Ferrocene based nonlinear optical chromophores: synthesis, characterization and study of optical properties

Accepted Manuscript Ferrocene based nonlinear optical chromophores: synthesis, characterization and study of optical properties

Reza Teimuri-Mofrad, Keshvar Rahimpour, Rahim Ghadari, Sohrab Ahmadi-Kandjani PII: DOI: Reference:

S0167-7322(17)32120-7 doi: 10.1016/j.molliq.2017.09.002 MOLLIQ 7838

To appear in:

Journal of Molecular Liquids

Received date: Revised date: Accepted date:

15 May 2017 8 August 2017 3 September 2017

Please cite this article as: Reza Teimuri-Mofrad, Keshvar Rahimpour, Rahim Ghadari, Sohrab Ahmadi-Kandjani , Ferrocene based nonlinear optical chromophores: synthesis, characterization and study of optical properties, Journal of Molecular Liquids (2017), doi: 10.1016/j.molliq.2017.09.002

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ACCEPTED MANUSCRIPT Ferrocene Based Nonlinear Optical Chromophores: Synthesis, Characterization and Study of Optical Properties Reza Teimuri-Mofrad,*, a Keshvar Rahimpour,a Rahim Ghadari,a Sohrab Ahmadi-Kandjani b Department of Organic and Biochemistry Faculty of Chemistry, University of Tabriz 29th

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a

Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, 5166614766, Iran.

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b

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Bahman Avenue, Tabriz 51666-16471 (I.R. Iran) E-mail: [email protected]

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ABSTRACT: In this work, the design and synthesise of a series of D-π-A-π-D analogs were

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carried out by incorporating well-defined building blocks (ferrocene and pyran) with Knoevenagel condensation aiming to use them in optical applications. After characterization of

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the structure of synthesized compounds using 1H and

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C NMR, FT-IR and mass spectroscopy

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and CHN analysis, the electrochemical, photochemical and photophysical properties of these compounds were studied. The third order nonlinear refractive index, n2, and nonlinear absorption

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coefficient, β, of the synthesized chromophores were assessed by the open and closed aperture Z-

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scan measurements, respectively. The quantum chemistry study was performed on synthesized compounds with the DFT approach. The theoretical and experimental results show that these

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light-weight molecules can be considered as alternatives to high-weight polymers in optical applications.

Keywords: Ferrocene; NLO-phores; Pyran.

1. Introduction

ACCEPTED MANUSCRIPT Design, synthesis and characterization of organic compounds for use in electro-optic (EO) applications are potentially useful areas that have attracted considerable research interest. The selection of proper materials for this purpose is now counted as a great challenge among researchers and the basic tenets for large nonlinearity are universally accepted [1, 2].

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In the first decade of nonlinear optics, research works were focused on inorganic materials such

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as quartz, lithium niobate, cadmium selenide, cadmium telluride, cadmium sulfide, potassium

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dihydrogen phosphate (KDP), and etc. Development of organic materials stimulated the progress

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in nonlinear optical (NLO) materials. Very soon, organic materials were suggested and investigated as alternatives to inorganic species due to their synthetic flexibility, large and fast

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nonlinear response, low cost and light-weight [3, 4].

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The basic structure of NLO materials is based on the π-bond system. The addition of electron

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acceptor and electron donor fragments improve this feature. Several kinds of donor-π-acceptor (D-π-A) dyes with broad and intense absorption features have been developed until now, but

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researches show that compounds with (D-π-A-π-D) skeleton have lower band gap and improved

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absorption features than those of D-π-A analogues [5,6]. The structure of π-conjugate spacer plays an important role in charge transfer process. 2, 6-

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dimethyl-4H-pyran-4-ylidene fragment is one of the most notable compounds, which was used as the backbone of this type of molecules [7]. In recent years, among many kinds of donor groups, ferrocene and its derivatives have received lots of interest [8] that could be attributed to their potential applications. For example they have been used as nonlinear optical materials [9], functionalizing nanotube materials [10], ionic recognition [11], aerospace materials production [12], redox fluorescent switch [13], catalysts [14], sensitive electrochemical sensors [15], antibacterial and anticancer drugs [16, 17].

ACCEPTED MANUSCRIPT In the present study, in continuance of our previous study on the synthesis of ferrocene containing materials [18], the aim is to incorporate the known properties of ferrocene into 2, 6dimethyl-4H-pyran-4-ylidene fragment. For this purpose, the key element to design ferrocenebased dyes is the conjugated pyran unit that links two ferrocene moieties to eachother. The newly

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synthesized compounds of this research are illustrated in Figure 1. Furthermore, electrochemical,

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photochemical, and photophysical properties of the compounds were studied for complementary

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data. The third order nonlinear optical properties were measured using Z-scan technique and the quantum chemistry study was performed on synthesized compounds with the DFT approach. The

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B3LYP method and 6-31G(d) basis set were used to optimize the structures in the gas-phase.

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Fig. 1. Structure of ferrocene-based dyes that were synthesized in this study.

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2. Experimental

2.1. General Methods. Ferrocenecarboxaldehyde [19], 2-(2, 6-dimethyl-4H-pyran-4-ylidene) malononitrile and 2-(2,6-dimethyl -4H-pyran-4-ylidine)-1,3-indandione were prepared according to the reference method [20]. Commercial compounds were used without further purification. Column chromatography was performed using SiO2 (60 Å, 230−400 mesh, particle size 0.040−0.063 mm) at 25 °C. 1H and 13C NMR spectra were obtained with Bruker FT-400 and 100 MHz spectrometers, respectively and the chemical shifts were reported in ppm and were

ACCEPTED MANUSCRIPT referenced to the residual solvent as follows: CHCl3 = 7.26 δ (1H), 76.0 δ (13C). For 1H NMR, coupling constants J were given in Hz and the resonance multiplicity was described as s (singlet), d (doublet), t (triplet), m (multiplet). The FT-IR spectra were reported as wavenumbers ν̃ (cm−1) with band intensities indicated as s (strong), m (medium), w (weak) with Bruker-Tensor

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270 spectrometer. The mass spectra operated at 70 eV by Agilent (5975C VL) instrument, the

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most important peaks were reported in m/z units with M+ as the molecular ion. The iron analysis

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was performed by Analytikjene (novaa 400) atomic absorption spectrophotometer and UV/vis spectroscopy was recorded on a SPECORD 250 analytikjena UV/vis spectrophotometer. The

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Elemental analyses were carried out with an Elementor Vario EL. III instrument. Cyclic

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voltammetry measurements were performed on 1 mM solutions of ferrocene derivative in acetonitrile in the presence of 0.100 M LiClO4, as supporting electrolytes, using

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potentiostat/galvanostat Autolab (PGASTAT 30) equipped with a standard three-electrode cell.

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A 2-mm-diameter glassy carbon (GC) was used as the working electrode. A silver/silver chloride (Ag/AgCl) electrode and a platinum electrode were used as the reference and the counter

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electrodes, respectively. All potentials in this study were reported with respect to the Ag/AgCl.

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2.2. General procedure for the synthesis of pyran derivatives. A solution of 4H-pyran derivative (1, 3a and 3b) (1.20 mmol), ferrocenecarboxaldehyde (2.40 mmol), and piperidine (1

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mL) in dry acetonitrile (10 mL) was refluxed for 24 hours under argon atmosphere. The reaction was controlled with TLC method by monitoring the ferrocenecarboxaldehyde in the solution of reaction. After the completion of the reaction, the solution was cooled to room temperature and the product purified using column chromatography over silica gel and EtOAc as eluent. Further purification was performed by recrystallization from hexane: EtOAc (8:2) to give the corresponding compound as a pure solid.

ACCEPTED MANUSCRIPT 2,6-diferrocenylvinyl-4H-pyran-4-one

(PF,

2):From

0.10

g

(0.47

mmol)

ferrocenecarboxaldehyde, 0.10 g (0.19 mmol) of dark orange solid was obtained in the yield of 86%. 1H NMR (400 MHz, CDCl3, 25°C) δ = 7.25 (d, 3J = 15.8 Hz, 1H), 6.33 (d, 3J = 15.8 Hz, 1H), 6.15 (s, 1H), 4.56 (t, 2H), 4.44 (t, 2H), 4.17 (s, 5H). 13C NMR (100 MHz, CDCl3) δ = 179.5,

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160.6, 135.2, 115.9, 110.7, 79.0, 69.6, 68.6, 67.0. FT-IR (KBr, cm-1): 3087, 3043 (w), 2924,

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2856 (w), 1632 (s), 1456 (m), 1041(w), 482 (w). Anal. Calc. for C29H24Fe2O2: C, 67.47; H, 4.68;

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Fe, 21.64; Found: C, 67.52; H, 4.56; Fe, 21.57. MS (70 eV): m/z = 516.1 [M]+. 2-(2,6-diferrocenylvinyl -4H-pyran-4-ylidine) malononitrile (CPF, 4a): From 0.10 g (0.47

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mmol) ferrocenecarboxaldehyde, 0.11 g (0.19 mmol) of dark red solid was obtained in the yield

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of 90%. 1H NMR (400 MHz, CDCl3, 25°C) δ = 7.35 (d, 3J = 15.7 Hz), 6.59 (s, 1H), 6.36 (d, 3J = 15.7 Hz), 4.59 (t, 2H), 4.52 (t, 2H), 4.22 (s, 5H). 13C NMR (100 MHz, CDCl3) δ = 178.3, 157.7,

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138.2, 115.0, 114.6, 104.0, 78.7, 70.7, 69.0, 67.7, 67.5. FT-IR (KBr, cm-1): 3098 (w), 2924, 2858

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(w), 2186 (m), 1481 (m), 1038(w), 481 (w). Anal. Calc. for C32H24Fe2N2O: C, 68.12; H, 4.28; Fe, 19.79; N, 4.96; Found: C, 68.27; H, 4.32; Fe, 20.07; N, 4.89. MS (70 eV): m/z = 564.1 [M]+.

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2-(2,6-diferrocenylvinyl -4H-pyran-4-ylidine)-1,3-indandione (IPF, 4b): From 0.10 g (0.47

1

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mmol) ferrocenecarboxaldehyde, 0.13 g (0.20 mmol) of black solid was obtained in 89% yield. H NMR (400 MHz, CDCl3, 25°C) δ = 8.40 (s, 1H), 7.75-7.77 (m, 1H), 7.59-7.61 (m, 1H), 7.37

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(d, 3J = 15.8 Hz), 6.53 (d, 3J = 15.8 Hz), 4.60 (t, 2H), 4.51 (t, 2H), 4.22 (s, 5H). 13C NMR (100 MHz, CDCl3) δ = 191. 9, 159.5, 147.9, 139.7, 136.5, 132.1, 132.0, 120.1, 116.3, 106.0, 79.1, 68.8, 67.7, 67.3. FT-IR (KBr, cm-1): 3083 (w), 2924, 2858 (w), 1630 (s), 1510 (m), 1040(w), 484 (w). Anal. Calc. for C38H28Fe2O3: C, 70.83; H, 4.37; Fe, 17.33; Found: C, 70.69; H, 4.44; Fe, 17.26. MS (70 eV): m/z = 644.2 [M]+.

ACCEPTED MANUSCRIPT 2.3. Theoretical Methods. All calculations were carried out using Gaussian 09 (Rev. D.01) [21] program package by using density functional theory (DFT) approach. The B3LYP method used for optimizing the structures [22] along with 6-31G (d) as the basis set [23]. The structure of compounds were optimized in the gas-phase. No symmetry constraints were imposed.

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2.4. Nonlinear optical measurements. The third-order NLO properties were measured by the Z-

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Scan technique using a continuous-wave diode laser in 36 μm of diameter width. The operating

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wavelength was also centered at 655 nm.

The experiments were performed at 22 °C in DMF solutions using a 1 mm-thick quartz cell. The

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spatial profiles of the optical pulses were nearly Gaussian. The laser beam was focused with a 10

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cm focal length focusing mirror so that the NLO properties of the samples could be manifested by moving the samples along the axis of the incident beam (Z-direction) with respect to the focal

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point. An aperture of 0.5 mm in radius was placed in front of the detector to assist the

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measurement of the self-focusing effect. All optical measurements were carried out in ambient

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atmosphere at room temperature. 3. Results and discussion

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In compared to inorganic compounds, light-weight organic compounds with charge transfer

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properties are widely adopted in the field of photonics. Therefore, it is important to synthesize low molecular mass organic compounds with improved properties, which make the new compounds more efficacious and economical to be used in photonic related areas. In order to implement this requirement, in the present study, the use of ferrocene for the synthesis of novel D-π-A-π-D type conjugated compounds is investigated.

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Scheme 1. Synthesis of ferrocene-based dyes. i) A, acetic anhydride, reflux. ii) ferrocene

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carboxaldehyde, piperidine, acetonitrile, reflux.

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Ferrocenecarboxaldehyde was synthesized from ferrocene according to the modified procedure described by Graham and co-workers in 71% [19]. The Knoevenagel condensation reaction of

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ferrocenecarboxaldehyde with derivatives of 4-substituted 4H-pyran-4-one that could be easily

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obtained by condensation of 2, 6-dimethyl-4H-pyran-4-one with active methylene groups, gives final products in considerably good yields (scheme 1). The elemental analyses, FT-IR, 1H NMR, 13

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C NMR and mass spectra, all well confirmed the predicted molecular structure.

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Well study of coupling constant and chemical shifts in NMR spectra is the main key to obtain the needed information about geometry and distribution of the electronic density. Acceptor group

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incorporation effect on proton magnetic resonance chemical shifts, was shown in Figure 2. This shift was applied to H-3 and H-5 of the pyran ring along with exocyclic vinylic hydrogen atoms. As might be expected, the clear downfield shift for H-3 and H-5 on passing from PF to CPF and IPF well confirmed that this atoms become progressively deshielded with increasing the electron withdrawing tendency in acceptor moiety. This evidence could be a reliable proof for the strength of 1,3- indandione in the place of an acceptor when compared to malononitrile acceptors. Using DFT calculation to predict the NMR chemical shifts for H-3 and H-5 of pyran

ACCEPTED MANUSCRIPT ring shows the similar deshielding trend for synthesized compounds (IPF>CPF>PF). Obtained results were tabulated in Table 2. The 3JH-H values (PF= 15.8, CPF= 15.7, IPF= 15.8) for

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exocyclic vinylic hydrogen atoms reveal that these compounds adopt an all-trans geometry.

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Fig. 2. 1H NMR spectra of PF, CPF and IPF in CDCl3 It should be noted that in this intramolecular charge transfer process the important of donor

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groups’ role is no less than that of acceptor groups. Till now generally bulky amino aryls have been used as know donors for these systems despite their commercially unavailability and

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special requirements in their synthesis process. According to obtained results in the present

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study, it’s clear that ferrocene could be function well enough or rather better than many other donor groups in D-π-A-π-D type systems. Comparison of H-3 and H-5 chemical shift in the herein reported compounds to other D-π-A-π-D type molecules is listed in table1. As a conclusion of this comparison, it is elicited that incorporation of ferrocenyl group instead of dialkylamino or alkoxy substituted aryl groups had a similar or even better result in donor ability of the final target system.

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Tabe 1. Effect of different donor groups on H-3 & H-5 chemical shifts. δ (ppm)

Compound

δ (ppm)

Compound

6.49[24b]

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6.59

8.40

8.36[24c]

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6.60[24a]

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6.45[24a]

8.35[24d]

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6.49[24b]

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To study the detailed electronic identity of the synthesized compounds, computational approach was used. To do so, the structures of all synthesized compounds were optimized using density

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functional theory (DFT) method. The well-known B3LYP method and the 6-31G (d) basis set were used in this step. The energies of the frontier orbitals, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) are shown in Figure 3. The results are in good agreement with experimental data that obtained from UV-Vis and CV spectra (Table 4). The HOMO state density was mainly distributed on the two ferrocenyl moieties and the electron density of LUMO was localized at 2, 6-dimethyl pyran moieties.

ACCEPTED MANUSCRIPT In agreement with experimental results, stabilization of positive charge on ferrocenyl unit was confirmed with DFT calculation of partial charge and band length for NLO-phores. Increase in positive charge on the H-3 and H-5 of the pyran ring in the series of chromophore, in this order PF
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malononitrile. In addition decreasing of bond length (a) in the pyran ring, in order of

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PF>CPF>IPF indicates that charge separation is facilitated with increasing the electron

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withdrawing ability of acceptor unit (table 2).

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Table2. Selected calculated 1H NMR shift, ESP charge and bond length (in A°) in the spacer

PF CPF

ESP charge H-3 & H-5

a

b

5.20

+ 0.203

1.46234

1.35920

5.72

+0.221

1.43440

1.36446

8.47

+0.252

1.43374

1.36471

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IPF

Chemical shift(ppm)

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Compound

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pyran

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Fig. 3. Optimized geometries and molecular orbital surfaces of the HOMO and LUMO of

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ferrocene-based NLO-phores obtained at B3LYP/6-31G (d) level.

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In order to observe phenomena such as solvatochromism and aggregation of the synthesized compounds, we investigated the UV-Vis absorption spectra of the synthesized NLO-phores

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across a range of concentrations in various solvents with different polarities (Figure 4). 1, 4-

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dioxane, chloroform, dichloromethane, acetone and acetonitrile were what we chose as solvents concentrating on their broad range of dielectric constants (ɛ), ɛ = 2.2, 4.8, 8.9, 20.7 and 37.5,

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respectively. It was found that, the shape of the absorption spectrum is the same in all solvents except for chloroform. Each compound shows two visible bands; according to literature the low energy band is assigned to metal-to-ligand charge transfer (MLCT) while the other one locating at the shorter wavelength is due to π-π* transition (table 3). Both transitions showed a small negative solvatochromism in going from 1, 4-dioxane to acetonitrile. UV-Vis absorption spectrums show no variation across a range of concentrations conforming that no aggregation was occurred. In the case of chloroform formation of charge–transfer complexes of ferrocene

ACCEPTED MANUSCRIPT with solvent was occur, this ferrocene to solvent charge transfer phenomenon (CTTS) has been predicted in previous studies [25]. For this reason the shape of UV-Vis absorption spectrum of chromophores in chloroform is different from other solvents. As expected red shift in max for chromophores was observed by increasing the electron

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withdrawing capability of the acceptor moiety in going from PF to IPF, this red shift in π-π*

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transition is bigger than that of MLCT transition. According to the results presented in the table 4

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band gap energy (Eg) decreases from PF to IPF due to the enhancement of electron accepting

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ability of the acceptor unit. On the other hand, it can be concluded that the band gap energy (Eg) depends substantially on the nature of both donor (D) and acceptor (A) moieties and here

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ferrocene could be considered as one of the suitable organometallic donors. The experimental band gap energies were calculated (Table 4) according to Eq. (1) [26]:

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Eg = 1240/ λ

(1)

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The wavelength at the absorption edge, λ, was determined as the intercept on the wavelength axis

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for a tangential line drawn on the absorption spectra.

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Fig. 4. UV−vis absorption spectra: (a) Normalized UV-Vis absorption of PF in series of solvents. (b) Normalized UV-Vis absorption of CPF in series of solvents. (c) Normalized UV-Vis absorption of IPF in series of solvents. (d) Normalized UV-Vis absorption of NLO-phores in acetonitrile. (e) Concentration dependence of UV−vis absorption spectra of PF in acetonitrile. (f) Concentration dependence of UV−vis absorption spectra of CPF in acetonitrile. (g)

ACCEPTED MANUSCRIPT Concentration dependence of UV−vis absorption spectra of IPF in acetonitrile. (h) Solvatochromism effect on MLCT and π→π* transition. Table3. Absorption spectral data of novel ferrocene-based NLO-phores in various solvents. Chloroform (39.1)

DCM (40.7)

π-π*

311 (33000)

364

312 (55920)

MLCT

479 (5500)

-

π-π*

386 (25920)

370

MLCT

524 (11160)

π-π*

466 (46320)

MLCT

533 (26160)

IPF

The solvent parameters ET in kcal. mol-1

482 (5500)

485 (3680)

406 (15380)

406 (39840)

407 (33360)

-

540 (8020)

535 (14810)

534 (11270)

364

469 (59520)

465 (42060)

464 (23200)

-

547 (28240)

544 (18880)

542 (10280)

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489 (8400)

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a

309 (24920)

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CPF

Acetonitrile (45.6)

330 (24560)

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PF

Acetone (42.2)

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Dioxane (36)a

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Compound

max /nm ( /M-1 cm-1)

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Solvent

The electrochemical property of ferrocene derivatives was measured by cyclic voltammetry (CV)

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using a 0.1 M solution of lithium perchlorate in anhydrous acetonitrile. Representative CVs of

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ferrocene derivatives are presented in Figure 5. Results exhibited reversible voltammetric behavior for the ferrocenyl group present in these compounds with ΔEp = Epa ˗ Epc ≤ 0.08 V at

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scan rates up to 0.50 V s-1 (Table 4). Based on the previous studies a fast one electron transfer would ideally have a ΔEp = 0.059 V at 298 K [27]. The discrepancy from this ideal value is attributed to any kinds of slow electron transfers and also solution resistance as the main reasons. The slow electron transfers origin from the nature of the compound and the groups connected to the ferrocene nucleus. As can be seen in Table 4, the increase in electron withdrawing effect of acceptor groups increased the deviation from the ideal state. Cathodic and anodic peak current ratios, measured for the derivatives, were in the range of 0.28 < ipc/ipa < 0.69, and Ep values were

ACCEPTED MANUSCRIPT independent of the scan rate. According to the results presented in Table 4, the obtained values followed PF > CPF > IPF proceeding. This also could be explained by electron withdrawing properties of electron acceptor fragments. Band gap energies were listed in Table 4. An increase in band gap is in line with the increase in electron withdrawing identity of the acceptor section of

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the synthesized compounds. Under this condition, it seems that the process of electron entering

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to the LUMO level of the molecule is not easily available and the reduction process takes place

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very difficult when compared to compounds without acceptor groups or with weakly

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withdrawing effect.

Fig. 5. CV curves of the PF, CPF and IPF in different scan rates (scan rates are given in mV s-1).

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Table 4. Experimental data for ferrocene-based NLO-phores.

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Compound

Eg (experiment UV–Vis) a

a

HOMO (eV)

LUMO (eV)

(experimental CV)

(experimental CV)

ΔEp

ipc/ipa

PF

2.17

-4.84

-2.67

0.058

0.69

CPF

1.90

-4.87

-2.97

0.070

0.36

IPF

1.82

-4.68

-2.86

0.080

0.28

The ICT energies (hICT) derived from the wavelength at the absorption edge18a from UV-Vis spectra in acetonitrile

As it is specified, oxidation process corresponds to extraction of electrons from the HOMO level correlating to the ionization potential, whereas the reduction potential is associated with electron affinity indicating the LUMO level. These processes could be scaled using CV method by

ACCEPTED MANUSCRIPT measuring redox potentials and here in the present study the HOMO energy levels were calculated using equation 2, where Eox and Eferrocene are the onset oxidation potentials for the dyad sample and the ferrocene against Ag/AgCl reference electrode, while the value – 4.8 eV is the HOMO energy level of ferrocene against vacuum.

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The LUMO energy levels were calculated with the HOMO levels attained via CV measurements

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and the optical band gap (Eg) obtained by UV-Vis measurements, equation 3 [28]:

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EHOMO = - [Eox + 4.8 - Eferrocene]

(3)

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ELUMO = EHOMO + Eg

(2)

The onset potentials of oxidation are determined from intersection of the tangents between the

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baseline and the signal current. The onset potentials of ferrocene oxidation vs. Ag/AgCl are

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reported as 0.27, in acetonitrile. The obtained values were listed in Table 4.

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The NLO properties of CPF and IPF were investigated with Z-scan technique under continuouswave diode laser radiation at 655 nm in DMF solution. The third order nonlinear refractive

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index, n2, and nonlinear absorption coefficient, β, of the DMF solution of chromophores were

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assessed by the open and closed aperture Z-scan measurements, respectively. Figure 6(a) and (b) show the open aperture (OA) and closed aperture (CA) Z-scan data for ferrocene derivatives

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solution. In the case of CA data, all samples have Peak-Valley configuration, which is corresponding to negative NLR effects which means that self-defocusing phenomena have occurred. The nonlinear refractive index, n2, is estimated by the following equation: ∆𝜑0

𝑛2 = 𝑘𝐼

0 𝐿𝑒𝑓𝑓

(4)

which, 𝐿𝑒𝑓𝑓 = [1 − 𝐸𝑋𝑃(−𝛼𝐿)]⁄𝛼

(5)

ACCEPTED MANUSCRIPT The Leff is the effective thickness of the sample and 𝐼0 is the intensity of the laser beam. ∆𝜑0, spatial phase distortion, obtained from the given relation: ∆𝑇(𝑝−𝑣) = 0.406 (1 − 𝑆)0.25 |∆𝜑0 |

(6)

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Here ∆𝑇(𝑝−𝑣) is peak to valley transmittance and 𝑆 is the linear transmittance of aperture defined

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by

(7)

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𝑆 = 1 − 𝐸𝑋𝑃(−2𝑟𝑎2 ⁄𝜔𝑎2 )

and in this experiment it is calculated as 0.14. The results (Table 3) demonstrated that present

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prepared compounds possess a good NLO effect in comparison to that of other ferrocene based

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chromophores reported in the literature [29].

using Eqs. (8) and (9) [30].

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∆𝑇(𝑍) = −𝑞0 ⁄2√2 [1⁄1 + 𝑍 2 ⁄𝑍02 ]

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The nonlinear absorption coefficient, β, can be estimated from the open aperture Z-scan data

(9)

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𝑞0 = 𝛽𝐼0 𝐿𝑒𝑓𝑓

(8)

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In accordance with the 𝑛2 and 𝛽 values, the real (𝑅𝑒𝜒(3) ) and imaginary (𝐼𝑚𝜒(3) ) parts of the

[31]:

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third-order nonlinear optical susceptibility (𝜒 (3) ) can be calculated by the following equations

𝑅𝑒𝜒(3) = 10−4

𝐼𝑚𝜒(3) = 10−2

𝜀0 𝑐 2 𝑛02 𝜋

𝑛2 (𝑐𝑚2 ⁄𝑊 )

𝜀0 𝑐 2 𝑛02 𝜆 4𝜋 2

𝛽 (𝑐𝑚⁄𝑊 )

(10) (11)

Obtained data for each compound were listed in Table 5. In continue the absolute value of 𝜒 (3) can be obtained from:

ACCEPTED MANUSCRIPT |𝜒

(3)

2 1⁄2

2

| = [(𝑅𝑒𝜒(3) ) + (𝐼𝑚𝜒(3) ) ]

(12)

There are various physical mechanisms that can give rise to a nonlinear refractive index. It seems that thermally induced variation in refractive index of the medium is dominate phenomena in

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large nonlinear refractive index of our compounds. Based on the obtained values of 𝜒 (3) , it can

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be concluded that these ferrocene derivatives have good potential to be used in nonlinear optical

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applications. Due to the simplicity of the ferrocenyl groups to be used as ideal donors, here by our ferrocene based derivations could be synthesized through a more convenient and versatile

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procedure reaching good to excellent yields which could well confirm the superiority of our

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study.

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Fig. 6. Z-scan data in DMF solution, (a) obtained in an OA configuration, (b) obtained in a CA configuration.

Table 5. Nonlinear parameters of synthesized compounds compound

𝜶(𝒄𝒎−𝟏 )

𝜷(𝒄𝒎⁄𝑾)

𝑰𝒎𝝌(𝟑) (𝒆𝒔𝒖)

PF

1.5

4.4×10-4

1.2×10-3

CPF

3

8.7×10-4

2.3×10-3

𝒏𝟐 (𝒄𝒎𝟐 ⁄𝑾)

𝑹𝒆𝝌(𝟑) (𝒆𝒔𝒖)

𝝌(𝟑) (𝒆𝒔𝒖)

1.4284

-2.5×10-7

-1.3×10-3

1.7×10-3

1.4294

-1.4×10-7

-7.2×10-4

2.4×10-3

𝒏𝟎

ACCEPTED MANUSCRIPT 1.4×10-3

2.6

IPF

3.7×10-3

1.4287

-1.5×10-7

-7.7×10-4

3.8×10-3

Acknowledgment We gratefully acknowledge the financial support for this work by the Research Council of University of Tabriz.

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Graphical abstract

ACCEPTED MANUSCRIPT Highlights

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Synthesis of light-weight organometallic chromophores containing ferrocenyl core. Using the simple synthetic methods without any complication. Investigation of electrochemical, photochemical and photophysical properties. Quantum chemistry study of synthesized compounds with the DFT approach.

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