Synthesis and properties of triphenylamine functionalized tetrathiafulvalene

Article abstract of DOI:10.1016/j.tetlet.2020.151949

A hybrid conjugated molecule TTPA-TTF was designed and synthesized by combing a tetrathiafulvalene core with tetra-triphenylamine derivative functionalized at the 4,4′,5,5′- positions. Studies revealed TTPA-TTF exhibits good thermal stability and hole mob

Full text of DOI:10.1016/j.tetlet.2020.151949

Tetrahedron Letters xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and properties of triphenylamine functionalized
tetrathiafulvalene
b,
Xia Tian a, Fang Qian b, Min Wu a, Xiaozhong Liang a, Fang Zhang a, Da Li a, Kunpeng Guo a, , Zhike Liu
⇑
⇑
,
Jie Li a,
⇑
a Ministry of Education Key Laboratory of Interface Science and Engineering in Advanced Materials, Research Center of Advanced Materials Science and Technology, Taiyuan
University of Technology, Taiyuan 030024, China
b School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A hybrid conjugated molecule TTPA-TTF was designed and synthesized by combing a tetrathiafulvalene
core with tetra-triphenylamine derivative functionalized at the 4,40,5,50- positions. Studies revealed
TTPA-TTF exhibits good thermal stability and hole mobility. To explore its primary application as
hole-transporting material in perovskite solar cells, TTPA-TTF -based cells exhibited a power conversion
efficiency of 10.95% without the use of any p-type dopants.
Received 15 February 2020
Revised 31 March 2020
Accepted 14 April 2020
Available online xxxx
Ó 2020 Elsevier Ltd. All rights reserved.
Keywords:
Tetrathiafulvalene
Triphenylamine
Chemical synthesis
Hole transporting material
Introduction
ity, as well as three-dimensional molecular structures [21–25]. For
example, spirotype molecule 2,20,7,70-tetrakis[N,N-di(4-methoxy-
Since the pioneering work on ‘‘organic metal” based tetrathia-
fulvalene-tetracyanoquinodimethane (TTF-TCNQ) reported by Fer-
raris et al. in 1973, many studies have focused on design and
synthesis of tetrathiafulvalene (TTF) derivatives due to its strong
electron-donating ability and polytropic chemical structure [1–5].
In the past decades, charge-transfer systems, magnetic compounds
and photovoltaics based on TTF derivatives have attracted great
interest due to their unique solid-state properties [6–12]. In these
contexts, versatile TTF derivatives have been developed, including
replacement of sulfur by other chalcogen atoms, peripheral func-
tionalization of the TTF core, and insertion of conjugated spacers
between the dithiafulventl units [13–16]. Among them, the periph-
eral functionalization of the TTF core with conjugated substituents
phenyl)amino]-9,90-spirobifluorene (SpiroOMeTAD) adopts
a
spirobifluorene core with four bis(4-methoxyphenyl)amine substi-
tuted at the 2,20,7,70- postions represented the most successful
commercial hole transporting material (HTM). Perovskite solar
cells (PSCs) based on SpiroOMeTAD with the use of p-type dopants
have shown the record power conversion efficiencies (PCEs) above
20% [26–28]. However, PSCs based dopant-free SpiroOMeTADT
often show poor PCEs below 10% [29–32]. It is well known that
dopant-free HTMs not only simplify the devices preparation pro-
cess, but also improve the stability of the devices. Notably, some
researches demonstrated replacing the spirobifluorene core in
SpiroOMeTAD with other heteroatom containing aromatic com-
pounds would be efficiency in molecular design toward dopant-
free HTMs [33–35]. Therefore, these researches arouse our inter-
ests in the functionalization of TTF with TPA-based peripheral
groups for novel functions. Motivated by this, we designed a mole-
cule TTPA-TTF which feature four TPA derivatives functionalized to
a TTF core at its 4,40,5,50- positions. We describe here the synthesis
and optical, electrochemical, thermal properties of TTPA-TTF and
its primary application as dopant-free HTM in PSCs.
would be an intriguing way not only to expand
p-conjugation
system, but also to achieve novel functions [17–20]. Therefore,
peripheral groups functionalized TTF derivatives should be
explored with altered aromatic groups, especially those containing
heteroatoms, for their next applications.
In heteroatom-containing aromatic derivatives, triphenylamine
(TPA) derivatives have been extensively studied because of their
excellent electronic donating ability and hole-transporting capabil-
Results and discussion
⇑
Corresponding authors.
E-mail addresses: guokunpeng@tyut.edu.cn (K. Guo), zhike2015@snnu.edu.cn
The synthetic route for compound TTPA-TTF was depicted in
Scheme 1. Compound 2 was prepared under a Barbier reaction
(Z. Liu), lijie01@tyut.edu.cn (J. Li).
https://doi.org/10.1016/j.tetlet.2020.151949
0040-4039/Ó 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: X. Tian, F. Qian, M. Wu et al., Synthesis and properties of triphenylamine functionalized tetrathiafulvalene, Tetrahedron Letters,
https://doi.org/10.1016/j.tetlet.2020.151949

2
X. Tian et al. / Tetrahedron Letters xxx (xxxx) xxx
according to the literature method [36]. Chlorine-hydroxyl exchange
by reaction of compound 2 and cyanuric chloride to produce com-
pound 3. Ethanone 3 was converted to 4 by the reaction with potas-
sium o-isopropyl xanthate, which was treated with 30% HBr/AcOH to
give 1,3-dithiole-2-ketone derivative 5. Notably, it is no need to
change the ketone 5 to a 1,3-dithiole-2-thione derivative, Horner-
Wittig coupling reaction of ketone 5 in the presence of triethylphos-
phite also proceeded to give bromide TTF derivative 6. Eventually,
Buchwald-Hartwig amination of compound 6 and 4,40-dimethoxy-
diphenylamine in the presence of tetrakis(triphenylphosphine)pal-
ladium and sodium tert-butoxide afforded the target compound
TTPA-TTF. The structures of the compounds were confirmed by
NMR and mass spectroscopy characterizations. TTPA-TTF showed
good solubility in common organic solvents such as dichloro-
methane, tetrahydrofuran (THF), toluene, and chlorobenzene.
To understand the configuration and frontier molecular orbital
distributions of TTPA-TTF, theoretical calculations using the Gaus-
sian 09 program at the B3LYP/6-31G* level were performed. As
rings. This result indicates the donor character of the molecule is
mainly stems from the TTF unit.
The absorption spectrum of TTPA-TTF in dilute chlorobenzene
at room temperature is shown in Fig. 2a. It was observed TTPA-
TTF exhibits two relatively strong absorption bands in the 300–
400 nm region, which can be attributed to a more localized
p-p*
in peripheral TPA rings and centered TTF. Compared to its solution,
the maximum absorption wavelength of TTPA-TTF in film was
still < 400 nm, indicating its high transparency to visible light
(Fig. S1). The little red-shifted absorption in film relative to its
solution spectra was attributed to the possible formation of aggre-
gates. To explore its electrochemical property, the molecular orbi-
tal energy levels of TTPA-TTF were obtained from the cyclic
voltammetry (CV) measurement in combination with the optical
band gap (Eg) determined by its absorption onset in solution. It
can be found that the Eg of TTPA-TTF was 2.25 eV, as shown in
Fig. 2a. As illustrated in Fig. 2b, the first oxidation peak of TTPA-
TTF was observed at 0.91 V. As a result, the HOMO level of
TTPA-TTF was calculated accordingly as ꢀ5.25 eV [34]. The LUMO
level of TTPA-TTF, calculated as HOMO + Eg, was ꢀ3.00 eV. It is
noted that the HOMO level of TTPA-TTF was higher than the
valence band (VB) of perovskite CH3NH3PbI3 (ꢀ5.43 eV), indicating
the hole injection from CH3NH3PbI3 to the TTPA-TTF is feasible. In
addition, its LUMO level is higher than the conduction band (CB) of
CH3NH3PbI3 (ꢀ3.91 eV). Based on this result, the energy barrier of
0.91 eV between the CB of CH3NH3PbI3 and the LUMO level of
TTPA-TTF would block the electrons efficiently from perovskites
to the metal electrodes and thus reduce the charge recombination
in the perovskites/HTM interface.
shown in Fig. 1, the centered TTF unit presented a
p-conjugated
planar structure. The dihedral angles between the peripheral TPA
groups and the centered TTF were in the range of 45°ꢀ47° for
TTPA-TTF, indicating the compound exhibited a twisted configura-
tion. The nonplanar molecular structure of TTPA-TTF endows it
good solubility in common organic solvents, which is beneficial
for its practicability for solution-processed organic electronic
materials. The electron distributions of the highest occupied
molecular orbital (HOMO) of TTPA-TTF was mainly localized on
the TTF center, while the lowest unoccupied molecular orbital
(LUMO) just slightly shifted from TTF unit to the adjacent phenyl
Scheme 1. Synthesis of TTPA-TTF.
Top view
HOMO
LUMO
Fig. 1. Optimized structure and the spatial distribution of the HOMO and LUMO orbitals of TTPA-TTF.
Please cite this article as: X. Tian, F. Qian, M. Wu et al., Synthesis and properties of triphenylamine functionalized tetrathiafulvalene, Tetrahedron Letters,
https://doi.org/10.1016/j.tetlet.2020.151949

X. Tian et al. / Tetrahedron Letters xxx (xxxx) xxx
3
(b)
(a)
-1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
300
350
400
450
500
550
Potential (V vs Fc/Fc+)
Wavelength (nm)
Fig. 2. (a) UV–vis absorption spectrum and (b) cyclic voltammogram of TTPA-TTF in dilute chlorobenzene (1 ꢁ 10ꢀ5 M).
The thermal property of TTPA-TTF was investigated by thermo-
gravimetric (TGA) and different scanning calorimetry (DSC) analy-
ses. As shown in Fig. 3a, TTPA-TTF showed good thermal stability
with a high decomposition temperature (Td) of 369.0 °C obtained
from the TGA measurement, and an endothermic step at 138.7 °C
corresponding to the glass transition temperature (Tg) observed
in the DSC curve.
coating its chlorobenzene solution, and the carrier mobility of the
compound was calculated using the space charge limited current
(SCLC) method. Herein, the structure of the hole-only device was
ITO/PEDOT: PSS/HTM/MoO3/Al, where the HTM referred to TTPA-
TTF. Light emission was not detected from the hole-only devices
during the measurement, indicating that the electron is not injected
and recombined with the hole. Thus, TTPA-TTF exhibited hole-
transporting characteristic. The mobility was determined by fitting
the dark current to the model of a single carrier SCLC, which was
To study the charge-transport property of TTPA-TTF, single
charge carrier device based on TTPA-TTF was fabricated by spin
(b)
(a)100
0.1
95.00%
369 C
95
90
85
80
75
70
0.01
1E-3
1E-4
1E-5
138.7 o
C
100
110
120
130
140
150
160
Temperature ( C)
100
200
300
400
500
0.01
1
Vol0t.a1ge(V)
Temperature ( C)
Fig. 3. (a) TGA and DSC (inset) curves of TTPA-TTF. (b) J-V curve of hole only device with an architecture of ITO/PEDOT: PSS/TTPA-TTF /MoO3/Al.
(a) 25
(b)
1.0
0.9
0.8
0.7
20
15
10
5
0
0.0
0.2
0.4
0.6
0.8
1.0
0
4
8
12
16
20
24
Voltage (V)
Time (days)
Fig. 4. (a) Current density–voltage curve of one of the best performing devices using undoped TTPA-TTF as HTM. (b) Stability test of undoped TTPA-TTF based PSCs.
Please cite this article as: X. Tian, F. Qian, M. Wu et al., Synthesis and properties of triphenylamine functionalized tetrathiafulvalene, Tetrahedron Letters,
https://doi.org/10.1016/j.tetlet.2020.151949

4
X. Tian et al. / Tetrahedron Letters xxx (xxxx) xxx
described by the Mott–Gurney law. As shown in Fig. 3b, the TTPA-
References
TTF exhibits a high hole-mobility of 1.06 ꢁ 10ꢀ4 cm2 Vꢀ1 Sꢀ1
.
[1] Ferraris John, D.O. Cowan, V. Walatka, J.H. Perlstein, J. Am. Chem. Soc. 95
(1973) 948–949.
[2] S. Rabaça, S. Oliveira, A.C. Cerdeira, D. Simão, I.C. Santos, M. Almeida,
Tetrahedron Lett. 55 (2014) 6992–6997.
[3] J. Liu, Y. Wu, C. Qin, X. Yang, T. Yasuda, A. Islam, K. Zhang, W. Peng, W. Chen, L.
Han, Energy Environ. Sci. 7 (2014) 2963–2967.
[4] V.A. Azov, Tetrahedron Lett. 57 (2016) 5416–5425.
[5] N. Martín, Chem. Commun. 49 (2013) 7025–7027.
[6] B. Xu, H. Chakraborty, R.C. Remsing, M.L. Klein, S. Ren, Adv. Mater. 29 (2017)
1605150.
[7] G. Chen, I. Mahmud, L.N. Dawe, Y. Zhao, Org. Lett. 12 (2010) 4.
[8] Y. Si, G. Yang, Z. Su, J. Mater. Chem. C 1 (2013) 1399.
[9] K. Guo, K. Yan, X. Lu, Y. Qiu, Z. Liu, J. Sun, F. Yan, W. Guo, S. Yang, Org. Lett. 14
(2012) 2214–2217.
[10] F. Pointillart, B. le Guennic, O. Cador, O. Maury, L. Ouahab, Acc. Chem. Res. 48
(2015) 2834–2842.
[11] M. Wu, J. Li, R. Zhang, X. Tian, Z. Han, X. Lu, K. Guo, Z. Liu, Z. Wang, Org. Lett. 20
(2018) 780–783.
[12] L. Jia, G. Zhang, D. Zhang, D. Zhu, Tetrahedron Lett. 51 (2010) 4515–4518.
[13] M.R. Cerón, M. Izquierdo, N. Alegret, J.A. Valdez, A. Rodríguez-Fortea, M.M.
Olmstead, A.L. Balch, J.M. Poblet, L. Echegoyen, Chem. Commun. 52 (2016) 64–
67.
The suitable energy levels, high thermal stability and hole-
mobility suggested TTPA-TTF could be developed as a dopant-free
HTM for PSCs. With these in mind, a PSC structured of FTO/TiO2/
CH3NH3PbI3 / TTPA-TTF /Au without any p-type dopants was
assembled and tested. The photovoltaic performances of the PCS
were measured under AM1.5G (100 mWcmꢀ2) irradiation, and
the current density–voltage (J-V) curve is displayed in Fig. 4(a).
The device based on TTPA-TTF displayed a short-circuit density
(Jsc) of 23.88 mA cmꢀ2, an open circuit voltage (Voc) of 0.88 V,
and a fill factor (FF) of 0.52, thus giving a PCE of 10.95%. Fig. S2
showed statistics data on the reproducibility of the PSCs perfor-
mance. The average PCEs for 40 devices based on TTPA-TTF were
9.61 0.84%, which indicated good reproducibility of the devices.
Furtherly, to explore the durability of the photovoltaic perfor-
mance of the PSCs based on TTPA-TTF, the PCE change with time
of unencapsulated device by storing them in air with a relative
humidity of 30% was investigated (Fig. 4b). After aging for 24 days,
the TTPA-TTF-based PSC retained 85.2% of its initial PCE, indicating
good stability of the device.
[14] G.-N. Li, D. Wen, T. Jin, Y. Liao, J.-L. Zuo, X.-Z. You, Tetrahedron Lett. 52 (2011)
675–678.
[15] M. Shao, Y. Zhao, Tetrahedron Lett. 50 (2009) 6897–6900.
[16] J.M. Fabre, Chem. Rev. 104 (2004) 5133–5150.
[17] X. Li, G. Zhang, H. Ma, D. Zhang, J. Li, D. Zhu, J. Am. Chem. Soc. 126 (2004)
11543–11548.
[18] M. Yamashita, H. Hayashi, N. Aratani, H. Yamada, Tetrahedron Lett. 56 (2015)
3804–3808.
Conclusion
In summary, to explore the properties and application of the
heteroatom-containing aromatic groups functionalized TTF deriva-
tives, a new TTF-centered, four TPA functionalized molecule TTPA-
TTF has been synthesized. Studies implied TPA functionalized TTF
compound would be promising hole-transporting candidates. As
a primary application, the PSC based on the dopant-free TTPA-
TTF yields a moderate PCE of 10.95% with good stability. This work
not only paves a new way for developing peripheral groups func-
tionalized TTFs but also sheds light on the future design of highly
efficient HTMs.
[19] M. Yamashita, K. Kawano, A. Matsumoto, N. Aratani, H. Hayashi, M. Suzuki, L.
Zhang, A.L. Briseno, H. Yamada, Chem. Eur. J. 23 (2017) 15002–15007.
[20] Nishida J. Naraso, S. Ando, J. Yamaguchi, K. Itaka, H. Koinuma, H. Tada, S.
Tokito, Y. Yamashita, J. Am. Chem. Soc. 127 (2005) 10142–10143.
[21] X. Liu, X. Ding, Y. Ren, Y. Yang, Y. Ding, X. Liu, A. Alsaedi, T. Hayat, J. Yao, S. Dai,
J. Mater. Chem. C 6 (2018) 12912–12918.
[22] R. Yuan, L. Zhang, L. Chen, H. Zhang, P. Dou, X. Ren, W. Chen, H. Zhou, Y. Wan,
H. Wu, Tetrahedron Lett. 60 (2019) 1803–1807.
[23] G. Wu, Y. Zhang, R. Kaneko, Y. Kojima, K. Sugawa, T.H. Chowdhury, A. Islam, Q.
Shen, Md Akhtaruzzaman, T. Noda, J. Otsuki, J. Sol. RRL. 1 (2017) 1700096.
[24] Y.-L. Xu, W.-L. Ding, Z.-Z. Sun, Nanoscale. 10 (2018) 20329–20338.
[25] J. Wang, K. Liu, L. Ma, X. Zhan, Chem. Rev. 116 (2016) 14675–14725.
[26] L.-L. Jiang, Z.-K. Wang, M. Li, C.-H. Li, P.-F. Fang, L.-S. Liao, J. Mater. Chem. A 7
(2019) 3655–3663.
[27] X. Wang, J. Wu, Y. Yang, X. Liu, Q. Guo, Z. Song, G. Li, Z. Lan, M. Huang, J. Mater.
Chem. A 7 (2019) 13256–13264.
[28] X. Niu, N. Li, C. Zhu, L. Liu, Y. Zhao, Y. Ge, Y. Chen, Z. Xu, Y. Lu, M. Sui, Y. Li, A.
Tarasov, E.A. Goodilin, H. Zhou, Q. Chen, J. Mater. Chem. A 7 (2019) 7338–7346.
[29] X. Zhou, F. Kong, Y. Sun, Y. Huang, X. Zhang, R. Ghadari, Dyes Pigm. 173 (2020)
107954.
[30] S. Paek, P. Qin, Y. Lee, K.T. Cho, P. Gao, G. Grancini, E. Oveisi, P. Gratia, K.
Rakstys, S.A. Al-Muhtaseb, C. Ludwig, J. Ko, M.K. Nazeeruddin, Adv. Mater. 29
(2017) 1606555.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
[31] S. Ranallo, A. Amodio, A. Idili, A. Porchetta, F. Ricci, Chem. Sci. 7 (2016) 66–71.
[32] J. Lee, M. Malekshahi Byranvand, G. Kang, S.Y. Son, S. Song, G.-W. Kim, T. Park,
J. Am. Chem. Soc. 139 (2017) 12175–12181.
Acknowledgment
[33] X. Yin, J. Zhou, Z. Song, Z. Dong, Q. Bao, N. Shrestha, S.S. Bista, R.J. Ellingson, Y.
Yan, W. Tang, Adv. Funct. Mater. 29 (2019) 1904300.
[34] X. Liang, K. Wang, R. Zhang, K. Li, X. Lu, K. Guo, H. Wang, Y. Miao, H. Xu, Z.
Wang, Dyes Pigm. 139 (2017) 764–771.
This work was supported by the National Natural Science Foun-
dation of China (NO. 21303117, 61704101).
[35] C. Yin, J. Lu, Y. Xu, Y. Yun, K. Wang, J. Li, L. Jiang, J. Sun, A.D. Scully, F. Huang, J.
Zhong, J. Wang, Y.-B. Cheng, T. Qin, W. Huang, Adv. Energy Mater. 8 (2018)
1800538.
Appendix A. Supplementary data
[36] X.-L. Sun, D.-M. Liu, D. Tian, X.-Y. Zhang, W. Wu, W.-M. Wan, Nat. Commun. 8
(2017) 1210.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2020.151949.
Please cite this article as: X. Tian, F. Qian, M. Wu et al., Synthesis and properties of triphenylamine functionalized tetrathiafulvalene, Tetrahedron Letters,
https://doi.org/10.1016/j.tetlet.2020.151949