New indolo[1,2-c]quinazolines for single-crystal field-effect transistor: A united experimental and theoretical studies

Article abstract of DOI:10.1002/poc.4276

Here, we account the synthesis and characterization of a series of symmetrical fused heterocyclic aromatic hydrocarbons (HAHs) with an indolo[1,2-c]quinazoline (IQ) as the core moiety. All the new HAHs IQ series were systematically investigated by using various spectroscopic methods. Furthermore, their photo-physical properties were supported by density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies to support the experimental findings. The tetramethyl-substituted indolo[1,2-c]quinazoline (TMIQ) compound is shown to exhibit the shifted type of π–π stacking interactions, which render this series as a new semiconducting material. Single-crystal-based field-effect transistor devices of TMIQ exhibited efficient charge transport behavior, giving a p-channel field-effect mobility of 0.25 cm²?V^?1?s^?1 with an on/off ratio of 5 × 10⁵.

Full text of DOI:10.1002/poc.4276

Received: 26 February 2021
DOI: 10.1002/poc.4276
Revised: 8 July 2021
Accepted: 4 August 2021
R E S E A R C H A R T I C L E
New indolo[1,2-c]quinazolines for single-crystal field-effect
transistor: A united experimental and theoretical studies
Venkat Swamy Puli1 | Suresh Kilaru2 | Yadagiri Bhongiri2
Sreenath Reddy Marri3 | Anuj Tripathi4 | Prabhakar Chetti4
|
|
Anindita Chatterjee1,5
| Kiran Kumar Vukoti1 | Someshwar Pola2
1Department of Chemistry, Koneru
Lakshmaih Education Foundation,
Vaddeswaram, Guntur, India
2Department of Chemistry, University
College of Science, Osmania University,
Hyderabad, India
3Department of Physics, Osmania
University, Hyderabad, India
4Department of Chemistry, National
Institute of Technology, Kurukshetra,
India
Abstract
Here, we account the synthesis and characterization of a series of symmetrical
fused heterocyclic aromatic hydrocarbons (HAHs) with an indolo[1,2-c]
quinazoline (IQ) as the core moiety. All the new HAHs IQ series were system-
atically investigated by using various spectroscopic methods. Furthermore,
their photo-physical properties were supported by density functional theory
(DFT) and time-dependent density functional theory (TDDFT) studies to sup-
port the experimental findings. The tetramethyl-substituted indolo[1,2-c]
quinazoline (TMIQ) compound is shown to exhibit the shifted type of π–π stac-
king interactions, which render this series as a new semiconducting material.
Single-crystal-based field-effect transistor devices of TMIQ exhibited efficient
charge transport behavior, giving a p-channel field-effect mobility of
0.25 cm2 Vꢀ1 sꢀ1 with an on/off ratio of 5 ꢁ 105.
5Department of chemistry, Raghu
Engineering College, Visakhapatnam,
India
Correspondence
Someshwar Pola, Department of
Chemistry, University College of Science,
Osmania University, Hyderabad, India.
Email: somesh.pola@gmail.com
K E Y W O R D S
π–π stacking, indolo[1,2-c]quinazoline, single-crystal field-effect transistors, TDDFT
Prabhakar Chetti, Department of
Chemistry, National Institute of
Technology, Kurukshetra, India.
Email: chetty_prabhakar@yahoo.com
studies
Anindita Chatterjee, Department of
chemistry, Raghu Engineering College,
Visakhapatnam, Andhra Pradesh, India.
Email: anindita.chemistry@gmail.com
Funding information
SERB - New Delhi, India, Grant/Award
Number: EMR/2014/000452; CSIR New
Delhi, India, Grant/Award Number: 02/
(0339)/18/EMR-II
1 | INTRODUCTION
applications in the field of organic and flexible electron-
ics.[1–3] The nature and size of the linear core, the num-
In recent years, there is a tremendous amount of effort in
the design and synthesis of linear fused heterocyclic aro-
matic compounds (FHAs) due to their outstanding
ber of rings present in the fused system, and the
geometry of the molecular structure all play active roles
in their packing prearrangement in the solid state, which,
J Phys Org Chem. 2021;e4276.
wileyonlinelibrary.com/journal/poc
© 2021 John Wiley & Sons, Ltd.
1 of 14
https://doi.org/10.1002/poc.4276

2 of 14
PULI ET AL.
in turn, regulates their charge-transporting properties
between molecules.[4,5]
while the definite packing specifics very much depend on
the molecular arrangement and substituents.[12–14]
The design and synthesis of new FHAs for enhanced
mobility and thermal/chemical stability entail a good
understanding of the packing arrangement of these mole-
cules.[6,7] Substantial advancement has been made in uti-
lizing linear/planar aromatic compounds such as
tetracene, rubrene, pentacene, oligothiophenes, and their
analogs for fabricating organic field-effect transistors
(OFETs).[8,9] Still, the structure/property correlation is a
challenge for the charge mobilities because the mobility
depends not only on the structure but also on crystal
packing of the molecule, film morphology, electrode con-
tacts, and so on. However, the morphology of the thin
film influences the mobility of the molecular packing.
The morphology issue can be overlooked by fabricating
single-crystal field-effect transistors (SCFETs) containing
only one crystal arrangement. The consequence may shed
light on the association between intrinsic charge trans-
port property and molecular structure.[10] For example,
high carrier mobility over 15 cm2 Vꢀ1 sꢀ1 was experimen-
tal with rubrene in single-crystal transistor arrangement,
whereas very low mobility was found in thin film transis-
tor approach because of poor crystallinity in thermally
deposited films.[11] Crystal packing of molecules is a com-
plex issue and narrates to the electrostatic and steric
interactions in the molecule. Some wide-ranging types of
packing motifs have been anticipated for pristine FHAs,
FHAs have been fascinating and potential systems for
their wide-ranging π-conjugation and electron distribu-
tion for π-cloud overlap (electronic coupling).[15] Fused
heteroaromatics have been considered to have a high ten-
dency to give co-facial packing due to the self-
complementarity to each other and, thus, a strong elec-
tronic coupling between the molecules, which improves
FIGURE 1 UV-vis spectra of IQ series as recorded in
dichloroethane
SCHEME 1 Synthesis of indolo[1,2-c]quinazoline derivatives (IQs [1G–10G])

PULI ET AL.
3 of 14
TABLE 1 Experimentally observed wavelength (in nm), ϵ (molꢀ1 Lꢀ1 cmꢀ1), λonset (nm), and band gap (in eV)
Compounds
IQ
Wavelength (nm)
241.52
276.89
285.60
337.19
353.61
232.47
252.95
289.97
309.54
354.59
371.02
231.67
246.78
283.13
291.21
301.45
340.89
358.05
240.23
272.88
296.46
339.05
354.59
231.84
247.04
282.82
292.14
341.21
358.03
232.16
246.78
283.08
291.14
341.83
357.98
233.08
246.72
284.12
292.75
340.28
358.31
ϵ (molꢀ1 Lꢀ1 cmꢀ1
8666
)
λonset (nm)
Band gap (eV)
367
3.37
17 333
19 333
4222
4066
TMIQ
7777
386
3.21
10 088
18 733
7733
5022
4311
TCIQ
7133
373
3.32
7355
17 733
15 088
9133
4111
4022
TFIQ
7355
378
3.28
14 444
7622
3911
3511
DCDMIQ
8005
8401
19 844
16 978
4623
4495
DFIQ
8889
374
3.31
9067
20 623
17 733
5402
5244
TFMIQ
10 644
11 088
24 844
21 288
6475
381
3.25
6378
(Continues)

4 of 14
PULI ET AL.
TABLE 1 (Continued)
Compounds
DMIQ
Wavelength (nm)
ϵ (molꢀ1 Lꢀ1 cmꢀ1
)
λonset (nm)
Band gap (eV)
231.85
11 112
377
3.29
247.42
282.83
292.44
341.56
358.30
255.26
270.18
306.34
314.89
364.05
382.08
249.89
263.84
299.73
308.72
357.73
374.55
11 622
25 600
21 955
7044
6888
DBIQ
12 911
13 422
31 844
27 088
7534
401
3.09
7467
DPIQ
12 111
12 712
29 911
25 688
7178
393
3.16
7000
the charge transporting property.[16] Recently, we
reported high-efficiency SCFETs using contorted pyreno
[4,5-a]coronenes, tetrabenzo[a,d,j,m]coronenes, and
dibenzo[a,d]coronenes as the channel materials.[17–19]
These compounds display exactly co-facial or shifted co-
facial packing. These molecules are nevertheless more
symmetrical in shape, which allows more opportunity in
ordered crystal packing.
In this work, we report the synthesis and characteri-
zation of indolo[1,2-c]quinazoline (IQ) derivatives as new
semiconducting molecules. The FHA derivative is linear,
with small dipole units present on the IQ core unit,
enhancing the noncovalent interactions between the mol-
ecules. As we demonstrated in this work, these molecules
pack in a much shifted and herringbone type of packing
of anilines with NIS in acetic acid was carried out (1A–
10A). Sonogashira coupling (twice) has been done to
obtain intermediate compounds (1E–10E) and followed
by a cyclization reaction to getting the indoles (1F–
10F).[21] Finally, compounds (1F–10F) react with triethyl
orthoformate to form IQ and its derivatives with high
yield (1G–10G).
The molecular structures of final compounds were
1
confirmed by H-NMR, 13C-NMR, high-resolution mass
spectrometry, and, with the TMIQ, by its single-crystal X-
ray analysis.[22]
2.2 | Photophysical studies
stacks,
likely
benzothieno[3,2-b][1]benzothiophene
The UV-vis absorption spectra recorded in dilute dichlo-
roethane are revealed in Figure 1 and Table 1. These
derivatives show a characteristic absorption pattern of
BTBT with their absorption maxima confines in the
region of 360–375 nm.[20] A small substituent effect on
the λmax has been noticed in the molecules TCIQ, TFIQ,
and DCDMIQ, having a bathochromic shift of ꢂ8–10 nm
comparative to the parent IQ. The UV-vis absorption as a
function of time is also measured, and no appreciable
change was observed after irradiating the dilute solutions
of IQs for 4 h (Figure 2). The heterocyclic linear and fused
framework prevents molecular photostability compared
(BTBT).[20] The single crystal of the molecule TMIQ is
prepared to give a hole mobility of 0.25 cm2 Vꢀ1 sꢀ1, rep-
resenting the potential of these IQs as a semiconductor.
2 | RESULTS AND DISCUSSION
2.1 | Synthesis
The IQ derivatives are synthesized via a six-step protocol
following the steps shown in Scheme 1.[21] The iodination

PULI ET AL.
5 of 14
FIGURE 2 UV-vis spectra of IQs series (1G–10G) as function of UV-irradiation time
TABLE 2 Calculated absorption maxima λmax (nm), oscillator
with benchmark material such as pentacene. This is due
to the presence of two heterocyclic units such as indole
and pyrimidine, which have connected each other.[21]
Further, to get more insight into the absorption ener-
gies, computational studies are also performed for all the
synthesized molecules. All the molecules are fully opti-
mized with B3LYP functional using a 6-31G (d, p) basis
set in Gaussian 16 package.[23] The optimized molecules
are without negative frequencies showing all are at the
lowest energy state. The time-dependent density func-
tional theory (TDDFT) calculations are accomplished to
get the absorption properties, and the obtained results are
in line with experimental results (Table 1). Further, in
order to get the effect of basis set on absorption proper-
ties, various basis sets from the polarized basis set to dif-
fused polarized basis sets (6-31G**, 6-31+G**, 6-31+
+G**, 6-311+G**, and 6-311++G**) with B3LYP func-
tional have been carried out, and the results are shown in
Table S1. It is observed from Table S1 that there is hardly
shift of 10 nm in absorption with a diffused basis set. To
verify the functionals, the TDDFT calculations are also
carried out with eight different functionals, namely,
B3LYP, B3P86, PBE0, M06, M062X, BHandHLYP, CAM-
B3LYP, and WB97XD, and the results are tabulated in
Table S2. It is also clear from Table S2, that functionals
B3LYP, B3P86, PBE0 and M06 results are in accordance
with the experimental results, while other functionals
show deviation from the experimental absorption ener-
gies. Because there is no considerable variation in the
absorption properties of these molecules with different
basis sets, further discussion is based on a 6-31G (d, p)
basis set with B3LYP functional. The calculated absorp-
tion maxima of the synthesized molecules are also in the
range of 350–370 nm, and all are having major transitions
(MTs) from highest-occupied molecular orbital (HOMO)
to lowest-unoccupied molecular orbital (LUMO)
strength (f), major transitions (MTs), and %weight (%Ci) using
6-31G (d, p) basis sets
Name
λexp
λmax
f
MT
%Ci
73
23
80
17
56
40
60
36
61
35
46
49
94
65
31
62
33
63
32
IQ
353
359
0.011
H ! L
H ! L + 1
H ! L
H ! L + 1
H ! L
H ! L + 1
H ! L
H ! L + 1
H ! L
H ! L + 1
H ! L
H ! L + 1
H ! L
H ! L
TMIQ
TCIQ
371
358
355
358
358
364
368
360
366
348
0.012
0.014
0.012
0.013
0.029
TFIQ
DCDMIQ
DFIQ
TFMIQ
DMIQ
358
358
369
358
0.015
0.012
H ! L + 1
H ! L
H ! L + 1
H ! L
DBIQ
DPIQ
382
375
358
358
0.014
0.013
H ! L + 1
(H ! L). Along with HOMO–LUMO, the other transi-
tions with minor contributions are also observed from
HOMO to LUMO + 1 (H ! L + 1). The calculated
absorption maxima (λmax in nm), oscillator strength (f),
MTs, and %weight (%Ci) using B3LYP/6-31G (d, p) basis
sets are tabulated in Table 2. The calculated results are
reproducing the experimental results with great accuracy.
The molecules TMIQ, TCIQ, and TFMIQ, DCDMIQ show

6 of 14
PULI ET AL.
5–10 nm red-shifted in absorption, while molecule DFIQ
shows blue-shift by 10 nm than IQ molecule. However,
molecules TFIQ, DMIQ, DBIQ, and DPIQ are showing
the same absorption as the parent IQ molecule.
the solid state are shown in Table 3. In solution, com-
pounds DPIQ, DBIQ, and TMIQ exhibited emission
intensity higher than that of the remaining compounds
of the IQ series (Figure 3). Nevertheless, the quantum
yield of all the IQ series is in between 0.27 and 0.62
(Table 3).
2.2.1 | Fluorescence
A bathochromic shift in emission maxima was
noticed for all the materials, IQ series, in the solid phase.
The emission maximum of TCIQ was a bathochromic
shift from 451 nm in DCB to 559 nm in the solid phase,
resulting in a red-shift of 129 nm (Table 3). Among all
the IQ series, compounds TCIQ and DFIQ exhibited the
most extensive bathochromic shift in the solid state. In
contrast, compounds DMIQ and DPIQ showed the
The emission spectra of compounds IQ series are esti-
mated at 350- and 2-nm slit conditions at the excitation
wavelength. The emission maxima of all the IQ series
were estimated in both solution and solid phases as
given in Table 3. The quantum yields of all the fused
heterocyclic compounds in dichlorobenzene (DCB) and
TABLE 3 Emission λmax and
Compound
IQ
λmax (nm)
436
ΦF
Solid-state excitation λmax (nm)
Stokes shift
quantum yield for compound IQ series
in dichlorobenzene and solid state
0.27
0.56
0.44
0.46
0.49
0.38
0.53
0.33
0.58
0.62
503
512
559
551
522
558
573
502
552
512
67
54
108
98
72
98
116
44
79
35
TMIQ
TCIQ
458
451
TFIQ
453
DCDMIQ
TFMIQ
DFIQ
450
460
457
DMIQ
DBIQ
458
473
DPIQ
477
FIGURE 3 Emission spectra of IQ series

PULI ET AL.
7 of 14
FIGURE 4 Cyclic voltagrams of IQ series
FIGURE 5 Calculated
highest-occupied molecular
orbital (HOMO)–lowest-
unoccupied molecular orbital
(LUMO) gap and molecular
orbital pictures of IQ, TMIQ,
and TCIQ molecules Gaussian
time-dependent density
functional theory (TDDFT)

8 of 14
PULI ET AL.
minimum bathochromic shift in the solid state. The more
impenetrable molecular packing in the solid phase is due
to π–π stacking, which recommends a bathochromic shift
in the emission.[24]
whereas TCIQ having the lowest. Yet, all these HOMO
levels are lower than that of BTBT (5.2 eV).[20] Also, as
shown in Table 4, the calculated HOMO energy of IQ mol-
ecule is ꢀ5.32 eV, whereas in the case of TMIQ molecule,
it is ꢀ5.04 eV due to destabilization of HOMO level when
a methyl group is substituted to parent IQ molecule. How-
ever, with the substitution of the chlorine atom in parent
IQ, stabilization of HOMO level takes place, and the calcu-
lated HOMO energy for TCIQ molecule is ꢀ5.94 eV. This
may have to do with the fused heterocyclic rings present in
the molecular framework. The conjugation is equivalent
to that of planar BTBT even though the equivalent number
2.3 | HOMO–LUMO energies and
thermal properties
Oxidation and reduction potentials for the existing IQ
series were estimated by cyclic voltammetry (CV). Cyclic
voltammograms of all the compounds in solution are
shown in Figure 4, and electrochemical data are given in
Table 3. All the compounds exhibit onset oxidation
potentials in the range of 0.903–1.13 V, (vs. standard calo-
mel electrode [SCE]) no noticeable reduction peaks.
The HOMO and LUMO energy levels are estimated
knowing that the SCE energy level at ꢀ4.8 eV below the
vacuum level EHOMO = [(Eox ꢀ E1/2[ferrocene]) + 4.8] eV
and bandgap estimated by optical absorption onset λ
maxima. The resulting data are compiled in Table 3. The
effect of a small substituent such as electron-donating/
withdrawing dipoles is accountable for the minor differ-
ence, which is noticed in LUMO values.[19]
The theoretically calculated HOMO–LUMO gap of IQ,
TMIQ, and TCIQ molecules with their molecular orbital
pictures are shown in Figure 5 (frontier molecular orbital
pictures of other molecules are shown in supporting
information Table S3). As can be seen, the TMIQ has a
higher HOMO energy level relative to the parent IQ,
FIGURE 6 Thermograms of IQ series
TABLE 4 Photophysical properties, HOMO–LUMO energies, and thermal data of IQ series
[a]
[b]
[c]
λ
E
HOMO
E
[d]Eg
(eV)
[e]Td
[f]EDFT
(eV)
[f]EDFT
(eV)
[f]EDFT
HLG
onset
LUMO
HOMO
LUMO
Compd.
IQ
(nm)
369
(eV)
(eV)
(ꢃC)
(eV)
ꢀ5.43
ꢀ5.41
ꢀ5.43
ꢀ5.44
ꢀ5.47
ꢀ5.41
ꢀ5.46
ꢀ5.42
ꢀ5.41
ꢀ5.41
ꢀ2.07
ꢀ2.26
ꢀ2.15
ꢀ2.11
ꢀ2.23
ꢀ2.25
ꢀ2.20
ꢀ2.17
ꢀ2.35
ꢀ2.28
3.36
3.15
3.28
3.31
3.22
3.19
3.26
3.25
3.06
3.13
328
383
402
396
372
351
348
346
337
342
ꢀ5.32
ꢀ5.04
ꢀ5.94
ꢀ5.70
ꢀ5.50
ꢀ5.59
ꢀ5.91
ꢀ5.20
ꢀ5.20
ꢀ5.21
ꢀ1.17
ꢀ0.95
ꢀ1.94
ꢀ1.59
ꢀ1.47
ꢀ1.48
ꢀ1.86
ꢀ1.07
ꢀ1.07
ꢀ1.08
4.15
4.09
4.00
4.11
4.03
4.11
4.05
4.13
4.13
4.13
TMIQ
TCIQ
TFIQ
394
378
375
DCDMIQ 385
DFIQ
389
380
381
405
396
TFMIQ
DMIQ
DBIQ
DPIQ
Abbreviations: DFT, density functional theory; HOMO, highest-occupied molecular orbital; LUMO, lowest-unoccupied molecular orbital.
aAbsorption maxima.
bEHOMO measured by CV.
cELUMO = EHOMO ꢀ Eg.
dOptical bandgap, Eg, was obtained from the intersection of absorption and emission spectra.
eThermal decomposition temperature measured at 5% weight loss.
fCalculated by DFT method.

PULI ET AL.
9 of 14
of rings is fused together. The lower HOMO levels suggest
that all these compounds are more stable against oxidation
than pentacene. The optical bandgaps of these IQ series
were measured from the absorption onsets of their UV-vis
spectra. LUMO energies are obtained by deducting the
optical band gap energies from HOMO energies.
Further, to predict intermolecular interactions (as a
region for electrophilic attack and nucleophilic attack) in
the molecule TMIQ, the molecular electrostatic potential
(MEP) surface of these the molecules is shown in
Table S4. In Table S4, the MEP surface of TMIQ is
shown; here, the blue region shows maximal negative
potential and hence results in a reactive region for
electrophile to attack. The red region corresponds to a
maximal positive potential and describes a reactive
region for nucleophilic attack. Increasing order of colors
are blue < cyan < green < yellow < red. The color code
of ESP maps ranges from ꢀ0.06 a.u. (deepest blue) to
0.06 a.u. (deepest red). From Table S4, it is possible to
predict some of the chemical reaction sites, as the maxi-
mum positive area (red region) is located on the central
aromatic region. All the negative sites are situated at the
substituent groups and hydrogens and are the most
noticeable sites for electrophile.[25] We also considered
the crystal structure in the form of dimer (without further
optimization) for TDDFT calculations to predict its
FIGURE 7 (A) Chemical
structure of
2,3,9,10-tetramethylindolo[1,2-c]
quinazoline (TMIQ) revealing
fused with central pyrrolo-
pyrimidine. (B) Oak Ridge
Thermal Ellipsoid Plot (ORTEP)
structure of TMIQ
FIGURE 8 (A) Crystal image of TMIQ, (B,C) molecule packing motif of TMIQ, and (D) molecular plane on b-axis of TMIQ

10 of 14
PULI ET AL.
absorption energies. It shows absorption at 358 nm with
mixed transitions (HOMO ꢀ 1 to LUMO, HOMO ꢀ 1 to
LUMO + 2, HOMO ꢀ 1 to LUMO + 3, HOMO
to LUMO + 1, HOMO to LUMO + 2, and HOMO to
LUMO + 3) and the corresponding MO pictures are
shown in the mixed transitions (HOMO ꢀ 1 to LUMO,
HOMO ꢀ 1 to LUMO + 2, HOMO ꢀ 1 to LUMO + 3,
HOMO to LUMO + 1, HOMO to LUMO + 2, and
HOMO to LUMO + 3), and the corresponding MO
pictures are shown in Table S5 and S6. This shows the
intermolecular interactions in the molecule, which is
important for charge mobility.
Thermal gravimetric plots of IQ series are shown in
Figure 6, with the decomposition temperatures estimated
at less than 5% weight loss (Table 4).[21] These IQ deriva-
tives exhibited high-thermal stability, decomposing at
>300ꢃC. In the IQ series, the compound TCIQ, implanted
with four chlorine atoms, has maximum Td.
TABLE 5 Comparison of bond lengths (in Å) and bond angles (in ꢃ) of crystal structure and optimized structure of molecule TMIQ
TMIQ
Bond lengths (BLs)
C1–C2
Expt. BLs
1.379
1.432
1.410
1.402
1.399
1.416
1.405
1.380
1.426
1.382
1.381
1.391
Cal. BLs
1.376
1.433
1.416
1.395
1.414
1.443
1.406
1.391
1.427
1.393
1.396
1.376
Bond lengths (BLs)
C22–N21
Expt. BLs
1.276
1.406
1.419
1.416
1.377
1.417
1.391
1.521
1.509
1.519
1.494
Cal. BLs
1.376
1.396
1.417
1.405
1.391
1.421
1.390
1.511
1.510
1.509
1.509
C2–C4
N21–C14
C4–C3
C14–C13
C3–N11
C13–C15
C1–N11
C15–C17
C1–C13
C17–C19
C4–C9
C16–C19
C9–C8
C8–C24
C8–C6
C6–C28
C6–C5
C17–C36
C3–C5
C19–C32
N11–C22
Bond Angles (BAs)
C16–C14–N21
C13–C1–C2
C22–N1–C3
C2–C4–C9
Expt. BAs
117.48
Cal. BAs
118.20
135.49
129.76
134.01
136.06
127.82
135.08

PULI ET AL.
11 of 14
FIGURE 9 (A) Molecular structure of TMIQ, (B) device structure, (C) the output characteristics, and (D) the transfer characteristics of
TMIQ single-crystal field-effect transistor (SCFET) on treated glass substrate
2.4 | Single-crystal XRD analysis
bond lengths and bond angles between the optimized
structure and crystal structure.
Single crystals were obtained through the physical vapor
transport (PVT) method[17] in a stream of ultrapure nitro-
gen. The compound TMIQ gave needle-like crystals,
whereas only very tiny and silk-like crystals were
obtained for other compounds of IQ series. Thus, single-
crystal X-ray measurements can only be carried out on
TMIQ (Figure 7). The X-ray analysis showed the linear
geometry for TMIQ.
The crystal growth direction is indexed to be along
the b-axis, as shown in Figure 7B. The molecule TMIQ
form a co-facial π–stacks along the b-axis. The interplanar
distance among the two nearer π systems is ꢂ3.4 Å.
This packing feature is similar to those highly sym-
metrical systems such as BTBT and DNTT.[20] Although
the herringbone-packed TMIQ molecule slightly shifts
and rotates comparative to each other, there is still
important in phase connection of their HOMOs, out-
standing to substantial electronic coupling as established
by the high mobility estimated from the SCFET
(Figure 8).
To study the ability of these FHAs to assist as p-
type material, SCFETs were invented with crystals of
TMIQ (Figure 9A–D). A top-gate, top-contact SCFET
was constructed by employing the crystal on a glass
substrate, with coated colloidal graphite on both sides
of the crystal as the drain and source electrodes. The
dielectric layer was flourished by using perylene film
on the TMIQ crystal, and for the top gate electrode, a
colloidal graphite was used.[19] The perylene thickness,
width, and channel length were 1.8–2.5 μm, 0.5–
1.0 mm, and 0.20–0.25 mm.
A high mobility of
0.25 cm2 Vꢀ1 sꢀ1 was revealed with an on/off ratio of
5 ꢁ 105, using TMIQ as channel material (Table 4).
This mobility is related to the benchmark material
pentacene,11 signifying the future of this IQ series as
p-type transporting material.
2.5 | Conclusions
Also, we compare the major bond lengths and bond
angles of the optimized geometry of TMIQ molecule with
crystal parameters and are tabulated in Table 5. The table
shows that there is hardly any difference in calculated
In conclusion, a new series of linear FHAs is synthe-
sized and thoroughly characterized. These materials are
thermally and chemically stable as compared to
pentacene. The absorption and emission properties of

12 of 14
PULI ET AL.
the reported compounds are in the range of 230–
385 nm, and 400 to 600 nm, respectively. The absorp-
tion spectra of these compounds are showing an intense
ϵ value indicates these are having strong absorption in
the visible region. The DFT studies support that these
molecules have major transitions from HOMO to
LUMO and HOMO to LUMO + 1. Electrochemical
results indicate the deeper HOMO–LUMO levels. The
crystal structure analysis of TMIQ shows that the linear
molecule packs in a column with neighboring π frame-
works stack shifted and rotated 45ꢃ relative to each
other. The needle-type crystals of TMIQ are used to
construct SCFETs, which show hole mobility of
0.25 cm2 Vꢀ1 sꢀ1 and a high on/off ratio of 106.
(20 mL). The organic layer was dried over anhydrous
sodium sulfate, filtered, and concentrated under reduced
pressure to get crude compound. Obtained crude was
purified by column chromatography using silica gel col-
umn chromatography by using 10–12% EtOAc in hexane
as eluent to get the corresponding silyl compound (60%)
as a pale brown color liquid.
3.3 | A general protocol for silyl de
protection
A stirred solution of silyl compound (1 g, 1.0 eq) in THF
(20 mL) was added TBAF 1 M in THF (1.5 eq) at 0ꢃC.
The reaction mixture was stirred at the same temp for
30 min. The reaction mixture was added in to water
(40 mL) and extracted with EtOAc (2 ꢁ 20 mL). Com-
bined organic layers were washed with water (20 mL)
and brine (20 mL). The organic layer was dried over
anhydrous sodium sulfate, filtered, and concentrated
under reduced pressure to get crude compound. Obtained
crude was purified by column chromatography using sil-
ica gel column chromatography by using 10–15% EtOAc
in hexane as eluent to get the corresponding acetylene
compound (90%) as a pale brown color liquid.
3 | EXPERIMENTAL SECTION
The starting materials were directly purchased from com-
mercial sources. The solvents were distilled and dried
before being used for spectrophotometric and spec-
trofluorimetric analyses.
3.1 | A general protocol for iodination
To a stirred solution of aniline (1 g, 1.0 eq) in acetic acid
(10 mL) was added NIS (0.9 eq) at room temperature
(RT). The reaction mixture was stirred at RT for 1 h. The
reaction mixture was added in to the water (20 mL) and
extracted with diethyl ether (2 ꢁ 20 mL). Combined
organic layers were washed with cold water (2 ꢁ 20 mL)
and brine (10 mL). The organic layer was dried over
anhydrous sodium sulfate, filtered, and concentrated
under reduced pressure to get crude compound. Obtained
crude was purified by column chromatography by using
silica gel column chromatography by using 10–15%
EtOAc in hexane as eluent to get corresponding iodo
compound (yield, 75%) as a pale brown color liquid.
3.4 | A general protocol for di-
Sonogashira coupling and indole
A stirred solution of iodo aniline (1 g, 1.0 eq) and acetylene
(1.0 eq) in Et3N (20 mL) was degassed under argon for
10 min. Then, added CuI (0.2 eq) at RT and the reaction
mixture was degassed for 10 min. To this degassed reaction
mixture, added PdCl2(dppf)DCM (0.1 eq). The reaction
mixture was stirred at RT for 4 h. The reaction mixture
was added to the water (40 mL) and extracted with EtOAc
(2 ꢁ 30 mL). Combined organic layers were washed with
water (20 mL) and brine (20 mL). The organic layer was
dried over anhydrous sodium sulfate, filtered, and concen-
trated under reduced pressure to get crude compound.
Obtained crude was purified by column chromatography
by using silica gel column chromatography by using 30–
60% EtOAc in hexane as eluent. During the column, one
new nonpolar spot was observed. Both the spots were sep-
arated and characterized. The nonpolar spot was comply-
ing with the corresponding indole, and the polar spot
indicates desired di-Sonogashira compound.
3.2 | A general protocol for sonogashira
coupling
A stirred solution of iodo aniline (1 g, 1.0 eq) in Et3N
(20 mL) was degassed under argon for 10 min. Then,
added CuI (0.2 eq) at RT and degassed the reaction mix-
ture for 10 min. To this degassed reaction mixture, added
PdCl2(dppf) in DCM (0.1 eq) and TMS- Acetylene (2 eq)
at RT. The reaction mixture was stirred at RT 6 h. The
reaction mixture was added to the water (40 mL) and
extracted with EtOAc (2 ꢁ 20 mL). Combined organic
layers were washed with water (20 mL) and brine
Note: During the purification process of di-
Sonogashira compounds with the column chromatogra-
phy, the crude product slurry was prepared with silica gel
in DCM and the removal of solvent was carried out by
using rotory evaporator and dried at 40ꢃC. Then it is

PULI ET AL.
13 of 14
observed, the direct cyclized indole-based products and
are confirmed from NMR.
thanks to Prof. Yu-Tai Tao, Institute of Chemistry,
Academia Sinica, Taipei, Taiwan.
CONFLICT OF INTEREST
The authors declare that they have no conflicts of
interest.
3.5 | General protocol for final
cyclisation
A stirred solution of indole derivative (0.2 g, 1.0 eq) in
triethyl orthoformate (10 mL) was heated to reflux at
120–130ꢃC for 5–6 h. The reaction mixture was concen-
trated under reduced pressure. The obtained thick syrup
was recrystallized with DCM and hexane to get solid. Pre-
cipitated solids were filtered and dried to get the
corresponding final compound (yield, 40–50%) as pale
brown color solid.
AUTHOR CONTRIBUTIONS
SP, SK, AC, and VSP planned and accomplished the
experiments to synthesize the IQ series of OFETs and its
detailed characterization, and CP and AT carried out the
theoretical studies. SP originated an idea of using IQ
series for SCFET device fabrication. YB carried out the
PL measurements. RG accomplished the devices fabrica-
tion, characterization, and SCFET property estimation
under the supervision of SRM and SP. AC, CP, and SP
discussed together about the achieved scientific results
and prepared the manuscript.
3.6 | Characterization techniques
Melting points verified on a Cintex apparatus. Mass spec-
tral data were collected by 6470B Triple quadrupole
LC/MS Agilent mass spectrometer. 1H- and 13C-NMR
spectra were recorded on a Bruker AV400 MHz Spec-
DATA AVAILABILITY STATEMENT
Research data that include all the analytical techniques
used for the characterization of reported compounds are
provided in supporting information, and there is no sepa-
rate available.
1
trometer with chemical shifts referenced using the H
resonance of residual CDCl3 and DMSO-d6. The elec-
tronic spectra were obtained in chloroform solutions on a
JASCO V-650 UV-vis spectrophotometer. The photo-
luminescence (PL) spectra of the catalysts were recorded
on a HORIBA Scientific Fluorescence Spectrophotome-
ter, and the samples were excited at their respective exci-
tation with slit width 3 nm. CV measurements were
conducted on a PC-controlled CHI 62C electrochemical
analyzer in a C2H4Cl2 solvent at a scan rate of 100 mV/s
using tetrabutylammonium perchlorate (0.1 M) as the
supporting electrolyte. The glassy carbon, standard calo-
mel electrode (SCE), and platinum wire were used as
working, reference, and counter electrodes, respectively.
To obtain HOMOꢀLUMO images, theoretical calcula-
tions were accomplished for IQ series using Gaussian
16 software with TDDFT method. The single-crystal X-
ray diffractions (XRDs) were attained on a Bruker
X8APEX X-ray diffractometer with Mo Kα radiation
(λ = 0.710, 73 Å), and the structure of molecule TMIQ
sample was resolved by the SHELX 97 program. Electri-
cal characteristics were recorded under organic semicon-
ductor device analyzer (Keithley 4200 parameter
analyzer).
ORCID
Prabhakar Chetti https://orcid.org/0000-0003-1773-
9429
Anindita Chatterjee https://orcid.org/0000-0001-6435-
3698
Someshwar Pola https://orcid.org/0000-0002-4831-5250
REFERENCES
[1] B. Lüssem, C. -M. Keum, D. Kasemann, B. Naab, Z. Bao, K.
Leo, Chem. Rev. 2016, 116(22), 13714.
[2] S. E. Root, S. Savagatrup, A. D. Printz, D. Rodriquez, D. J.
Lipomi, Chem. Rev. 2017, 117(9), 6467.
[3] C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012,
112(4), 2208.
[4] N.-X. Zhang, A.-M. Ren, L.-F. Ji, S.-F. Zhang, J.-F. Guo, J. Phy.
Chem. C 2018, 122(33), 18880.
[5] H. Oberhofer, K. Reuter, J. Blumberger, Chem. Rev. 2017,
117(15), 10319.
[6] K. Kobayashi, H. Masu, A. Shuto, K. Yamaguchi, Chem. Mater.
2005, 17(26), 6666.
[7] J. T. Kintigh, J. L. Hodgson, A. Singh, C. Pramanik, A. M.
Larson, L. Zhou, J. B. Briggs, B. C. Noll, E. Kheirkhahi, K.
Pohl, N. M. McGruer, G. P. Miller, J. Phy. Chem. C 2014,
118(46), 26955.
[8] L. Jiang, H. Dong, W. Hu, J. Mater. Chem. 2010, 20(24), 4994.
[9] M. E. Gershenson, V. Podzorov, A. F. Morpurgo, Rev. Mod.
Phys. 2006, 78(3), 973.
[10] S.-Z. Weng, P. Shukla, M.-Y. Kuo, Y.-C. Chang, H.-S. Sheu,
I. Chao, Y.-T. Tao, ACS Appl. Mater. Interf. 2009, 1(9),
2071.
ACKNOWLEDGEMENT
SP and CP thank SERB - New Delhi, India and CSIR
New Delhi, India for financial support under EMR
(EMR/2014/000452) and CSIR (02/(0339)/18/EMR-II),
respectively, and thank DST-FIST, New Delhi. Special

14 of 14
PULI ET AL.
[11] K. A. McGarry, W. Xei, C. Sutton, C. Risko, Y. Wu, V. G.
Young Jr., J.-L. Bredas, C. D. Frisbie, C. J. Douglas, Chem.
Mater. 2013, 25(11), 2254.
[12] T. Hasegawa, J. Takeya, Sci. Technol. Adv. Mater. 2009, 10, 024314.
[13] C. Reese, Z. Bao, Mater. Today 2007, 10(3), 20.
[14] H. Xin, J. Li, R. Q. Lu, X. Gao, T. M. Swager, J. Am, Chem.
Soc. 2020, 142(31), 13598.
[15] V. Rühle, A. Lukyanov, F. May, M. Schrader, T. Vehoff, J.
Kirkpatrick, B. Baumeier, D. Andrienko, J. Chem. Theory &
Comp. 2011, 7, 3335.
[16] M. M. Islam, S. Pola, Y. T. Tao, Chem. Commun. 2011, 47(22), 6356.
[17] Y. T. Tao, S. Pola, S. Kumar, M. M. Islam, J. Org. Chem. 2017,
82(15), 8067.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega,
J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox,
Gaussian 16, Revision B.01, Gaussian, Inc., Wallingford, CT 2016.
[24] K. Ono, H. Yamaguchi, K. Taga, K. Saito, J. Nishida, Y.
Yamashita, Org. Lett. 2009, 11(1), 149.
[18] S. Pola, C.-H. Kuo, W.-T. Peng, M. M. Islam, I. Chao, Y.-T.
Tao, Chem. Mater. 2012, 24(13), 2566.
[25] Y. Li, J. Liu, D. Liu, X. Li, Y. Xu, Comput. Mater. Sci. 2019, 161, 163.
[19] S. Kumar, S. Pola, C. -W. Huang, M. M. Islam, S.
Venkateswarlu, Y.-T. Tao, J. Org. Chem. 2019, 84(13), 8562.
[20] T. Mori, T. Nishimura, T. Yamamoto, I. Doi, E. Miyazaki, I.
Osaka, K. Takimiya, J. Am. Chem. Soc. 2013, 135(37), 13900.
[21] V. S. Puli, M. Subburu, Y. Bhongiri, A. Tripathi, K. R. S.
Prasad, A. Chatterjee, S. Pola, C. Prabhakar, J. Mol. Struct.
2020, 129491.
SUPPORTING INFORMATION
Additional supporting information may be found in the
online version of the article at the publisher's website.
[22] T. Sasada, F. Kobayashi, N. Sakai, T. Konakahara, Org. Lett.
2009, 11(10), 2161.
How to cite this article: V. S. Puli, S. Kilaru,
Y. Bhongiri, S. R. Marri, A. Tripathi, P. Chetti,
A. Chatterjee, K. K. Vukoti, S. Pola, J Phys Org
Chem 2021, e4276. https://doi.org/10.1002/poc.
4276
[23] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L.
Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.