Multifunctional geometrical isomers of ferrocene-benzo[1,2-b:4,5-b′]difuran-2,6-(3H,7H)-dione adducts: second-order nonlinear optical behaviour and charge transport in thin film OFET devices

Article abstract of DOI:10.1039/c6tc03876j

Geometrical isomers of a set of new ferrocene-benzo[1,2-b:4,5-b′]difuran-2,6-(3H,7H)-dione dyads were synthesized and their optical, nonlinear optical (NLO) and electrochemical properties were investigated. The compounds were fully characterized by spectroscopic data and single crystal X-ray analysis in few cases. The second-order nonlinear polarizabilities were measured in chloroform using a femtosecond hyper-Rayleigh scattering (HRS) method at 1300 nm. The dyads exhibit structure-dependent NLO properties, which could be rationalized by correlation with electrochemical and theoretical data. The (Z)-6 chromophore recorded higher β_HRS values than the corresponding (E)-6 isomer, in the donor-acceptor (D-A) type dyads. Similarly, in D-A-D chromophore 7, the β_HRS values of isomers follow the order (Z,Z) > (E,Z) > (E,E), which matches with the trend of the wavelength of their maximum absorption as well as an increasing band gap in that order. Owing to the inbuilt structural features, two of these D-A compounds were also explored as semiconducting materials in vacuum deposited top contact bottom gated thin film organic field-effect transistors (OFETs). Defying steric restrictions of the ferrocene unit, the triad (Z,Z)-7 depicted an unbalanced (μ_e: 3 × 10^?3 cm^?2 V^?1 s^?1 and μ_h: 7 × 10^?5 cm^?2 V^?1 s^?1) charge transport behaviour. Evaluation of the isomers of the type studied in this investigation constitutes one of very few reports, in particular this study reveals for the first time the semiconducting behaviour of thermally stable redox active Fc based semiconductors.

Full text of DOI:10.1039/c6tc03876j

View Article Online
View Journal
Journal of
Materials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: P. Singla, N. Van
Steerteghem, N. Kaur, A. Z. Ashar, P. Kaur, K. Clays, K. S. Narayan and K. Singh, J. Mater. Chem. C, 2016,
DOI: 10.1039/C6TC03876J.
This is an Accepted Manuscript, which has been through the
Volume
4 Number 1 7 January 2016 Pages 1–224
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry C
Accepted Manuscripts are published online shortly after
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7526
PAPER
~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
rsc.li/materials-c

Please do not adjust margins
Journal of Materials Chemistry C
Page 1 of 12
View Article Online
DOI: 10.1039/C6TC03876J
Journal Name
ARTICLE
Multifunctional geometrical isomers of ferrocene-benzo[1,2-b:4,5-
b']difuran-2,6-(3H,7H)-dione adducts: Second-order nonlinear
optical behaviour and charge transport in thin film OFET devices
+Received 00th January 20xx,
Accepted 00th January 20xx
Priya Singla,a Nick Van Steerteghem, b Navdeep Kaur,a A. Z. Ashar,c Paramjit Kaur,*,a Koen Clays,b
DOI: 10.1039/x0xx00000x
K. S. Narayanc and Kamaljit Singh*,a
www.rsc.org/
Geometrical isomers of a set of new ferrocene-benzo[1,2-b:4,5-b']difuran-2,6-(3H,7H)-dione dyads were synthesized and
their optical, nonlinear optical (NLO) and electrochemical properties were investigated. The compounds were fully
characterized with spectroscopic data and single crystal X-ray analysis in few cases. The second-order nonlinear
polarizabilities were measured in chloroform using femtosecond hyper-Rayleigh scattering (HRS) method at 1300 nm. The
dyads exhibit structure-dependent NLO properties, which could be rationalized by correlation with electrochemical and
theoretical data. The (Z)-6 chromophore recorded higher βHRS than the corresponding (E)-6 isomer, in the donor-acceptor
(D-A) type dyads. Similarly, in D-A-D chromophore 7, βHRS values of isomers follow the order (Z,Z) > (E,Z) > (E,E), which
matches with the trend of the wavelength of their maximum absorption as well as increasing band gap in that order.
Owing to the inbuilt structural features, two of these D-A compounds were also explored as semiconducting materials in
vacuum deposited top contact bottom gated thin film field-effect transistors (OFETs). Defying steric restrictions of
ferrocene unit, the triad (Z,Z)-7 depicted an unbalanced (e: 3 x 10-3 cm-2V-1s-1 and h: 7 x 10-5 cm-2V-1s-1) charge transport
behaviour. Evaluation of the isomers of the type studied in this investigation constitute one of very few reports, in
particular this study reveals for the first time semiconducting behaviour of thermally stable redox active Fc based
semiconductors.
organometallic chromophores,18-22 owing to their inbuilt
structural features, redox behaviour, flexibility and ease of
synthesis, thermal stability etc. constitute excellent candidates
INTRODUCTION
Multifunctional organic materials1 capable of performing
different tailorable functions are in the forefront of future
for potential applications in the field of electro-optical
materials, photonics and semiconductors. This has additionally
been attributed to their intense low energy electronic
transitions originating from metal-to-ligand charge-transfer
(MLCT) or ligand-to-metal charge-transfer (LMCT) transitions.
Amongst the organometallics, ferrocene (Fc) owing to many
attractive features such as electron donating strength and low
oxidation potential facilitating the charge-transfer process, has
presented itself as a good, tuneable electron donor alongside a
variety of electron acceptors to probe NLO activity of the
resulting various donor-acceptor (D-A) designs.15-17 However,
depending upon the oxidation state of the metal centre, the Fc
unit can turn as a strong donor or acceptor, a feature that has
been exploited for switching of the NLO activity, important in
interfacing electronic data to wide band communication.19,20,23-
technologies. The donor-acceptor architects of -conjugated
compounds on one hand show optical nonlinearity, on the
other hand these have been used in photovoltaics as well as
thin film transistor devices etc.2,3 Nonlinear optical (NLO)4-7
materials have wide applications in the field of photonics,8,9
nanophotonics10 and optoelectronics,11-14 such as optical signal
processing, broad-band optical communications, integrated
optics, optical sensing, optical poling, optical computing and
optical limiting etc. and have received considerable recent
interest. Out of a wide range of NLO active chromophores,15-17
a.Department of Chemistry, UGC Centre of Advance Study-II, Guru Nanak Dev
University, Amritsar – 143 005, India. E-mail: kamaljit.chem@gndu.ac.in (K.
Singh), paramjit19in@yahoo.co.in (P. Kaur). Tel.: +91 183 2258853; fax: +91 183
2258819/20
26
In our previous reports, we have deduced the structure-
b.Department of Chemistry, University of Leuven, Celestijnenlaan 200D, B-3001
Leuven, Belgium. E-mail: Koen.Clays@fys.kuleuven.be (K. Clays).
property relationships of NLO active chromophores by varying
the conjugation path and/or acceptor strength.25,27,28
Interestingly, in one of these reports, switching of the second-
order NLO response of Fc push-pull chromophores was
demonstrated.25 Here in the present investigation, we report
new class of dyads obtained by linking a donor Fc to benzo[1,2-
b:4,5-b']difuran-2,6-(3H,7H)-dione acceptor to furnish D-A type
c. Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced
Scientific Research, Bangalore 560064, Karnataka, India.
Electronic Supplementary Information (ESI) available: [X-ray crystallographic data,
microanalytical data, cyclic voltammograms, cartesian coordinates of theoretically
optimized geometries, contour diagrams and complete reference 44, CCDC
1499221 and 1499222]. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 2 of 12
ARTICLE
Journal Name
dyad, or the D-A-D type chromophore, where the acceptor is value of 434 x 10-30 esu at 1300 nm for the octopolar41-43 βXXX
View Article Online
DOI: 10.1039/C6TC03876J
flanked by two Fc units. Interestingly, we have isolated hyperpolarizability tensor component.
different geometrical isomers of the D-A constructs, which
allowed us to deduce interesting comparisons on the NLO
Computational methods
behaviour of these isomeric compounds. Despite of
a
All theoretical calculations were carried out by using the
Gaussian 09 suite of programs.44 The molecular geometries of
the chromophores and related calculations were performed by
density functional theory (DFT) method using B3LYP functional
group and 6-31G(d) as the basis set.45,46 The first 15 excited
states were calculated by using time-dependent density
functional theory (TD-DFT calculations) in dichloromethane as
the solvent medium (CPCM model). The molecular orbital
contours were plotted using Gauss view 5.0.9. (For Cartesian
co-ordinates see, Table S1-S5, see †ESI)
significant number of studies reporting second order harmonic
generation in Fc chromophores, only a few studies have been
reported where such comparisons have been drawn.29-34
Additionally, we explored charge transport behaviour of
selected compounds in thin film organic field-effect transistor
devices and found that these exhibit, both p-type as well as n-
type charge transport behaviour.
EXPERIMENTAL SECTION
Materials and characterization
Fabrication and characterization of OFET devices
All liquid reagents were dried/purified by using the
recommended drying agents and/or distilled over 4Å
molecular sieves. Toluene was dried using sodium
benzophenone ketyl. Ferrocene and benzoquinone were
purchased from Spectrochem and used as such. IR spectrum
was recorded on Perkin-Elmer FTIR-C92035 Fourier-transform
Top contact/ bottom gate geometry was adapted to fabricate
FETs (with results represented from five devices of each of (E)-
6
and (Z,Z)-7). Glass substrates cut in definite sizes (1”×3/4”)
were thoroughly cleaned by sonication in hot soapy water,
deionized water, 1:1 mixture of isopropyl alcohol (IPA) and
acetone. The substrates were then kept in a boiling mixture
1
spectrophotometer in range 400–4000 cm-1 as KBr pellets. H
o
(100 C) of ammonia, hydrogen peroxide and water (1:1:5) for
NMR and 13C NMR spectra were recorded on Bruker Biospin
Avance III HD at 500 MHz, in CDCl3 and/or DMSO-d6 containing
TMS as internal standard. Data are reported as follows:
chemical shift in ppm (δ), integration, multiplicity (s = singlet, d
= doublet, t = triplet, m = multiplet) and coupling constant J
(Hz). Mass spectrum (HRMS) was recorded on Bruker HRMS
MICROTOF II spectrometer. Melting points were recorded in
open capillaries and are uncorrected. For column
chromatography, silica gel (60–120 mesh) and (230-400 mesh)
was employed and eluted with ethyl acetate/ hexane,
chloroform/ hexane or dicloromethane/hexane mixtures. UV-
visible studies were carried out using HITACHI U-2910
Spectrophotometer. The cell holder of the spectrophotometer
15 min. to get clean-hydrophilic substrates. The substrates
were then cleaned in boiling IPA and made dry with N2 gas
flow. 40 nm thick aluminium gate electrodes were made on
these substrates using thermal evaporation at 5 × 10-6 mbar.
BCB dielectric in mesitylene was spin coated at 1000 rpm for
o
60 sec and is annealed at 290 C for 2 h in N2 filled glove box.
Dielectric surface is then passivated with HMDS spin coated at
1000 rpm and annealed at 110 oC for 1 h. Molecules were
slowly evaporated using programmed heater from a silica
o
crucible at ~110 C temperature and 3 x 10-5 mbar pressure,
while keeping the substrate at room temperature. Thickness of
the layer was monitored by quartz crystal monitor during the
evaporation and was further verified by atomic force
microscopy (AFM) studies. Source-drain Au contacts of
thickness 40 nm and width ~2 mm were made using patterned
mask and thermal evaporation at 5 × 10-6 mbar. Geometrical
dimensions of OFET are in the range of channel length (L): 30-
60 µm, channel width (W): 1-2 mm. OFET characterization
were done in evacuated chamber connected with probes.
OFET saturation mobility was calculated using the equation: Ids
ο
was maintained at 25 C for consistency in the recordings. The
redox
ferrocene/ferrocenium (Fc/Fc+) redox couple were determined
by cyclic voltammetry on CHI 660D Electrochemical
behaviour
and
the
reversibility
of
the
a
Workstation with a conventional three-electrode configuration
consisting of glassy carbon electrode as working electrode,
platinum wire as counter electrode and Ag/AgCl as the
reference electrode. The experiments were carried out in a 1 x
10-4 M solution of sample in dichloromethane containing 0.025
M tetrabutylammoniumhexaflorophosphate, n-Bu4NPF6 as the
supporting electrolyte at room temperature. Deoxygenation of
the solutions was achieved by bubbling nitrogen for 10 min
and the working electrode was cleaned after each run. The
voltammograms were recorded with a scan rate of 100 mV s-1.
Thermogravimetric analyses (TGA) were performed (0–1000
oC) on an EXSTAR TG/DTA 6300 instrument under N2
atmosphere, at a heating rate of 10 oC min-1. Femtosecond HRS
measurements35-40 were performed at 1300 nm using a
commercial Ti:sapphire laser at ambient temperature. Crystal
violet (D3h) in methanol was used as the reference, with a
sat
= [(µFET CoxW)/2L](VG-Vt)2, where Ids is the saturation current,
sat
µFET is the saturation mobility, Cox is the capacitance per unit
area of dielectric, W is the width of channel, VG is the gate
voltage, Vt is the threshold voltage and L is the length of the
channel. Capacitance per unit area (Cox) of a 400 nm thin film
of divinyltetramethylsiloxane bisbenzocyclobutene (BCB) is
measured as 2.1 nF/cm2. Keithley 4200-SCS was used for
electronic characterization of OFET. Atomic force microscopy
(AFM) topographic images were taken using JPK Nanowizard 3
AFM in tapping mode (cantilever force constant: 40 N/m,
resonant frequency: 310 kHz).
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 12
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
Synthesis
(10% w/v) solution at 0 oC and allowed to stir VoievweArrnticilgehOtnlianet
room temperature and then extracted with diethyl ether (2 x
DOI: 10.1039/C6TC03876J
All compounds have been adequately characterized using
spectroscopic as well as microanalytical data (Fig. S1-S27, see
†ESI)
50 ml). The organic layer was treated, in sequence, with HCl
(1N,
2 x 25 ml) solution, saturated aqueous sodium
bicarbonate solution (2 x 25 ml) and water (3 x 25 ml), after
which it was dried over anhydrous sodium sulphate. Finally the
ether layer was evaporated under reduced pressure and the
residue was purified by column chromatography using
hexane:ethyl acetate (5:95, v/v) as eluents to afford ferrocene-
Synthesis of 2-2’-(2,5-dihydroxy-1,4-phenylene)diacetic acid 3
A three-necked round-bottomed flask equipped with two
dropping funnels, was charged with ethyl cyanoacetate (8.50
g, 8 ml, 75 mmol) in ethanol (30 ml), to which concentrated
ammonium hydroxide (6.37 g, 7 ml, 181.79 mmol) was added.
Meanwhile, additional ethyl cyanoacetate (12.75 g, 12 ml,
112.76 mmol) and p-benzoquinone (10 g, 92.5 mmol) in
ethanol (100 ml, 95%, v/v) was dissolved by stirring at 40 oC for
30 min. This solution was transferred to one of the dropping
funnels while a dilute solution of ammonium hydroxide (22.75
g, 25 ml, 649.25 mmol) in water (40 ml) was added to the
other dropping funnel. Stirring was started and the rates of
addition of the dropping funnels was adjusted in such a way
that the solutions were delivered into the flask at a uniform
rate. After completion of the addition, the reaction mixture
was stirred for additional 1 h. The precipitates formed were
filtered under vacuum and washed with ethanol until the
1-carboxaldehyde
5 as a thick red oil. Upon recrystallization in
hot hexane, (1.10 g, 98%) was obtained as bright orange red
5
crystalline solid. Rf: 0.15 (ethyl acetate:hexane/ 10:90). m.p.:
o
105 C. IR (KBr): υmax 3095 (aromatic C-H), 1660 (CHO), 1030
(Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 oC): δ 4.19 (s, 5H, CpH),
4.38 (s, 2H, CpH), 4.47 (2H, CpH), 9.92 (s, 1H, CHO). 13C NMR
o
(125 MHz, CDCl3, 25 C): δ 66.4, 68.1, 68.9, 82.4, 192.5. HRMS:
m/z calculated for C11H10OFe: 214.0081. Found: 213.8000 (M+).
General procedure for synthesis of 3-(ferrocen-1-ylidene) benzo
[1,2-b-4,5-b]difuran-2,6-(3H,7H)-dione, 6 and 3,7-di-(ferrocen-1-
ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-dione 7
A solution of benzo[1,2-b-4,5-b']difuran-2,6-(3H,7H)-dione
4
(0.50 g, 2.63 mmol), ferrocene-1-carboxaldehyde (0.42 g,
5
filtrate turned colourless. Compound
obtained as a dark purple solid.
For subsequent hydrolysis, a suspension of
2
(7.5 g, 25%) was
1.90 mmol), and p-toluenesulfonic acid (p-TsOH) (0.08 g, 0.47
o
mmol) in acetic acid (25 ml) was refluxed at 115 C in a two-
2 (4 g, 12 mmol) in
neck round bottomed flask equipped with reflux condenser,
under nitrogen atmosphere for 8 h. After completion (TLC), the
reaction mixture was cooled to room temperature; water (30
ml) was added and was stirred for additional 15 min. This
reaction mixture was then extracted with DCM (3 x 25 ml). The
organic extract was washed with water (2 x 20 ml), dried over
anhydrous sodium sulphate and evaporated under reduced
concentrated hydrochloric acid (0.037g, 25 ml, 1.02 mmol) and
water (25 ml) was refluxed at 110 oC for about 20 h. To this hot
reaction mixture, water (20 ml) and charcoal (2 g) were added
and the reaction was stirred for additional 5 min, after which it
was rapidly filtered under vacuum. The filtrate was cooled and
3
(2.8 g, 49%) was obtained as creamish white crystalline solid.
pressure to obtain crude 6, comprising of two isomers of the
Synthesis of benzo[1,2-b-4,5-b’]difuran-2,6-(3H,7H)-dione 4
To a suspension of (1.0 g, 4.10 mmol) in dry toluene (50 ml),
product in 33.68 and 66.31 % (1H NMR, Fig. S28, see †ESI)
ratio, respectively. The mixture was purified by column
chromatography over 120-160 silica using chloroform:hexane
(70:30 v/v) mixture as eluent and the isomeric product mixture
was obtained in (0.25 g, 25%) yield. The isomers were resolved
upon repeated (2-3 times) column chromatography over
230:400 silica using hexane:DCM (40:60, v/v) as eluent and the
3
acetic anhydride (10.82 g, 10 ml, 105.90 mmol) was added.
o
The mixture was stirred at 100 C for 5 h and the solvent was
removed under reduced pressure. The residue was purified by
column chromatography using chloroform as eluent and the
product was recrystallized from toluene to obtain
4 (0.79 g, 64
%) as white crystalline solid. Rf: 0.20 (chloroform). m.p.: 260
oC. IR (KBr): υmax 3096 (aromatic C-H str), 2925 (C-H str), 1787
pure isomers (Z)-6 and (E)-6 were isolated as dark purple and
1
o
(cyclic ester) cm-1. H NMR (500 MHz, DMSO, 25 C): δ 3.96 (s,
dark red coloured solids, respectively.
Following a similar procedure, a refluxing (85 oC) solution of
4H, -CH2), 7.24 (s, 2H, ArH). 13C NMR (125 MHz, DMSO, 25 C):
o
benzo[1,2-b-4,5-b']difuran-2,6-(3H,7H)-dione
mmol), ferrocene-1-carboxaldehyde (0.49 g, 2.32 mmol), p-
TsOH (0.051 g, 0.29 mmol) in acetic acid (15 ml) during 24 h,
furnished crude , which was purified over 120-160 mesh silica
4 (0.20 g, 1.05
δ 33.8, 107.8, 124.4, 150.6, 174.8. HRMS: m/z calculated for
C10H6O4: 190.0266. Found: 190.0000 (M+).
5
7
Synthesis of ferrocene-1-carboxaldehyde 5
using chloroform:hexane (70:30 v/v) mixtures to isolate the
isomeric products in (0.32 g, 52%) overall yield and 36.74%,
28.59% and 34.66% (1H NMR, Fig. S29 and S30, see †ESI) ratio,
respectively. The isomeric product mixture was resolved by
repeated (2-3 times) column chromatography over 230:400
silica using hexane:DCM (50:50, v/v) as eluents to isolate pure
isomers (Z,Z)-7, (E,Z)-7 and (E,E)-7 as dark green coloured
solids. The characteristic data of the products is given below;
however additional 2D NMR data is given in (Fig. S13-S17, see
A mixture of N-methyl-formanilide (1.88 g, 1.90 ml, 14 mmol)
and POCl3 (1.35 g, 0.80 ml, 8 mmol), was stirred at 0 C for 15
o
min. To the resultant suspension, finely powdered ferrocene
(1.00 g, 0.005 mol) was added in small portions using a solid
addition tube under the atmosphere of dry nitrogen gas. The
resultant purple mixture was allowed to stir for additional 60
min. at room temperature until complete consumption of
ferrocene was confirmed from the TLC. The reaction was
quenched by the addition of cold aqueous sodium acetate
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 4 of 12
ARTICLE
Journal Name
1
o
†ESI). Further, to facilitate the H NMR assignment, relevant ester), 1037 (Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 C): δ 4.24
View Article Online
DOI: 10.1039/C6TC03876J
protons are labelled (Fig. S1-S6, see †ESI).
(s, 10H, CpH 1), 4.73 (s, 4Hb, CpH 2), 5.31 (s, 4Hc, CpH 2), 7.16
(s, 2Hd, ArH), 7.49 (s, 2He, =CH-). 13C NMR (125 MHz, CDCl3, 25
oC): δ 70.25, 73.69, 73.76, 100.58, 115.56, 125.76, 142.60,
148.34, 166.34. HRMS: m/z calculated for C32H22O4Fe2:
582.0217 Found: 581.9723 (M+).
3-(Ferrocen-1-ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-
dione, (Z)-6
o
Purple solid. Rf: 0.38 (hexane:DCM/ 30:70). m.p. >280 C. IR
(KBr): υmax 3084 (aromatic C-H), 3036 (=CH-), 2921 (-CH2), 1763
o
(cyclic ester), 1039 (Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 C):
3,7-Di-(ferrocen-1-ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-
dione, (E,Z)-7
δ 3.76 (s, 2Hg, -CH2), 4.24 (s, 5H, CpH 1), 4.74 (s, 2Hb, CpH 2),
o
5.31 (s, 2Hc, CpH 2), 7.02 (s, 1Hf, ArH), 7.22 (s, 1Hd, ArH), 7.51 Dark green solid. Rf: 0.62 (hexane:DCM/ 30:70). m.p. >280 C
(s, 1He, =CH-). 13C NMR (125 MHz, CDCl3, 25 oC): δ 33.70, 70.25, IR (KBr): υmax 3083 (aromatic C-H), 3039 (=CH-), 1764 (cyclic
73.81, 73.85, 100.85, 107.51, 114.72, 122.15, 126.47, 143.84, ester), 1030 (Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 C): δ 4.25
o
148.10, 150.96, 166.17, 173.62 HRMS: m/z calculated for (s, 5H, CpH 1), 4.27 (s, 5H, CpH 1′), 4.73 (s, 2Hb, CpH 2), 4.75 (s,
C21H14O4Fe: 386.0242 Found: 386.3416 (M+).
2Hb′, CpH 2′), 4.78 (s, 2Hc′, CpH 2′), 5.32 (s, 2Hc, CpH 2), 7.22
(s, 1Hd, ArH), 7.52 (s, 1He, =CH-), 7.71 (s, 1Hd′, ArH′), 7.75 (s,
o
1He′, =CH′-). 13C NMR (125 MHz, CDCl3, 25 C): δ 70.26, 70.33,
3-(Ferrocen-1-ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-
dione, (E)-6
Red solid. Rf: 0.33 (hexane:DCM/ 30:70). m.p. >280 oC. IR (KBr):
71.70, 72.87, 73.89, 73.95, 100.71, 104.55, 115.22, 117.42,
122.19, 126.80, 142.60, 143.54, 147.80, 150.15, 166.35,
169.61. HRMS: m/z calculated for C32H22O4Fe2: 582.0217
Found: 581.9733 (M+).
υmax 3079 (aromatic C-H), 3039 (=CH-), 2923 (-CH2), 1770
(cyclic ester), 1035 (Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 C):
o
δ 3.77 (s, 2Hg, -CH2), 4.27 (s, 5H, CpH 1), 4.73 (s, 2Hb, CpH 2),
4.76 (s, 2Hc, CpH 2), 7.08 (s, 1Hf, ArH), 7.73 (s, 1Hd, ArH), 7.78
(s, 1He, =CH-). 13C NMR (125 MHz, CDCl3, 25 oC): δ 33.73, 70.33,
3,7-Di-(ferrocen-1-ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-
dione, (E,E)-7
o
71.71, 72.96, 104.73, 107.70, 116.75, 123.15, 123.45, 143.98, Dark green solid. Rf: 0.59 (hexane:DCM/ 30:70). m.p. >280 C.
149.95, 150.58, 169.14, 173.28. HRMS: m/z calculated for IR (KBr): υmax 3093 (aromatic C-H), 3039 (=CH-), 1767 (cyclic
o
C21H14O4Fe: 386.0242 Found: 386.7609 (M+).
ester), 1045 (Cp) cm-1. 1H NMR (500 MHz, CDCl3, 25 C): δ 4.28
(s, 10H, CpH 1), 4.76 (s, 4Hb, CpH 2), 4.80 (s, 4Hc, CpH 2), 7.74
(s, 2Hd, ArH), 7.77 (s, 2He, =CH-). 13C NMR (125 MHz, CDCl3, 25
oC): δ 70.39, 71.80, 73.10, 104.61, 117.08, 123.25, 143.50,
149.65, 169.34. HRMS: m/z calculated for C32H22O4Fe2:
582.0217 Found: 581.9727 (M+).
3,7-Di-(ferrocen-1-ylidene)-benzo[1,2-b-4,5-b]difuran-2,6-(3H,7H)-
dione, (Z,Z)-7
o
Dark green solid. Rf: 0.67 (hexane:DCM/ 30:70). m.p. >280 C.
IR (KBr): υmax 3098 (aromatic C-H), 3033 (=CH-), 1758 (cyclic
Scheme1: Synthesis of isomers of 6 and 7.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 12
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C6TC03876J
RESULTS AND DISCUSSION
Synthesis
Condensation of ferrocene 1-carboxaldehyde
with benzo[1,2-b:4,5-b’]difuran-2,6-(3H,7H)-dione
toluenesulphonic acid in acetic acid furnished isomeric mixture
of 3,7-di-(ferrocen-1-ylidene)-benzo[1,2-b-4,5-b ]difuran-2,6-
(3H,7H)-dione , which were isolated after rigorous flash
5
(2.2 equiv.) Theoretical study
4
using p-
We initiated our study on
first conducting
6
(D-A) and
7
(D-A-D) compounds by
a
theoretical calculations (Gaussian09,
B3LYP/6-31G(d))44-46 for both, on the individual donor and
acceptor molecules as well as their isomers, to visualize the
density functional theory (DFT) optimized molecular
geometries (Fig. S33, see †ESI) and charge density isosurfaces
for the highest occupied molecular orbitals (HOMOs) and
lowest unoccupied molecular orbitals (LUMOs) (Fig. 1) as well
as their associated energies (Fig. S34 and S35, Table S6 and S7,

7
chromatography and identified as (Z,Z), (E,Z) and (E,E) isomers
(Scheme 1) corresponding to D-A-D architect. However, when
0.75 equiv. of
type 3-(ferrocen-1-ylidene)-benzo[1,2-b-4,5-b
(3H,7H)-dione were isolated (Scheme 1). Compound
prepared by subjecting 2,2’-(2,5-dihydroxy-1,4-phenylene)
diacetic acid to a dehydration reaction using acetic anhydride
following a reported procedure.47-49 Compound
in turn was
5
were employed, Z and E isomers of the D-A
]difuran-2,6-
was

6
4
see †ESI). Both
6 as well as 7 maintain the coplanarity of the
3
benzodifuranone unit due to rigid C=C bonds of the molecular
core flanked by one and two Fc units, respectively. The
electron density in the HOMO-1 is exclusively localized on the
donor Fc unit(s), while it is additionally distributed over the π-
3
obtained through condensation of 1,4-benzoquinone and ethyl
cyanoacetate using ammonium hydroxide as base.50 Selected
compounds (E)-6 and (Z,Z)-7 showed good thermal stability
conjugated framework in the HOMO (Fig. 1) orbitals, both in
6
with a decomposition temperature of 251 oC and 254 oC
as well as . It is localized on the acceptor benzodifuranone
7
respectively (Fig. S31 and S32, see †ESI). The structures and
geometry of (Z)-6 and (E,E)-7 isomers have additionally been
confirmed by single crystal X-ray crystallography, while the
geometries of the remaining isomers were assigned in analogy
with the single crystal X-ray structures.
part in the LUMO and LUMO+1 orbitals indicating greater
electron affinity. This unequivocally supports existence of
charge transfer considering appropriate HOMO and LUMO.
(Z)-6
(E)-6
(Z,Z)-7
(E,Z)-7
(E,E)-7
LUMO+1
-1.8090 eV
-0.5640 eV
-0.5605 eV
-1.8691 eV
-2.4607 eV
-5.3197 eV
-5.5763 eV
-1.7319 eV
LUMO
-2.2487 eV
-2.1967 eV
-2.4664 eV
-2.4653 eV
HOMO
-5.4839 eV
-5.5535 eV
-5.3668 eV
-5.4136 eV
HOMO-1
-5.6221 eV
-5.6792 eV
-5.5965 eV
-5.6348 eV
Fig. 1 Contour surfaces of frontier molecular orbitals involved in electronic transitions of HE bands of the isomers of
6
and
7, obtained from TD-DFT calculations using
B3LYP/6-31G(d) in DCM as solvent at an isosurface value of 0.02 au.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 6 of 12
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/C6TC03876J
(b)
(a)
(c)
(f)
(d)
(e)
Fig. 2 ORTEP diagrams of (Z)-
(E,E)-7.
6 and (E,E)-7: (a-c) side view, front view and crystal packing diagram of (Z)-6; (d-f) side view, front view and crystal packing diagram of
Single crystal X-ray structures of (Z)-6 and (E,E)-7
Crystals of both (Z)- and (E,E)- suitable for single crystal
were performed using B3LYP/6-31G(d) basis set using CPCM
model in dichloromethane (DCM) phase. The TD-DFT deduced
6
7
frontier molecular orbitals (FMOs) of the isomers (Z)- and (E)-
and their associated energies are depicted in fig. 4. The LE
band at 542 nm in (Z)- is essentially a MLCT band comprising
6
structural analysis could conveniently be grown by slow
evaporation of their respective solutions (hexane:DCM/4:6
v/v) at room temperature. ORTEP diagrams of the side and
front views and crystal packing structures are shown in fig. 2.
The refinement details, bond lengths, bond angles and other
crystallographic data are tabulated (Tables S8-S19, see †ESI).
6
of mainly: H→L (CI = 0.5156), H-3→L (CI = 0.4285) and H-
1→L+3 (0.3687), while the HE bands at 386 and 328 nm are
assigned as π→π* transitions with some contribution from
MLCT also. The positions of these bands get blue shifted in (E)-
The chromophore (Z)-
6 crystallised in centrosymmetric
6
with LE band (H→L, CI = 0.4731) appearing at 528 nm and
monoclinic P lattice with P21/c space group and has an almost
perfect coplanar arrangement between the Fc donor and the
acceptor. The two Cp rings are slightly tilted (0.47°) w.r.t each
other. The crystal packing structure (Fig. 2c) indicates that the
the HE bands at 380 and 320 nm, which may be due to the
influence of the trans- geometry weakening the charge-
transfer in (E)-6 as compared to its cis- counterpart. Further,
the LE bands depicted a large hypsochromic shift (∆λ=14 nm)
in comparison to HE bands (∆λ= 6-8 nm) while moving from
(Z)-6 to (E)-6.
dimer pairs adopt a head to tail (D-AA-D) alignment in which
the molecular dipoles are aligned antiparallel w.r.t each
other.30
The chromophore (E,E)-7 crystallised in centrosymmetric
triclinic P lattice with P-1 space group with the two Cp rings of
each Fc group tilted (1.14°) w.r.t each other. While the
acceptor unit in both the cases maintain planarity, the two Fc
units in the latter case point to the same side w.r.t the
molecular plane of the central acceptor but are slightly tilted
w.r.t each other (Fig. 2d). In the packing diagram, contrary to
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
(Z)-6
(E)-6
(Z,Z)-7
(E,Z)-7
(E,E)-7
(Z)-
6
, one Fc group out of the two of one D-A-D
7
, slightly
, thus
overlaps with a Fc group of the second molecule of the
leading to a shifted stacking pattern.
7
Linear optical data
The UV-visible absorption spectra of both (Z)- and (E)-6 (Fig. 3)
0
are characterised by broad low energy (LE) bands in the range
of 458-624 nm and relatively intense high energy (HE) bands in
the range of 278-458 nm. In order to get a deeper insight into
the contributing transitions to these absorption bands, time
dependent density functional theory (TD-DFT) calculations
250
350
450
550
650
750
Wavelength (nm)
Fig. 3 Overlay of UV-visible absorption spectra in DCM (1 x 10-5 M) at 293 K, and
oscillator strength calculated from DFT calculations using B3LYP/6-31G(d) in
DCM phase, of isomers of
6 and 7.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 12
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C6TC03876J
with the predicted band gap (Fig.4) which follows the reverse
order of λabs (Fig. 3 and Table S20, see †ESI). Similarly trends
could be traced for the HE bands (π→π* transition) also (Table
S20, see †ESI).
-2.1967
-2.2487
-2.4664
-2.4653
-2.4607
-2.45
-3.1
LUMO
HOMO
-3.75
-4.4
∆E=3.2352
∆E=2.8583
∆E=3.3569
∆E=2.9004
∆E=2.9483
Electrochemistry
All isomers of chromophores
6 and 7 show electrochemically
-5.05
-5.7
reversible oxidation peaks (Table 1 and Fig. S36, see †ESI) in
-5.3190
-5.3668
-5.4136
analogy with the redox behaviour of Fc. Chromophore (Z)-
shows an anodic shift in the E1/2 in comparison to Fc (∆E1/2
6
=
-5.4839
-5.5536
0.100 V) reflecting the effect of electron withdrawal by
benzo[1,2-b:4,5-b’]difuran-2,6-(3H,7H)-dione
rendering Fc more difficult to oxidize. The (E)-
acceptor
6 isomer
(E,Z)-7
(E)-6
(Z,Z)-7
(E,E)-7
(Z)-6
however saw a greater anodic shift ((Z)-
V) (Table 1). This anodic shift is attributed to stabilization of
the HOMOs of (E)- (Table 1) compared to (Z)- . Similar trend
is observed upon comparing isomers of chromophore , where
the order of oxidation potential as well as half wave potential
of the three isomers follow the order: (Z,Z) < (E,Z) < (E,E)
6→(E)-6, ∆E1/2 = 0.059
Fig. 4 Comparison of the TD-DFT (B3LYP/6-31G(d)/DCM phase) calculated energies of
the FMOs and HOMO-LUMO band gaps (∆E) of isomers of 6 and 7.
6
6
7
The theoretical data furnished supporting evidence to the
observed blue shift, as the calculated energy of the HOMO of
(E)-
LUMO of (E)-
increased band gap in (E)-
6
is less than that of (Z)-
is raised in comparison to (Z)-
and consequent blue shift in the
6
, whereas the energies of the
[(∆E1/2 = 0.046V, Fc→(Z,Z)-
7; 0.078V, (Z,Z)-7→(E,Z)-7; 0.113V,
6
6
leading to
(Z,Z)- →(E,E)- ) (Table 1)]. These observations are also in good
7
7
6
agreement with the calculated energies of the corresponding
HOMO’s (Table 1).
absorption band (Tables S20 and S21, see †ESI).
Similar spectral behaviour is observed in the isomers of 7. The
LE and HE bands of the three isolated isomers of
7 were in the
Quadratic hyperpolarizability
range 494-734 nm and 302-494 nm, respectively (Fig. 3) and
the energies of their FMO are plotted in fig. 4. It can be seen
that the isomers with preponderance of (Z)- stereochemistry
exhibit MLCT (LE) bands in the order: (Z,Z) > (E,Z) > (E,E) (λabs
582, 570 and 568 nm, respectively). This is in good agreement
The first hyperpolarisability
and was measured in chloroform using the femtosecond
hyper-Rayleigh scattering (HRS) method35-40 at 1300 nm.
β, of the isomers of chromophores
6
7
=
Chromophore (Z)-6
recorded higher βHRS (52 x 10-30 esu) than
Table 1. HOMO-LUMO energies, band gaps and electrochemical data of isomers of 6 and 7
.
opt
EHOMO
(eV)a
ELUMO
(eV)a
Eg
µ(D)a
EHOMO
(eV)b
ELUMO
(eV)b
Eg
edge
Epa
E1/2 (V)f
ipa x 10-6
(A)g
(eV)a
(eV)c
(nm)d
(V)e
(Z)-6
-5.580
-2.303
3.277
3.1308
-4.950
-3.005
1.945
637.5
0.667
0.622
-1.793
(-5.484)
(-2.249)
(3.235)
(3.6327)
(0.577)
(3.066)
(E)-6
-5.689
(-5.554)
-5.294
(-5.319)
-5.356
-2.239
(-2.197)
-2.428
(-2.461)
-2.426
3.450
(3.357)
2.866
(2.858)
2.930
3.1228
(3.5947)
1.4131
(1.7609)
2.4746
-4.990
-4.950
-4.960
-5.050
-2.944
-3.113
-3.088
-3.171
2.046
1.837
1.872
1.879
606
670
0.725
(0.638)
0.690
(0.446)
0.735
0.681
0.568
0.646
0.681
-0.953
(1.210)
-4.013
(16.620)
-2.203
(Z,Z)-7
(E,Z)-7
(E,E)-7
662.5
660
(-5.367)
-5.417
(-2.467)
-2.423
(2.900)
2.994
(2.9771)
2.4799
(0.558)
0.789
(3.956)
-2.455
(-5.413)
(-2.465)
(2.948)
(3.0118)
(0.574)
(3.019)
aCalculated from DFT calculations using B3LYP/6-31G(d) in gas phase (The values in parenthesis are DFT calculated values in DCM phase); bCalculated as EHOMO
=
onset
opt
onset
-e[Eox
+ 4.4] and ELUMO = Eg + EHOMO (Eox
was determined from CV in DCM at 1 x 10-4 M in the presence of n-Bu4NPF6 (0.025 M) at 100 mVs-1) versus
ferrocenium/ferrocene redox couple; ccalculated from the absorption edge Egopt = 1240/edge; drecorded in DCM (1 x 10-5 M); eEpc values in parenthesis (Epa Fc = 0.572 V
and Epc Fc =0.472 V); fHalf-wave potential, E1/2= (Epc + Epa)/2, where Epc and Epa correspond to the cathodic and anodic peak potentials, respectively; ∆Ep = 80–120 mV;
and a scan rate of 100 mV s-1 (E1/2 Fc = 0.522 V).gAmplitudes of the anodic and cathodic (in parenthesis) peaks (ipa Fc = -2.116 A and ipc Fc = 2.180 A).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 8 of 12
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/C6TC03876J
(E)-6
(46 x 10-30 esu) (Table 2), which is in good agreement with
Table 2. Quadratic nonlinear optical parameters for isomers of
6 and 7.
the calculated dipole moments in gas as well as DCM phases,
and the optical band gap (Table 1). This decrease, albeit small,
is attributed to the comparatively weaker charge transfer
owing to stabilization of the HOMOs (Table 1) in the latter.
Further, assuming that these chromophores can be described
as one-dimensional dipolar chromophores with a single
dominating dipolar βZZZ tensor component,51 this tensor
component along the molecular z-axis is relevant for these two
isomers and has been calculated corresponding to the βHRS
a
b
c
Comp.
λmax
βHRS,1300
βZZZ
βHRS,0
(10-30esu)
(10-30 esu)
(10-30esu)
12.6
(Z)-6
546
52
126
(E)-6
(Z,Z)-7
526
582
46
132
111
-----
13.3
21
(E,Z)-7
(E,E)-7
574
564
125
96
-----
-----
22
19
from the relation βZZZ
=
βHRS (35/6)1/2 as 126 x 10-30 esu and 111
isomers.
, the
aSecond-order nonlinear polarizability, βHRS recorded at 1300 nm (10-30 esu) in
x 10-30 esu (Table 2), respectively for (Z)- and (E)-
6
CHCl3. bSecond-order nonlinear polarizability recorded along molecular z-axis,
Similarly, in the disubstituted D-A-D chromophore
7
βZZZ
.
cSecond-order nonlinear polarizability corrected for resonance
observed trend in the βHRS values of its isomers: (Z,Z: 132 x 10-
30 esu) > (E,Z: 125 x 10-30 esu ) > (E,E: 96 x 10-30 esu) (Table 2), is
essentially the same as the wavelength of their maximum
absorption as well as increasing band gap (Table 1) in that
enhancement, βHRS,0
.
Interesting results are obtained on relating the dynamic
βHRS,1300 to the resonance-corrected βHRS,0 (Table 2), assuming
that the LE (MLCT) band is the single NLO determining band.
The close proximity of the MLCT transitions (λLE = 550 nm
approx.) and the second harmonic wavelength (650 nm)
resulted in resonantly enhanced values of
values for this resonance enhancement, βHRS,0 was calculated
(Table 2) using the simple two-level model by the expression
order. However, unlike isomers of
6, these are not
characterised by a single major charge-transfer axis and thus
cannot be classified as one-dimensional chromophores.
Therefore βZZZ hyperpolarizability tensor component could not
β.
55,56 To correct the
β
be calculated. Compared to
first hyperpolarizability values in the isomers of disubstituted
analogues of is attributed to the addition of a second dipolar
6, the observed increase in the
7
2
2
β
(ω) / β
(0) = [(ωo)4/(ωo - ω2)(ωo - 4ω2)] ………..(3)
charge-transfer moiety. But a simplified model could be
where, ωo is the single photon absorption maximum of the
molecule in wave numbers, and ω is the laser fundamental
constructed, if it is assumed that the two dipolar βZZZ tensor
elements add up vectorially in the
crystal structure, at least for (E,E)- , vector model could be
constructed that allowed calculation of the vector sum of two
βZZZ components in (E,E)- from the given expressions,
7
triads.52-54 From the
frequency. Comparing the average of the intrinsic
β
values
7
(βHRS,0, without resonance enhancement) of the isomers of the
dyad
6 with the averaged values of the three isomers of the
7
triad, it could be seen that βHRS,0 values of the latter are
roughly doubled (Table 2).
βZZZ,0(avg.7) = 2 (cos θ/2)3 βZZZ,0 (avg.6) ………..(1)
βZZZ,0(avg.) ………..(2)
βHRS,0(avg.) (35/6)1/2
Charge transport behaviour
=
The intramolecular charge transfer in the donor-acceptor (D-A)
This yielded opening angle (Fig. 5) between the two Fc-A arms
in (E,E)-
to be approx. 44ο. Thus, the non-zero value for the
opening angle for a D-A-D triad clearly shows that the
molecular structure is non-centrosymmetric, which is further
corroborated by the crystal structure (Fig. 2d).
dyads of the types
6 and 7 bearing redox active organometallic
7
species such as Fc as donor linked to appropriate acceptor
have been also used as promising semiconducting materials.
Although large number of D-A systems have been used in thin
film57-60 as well as single crystal organic field effect transistors
(OFETs) devices,61-70 however, in no instance has a Fc based
semiconducting materials used in OFETs. Incorporation of Fc in
such chromophores can provide attractive features such as
flexibility in molecular design, light weight, low cost, thermal
stability apart from redox behaviour, which can induce
Z
switching of
a function. In the latter context, using
spectroelectrochemistry, we previously reported27,29,30
switching of second-order NLO polarizability of Fc based
chromophores as well as demonstrated switching of their NLO
response. To test the above hypothesis, and in continuation of
our interest,71-74 we fabricated thin film OFET devices of
θ
selected (E)-6 and (Z,Z)-7. Interestingly, the latter behaves as a
X
stable charge transport material with dominating n-type
charge transport. It is worth mentioning that although a
number of small molecules based p-channel semiconductor
materials have been reported75-79 with attractive charge carrier
F
ig. 5 Representation of opening angle (θ) for (E,E)-7. Green lines refer to
βzzz(mono).
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 12
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
mobility, only a few n-channel80-83 and even less number of characteristics in the Id(Vg) response with µeFET of 3 x 10-3 cm2V-
View Article Online
DOI: 10.1039/C6TC03876J

103 (Fig. 6a and 6b). However, the field-effect mobility due to
FET
ambipolar materials based on small molecules have been 1s-1 and µh of 7 x 10-5 cm2V-1s-1 and with on/off ratio, Ion/off
reported.84-87
The stronger oxidation peak of (Z,Z)-
7
compared to (E)-
6
holes and electrons is unbalanced and inclined in favour of n-
, FET characteristics were
. Comparison of the calculated energy levels of HOMOs not observed, primarily due to the absence of smooth film
and LUMOs revealed (Table 1) that compared to LUMO (- formation (Fig. 6c), unlike the optical quality films of (Z,Z)-
2.197) in (E)- , attachment of second Fc led to lowering of (Fig. 6d). The film formation features could possibly be
LUMO (-2.461 eV) in (Z,Z)- . However, attachment of the attributed to the molecular packing tendency of these hybrids
second Fc further raised the energy of the HOMO (-5.319 eV), The X-ray powder diffraction pattern of thin films of (E)- and
compared to (E)- (-5.554 eV) and also led to decrease in the (Z,Z)- deposited on silica substrates is shown in (Fig. S37, see
HOMO-LUMO gap (2.858 eV) in (Z,Z)- These results †ESI). A slightly broad peak was observed at a d-spacing of 3.84
suggested (Z,Z)- to be a narrow band gap dyad, compared to Å and 3.71 Å for (E)- and (Z,Z)- , respectively. The AFM height
3.357 eV) as also revealed from the optical band image of (E)- showed amorphous network while a slight
Eg 0.209 eV) (Table 1). A similar lowering of the crystalline network is shown for (Z,Z)- with a root mean-
(Table 1) compared to square (RMS) deviation of 70.95 nm and 2.42 nm, respectively
as shown in (Fig. 6c and 6d). Thus, low mobility values were
while (E)- showed no mobility in
good correlation with the theoretically calculated values (Table accordance with the high roughness obtained.90 Based on the
1). For most n-type organic semiconductors, the LUMO levels low mobility values of (Z,Z)- , we believe that although Fc acts
are in the range -3.5 to -4.0 eV.88,89 In the present case, while as a good donor, the non-planarity91 and steric restrictions
(E)- has LUMOs at -2.944 eV, (Z,Z)- has lower (-3.113 eV) caused by it in the present systems, might be one of the
LUMO levels, which are however optimal for n-type charge possible reasons for the lower field-effect mobility.
transport. Compared to (E)- , the lower band gap in (Z,Z)-
indicated greater p-doping process of the former compared to type charge transport. In case of (E)-
(E)-
6
6
7
6
7
.
6
6
7
7
.
7
6
7
calcd
(E)-
6
(Eg
6
opt
gap (

7
HOMO-LUMO gap of (E)-6 and (Z,Z)-7
that of Fc was also noted.
Further, the experimental HOMO-LUMO energies showed observed for (Z,Z)-
7
6
7
6
7
6
7
suggests operation of a strong intramolecular charge transfer,
which could be attributed to the enhanced π-conjugation
owing to the additional Fc donor. Further, since the LUMOs in
CONCLUSIONS
We have described intrinsic second-order nonlinear
polarizability (quadratic/first hyperpolarizability,
having Fc donor linked to benzo[1,2-b:4,5-b']difuran-2,6-
(3H,7H)-dione acceptor (D-A type) and the acceptor flanked by
β) of dyads
(Z,Z)-
injection by the Au electrodes of the OFET device is expected.
FET devices of (Z,Z)- obtained from 10 set of measurements
7 are more stabilized compared to (E)-6, a facile electron
7
two
Fc
units
(D-A-D
type).
clearly showed both n-type and p-type transport
(a)
(b)
(c)
(d)
Fig. 6 (a) Representative transfer and (b) output characteristics of (Z,Z)-
7
on HDMS passivated BCB dielectric. AFM height images of thin films of (c) (E)-
6
and (d) (Z,Z)-
7
coated on BCB.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 10 of 12
ARTICLE
Journal Name
9
P. N. Prasad, Nonlinear Optical PropertiesVieowfArtOiclregOannlinice
Interestingly, different geometrical isomers of these D-A
constructs were isolated, which allowed us to deduce
interesting comparisons on the NLO behaviour of these
isomeric compounds. Femtosecond HRS measurements were
performed at 1300 nm using a commercial Ti:sapphire laser at
ambient temperature and revealed structure dependent
quadratic hyperpolarizabilities. In UV-visible absorption
spectrum, positions of the bands get blue shifted in (E)-6 as
compared to its cis- counterpart, which has been attributed to
the influence of the trans- geometry weakening the charge-
Materials, Plenum, New York, 1991.
DOI: 10.1039/C6TC03876J
10 P. N. Prasad, Nanophotonics, Wiley, New York, 2004.
11 R. W. Boyd, Nonlinear Optics, Academic Press, New York,
1992.
12 Y. Shirota, J. Mater. Chem., 2000, 10, 1–25.
13 K. Clays, Chem. Mater., 2003, 15, 642–648.
14 M. G. Kuzyk, J. Mater. Chem., 2009, 19, 7444–7465.
15 S. Barlow and S. R. Marder, Chem. Commun., 2001, 1555–
1562.
16 P. Debroy and S. Roy, Coord. Chem. Rev., 2007, 251, 203–
221.
17 R. Horikoshi and T. Mochida, Eur. J. Inorg. Chem., 2010,
5355–5371.
18 F. Paul, K. Costuas, I. Ledoux, S. Deveau, J. Zyss, J.- F. Halet
and C. Lapinte, Organometallics, 2002, 21, 5229-5235.
19 T. Weyland, I. Ledoux, S. Brasselet, J. Zyss, and C. Lapinte,
Organometallics, 2000, 19, 5235-5237.
20 M. Samoc, N. Gauthier, M. P. Cifuentes, F. Paul, C. Lapinte
and M. G. Humphrey, Angew. Chem. Int. Ed., 2006, 45, 7376-
7379.
21 M. L. H. Green, S. R. Marder, M. E. Thompson, J. A. Bandy, D.
Bloor, P. V. Kolinsky and R. J. Jones, Nature, 1987, 330, 360-
362.
transfer in (E)-
theoretical data. Similar trends were observed in the isomers
of . Electrochemical data revealed that (E)- isomer shows
greater anodic shift than (Z)- due to stabilization of the
HOMOs of (E)- compared to (Z)- . Among the isomers of
chromophore , the oxidation potential as well as half-wave of
the three isomers followed the order: (Z,Z) < (E,Z) < (E,E).
Chromophore (Z)- recorded higher βHRS than (E)- , which is
attributed to weaker charge transfer. Similarly, in D-A-D
chromophore βHRS values of isomers follow the order (Z,Z) >
6, that was in good agreement with the
7
6
6
6
6
7
6
6
7
,
22 B. J. Coe, R. J. Docherty, S. P. Foxon, E. C. Harper, M.
Helliwell, J. Raftery, K. Clays, E. Franz and B. S. Brunschwig,
Organometallics, 2009, 28, 6880-6892.
23 C. Sporer, I. Ratera, D. Ruiz-Molina, Y. Zhao, J. Vidal-
Gancedo, K. Wurst, P. Jaitner, K. Clays, A. Persoons, C. Rovira
and J. Veciana, Angew. Chem., Int. Ed., 2004, 43, 5266–5268.
24 B. J. Coe, Acc. Chem. Res., 2006, 39, 383–393.
25 P. Kaur, M. Kaur, G. Depotter, S. van Cleuvenbergen, I.
(E,Z) > (E,E), which matches with trend noted in the
wavelength of their maximum absorption as well as increasing
band gap in that order. Thus, a good correlation of the
structural changes of these isomers as well with the
experimental
β-values was established. Further, the triad (Z,Z)-
7
exhibited moderate electron as well as hole mobility.
Further, structural modifications could possibly improve the
semiconducting characteristics of such multifunctional
systems.
Asselberghs, K. Clays and K. Singh, J. Mater. Chem., 2012, 22
10597–10608.
,
26 W.-Y. Wang, N.-N. Ma, S.-L. Sun and Y.-Q. Qiu, Phys. Chem.
Chem. Phys., 2014, 16, 4900–4910.
27 S. Kaur, S. Dhoun, G. Depotter, P. Kaur, K. Clays and K. Singh,
RSC Adv., 2015, 5, 84643–84656.
Acknowledgements
This work was supported by SERB-DST, New Delhi for financial
28 S. Dhoun, G. Depotter, S. Kaur, P. Kaur, K. Clays and K. Singh,
RSC Adv., 2015, , 50688–50696.
6
assistance (project SB/S1/OC-45/2013) to KS. Authors also 29 J. Chiffre, F. Averseng, G. G. A. Balavoine, J.- C. Daran, G.
Iftime, P. G. Lacroix, E. Manoury and K. Nakatani, Eur. J.
thank Guru Nanak Dev University, Amritsar (UPE Programme)
for facilities. We also thank single crystal X-ray diffraction
facility at IIT Indore for determining the single crystal X-ray
structures.
Inorg. Chem., 2001, 9, 2221-2226.
30 J. A. Mata, E. Peris, R. Llusar, S. Uriel, M. P. Cifuentes, M. G.
Humphrey, M. Samoc and B. L. Davies, Eur. J. Inorg. Chem.,
2001, 8, 2113-2122.
31 J. A. Mata, E. Peris, R. Llusar and E. Peris, Organometallics,
2000, 19, 3797-3802.
32 H. K. Sharma, K. H. Pannell, I. Ledoux, J. Zyss, A. Ceccanti and
P. Zanello, Organometallics, 2000, 19, 770-774.
33 J. A. Mata, E. Peris, I. Asselberghs, R. Van Boxel and A.
Persoons, New J. Chem., 2001, 25, 1043-1046.
34 J. A. Mata, E. Peris, I. Asselberghs, R. Van Boxel and A.
Persoons, New J. Chem., 2001, 25, 299-304.
35 K. Clays and A. Persoons, Phys. Rev. Lett., 1991, 66, 2980–
2983.
36 K. Clays and A. Persoons, Rev. Sci. Instrum., 1992, 63, 3285–
3289.
37 K. Clays, A. Persoons and L. De Maeyer, Adv. Chem.
Phys.,1994, 85, 455–498.
Notes and References
1
2
3
X. Zhang, Z. Chi, B. Xu, L. Jiang, X. Zhou, S. Liu and J. Xu,
Chem. Commun. 2012, 48, 10895-10897.
Y. Lei, P. Deng, J. Li, M. Lin, F. Zhu, T.-W. Ng, C.-S. Lee and B.
S. Ong, Sci. Rep. 2016, 6, 24476; doi: 10.1038/srep24476.
A.-J. Payne, A. D. Hendsbee, S. M. McAfee, D. K. Paul, K.
Karan and G. C. Welch, Phys. Chem. Chem. Phys., 2016, 18
,
14709-14719.
4
5
6
7
8
D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994,
94, 195–242.
S. R. Marder, B. Kippelen, A. K.-Y. Jen and N. Peyghambarian,
Nature, 1997, 388, 845–851.
I. R. Whittall, A. M. McDonagh, M. G. Humphrey and M.
Samoc, Adv. Organomet. Chem., 1998, 42, 291–362.
K. A. Green, M. P. Cifuentes, M. Samoc and M. G. Humphrey,
Coord. Chem. Rev., 2011, 255, 2025–2038.
P. N. Prasad and D. J. Williams, Nonlinear Optical Effects in
Molecules and Polymers, Wiley, New York, 1991.
38 K. Clays and A. Persoons, Rev. Sci. Instrum., 1994, 65, 2190–
2194.
39 G. Olbrechts, R. Strobbe, K. Clays and A. Persoons, Rev. Sci.
Instrum., 1998, 69, 2233–2241.
40 G. Olbrechts, K. Wostyn, K. Clays and A. Persoons, Opt. Lett.,
1999, 24, 403–405.
41 T. Verbiest, S. Houbrechts, M. Kauranen, K. Clays and A.
Persoons, J. Mater. Chem., 1997, 7, 2175–2189.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 12
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
42 S. D. Bella, Chem. Soc. Rev., 2001, 30, 355–366.
43 H. M. Kim and B. R. Cho, J. Mater. Chem., 2009, 19, 7402–
7409.
73 J. Zhang, J. Tan, Z. Ma, W. Xu, G. Zhao, H. Geng, C. Di, W. Hu,
Z. Shuai, K. Singh and D. Zhu, J. Am. CDhOemI: 1.0S.1o0c3V.9,ie/wC26A0rTt1iCc3l0e,3O18n73li6n5Je
,
558-561.
44 M. J. Frisch, et al., Gaussian 09, Revision B.01, Gaussian, Inc., 74 J. Zhang, H. Geng, T. S. Virk, Y. Zhao, J. Tan, C. A. Di, W. Xu, K.
Wallingford, CT, 2010 (for complete reference see ESI†).
45 C. Adamo and D. Jacquemin, Chem. Soc. Rev. 2013, 42, 845-
856.
Singh, W. Hu, Z. Shuai, Y. Liu and D. Zhu, Adv. Mater., 2012,
24, 2603-2607
75 M. M. Payne, S. R. Parkin, J. E. Anthony, C. C. Kuo and T. N.
Jackson, J. Am. Chem. Soc., 2005, 127, 4986-4987.
76 Y. Zhu, R. D. Champion and S. A. Jenekhe, Macromolecules,
2006, 39, 8712-8719.
77 P. Qin, H. Zhu, T. Edvinsson, G. Boschloo, A. Hagfeldt and L.
Sun, J. Am. Chem. Soc., 2008, 130, 8570-8571.
78 Y. Li, S. P. Singh and P. A. Sonar, Adv. Mater., 2010, 22, 4862-
4866.
79 J. S. Ha, K. H. Kim and D. H. Choi, J. Am. Chem. Soc., 2011,
133, 10364-10367.
80 A. Facchetti, J. Letizia, M. H. Yoon, M. Mushrush, H. E. Katz
and T. J. Marks, Chem. Mater., 2004, 16, 4715-4727.
81 T. Kono, D. Kumaki, J. I. Nishida, T. Sakanoue, M. Kakita, H.
Tada, S. Tokito and Y. Yamashita, Chem. Mater., 2007, 19,
1218-1220.
82 R. Schmidt, J. H. Oh, Y. S. Sun, M. Deppisch, A. M. Krause, K.
Radacki, H. Braunschweig, M. Konemann, P. Erk, Z. Bao and
F. Wurthner, J. Am. Chem. Soc., 2009, 131, 6215-6228.
46 S. M. Islam, S. D. Huelin, M. Dawe and R. A. Poirier, J. Chem.
Theory Comput. 2008, 4, 86-100.
47 T. Lei, J. H. Dou, X. Y. Cao, J. Y. Wang and J. Pei, J. Am. Chem.
Soc., 2013, 135, 12168-12171.
48 Z. Yan, B. Sun and Y. Li, Chem. Commun. 2013, 49, 3790-
3792.
49 B. Sun, W. Hong, E. Thibau, H. Aziz, Z. H. Lu and Y. Li, Org.
Electron., 2014, 15, 3787-3794.
50 J. H. Wood and L. Cox. Organic Syntheses. Coll., 1955,
1946, 26, 24.
3, 286 ;
51 C. H. Wang, Y. C. Lin, O. Y. Tai, and A. K.-Y. Jen, J. Chem.
Phys., 2003, 119, 6237-6244.
52 G. Hennrich, M. T. Murillo, P. Prados, K. Song, I. Asselberghs,
K. Clays, A. Persoons, J. B. Buchholz and J. De Mendoza,
Chem. Commun., 2005, 2747–2749.
53 G. Hennrich, M. T. Murillo, P. Prados, H. Al-Saraierh, A. El-
Dali, D. W. Thompson, J. Collins, P. E. Georghiou, A.
Teshome, I. Asselberghs and K. Clays, Chem. Eur. J., 2007, 13, 83 X. Gao, C. A. Di, Y. Hu, X. Yang, H. Fan, F. Zhang, Y. Liu, H. Li
7753– 7761. and D. Zhu, J. Am. Chem. Soc., 2010, 132, 3697-3699.
54 E. Hendrickx, C. Boutton, K. Clays, A. Persoons, S. Van Es, T. 84 A. P. Kulkarni, Y. Zhu, A. Babel, P. T. Wu and S. A. Jenekhe,
Biemans, B. Meijer, Chem. Phys. Lett., 1997, 270, 241-244. Chem. Mater., 2008, 20, 4212-4223.
55 C. A. Van Walree, O. Franssen, A. W. Marsman, M. C. Flipse 85 J. C. Bijleveld, A. P. Zoombelt, S. G. J. Mathijssen, M. M.
and L. W. Jenneskens, J. Chem. Soc., Perkin Trans., 1997,
2
,
Wienk, M. Turbiez, D. M. D. Leeuw and R. A. J. Janssen, J.
Am. Chem. Soc., 2009, 131, 16616-16617.
799-807.
56 S. H. Mashraqui, R. S. Kenny, S. G. Ghadigaonkar, A. Krishnan, 86 F. S. Kim, X. Guo, M. D. Watson and S. A. Jenekhe, Adv.
M. Bhattacharya, P. K. Das, Opt. Mater., 2004, 27, 257–260.
57 F. Fungo, L. Otero, C. D. Borsarelli, E. N. Durantini, J. J. Silber 87 S. Cho, J. Lee, M. Tong, J. H. Seo and C. Yang, Adv. Funct.
and L. Sereno, J. Phys. Chem. B., 2002, 106, 4070-4078. Mater., 2011, 21, 1910-1916.
58 D. M. Guldi, C. Luo, D. Koktysh, N. A. Kotov, T. D. Ros, S.Bosi 88 A. Wan, J. Hwang, F. Amy and A. Kahn, Org. Electron., 2005,
and M. Prato, Nano Lett., 2002, , 775-780. , 47-54.
Mater., 2010, 22, 478-482.
2
6
59 C. E. Mauldin, C. Piliego, D. Poulsen, D. A. Unruh, C. Woo, B. 89 S. Braun, W. R. Salaneck and M. Fahlman, Adv. Mater., 2009,
Ma, J. L. Mynar and J. M. J. Frechet, Applied Materials and
21, 1450-1472.
interfaces, 2010,
2
, 2833-2838.
90 S. Steudel, S. D. Vusser, S. D. Jonge, D. Janssen, S. Verlaak, J.
Genoe and P. Heremans, Appl. Phys. Lett., 2004, 85, 4400-
4402.
60 A. W. Hains, Z. Liang, M. A. Woodhouse and B. A. Gregg,
Chem. Rev., 2010, 110, 6689-6735.
61 C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater., 91 T. Hasegawa, M. Ashizawa and H. Matsumoto, RSC Adv.,
2002, 14, 99-117.
2015, 5, 61035-61043.
62 H. Meng, F. Sun, M. B. Goldfinger, F. Gao, D. J. Londono, W.
J. Marshal, G. S. Blackman, K. D. Dobbs, E. Dalen and D. E.
Keys, J. Am. Chem. Soc., 2006, 128, 9304-9305.
63 D. Cahen and G. Hodes, Adv. Mater., 2002, 14, 789-798.
64 K. Singh, A. Sharma, J. Zhang, W. Xu and D. Zhu, Chem.
Commun., 2011, 47, 905-907.
65 T. Zhao, Z. Wei, Y. Song, W. Xu, W. Hu and D. Zhu, J. Mater.
Chem., 2007, 17, 4377-4381.
66 J. M. Mativetsky, M. Kastler, R. C. Savage, D. Gentilini, M.
Palma, W. Pisula, K. Mullen and P. Samorı, Adv. Funct.
Mater., 2009, 19, 2486-2494.
67 A. Mishra, C. Q. Ma and P. Bauerle, Chem. Rev., 2009, 109
,
1141-1276.
68 L. E. Polander, S. P. Tiwari, L. Pandey, B. M. Seifried, Q.
Zhang, S. Barlow, C. Risko, J. L. Bredas, B. Kippelen and S. R.
Marder, Chem. Mater., 2011, 23, 3408-3410.
69 S. Wang, A. Kiersnowski, W. Pisula and K. Mullen, J. Am.
Chem. Soc., 2012, 134, 4015-4018.
70 M. S. Chen, J. R. Niskala, D. A. Unruh, C. K. Chu, O. P. Lee and
J. M. J. Freechet, Chem. Mater., 2013, 25, 4088-4096.
71 K. Singh, T. S. Virk, J. Zhang, W. Xu and D. Zhu, Chem.
Commun., 2012, 48, 12174-12176.
72 K. Singh, T. S. Virk, J. Zhang, W. Xu and D. Zhu, Chem.
Commun., 2012, 48, 121-123.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Journal of Materials Chemistry C
Page 12 of 12
View Article Online
DOI: 10.1039/C6TC03876J
Multifunctional geometrical isomers of ferrocene-benzo[1,2-b:4,5-b']difuran-2,6-(3H,7H)-
dione adducts: Second-order nonlinear optical behaviour and charge transport in thin film
OFET devices
Priya Singla,a Nick Van Steerteghem,b Navdeep Kaur,a A. Z. Ashar,c Paramjit Kaur,*,a Koen
Clays,b K. S. Narayanc and Kamaljit Singh*,a
New ferrocene based donor-acceptor chromophores depict structure dependent second-order
nonlinear polarizability and charge transport in thin film OFET devices.