New one- and two-dimensional p-conjugated materials containing a tetraoxa[8]circulene monomer are theoretically predicted on the basis of density functional theory techniques. These novel materials are predicted to demonstrate a promising hole/electron mobility properties which are typical for the ambipolar organic semiconductors. Furthermore, the growth of p-conjugation determines the strong visible light absorption of the studied systems in a great contrast to the initial lack of color of the tetraoxa[8]circulene compound. The synthesis of these new organic p-conjugated materials is an important task because of their potential practical applications in optoelectronic devices

Baryshnikov, G.V.

Karaush, N.N.

Minaev, B.F.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 3 No 1, 01CBNM01(3pp) (2014) 
 
 
2304-1862/2014/3(1)01CBNM01(3) 01CBNM01-1  2014 Sumy State University 
New 1D and 2D Nanoscaled Materials Based on the Tetraoxa[8]circulene Monomer 
 
N.N. Karaush1,*, G.V. Baryshnikov1, B.F. Minaev1,2 
 
1 Bohdan Khmelnytsky National University, 18031 Cherkasy, Ukraine 
2 Tomsk State University, 634050 Tomsk, Russian Federation 
 
(Received 13 August 2014; published online 29 August 2014) 
 
New one- and two-dimensional p-conjugated materials containing a tetraoxa[8]circulene monomer are 
theoretically predicted on the basis of density functional theory techniques. These novel materials are pre-
dicted to demonstrate a promising hole/electron mobility properties which are typical for the ambipolar organ-
ic semiconductors. Furthermore, the growth of p-conjugation determines the strong visible light absorption of 
the studied systems in a great contrast to the initial lack of color of the tetraoxa[8]circulene compound. The 
synthesis of these new organic p-conjugated materials is an important task because of their potential practical 
applications in optoelectronic devices. 
 
Keywords: Tetraoxa[8]circulene, Density functional theory, Nanotubes, Hole/electron mobility, Reor-
ganization energy, Cyclooctatetraene core, Ambipolar semiconductors. 
 
 PACS numbers: 72.80.Le, 78.40.Me 
 
 
                                                          
* karaush22@ukr.net 
1. INTRODUCTION 
 
Symmetrical tetraoxa[8]circulene [1–4] are planar 
p-extended compounds with a circular system of con-
densed furan and benzene rings that has a planar cy-
clooctatetraene ring at the center. Some tetrao-
xa[8]circulenes have recently found numerous applica-
tions, for instance, for the preparation of discotic liquid 
crystals [3], blue organic light-emitting diodes (OLEDs) 
[4]. 
The first representative of the tetraoxa[8]circulene 
family was synthesized in 1968 [1] by the cyclooli-
gomerization of a-naphthoquinone in the presence of 
strong mineral acids. Soon after, the simplest tetrao-
xa[8]circulene was also synthesized using the same 
method [1] from p-benzoquinone [2]. All tetrao-
xa[8]circulenes are thermally and chemically stable 
compounds and can be easily functionalized using the 
free CH vacancies. In this way we have predicted the 
possibility of their evolution to the 1D and 2D na-
noscaled tetraoxa[8]circulene materials following chem-
ical modification. A similar phenomenon was experi-
mentally observed for the porphyrin molecules which 
form stable porphyrin sheets (porphyrin tetramer) with 
a planar cyclooctatetraene core [5, 6]. 
 
2. COMPUTATIONAL METHODS 
 
The equilibrium structural parameters of the studied 
1D and 2D compounds (see Fig. 1, 2) were optimized at 
the B3LYP/6-21G(d) level of the density functional theory 
(DFT) [7, 8] with the control of possible symmetry con-
straints, using the Gaussian 09 software package. With 
the same method the IR spectra were calculated for the 
1D oligomers (n = 1–4) and for the simplest 2D square 
sheet structures containing four tetraoxa[8]circulene 
(TOC) units (2 × 2, Fig. 1) to determine the true mini-
mum of the total energy. All vibrational mode frequen-
cies are real, which indicates the true minimum of the 
total energy finding. The electronic absorption spectra 
of all the studied molecules were calculated by the time 
dependent (TD) DFT method [9] in gas phase using the 
same B3LYP functional and 3-21G basis set. 
 
 
 
Fig. 1 – The structure of the tetraoxa[8]circulene sheets (n 
denotes the total numbers of tetraoxa[8]circulene units, 
whereas √n indicates the size of the corresponding compounds 
along xz and yz directions (except compounds 2 and 6 for 
which longitudinal and transversal n values are not equiva-
lent). 
 
All calculations were performed at the PDC super-
computers of the Royal Institute of Technology (Stock-
holm). 
 
 N.N. KARAUSH, G.V. BARYSHNIKOV, B.F. MINAEV PROC. NAP 3, 01CBNM01 (2014) 
 
 
01CBNM01-2 
3. RESULTS AND DISCUSSION  
 
3.1 Structural features 
 
All the designed compounds, including the linear 
1D oligomers and 2D sheets represent completely pla-
nar nanoscaled species. The square sheets and the 
simplest tetraoxa[8]circulene correspond to the D4h 
symmetry point group, whereas the linear oligomers 
are described D2h symmetry.  
The linear compounds (2 × 4) and other p-extended 
tetraoxa[8]circulene sheets are characterized by the ad-
vent of a bending opportunity. In this way, their saddle-
shaped structures are formed and finally they curved 
into the single-wall nanotubes according to a spiraliza-
tion mechanism ‘‘cochlea’’ model [10] (see Fig. 2, com-
pounds 9, 10). The diameter and length of such nano-
tubes depend on the size parameters a and b of the ini-
tial sheet. Another way to modify the size of TOC-based 
nanotubes is the inclusion of additional benzene rings, 
which take place in the the naphthalene-substituted 
tetraoxa[8]circulene species [1–4, 11, 12]. 
An important observation is that the tetrao-
xa[8]circulene sheets 1–4 and nanotube 9, contain the 
16-crown-4 system [13, 14] (blue square in Fig. 2) 
which is active in respect to the metal ions extraction 
[13, 14] (the distance between two opposite oxygen at-
oms equals 4.09 °A). 
 
 
4 9 
 
8 10 
 
Fig. 2 – The optimized structure of the tetraoxa[8]circulene 
sheets 4, 8 and corresponding nanotubes 9, 10 all of them 
constructed from 16 basic TOC monomers. 
 
3.2 Electronic absorption spectra 
 
Experimental and calculated electronic absorption 
spectra of the simplest tetraoxa[8]circulene molecule 
were previously published and are well described [11, 
12]. In particular, the absence of a visible absorption in 
the observed and calculated UV-vis spectra of the free 
TOC molecules was stressed.  
Surprisingly, we have found that the tetrao-
xa[8]circulene sheets and nanotubes can strongly ab-
sorb light in the visible region (around 560 for com-
pounds 1–4, 9 and 500 nm for compounds 5–8, 10) in 
great contrast to the free TOC monomer and other p-
extended tetraoxa[8]circulenes [3, 10], which demon-
strate only a weak light absorption near the blue edge 
of the visible region (below 410 nm). Such unprece-
dented strong absorption by compounds 1–10 can be 
assigned to the formation of cyclic acene chromophores 
and their p-conjugation through the tetrao-
xa[8]circulene units. The increase in visible absorbance 
with the growth of the molecular surface is in good 
agreement with the acene chromophore dominant role. 
 
3.3 The HOMO–LUMO gap engineering and 
charge carrier motilities 
 
The HOMO–LUMO gap (HLG) of the TOC-based 
compounds is varied with increasing of their length 
from 2.69 eV for 1 compound to 2.08 eV for 4; and from 
2.74 eV for 5 to 2.51 eV for 8 (Table 1) Thus the TOC-
based 2D sheets are predicted to possess a very low 
HLG (≈1.7 eV at the boundary condition) compared 
with most of the known 2D conjugated polymers [15]. 
 
Table 1 – The HOMO–LUMO gap values for the 
TOC-based nanotubes 
 
TOC-
compounds 
HOMO–LUMO gap 
energies, eV 
(1) 2×2 2.69 
(2) 2×4 2.32 
(3) 3×3 2.28 
(4) 4×4 2.08 
(5) 2×2 2.74 
(6) 2×4 2.62 
(7) 3×3 2.58 
(8) 4×4 2.51 
(9) 2×8 2.07 
(10) 2×8 2.48 
 
All p-extended TOC-based 2D frameworks 1–8, 1D 
ribbons and nanotubes 9–10 are characterized by the 
very small values of the electron/hole reorganization 
energies, calculated at the B3LYP/6-21G(d) level of 
theory using the algorithm described in Ref. 16, 17. In 
this way, the studied compounds are predicted to be 
good electron donors/acceptors, which is a general fea-
ture of the ambipolar semiconductors. 
 
4. CONCLUSIONS 
 
Nanoscaled 1D ribbons, 2D sheets and single-wall 
nanotubes containing directly fused tetrao-
xa[8]circulene monomers have been designed and de-
scribed in the present work at the DFT level. The 
tetraoxa[8]circulene based compounds are absolutely 
planar compounds which exhibit bending in a prolon-
gated ribbon and subsequently spiralling and closing 
into a single-wall nanotube.  
  PROC. NAP 3, 01CBNM01 (2014) 
 
 
01CBNM01-3 
The designed compounds are characterized by a 
strong size-dependent visible absorption because of the 
specific p-conjugation producing cyclic acene chromo-
pores. All designed compounds (except the initial 
tetraoxa[8]circulene monomer) are predicted to be good 
ambipolar organic semiconductors. This prediction is 
supported by the very small values of the electron/hole 
reorganization energies. 
 
AKNOWLEDGEMENTS 
 
All computations are performed with resources 
provided by the Swedish National Infrastructure for 
Computing (SNIC) at the Parallel Computer Center 
(PDC) through the project "Multiphysics Modeling of 
Molecular Materials", SNIC 020/11-23. This research 
was also supported by the Ministry of Education and 
Science of Ukraine (project number 0113U001694). 
 
 
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New 1D and 2D Nanoscaled Materials Based on the Tetraoxa[8]circulene Monomer

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New 1D and 2D Nanoscaled Materials Based on the Tetraoxa[8]circulene Monomer

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