Synthesis, characterization and electrical conductance of ferrocenylazobenzene

Article abstract of DOI:10.1080/15421406.2014.968081

Ferrocenylazobenzene was synthesized by condensing an aminoazobenzene dye with ferrocenecarboxylic acid previously treated with oxalyl chloride. The compound displayed an anticipated chemically reversible one-electron oxidation process and gave a formal potential, E° = 0.65 V. In the UV-Vis region, the azo π-π and n-π transitions appeared at 355 and 460 nm respectively. On oxidation of the ferrocenyl moiety, the azo π-π band was blue-shifted to 348 nm with an increase in intensity, while a new broad, lower energy absorption band assigned to the ligand-to-metal charge transfer appeared at 622 nm. The growth of this new band was concurrent with the bleaching of the metal-to-ligand charge transfer band which was largely obscured by the azo n-π band at 460 nm. The compound in the form of thin film gave an average electrical conductivity of 0.239 ± 0.001 Scm^-1 and a non-linear I-V curve with knee voltage at 2.3 V in dark condition.

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Synthesis, Characterization
and Electrical Conductance of
Ferrocenylazobenzene
Tei Tagga, Siti Athirah Mohamad Jamalia, Hasiah Sallehb &
Gurumurthy Hegdec
a School of Fundamental Science, Universiti Malaysia Terenggan,
Kuala Terengganu, Malaysia
b School of Ocean Engineering, Universiti Malaysia Terengganu,
Kuala Terengganu, Malaysia
c Faculty of Industrial Sciences and Technology, Universiti Malaysia
Pahang, Kuantan, Malaysia
Published online: 15 Dec 2014.
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To cite this article: Tei Tagg, Siti Athirah Mohamad Jamali, Hasiah Salleh & Gurumurthy Hegde (2014)
Synthesis, Characterization and Electrical Conductance of Ferrocenylazobenzene, Molecular Crystals
and Liquid Crystals, 604:1, 142-150, DOI: 10.1080/15421406.2014.968081
To link to this article: http://dx.doi.org/10.1080/15421406.2014.968081
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Mol. Cryst. Liq. Cryst., Vol. 604: pp. 142–150, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.968081
Synthesis, Characterization and Electrical
Conductance of Ferrocenylazobenzene
TEI TAGG,1,∗ SITI ATHIRAH MOHAMAD JAMALI,1
HASIAH SALLEH,2 AND GURUMURTHY HEGDE3
1School of Fundamental Science, Universiti Malaysia Terenggan,
Kuala Terengganu, Malaysia
2School of Ocean Engineering, Universiti Malaysia Terengganu,
Kuala Terengganu, Malaysia
3Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang,
Kuantan, Malaysia
Ferrocenylazobenzene was synthesized by condensing an aminoazobenzene dye with
ferrocenecarboxylic acid previously treated with oxalyl chloride. The compound dis-
played an anticipated chemically reversible one-electron oxidation process and gave a
formal potential, E◦ = 0.65 V. In the UV-Vis region, the azo π-π∗ and n-π∗ transitions
appeared at 355 and 460 nm respectively. On oxidation of the ferrocenyl moiety, the
azo π-π∗ band was blue-shifted to 348 nm with an increase in intensity, while a new
broad, lower energy absorption band assigned to the ligand-to-metal charge transfer
appeared at 622 nm. The growth of this new band was concurrent with the bleaching of
the metal-to-ligand charge transfer band which was largely obscured by the azo n-π∗
band at 460 nm. The compound in the form of thin film gave an average electrical
conductivity of 0.239 0.001 Scm−1 and a non-linear I-V curve with knee voltage at
2.3 V in dark condition.
Keywords Ferrocene; azobenzene; electrical; conductivity
1. Introduction
Azobenzene is a diazene (NH NH) compound, where both hydrogens are substituted by
phenyl groups. Its versatility, chemical stability and facile color tuning makes it one of the
important dyes in the broad class of aromatic azo compounds [1–3]. In theory, azobenzene
is a π-conjugated molecule with an electron-withdrawing effect [4], but there is no in-
vestigation using azobenzene as an electron acceptor in molecular electronics because the
intramolecular electronic communication between azobenzene and adjacent chromophore
can alter its original feature [5]. In contrast, azobenzene is mostly employed as a photo
responsive linker between chromophores since its readily induced and reversible isomer-
ization about the azo bond between the trans and cis geometric isomers proved useful in
∗Address correspondence to Tei Tagg, School of Fundamental Science, Universiti Malaysia
Terenggan, 21030 Kuala 6 Terengganu, Malaysia. E-mail: woochiat@umt.edu.my
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
[398]/142

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Synthesis and Characterization of FcAzoben
[399]/143
regulating molecular motion for photo switchable devices [6,7]. However, we are inter-
ested in employing azobenzene as an acceptor by conjugating it to a redox active (electron
donating) chromophore like ferrocene in a donor-acceptor array. There are a few reports
on azobenzenes functionalized with ferrocenes [8–13], and they are limited to the study
of photoisomerization behaviors of azobenzenes on switching the oxidation state of the
ferrocenyl moieties. In this paper, we report the preparation of a new ferrocenylazobenzene
(FcAzoben) and its spectroscopic, electrochemical and spectroelectrochemical properties.
The electrical conductance studies were carried out in dark condition to omit any photo
response of the azo moiety.
2. Experimental
a. Synthesis of Ferrocenylazobenzene (FcAzoben)
All chemicals were purchased and used without further purifications except for triethy-
lamine which was distilled prior to use. All reactions were carried out under nitrogen atmo-
sphere. Ferrocenoyl chloride was prepared by a modified literature method [14]. Preparation
of ferrocenylazobenzene (FcAzoben): Ferrocenoyl chloride (0.43 g, 1.73 mmol) was dis-
solved in 30 mL of dry CH2Cl2, and 2.5 mL of distilled NEt3 was added to the solution. After
being stirred for 30 min at room temperature, 4-aminoazobenzene (0.11 g, 0.57 mmol) in
30 mL of dry CH2Cl2 was added dropwise within 1 h. The reaction mixture was stirred for
48 h at room temperature, and then heated to reflux for 2 h. Solvent was removed in vacuo
and the residue purified by column chromatography (SiO2, CH2Cl2) gave yellow solid of
FcAzoben (0.16 g, 70%). Anal. Calcd. for C23H19FeN3O: C, 67.50; H, 4.68; N, 10.27.
Found: C, 67.32; H, 4.64; N, 9.97. EI-MS: (M + Na)+, m/z = 432.07. 1H NMR (CDCl3),
δ (ppm): 4.31 (s, 5H, C5H5); 4.49 (s, 2H, β-C5H4); 4.84 (s, 2H, α-C5H4); 7.48–7.56 (m,
4H, C6H4 + NH); 7.80 (d, JHH = 9 Hz, 2H, C6H4); 7.94 (d, JHH = 7 Hz, 2H, C6H4); 8.00
(d, JHH = 9 Hz, 2H, C6H4). 13C NMR (CDCl3), δ (ppm): 68.34 (α-C5H4); 69.98 (C5H5);
71.19 (β-C5H4); 75.87 (Cα C C O); 119.61, 122.74, 124.18, 129.08, 130.72, 140.71,
148.84, 152.75 (C6H4 + C6H5); 168.80 (C O).
b. Deposition of FcAzoben on ITO Substrate
FcAzoben was deposited on the ITO substrate by electrochemical method using the Elec-
trochemical Impedance Spectroscopy (EIS) PGSTAT302. The experimental set-up consists
of an electrochemical cell, a potentiostat/galvanostat, and a General Purpose Electrochem-
ical System (GPES). Using the GPES software, cyclic voltammetry (Staircase) method
was set to be in Normal method. The cyclic process was set for 20 cycles. Deposition was
completed in acetonitrile (ACN) with the following conditions; scan rate of 0.05 Vs−1
,
potential range of 0–1.5 V, solution of ∼10−4 M in electroactive material and 0.1 M in
lithium tetrafluroborate (LiBF4) as supporting electrolyte.
c. Characterizations
Elemental analysis was obtained using FLASH EA 1112 CHNS-O analyzer. Mass spectrum
1
was recorded on Shimadzu LCMS-QP8000 spectrometer. H and 13C NMR spectra were
recorded using Bruker Avance III 400 MHz spectrometer in CDCl3 at 25◦C. IR spectrum
was recorded via FTIR Perkin Elmer 100 spectrophotometer using potassium bromide
(KBr) pellet. UV-Vis spectrum was recorded on Shimadzu 1601 series in ACN using 1 cm
path length quartz cell. Cyclic voltammetry was performed in ACN using Electrochemical
Impedance Spectroscopy (EIS) PGSTAT302 with a three-electrode cell consisting of a pol-
ished Pt rod working electrode, Pt disc counter electrode and AgCl reference electrode. The