. Hx showed at δ 5.73 as doublet of doublet due to coupling with adjacent protone Ha and Hb with the coupling constant (J) equal to 5.6 and 5.2 Hz respectively. The other two methylene protons (Ha and Hb) showed doublet of doublet at δ 4.45 and δ 3.46 due to coupling with Ha and Hb and Ha with Hx. The coupling constant value equal to 6.8 Hz when Ha couple with Hb and 6.8 Hz when couple with Hx. As similar the coupling constant Hb equal to 4.0 5

Hz when couple with Ha and 4.0 Hz when couple with Hz consequently. These chemical shifts proved the formation of pyrazoline moiety.

The 1H-NMR spectra of aromatic protons of

compound showed singlet, doublet and double doublet at region δ 6.93-8.06 (C-HAromatic). The 13

C NMR spectrum of pyrazoline was measured at 125 MHz in DMSO-d6. The spectral pecks are

in good conformity with the molecular structure information and the details of the signals are given in the synthesis section. 13C-NMR spectra of showed downfield resonances at δ 164.23 is due to (C-N) benzothiazolyl, 153.68 is due to (C=N) pyrazoline ring and 144.32 is due to (C-N) pyrazoline ring. Other resonances in the aromatic region were placed at region δ 135.92-119.23 (Ar-C). Finally structure of the pyrazoline was confirmed by the elemental analysis. 3.2.Photophysical properties of BTDP as donor acceptor chromophore Figure 1, shows the normalized UV-vis spectrum of the BTDP in ten different solvent such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), ethanol (EtOH), methanol(MeOH), chloroform (CHCl3), dicholoro methane (CH2Cl2), acetonitrile (CH3CN), 1,4-dioxane, Ethylene glycol (Elgy) and n-Hexane have shown in Figure 1. Maximum absorption band of the BTDP were significantly affected on the polarity of the solvents. The absorption maxima of the BTDP shifted to longer wavelength red shift 12 nm from n-hexane (344 nm) to DMSO (356 nm) (bathochromic shift) and intensity of the absorption increased (hyperchromic shift) when polarity of the solvent increased indicating the BTDP chromophore has more polar nature in ground state. The molar absorption coefficient (Ɛ) also effected with the polarities of the solvents its value were presented in Table 1. As expected bathochromic shift is due to intramolecular charge transfer (ICT) from donor group (Methoxy) to acceptor group (pyrazole ring) [22]. On excitation at 350 nm, the fluorescence spectrums of the BTDP were strongly correlates with the polarities of the solvents. As shown in Figure 2, the BTDP chromophore displayed one broad 6

band which characterized electronic transition from S1 to So. It was examined that the bathochromic shift in the emission maxima with the polarity of the solvent increases 26 nm from n-Hexane (428 nm) to DMSO (454 nm) were more than the bathochromic shift in the emission maxima (Table 1). The excited state energy of BTDP chromophore was more affected with solvent polarities as compared to the ground state energy of the BTDP indicated due to the π-π* transition [23]. The empirical Dimroth polarity parameters ET(30) of the different solvent correlate with the absorption energy (Ea) and emission energy (EF) of the BTDP in various solvent as mention in Figure 3. One dimensional correlation between different polarity of solvent and absorption, emission energy were acquired by the following equations [24]. Ea= 81.76 – 0.022x ET(30)

(1)

Ef = 69.84 – 0.078 x ET(30)

(2)

3.3.Determination of transition dipole moment and oscillator strength The solvatochromic behavior of BTDP enable to determine the different dipole moments between the singlet excited state and ground state ∆µ = µe–µg. Lippert-Mataga equation can be used to obtain these variations on the optical properties of BTDP [25]. ∆ν st

= ν abs −ν em =

2∆µ 2 ∆f + Const. h c a3

(3)

where, ∆ν st is represent the stokes shift as mention in the Table 1, the value of stokes shift increasing with increasing the polarity of the solvents (n-Hexane to DMSO), signifying strong

7

stabilization of excited state in polar solvent, h is the plank constant, a is the raids cavity, c is the velocity of light and ∆f is the orientation polarizability of the different solvents have explained by following equation (eq. 4). ∆f =

ε −1 η 2 −1 − 2ε + 1 2η 2 + 1

(4)

where η and ε are the refractive index of the solvents and dielectric constant correspondingly. The plot of stokes shift ( ∆ν st ) versus orientation polarizability (∆f) as showed Figure 4. The linear associations between orientation polarizability versus stokes shift identified that stokes shift was dependent on the polarity of the solvents’ or polarizability. The dipole moments ( ∆µ ) different between ground and excited state of BTDP was calculated by using Lippert –Mataga equation (3). At the Equation 3 the a is the cavity radius of the BTDP was estimated by the following equation (5)

 3M   a =   4Nπ d 

1/ 3

(5)

where, N is the Avigadro number, M is molecular mass and d is the assumed density of the chromophore of 1g / cm3. The different dipole moment of BTDP was found 2.96 Debye (Figure 4). Positive vale indicated that excited state is more polar than ground state [26]. The transition dipole moments of the BTDP chromophore between ground state and excited state in different solvent were calculates as following equation (eq. 6) [27]. The values were listed in Table 1.

µ2 =

f 4.72 × 10 −7 E max

( 6)

8

where f is the oscillator strength and Emax is the maximum energy of the absorption in cm-1. The oscillator strength (f) of the BTDP chromophore in different solvent were calculated by the following equation [28] (7); f = 4.32 × 10 −9 ∫ ε (ν ) dν

(7 )

where Ɛ is the dielectric constant (M-1cm-1) and ν is the wavenumber (cm-1). The calculated values of the oscillator strength (f) in different solvent were present in the Table 1. The oscillator strength of the BTDP was directly dependent to the polarity of the solvent.

3.4.Fluorescence quantum yields of BTDP The fluorescence quantum yields (ɸf) of the pyrazoline (BTDP) in different solvents were calculated with the reference of the standard dye (Quinine sulphate ɸr = 0.55 in 0.1 M H2SO4 solution). The flowing equation was applied for the calculation of fluorescence quantum yields (ɸf) for the BTDP [29].

Φ

f

I x Ar x n 2 = Φr Ir x A x n 2r

(8)

where ɸf is the calculated fluorescence quantum yields of the BTDP in different solvent, ɸr is the fluorescence quantum yield of the Quinine sulphate as standard dye, I is the integrated emission intensity, A is the absorbance of BTDP and reference dye at the excited wavelength and n is the refractive index of the solvent. The fluorescence quantum yield (ɸf) of BTDP depending on the polarity of the solvents, because the fluorescence spectra have an effected on solvent polarity. The value ɸf in different solvents were listed in Table 1. In addition the relationship between of value fluorescence quantum yield of the BTDP in different solvents and ET(30) of the different solvent were shown in Figure 5,

9

where ET(30) is the solvent polarity parameter identified by Reichardt [30]. The obtained data displayed that significantly dependent to the solvent properties such as polarizabilty and hydrogen bonding. The fluorescence quantum yield increased when solvent polarity increased (0.32 in n-Hexane to 0.51 in DMSO). This phenomenon can be explained by the negative solvatokinetic effects. The hydrogen bonding between the solvent and methoxy pyrazoline group of the BTDP is accounted for the reduction of ɸf in Ethylene glycol due to enhance radiation less processes. The reduction in ɸf going from the DMSO to polarprotic solvent like Ethylene glycol (positive solvatokinetic effect) can be attributed to strong ICT interaction. The fluorescence quantum yield value of the BTDP dye strongly decreases in highly proton donor solvent due to the intermolecular hydrogen bonding interaction between the solvent and excited dye. 3.5. Effect of surfactant on BTDP chromophore

The effect of the cationic and anionic surfactants such as cetyl trimethyl ammonium bromide (CTAB) and Sodium dodecyl sulphate (SDS) on the fluorescence spectrum of BTDP dye. The chosen of these two specific surfactants due to the ionic charged obsessed by the BTDP can be prejudiced by the positively charged and negatively charged surfactant. Thus, the emission behavior of the TCPT dye was based on the charge interaction between BTDP dye with CTAB or SDS. The fluorescence emission spectrum of the BTDP was measured in the absence of the CTAB and SDS. The fluorescence intensity of the BTDP increases with increase the concentration of the both type of the surfactants. The emission intensity of the BTDP increase with increases the concentration of CTAB (1 x 10-4 to 1.8 x 10-3 M) and as same the fluorescence intensity of the BTDP increases with increasing the concentrations of the SDS (2 x 10-3 to 1.8 x 10-2 M) such enrichment of the fluorescence strength of 1x 10-5 M of BTDP at unchanging molar concentration with an increase the concentration of the CTAB and SDS might probable be

10

recognized to the association mechanism of the BTDP dye with CTAB and SDS as presented in the Figure 6 & Figure 7. The fluorescence band maximum observed at 478 nm in water and blue shifted 28 nm and 30 nm on adding the CTAB and SDS, respectively. This shift is accompanied by a uniform increasing the emission intensity. It has been shown that BTDP possess ICT excited state; therefore lowering the polarity of the medium destabilizes this state more than the ground state. As a consequence energy gap between the emitting and ground stare increases, thus the emission maximum is shifted to the blue side. This shift is also accompanied by greater enhancement of emission with increasing the concentration of CTAB and SDS. As the probe enters the micelle from bulk water the hydrogen bond gets broken in less polar hydrophobic environment [31]. Present of different concentration of the CTAB and SDS with sudden change the intensity of the fluorescence spectra of BTDP taking place at surfactant concentration 7.96 x 10-4 and 6.34 x 10-3mol dm-3, which are very near to critical micelle concentration of the CTAB and SDS surfactant [32] Figure 8 and Figure 9. Thus the molecules BTDP can be used as probe analyzes the CMC of the cationic and anionic surfactants. 3.6.Sensitive fluorescent chemosensor of BTDP for metal ion

In order to examined the selective and sensitive chemosensor behavior of pyrazoline derivative (BTDP) for ten different metal cations by the fluorescence spectra. The effect of the ten different metal ions namely Cu2+, Sr2+, Sn2+, Cd2+, Co2+, Cr3+, Zn2+, Mn2+, Al3+ and Fe3+ on the photophysical properties of the hydroxy chalcone BTDP in the DMF/ Water (9:1, V/V). Emission spectra of BTDP displayed extremely good peak when excited at 350 nm wavelength and no significant effect on the fluorescence intensity after addition of 9 eqiv of metal ion Cu2+, Sr2+, Sn2+, Cd2+, Co2+, Cr3+, Zn2+, Mn2+ and Al3+ as shown in Figure 10. On the other hand upon addition of equivalent amount of Fe3+ metal ion to the BTDP, the fluorescence intensity 11

decreased the fluorescence intensity 7-fold and the fluorescence color also changing from greenish blue-green to brown like an on-off fluorescence response as presented in Figure 11. The fluorescence quantum yield of BTDP in the absence of Fe3+ metal ion was calculated to be 0.46 and fluorescence quantum yield of BTDP was calculated to be 0.075 in the presence of Fe3+ metal ion, which is greatly lower than the absence of Fe3+ metal ion. This fluorescence quenching performance was examined due to chelation-enhanced quenching sensing mechanism (Scheme 3) [33]. To further gauge selectivity for Fe3+ ion over other metal ion competition experiments of Fe3+ ion mixed with other metal ion were carried out from fluorescence spectra and the result are shown in Figure 12. The fluorescence intensity of Fe3+ ion was almost unaffected by the addition of competing metal ion (Cu2+, Sr2+, Sn2+, Cd2+, Co2+, Cr3+, Zn2+, Mn2+ and Al3+). These results suggested that molecules BTDP could be used as Fe3+ selective fluorescent chemosensor. The fluorescence quenching activities of the Fe3+ was explored during emission spectrum of BTDP upon Fe3+ ion was gradually titrated (Figure. 13). The fluorescence intensity of the BTDP gradually decreased with increased the concentration of the Fe3+ metal ion and when the mount of Fe3+ added was about 9 x 10-5 M, the fluoresce intensity of the BTDP almost reached a minimum due to utilized of BTDP for the complexation with Fe3+ metal ion. Initially the fluorescence intensity of BTDP was quickly reduced after addition of low concentration of ranges of Fe3+ as presented in Figure 14 and in the range 1 to 5 x 10-5 M its showed good linear response (R = 0.97), which was capable to quantitatively analyzed the coordination of the Fe3+ metal ion with BTDP molecule. To explore the association constant and binding stoichimerty between the BTDP with Fe3+ metal ion, which is fundamental in relation to the fluorescence chemosensor properties, we have created the benesi-Hildebrand plot from the equation. 9 [34]

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The plot between 1/ (F-Fo) vs 1/ Fe3+ as presented in Figure 15, exhibited the linearity of BenesiHildebrand, indicated complexation between BTDP with Fe3+ metal having 1 : 1 stoichiometric ratio.

1 1 1 1 = o + X o F − F ' F − F ' K app ( F − F ' ) [ Fe 3+ ]

(9)

o

Where F is the emission intensity of the BTDP molecule absence of Fe3+ metal ion, Fo is the emission intensity of BTDP in the presence of Fe3+ metal ion and Kapp is the evident association constant. The Benesi-Hildebrand plot between 1/ F-Fo vs 1/ Fe3+ showed linearity as showed in Figure 16, indicate complexation between the BTDP and Fe3+ metal ion having 1: 1 stoichiometric ratio. The Kapp association constant for the complexation between BTDP molecule and Fe3+ metal ion was predictable from this nonlinear curve fitting process of the fluorescence titration data was found to be 3.9 x 10-5 M-1. The fluorescence quenching behavior of the BTDP with Fe3+ metal ion was further understood by the Stern-Volmer plot and the coverage of fluorescence quenching has been quantitatively investigated by the Sterm-Volmer equation 10 [35]. Io = 1 + K sv [ Fe 3+ ] I

(10)

where, I and Io are the flourdsence intensity of the BTDP in the absence and presence of Fe3+ metal ion and Ksv is the Stern-Volmer constant. The Stern-Volmer constant (Ksv) was designed by the plot of Stern-Volmer and originate 8.3 x 104 M-1 with correlation coefficient (R2) equal to 0.97 as shown Figure 15. The elevated value of the Stern-Volmer constant indicates the effectual interaction involving the BTDP with Fe3+ metal ion.

13

Binding stoichiometry of Fe3+ with BTDP also determined by the job plot method, we claculated that the binding stoichiometry of BTDP and Fe3+ was 1: 1 by Job’s plot, and the fluoresence intensity would reach the maximum value when the mole fraction was 0.5 as mentaion in Figure 17 [36]. To investigate the mechanism of the fluorecence quenching for BTDP, Fe3+ may be easily establish coordination interaction with the pyrazoline and benzo[ d] thiazole moiety than the other metal ions, examined, the capture of Fe3+ resulted in the electron or energy transfer from BTDP to Fe3+ metal ion; thus, BTDP showed quenching of the fluorescence for Fe3+ and provided a high slectivity for Fe3+ over the other tested metal ions.

4. Conclusion Heterocyclic containing donor-π-acceptor chromophore

2-(1-(benzo[d]thiazol-2-yl)-5-(3,4-

dimethoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol (BTDP) has been synthesized by reaction of (E)-3-(3,4-dimethoxyphenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one (DMPO) with 2hydrazinylbenzo[d]thiazole. Photophysical and physicochemical study of chromophore has been described and specific solvent-chromophore interaction was celebrated by examined the absorbance and emission spectra in ten different solvents. It’s showed good photophysical properties; extremely high solvatochromism of the normal emission band of the makes it one of the most effective solvatochromic dye in pyrazoline family. Pyrazoline derivative experiences micellization in two different micelles, its can be used as probe to determine the critical micelle concentration of surfactant such as CTAB and SDS. In addition, it was focused on the effect of ten metal ions on photophysical behavior of the pyrazoline derivative and designate. The fluorescence spectra of BTDP did not affected by the presence of any metal ions among the ten metal ions exemption Fe3+ metal ion. Fe3+ metal ion decreased the emission intensity of BTDP spectacularly when the concentration of Fe3+ metal ion increased. The complexation reaction of 14

BTDP with respect to Fe3+ has explained by the Benesi-Hildebrand, Stern-volmer and job’s plot method proposed that 1: 1 ratio complex formation and the non-linearity of the Stern-volmer plot designated that decreased the emission intensity through the dynamic and static system.

Acknowledgement This work was supported by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under grant No. (G: 482-130-1440). The author, therefore, acknowledge with thanks DSR for technical and financial support.

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NH2 S NH

Br2

N

S

HAc

NH2NH2.H2O

H2N

HN

37 % HCl

N

H2N

20

S

Scheme 1: Synthesis of 2-Hydrazinobenzothiazole

Scheme 2: Synthesis of Pyrazoline (BTDP)

21

Scheme 3: Chemosensor behavior of BTDP with Fe3+ ion

22

Table 1: Optical parameters and fluorescence quantum yields of BTDP in various solvents ∆f

Solvent

DMSO

ETN

ET (30) Kcal mol-1

λab(nm) λem(nm)

ε M -1cm-1

f

∆ ν st

µ 12 Debye

(cm )

Φf

-1

0.263

0.441

45.1

356

454

22120

0.53

6.32

6063

0.51

DMF 0.274 EtOH 0.305 MeOH 0.308 CHCl3 0.217 CH2Cl2 0.255 CH3CN 0.274 Dioxane 0.148 Egly 0.276 n-Hexane 0.0014

0.404 0.654 0.762 0.259 0.472 0.164 0.210 0.790 0.0002

43.8 51.9 55.4 39.1 41.1 45.6 36.0 56.3 31.1

354 351 347 352 351 349 350 347 344

450 447 452 445 444 441 439 454 428

21300 20410 18000 21700 19880 19300 19290 17400 17800

0.51 0.49 0.48 0.50 0.47 0.46 0.44 0.47 0.40

6.18 6.03 5.93 6.10 5.91 5.83 5.71 5.87 5.39

6026 6119 6695 5938 5908 5978 5792 6792 5705

0.46 0.47 0.40 0.43 0.44 0.43 0.38 0.17 0.32

0.25 DMSO DMF EtOH MeOH CHCl3

Absorbance

0.20

0.15

CH2CH2 CH3CN Dioxane Elgy n-Hexane

0.10

0.05

0.00 300

350

400

450

Wavelength (nm)

Figure 1: UV absorbance spectra of 1 x 10-5 M of BTDP in various solvents.

23

Emission Intensity (arb. units)

500

400

DMSO DMF EtOH MeOH CHCl3

300

CH2Cl2

200

CH3CN

100

Dioxane Egly n-Hexane

0

400

450

500

550

600

650

Wavelength (nm)

Figure 2: Fluorescence spectra of 1 x 10-5 M of BTDP in various solvents. 85

E(kcal mol-1)

80 Ea Ef

75

70

65

60

30

35

40

45

50

55

60

ET(30)kcal mol-1

Figure 3: Plot of energy of absorption (Ea) and emission (Ef) versus ET(30) of different solvents.

24

6200 6100

Delta f

6000 5900 5800 5700 0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Stokes Shift

Figure 4: Plot of ∆f versus stokes shift. 0.55

Fluorescence quantum yields

0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 30

35

40

45

50

55

60

ET(30) kcal mol-1

Figure 5: Plot of ɸf versus ET(30) of the different solvents.

25

80

Emission Intensity

60

40

20

0

400

450

500

550

600

650

Wavelength (nm)

Figure 6: Emission spectrum of 1x 10-5mol dm-3 of BTDP at different concentration of CTAB, the concentration of CTAB at increasing emission intensity is 0.0, 2.0 x 10-4, 4.0 x 10-4, 6.0 x 104 , 8.0 x 10-4, 1.0 x 10-3, 1.2 x 10-3, 1.4 x 10-3, 1.6 x 10-3, 1.8 x 10-3mol dm-3. 100

Emission Intensity

80

60

40

20

0

400

450

500

550

600

Wavelength (nm)

Figure 7: Emission spectrum of 1x 10-5mol dm-3 of BTDP at different concentration of SDS, the concentration of SDS at increasing emission intensity is 0.0, 2.0 x 10-3, 4.0 x 10-3, 6.0 x 10-3, 8.0 x 10-3, 1.0 x 10-2, 1.2 x 10-2, 1.4 x 10-2, 1.6 x 10-2, 1.8 x 10-2 mol dm-3.

26

80

70

If

60

50

40

30

0.0000

0.0004

0.0008

0.0012

0.0016

0.0020

[CTAB] mol dm-3

Figure 8: Plot of If versus the concentration of CTAB.

100 90 80 70 If

CMC

60 50 40 30 20

0.000

0.004

0.008

0.012

[SDS] mol dm-3

Figure 9: Plot of If versus the concentration of SDS.

27

0.016

500 450

Dye 2+ Cu 2+ Sr 2+ Sn 2+ Cd 2+ Co 3+ Cr 2+ Zn 2+ Mn 3+ Al 3+ Fe

Emission Intensity

400 350 300 250 200 150 100 50 0

400

450

500

550

600

650

Wavelength (nm)

Figure 10: Emission spectra of 1.0 x 10-5moldm-5 of BTDP upon addition of 5.0 x 10-5 M Cu2+, Sr2+, Sn2+, Cd2+, Co2+, Cr3+, Zn2+, Mn2+, Al3+ and Fe3+in DMF/ water (9:1, v/v)

500

Emission Intensity

400 300 200 100

B BT TD DP P + BT Cu D P BT + S DP r BT + Sn D P + BT C DP d BT + C o D P BT + C r D P BT + Z DP n BT + M n D P BT + A l DP + Fe

0

Figure 11: Emission of BTDP in presence of different metal ions.

28

90

Imisstion Intensity

75 60 45 30 15

BT D BT P + F D P+ e BT Fe+ C D u P+ Fe BT +S D r P BT +F e + D P+ Sn BT Fe +C D d P+ F BT e+ C D o P+ BT Fe+ C D r P+ F BT e+ Zn D P+ Fe BT +M D n P+ Fe +A l

0

A

Figure 12: Competitive experiments in the BTDP + Fe3+ system with interfering metal ion. [BTDP]= 1 x 10-5M, [Fe3+] = 5 x 10-5M, and [Mn+] = 5 x 10-5M, excited at 345 nm

500 0.0 eq

Emission Intensity

400

300 9.0 eq.

200

100

0

400

450

500

550

600

650

Wavelength (nm)

Figure 13: Emission spectra of BTDP (1 x 10-5M) exposed to various concentration of Fe3+ in DMF: water (9:1, v/v).

29

500

400

If

300

200

100

0

0

2

4

6

8

10

[Fe3+] x 10-5 M

Figure 14: Inset: Fluorescence titrations cure of BTDP (1 x 10-5M) with Fe3+ in aqueous solution.

0.008 0.007

Equation

y = a + b*x

Weight

No Weighting 9.61429E-8

Residual Sum of Squares

0.99456

Adj. R-Square

Value Intercept B

1/ I0-If

0.006

Slope

Standard Error

0.00142

6.01003E-5

5.55856E-8

1.45302E-9

0.005 0.004 0.003 0.002 20000

40000

60000

80000

100000

1/ [Fe3+] M

Figure 15: Benesi-Hildebrand plot for BTDP (1 x 10-5M) at various concentration of Fe3+ ion.

30

20 18 16 14

I0/If

12 10 8 6 4 2 0 0

2

4

6

8

10

[Fe3+] x 10-5 M

Figure 16: Stren-Volmer plot for BTDP (1 x 10-5M) at various concentration of Fe3+ ion.

20

If

15

10

5

0.0

0.2

0.4

0.6

0.8

1.0

Fe3+/ Fe3+ + BTDP

Figure 17: Job’s plot, Fluorescence Intensity vs. mole fraction of Fe3+ Job’s plot.

31

► Synthesis of 2-(1-(benzo[d]thiazol-2-yl)-5-(3,4-dimethoxyphenyl)-4,5dihydro-1H-pyrazol-3-yl)phenol (BTDP) ► Physicochemical and Photophysical investigations of BTDP dye ► Determine the critical micelle concentration (CMC) of CTAB and SDS ► BTDP can be used as On-Off fluorescent chemosensor for the detection of Fe3+ ion

With this proposal, I designed the some novel heterocyclic D- π -A chromophores by one pot multi-component reaction with various reaction conditions, which give highly florescence and highly photostable dye to generate novel photophysical application. During this project, my aim to developed novel heterocyclic chromophores by the one pot multi-component reaction, which might be applicable in different field of the optical material, like luminescence dyes, organic light emitting diode, dye sensitized solar cell. These newly synthesized donor acceptor chromophores can be use as fluorescence chemo sensor for the detraction various toxic metals by enhancement or quenching the fluorescence intensity.