ChemComm
View Article Online
Published on 19 November 2012. Downloaded by CNR Bologna on 20/03/2014 15:50:09.
COMMUNICATION
Cite this: Chem. Commun., 2013,
49, 4298
Received 28th September 2012,
Accepted 5th November 2012
DOI: 10.1039/c2cc37053k
View Journal | View Issue
p-Core tailoring for new high performance
thieno(bis)imide based n-type molecular
semiconductors†‡
Margherita Durso,a Denis Gentili,b Cristian Bettini,c Alberto Zanelli,a
Massimiliano Cavallini,b Filippo De Angelis,d Maria Grazia Lobello,d
Viviana Biondo,be Michele Muccini,be Raffaella Capellibe and Manuela Melucci*a
www.rsc.org/chemcomm
The synthesis and characterization of two thieno(bis)imide based n-type
semiconductors with electron mobilities of up to 0.3 cm2 V
1
s
1
are
described. The relationships between the electronic features of the
p-inner core and the functional properties of the new materials are also
discussed.
Organic field effect transistors (OFETs) based on p-conjugated
molecular materials attract great attention because of many
advantages in contrast to conventional silicon-based transistors,
for instance, low fabrication cost, large-area manufacturing, and
flexibility.1 Among molecular materials, thiophene-based ones2 are
widely investigated for their chemical versatility and functionality as
p-type semiconductors.1,3 In contrast, thiophene based molecular
materials featuring electron1,4 and ambipolar5 charge transport
have been more rarely documented.
Arylene(bis)imide frameworks are commonly exploited building
blocks to promote electron6 and ambipolar charge transport.1b,7 A
combination of phenylene(bis)imide frameworks (n-type blocks) and
oligothiophenes (p-type blocks) has been proposed as a two block
strategy toward the synthesis of ambipolar semiconductors.8 In this
segment, we have recently developed the thiophene(bis)imide
(TBI, N) moiety as an end group capable of promoting ambipolar
charge transport in quaterthiophene. Indeed, T4DIM9 having two
TBI end moieties of bithiophene (TT) showed ambipolar charge
transport with major electron charge transport contribution and
mobilities of up to me = 5.3 10 2 cm2 V 1 s 1.9
In accordance with the current need for highly performing
electron charge transport materials, we report here two novel
compounds featuring fine-tunable inner cores such as: bithiazole
(Tz - NTzN, Scheme 1) and thienothiophene (ThT - NThTN,
Scheme 1). Thienothiophene insertion into linear oligothiophenes
has been related to efficient hole charge transport.10a In contrast,
the insertion of thiazole rings into trifluorophenyl ended oligothiophenes improves electron charge transport and threshold voltages
with respect to all-thiophene based analogues.10b Accordingly,
we envisioned the possibility of controlling the n-type behaviour
of TBI based semiconductors by using p-inner cores more
electron-deficient than TT (as for T4DIM). To further validate
this strategy, a probe compound featuring a dimethylated
bithiophene inner core was also synthesized and investigated
(TMe - NTMeN, Scheme 1).
The title compounds were prepared through Stille crosscoupling reaction between brominated thieno(bis)imide (N-Br)9
and the proper distannyl derivative as depicted in Scheme 1.
Differential scanning calorimetry (DSC, Fig. S1–S3, ESI‡)
revealed liquid crystalline properties of NThTN and NTMeN.
The UV-Vis absorption and emission spectra of compounds 1–3
are shown in Fig. 1a and the complete list of the optical and
electrochemical data is summarized in Table 1. Interestingly, the
introduction of the Tz core causes a blue shift of the maximum
a
`, (ISOF),
Istituto per la Sintesi Organica e la Fotoreattivita
Consiglio Nazionale delle Ricerche, (CNR) via P. Gobetti 101, 40129 Bologna, Italy.
E-mail: manuela.melucci@isof.cnr.it; Fax: +39 051 6398349; Tel: +39 051 6398271
b
CNR - Istituto per lo studio dei Materiali Nanostrutturati (ISMN),
via P. Gobetti 101, 40129 Bologna, Italy
c
MIST-ER Laboratory, via p. Gobetti 101, 40129 Bologna, Italy
d
CNR- Istituto di Scienze e Tecnologie Molecolari (ISTM), via Elce di Sotto 8, I-6123,
Perugia, Italy
e
E.T.C. srl, via P. Gobetti 101, 40129 Bologna, Italy
† This article is part of the ChemComm ‘Emerging Investigators 2013’ themed issue.
‡ Electronic supplementary information (ESI) available: Experimental procedures
of synthesis, 1H-NMR spectra, DSC analyses, CVs, DFT calculations, LCW, device
fabrication and additional electrical parameters. See DOI: 10.1039/c2cc37053k
4298
Chem. Commun., 2013, 49, 4298--4300
Scheme 1 Synthetic route to compounds 1–3. (i) 5 mol% of in situ formed
Pd(AsPh3)4, refluxing toluene.
This journal is
c
The Royal Society of Chemistry 2013
View Article Online
Published on 19 November 2012. Downloaded by CNR Bologna on 20/03/2014 15:50:09.
Communication
ChemComm
Fig. 1 (a) UV-vis and PL spectra in CH2Cl2, (b) CVs at 0.2 Vs 1 of NTzN, NThTN,
and NTMeN saturated solutions in CH2Cl2 containing 0.1 M (C4H9)4NClO4, (c)
isodensity plots for NTzN, NThTN and NTMeN.
absorption wavelength lmax of about 15 nm and 20 nm with
respect to NThTN and NTMeN respectively. The same trend is
observed for the maximum emission wavelengths that are strongly
blue shifted for NTzN with respect to the other compounds.
In detail, NTzN showed structured emission with two maxima
located at 489 nm and 514 nm respectively. NThTN and NTMeN
displayed unstructured emission with the maxima shifted by 32 nm
and 67 nm respectively (Fig. 1a). The optical energy band gap Eopt
g of
NTzN was about 0.10 eV higher than those of the other compounds.11a
CVs of compounds NTzN and NThTN show a quasi-reversible
reduction wave12 while NTMeN shows both reduction and oxidation
quasi-reversible waves in the electrochemical window of the electrolytic solution (Fig. 1b), in agreement with the smaller Eopt
g (Table 1).
The reduction potential Eored becomes more negative on passing from
NTzN to NTMeN suggesting a less delocalized LUMO in the latter.
Accordingly, DFT calculations performed with the B3LYP functional13 and a 6-31G* basis set show that in NTzN both the HOMO
and LUMO are almost uniformly delocalized on the entire molecular backbone (Fig. 1c). In contrast, for NThTN and NTMeN the
HOMO is mainly localized in the inner core while the LUMO is
localized at the periphery of the electron-withdrawing TBI ends.
Such orbital distribution suggests higher suitability to
charge transport for NTzN since higher intermolecular overlap
(favourable to charge transport) can be expected for conjugated
oligomers having uniformly distributed frontier orbitals.1b,14
Thin deposits of the newly synthesized compounds were analysed
by polarised optical microscopy (POM) to investigate the self-organization capability of these materials at the surface. Upon drop
casting, all compounds form isolated micrometre sized, birefringent
crystals whose shape depends on the substrate and the solvent used
Table 1
labsa (nm)
lema (nm)
Eooxb (V)
NTzN
NThTN
NTMeN
428
443
449
489/514
546
581
>1.6
>1.6
+1.28
e
(Fig. 2b).15a However, lithographically controlled wetting (LCW,
Fig. 2a)15b,c allows the fabrication of parallel micrometre-sized stripes
(m-stripes) of a few millimetres length (Fig. 2c) covering the entire
substrate. Despite some cracks that are present along some m-stripes,
detailed investigation by POM (see ESI‡) reveals long range coherent
molecular ordering along each stripe. The electrical properties of the
Fig. 3 (a) Multiple output n-type and (b) locus n-type curves for NTzN, (c)
multiple n-type output curves for NThTN, (d) multiple output p-type curves for
NThTN, (e) multiple output n-type output curves for NTMeN, (f) multiple output
p-type curves for NTMeN.
List of experimental and calculated optoelectronic parameters
Comp.
a
Fig. 2 Thin deposit and m-stripes of NTMeN fabricated by LCW on the Si/SiO2
surface. (a) Scheme of the LCW process. (b) POM image of a drop cast film, taken
with crossed polars oriented along the axes of the image. Scale bar 20 mm. (c)
Optical micrographs of m-stripes. Scale bar: 5 mm.
In CH2Cl2. b Vs. SCE in CH2Cl2 containing 0.1 mol L
EHOMO = ELUMO Eopt
g .
This journal is
c
The Royal Society of Chemistry 2013
1
Eoredb (V)
1.13
1.2
1.26
EHOMO (eV) (theor)
5.81e ( 5.89)
5.69e ( 5.58)
5.65e ( 5.38)
ELUMOc (eV) (theor)
3.24 ( 3.00)
3.2 ( 2.79)
3.11 ( 2.73)
(C4H9)4NClO4. c ELUMO = e(4.37 + Eored), EHOMO = e(4.37 + Eoox).11b,c
d
Eopt
(eV)
g
2.57
2.49
2.39
d
Eopt
= 1240/lonset.11d
g
Chem. Commun., 2013, 49, 4298--4300
4299
View Article Online
ChemComm
Table 2
Comp.
Published on 19 November 2012. Downloaded by CNR Bologna on 20/03/2014 15:50:09.
NTzN
NThTN
NTMeN
Communication
Notes and references
Electrical parameters for compounds 1–3
2
1
mh (cm V
nd
6.4 10
3.0 10
5
6
1
s )
VPT/V
Ion/Ioff
nd
–67.3
–45.0
7
10
106
104
2
1
me (cm V
1.6 10
3.0 10
1.3 10
1
1
5
1
s )
VN
T /V
39.7
62.6
56.9
newly synthesized materials were measured in bottom gate-top
contact OFET devices (nitrogen atmosphere, 1 ppm O2, 1 ppm
H2O, other details in ESI‡). The device responses are reported in
Fig. 3 showing the multiple output curves for each compound. NTzN
shows exclusively electron charge transport with charge mobility
values of up to me = 0.16 cm2 V 1 s 1 and a threshold voltage VN
T =
39.7 V (Table 2). In contrast, NThTN shows ambipolar charge
transport with an excellent electron charge mobility of me =
0.3 cm2 V 1 s 1 but higher threshold voltage (with respect to NTzN)
and a hole mobility of mh = 6.4 10 5 cm2 V 1 s 1 (Table 2). Both
electron mobility values are one order of magnitude higher than that
observed for the already reported T4DIM9 (me = 5.3 10 2 cm2 V 1 s 1)
and comparable or even better than the best performances so far
achieved for n-type thiophene based materials.16 It should be noted
that no device optimization (i.e. substrate functionalization or annealing procedures) was performed. The electron mobilities drop by about
three orders of magnitude on passing to NTMeN having the more
electron rich methylated bithiophene inner core (Table 2).
Although the beta methyl substitution could prevent a close
molecular overlap required for efficient charge transport, it
appear that electron deficient cores strongly improve the charge
transport capability of thieno(bis)imide based materials.
The unipolar rather than ambipolar behaviour observed for
NTzN could be due to the less favourable matching of the estimated
HOMO energy of NTzN (lower than the other compounds) with the
gold electrode FERMI level which limits the hole injection.
In conclusion, two new efficient and highly processable
n-type molecular semiconductors based on the combination
of thieno(bis)imide end units with thiazole and thienothiophene p-inner cores have been presented. Electron charge
mobility values of up to 0.3 cm2 V 1 s 1 (in un-optimized
devices) were measured for these materials.
Such OFET performance is one order of magnitude higher
than those achieved by using unsubstituted bithiophene p-cores
(T4DIM)9 and three orders of magnitude higher with respect to
NTMeN having a more electron rich core. Given the lack of
n-type materials and the poor level of understanding of their
structure–property relationships, these results provide important
perspectives towards the development of new molecular n-type
semiconductors.
Current work is focused on the use of different cores as well
as on the device tailoring to further improve the electrical
performance.
The authors gratefully acknowledge the support of this work
by the Consorzio MIST-ER through project FESR-tecnopolo
AMBIMAT, by the EU through project FP7-ICT-248052
(PHOTO-FET) and by the Italian MSE through project Industria
2015 (ALADIN). MC and DG were supported by the Project
European Science Foundation EURYI DYMOT. MM thanks L.
Favaretto and M. Zambianchi for their precious support.
4300
Chem. Commun., 2013, 49, 4298--4300
1 (a) Organic Field-Effect Transistors, ed. Z. Bao and J. Locklin, CRC, New
York, 2007; (b) C. Wang, H. Dong, W. Hu, Y. Liu and D. Zhu, Chem. Rev.,
2012, 112, 2208; (c) H. Usta, A. Facchetti and T. J. Marks, Acc. Chem. Res.,
2011, 44, 501; (d) A. C. Arias, J. D. MacKenzie, I. McCulloch, J. Rivnay and
¨llen, Chem.
A. Salleo, Chem. Rev., 2010, 110, 3; (e) H. N. Tsao and K. Mu
´chet, Chem.
Soc. Rev., 2010, 39, 2372; ( f ) A. R. Murphy and J. M. J. Fre
Rev., 2007, 107, 1066; (g) S. Allard, M. Forster, B. Souharce, H. Thiem and
U. Scherf, Angew. Chem., Int. Ed., 2008, 47, 4070.
2 (a) C. Wang, H. Dong, W. Hu, Y. Liu and D. Zhu, Chem. Rev., 2011,
¨erle, Chem. Rev., 2009,
112, 2208; (b) A. Mishra, C.-Q. Ma and P. Bau
109, 1141; (c) G. Barbarella, M. Melucci and G. Sotgiu, Adv. Mater.,
2005, 17, 1581; (d) T. Benincori, M. Capaccio, F. De Angelis,
L. Falciola, M. Muccini, P. Mussini, A. Ponti, S. Toffanin, P. Traldi
and F. Sannicolo, Chem.–Eur. J., 2008, 14, 459.
3 (a) M. Melucci, L. Favaretto, A. Zanelli, M. Cavallini, A. Bongini,
P. Maccagnani, P. Ostoja, G. Derue, R. Lazzaroni and G. Barbarella,
Adv. Func. Mat., 2010, 20, 1.
4 For a recent review on n-type materials, see: J. E. Anthony, A. Facchetti,
M. Heeney, S. R. Marder and X. Zhan, Adv. Mater., 2010, 22, 3876.
5 (a) T. Yamao, Y. Shimizu, K. Terasaki and S. Hotta, Adv. Mater., 2008,
20, 4109; (b) K. Yamane, H. Yanagi, A. Sawamoto and S. Hotta, Appl.
Phys. Lett., 2007, 90, 162108; (c) R. Capelli, F. Dinelli, S. Toffanin,
F. Todescato, M. Murgia, M. Muccini, A. Facchetti and T. J. Marks,
J. Phys. Chem., 2008, 112, 12993; (d) M.-H. Yoon, S. A. Di Benedetto,
A. Facchetti and T. Marks, J. Am. Chem. Soc., 2005, 127, 1348.
6 (a) X. W. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner,
M. R. Wasielewski and S. R. Marder, Adv. Mater., 2011, 23, 268;
(b) K. C. See, C. Landis, A. Sarjeant and H. E. Katz, Chem. Mater., 2008,
20, 3609; (c) D. Shukla, S. F. Nelson, D. C. Freeman, M. Rajeswaran,
W. G. Ahearn, D. M. Meyer and J. T. Carey, Chem. Mater., 2008, 20, 7486;
(d) J. G. Laquindanum, H. E. Katz, A. Dodabalapur and A. J. Lovinger,
J. Am. Chem. Soc., 1996, 118, 11331; (e) G. Horowitz, F. Kouki,
P. Spearman, D. Fichou, C. Nogues, X. Pan and F. Garnier, Adv. Mater.,
1996, 8, 242; ( f ) P. R. L. Malenfant, C. D. Dimitrakopoulos, J. D. Gelorme,
L. L. Kosbar, T. O. Graham, A. Curioni and W. Andreoni, Appl. Phys. Lett.,
2002, 80, 2517; (g) R. J. Chesterfield, J. C. McKeen, C. R. Newman,
P. C. Ewbank, D. A. daSilvaFilho, J. L. Bredas, L. L. Miller, K. R. Mann
and C. D. Frisbie, J. Phys. Chem. B, 2004, 108, 19281.
7 (a) H. N. Tsao, W. Pisula, Z. H. Liu, W. Osikowicz, W. R. Salaneck
and K. Mullen, Adv. Mater., 2008, 20, 2715; (b) C. A. Liu, Z. H. Liu,
H. T. Lemke, H. N. Tsao, R. C. G. Naber, Y. Li, K. Banger, K. Mullen,
M. M. Nielsen and H. Sirringhaus, Chem. Mater., 2010, 22, 2120.
8 (a) H. Usta, C. Newman, Z. Chen and A. Facchetti, Adv. Mater., 2012,
24, 3678; (b) R. P. Ortiz, H. Herrera, C. Seoane, J. L. Segura,
A. Facchetti and T. J. Marks, Chem.–Eur. J., 2011, 18, 532.
9 M. Melucci, M. Zambianchi, L. Favaretto, M. Gazzano, A. Zanelli,
M. Monari, R. Capelli, S. Troisi, S. Toffanin and M. Muccini, Chem.
Commun., 2011, 47, 11840.
10 (a) S. Oku, K. Takamiya, D. Adachi, S. Ishikawa, S. Nagamatsu,
W. Takashima, S. Hayase and K. Kaneto, Chem. Lett., 2010, 1315;
(b) W. Li, H. E. Katz, A. J. Lovinger and J. G. Laquindanum, Chem. Mater.,
1999, 11, 458; (c) S. Ando, R. Murakami, J.-I. Nishida, H. Tada, Y. Inoue,
S. Tokito and Y. Yamashita, J. Am. Chem. Soc., 2005, 127, 14996;
(d) S. Ando, J. Nishida, H. Tada, Y. Inoue, S. Tokito and Y. Yamashita,
J. Am. Chem. Soc., 2005, 127, 5336.
11 (a) J. Roncali, Macromol. Rapid Commun., 2007, 28, 1761;
(b) S. Trasatti, Pure Appl. Chem., 1986, 58, 955; (c) G. Gratzner and
J. Kuta, Pure Appl. Chem., 1984, 56, 461; (d) J. Heinze, B. A. FrontanaUribe and S. Ludwigs, Chem. Rev., 2010, 110, 4724.
12 NThTN gives a current too low to allow an accurate determination of
reduction potential.
13 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
14 J.-L. Bredas, Chem. Rev., 2007, 107, 926–952.
15 (a) M. Cavallini, J. Mater. Chem., 2009, 19, 6085; (b) M. Cavallini,
C. Albonetti and F. Biscarini, Adv. Mater., 2009, 21, 1043;
(c) M. Cavallini, D. Gentili, P. Greco, F. Valle and F. Biscarini, Nat.
Protocols, 2012, 7, 1668.
16 (a) A. Facchetti, M.-H. Yoon, C. L. Stern, G. R. Hutchison, M. A. Ratner
and T. J. Marks, J. Am. Chem. Soc., 2004, 126, 13480; (b) M.-H. Yoon, S. A.
Di Benedetto, A. Facchetti and T. J. Marks, J. Am. Chem. Soc., 2005, 127,
1348; (c) J. A. Letizia, S. Cronin, R. P. Ortiz, A. Facchetti, M. A. Ratner and
T. Marks, Chem.–Eur. J., 2010, 16, 1911; (d) M.-H. Yoon, S. A. DiBenedetto,
M. T. Russell, A. Facchetti and T. J. Marks, Chem. Mater., 2007, 19, 4864.
This journal is
c
The Royal Society of Chemistry 2013