Transistors from a conjugated macrocycle molecule: Field and photo effects

Article abstract of DOI:10.1039/b806601a

This study explores a conjugated macrocycle molecule and details its synthesis, molecular structure, assemblies in the solid state and application in phototransistors. The Royal Society of Chemistry.

Full text of DOI:10.1039/b806601a

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Transistors from a conjugated macrocycle molecule: field and photo
effectsw
Wei Zhao,a Qin Tang,a Hoi Shan Chan,a Jianbin Xu,b Ka Yuen Loa and
Qian Miao*a
Received (in Cambridge, UK) 18th April 2008, Accepted 6th June 2008
First published as an Advance Article on the web 18th July 2008
DOI: 10.1039/b806601a
This study explores a conjugated macrocycle molecule and
details its synthesis, molecular structure, assemblies in the solid
state and application in phototransistors.
inside the macrocycle (Ha of 1b shown in Scheme 1) having a
chemical shift of 9.30 ppm, which shifts downfield compared
to that of Hb (9.16 ppm) in 2b. This is similar to the properties
of kekulene12 and indicates that the 18-membered ring of 1b is
not annulenoid-aromatic. The longest wavelength absorbance
for 1a (468 nm, obtained from a dilute solution of 1a in 1,2,4-
trichlorobenzene) is essentially the same as that of di-9-
anthryldiacetylene (470 nm)13 suggesting that the anthrylene
diacetylene macrocycle has an electronic structure similar to
its acyclic analogue.
Arylene ethynylene macrocycles1 are useful building blocks for
porous molecular crystals,2 carbon nanostructures,3 fluores-
cent sensors,4 polymeric nanotubes5 and 3D molecular archi-
tectures.6 Although such class of macrocycles has aroused a
broad range of interests, exploring their use in organic electro-
nics has not been reported. As shown in Fig. 1, 1a has two
anthracene subunits, which are useful building blocks of
environmentally stable organic semiconductors for application
in organic field effect transistors (OFETs),7 linked by two
diacetylene groups in a macrocycle structure. Our findings are
that the thin films of macrocycle 1a function as transistors
showing not only a field effect but also a photo effect. The
electrical response to photoirradiation allows the device to
work as a phototransistor combining dual functions of light
detection and signal magnification in a single device.8,9
Although 1a was first synthesized about half a century
ago,10 it was almost forgotten by chemists thereafter and this
study appears to be the first for its soluble derivatives,
assembly and electrical properties being investigated.
To test the stability of these macrocycle molecules, 1a and 1b
were subject to photoirradiation and heating in ambient air.
Crystalline powders of 1a and 1b appeared stable to photoirra-
diation with a 500 W tungsten lamp for 12 hours. As monitored
by differential scanning calorimetry (DSC), 1a and 1b undergo
an irreversible exothermic reaction at ca. 402 and 320 1C,
respectively prior to melting yielding insoluble black solids with
a metallic luster. Micrographs of the thermal product of 2b and
DSC thermograms of 1a and 1b are shown in Fig. S1 of ESI.w
Such exothermic reaction can be attributed to thermal polymer-
ization of macrocycle molecules, which was reported for other
arylene ethynylene macrocyles with similar structures.14
Slowly cooling a hot solution of 1b in 1,2,4-trichlorobenzene
resulted in orange crystals. X-Ray crystallographyz for these
crystals indicates that the macrocycle backbone is essentially
flat and reveals an offset stacked orientation of the macrocycles
Unsubstituted macrocycle 1a is an orange crystalline solid,
which is practically insoluble in common organic solvents at
room temperature and can only be dissolved in hot high-
boiling-point aromatic solvents, such as 1,2,4-trichloro-
benzene. To increase the solubility of 1a, two flexible alkyl
chains are introduced to the anthracene subunits. Scheme 1
shows the synthesis of macrocycles 1a and 1b, in which the
acyclic precursors 2a,b were prepared by modifying the re-
ported processes.11 The relatively good yields of 1a,b from
oxidative cyclic dimerization of 2a,b should be related to the
favorable orientation of ethynyl groups in the rigid backbones
of 2a,b.10 1b dissolves in organic solvents such as chloroform
and toluene at room temperature with solubility lower than
1 mg mlꢀ1 and forms yellow solutions with intense green
fluorescence. The 1H NMR spectra of 1b show the protons
Fig. 1 (a) Molecular structure of the macrocycles with anthracene
and diacetylene moieties highlighted, respectively; (b) side view of
molecular packing of 1b from the crystal structure showing the
distance between p-surfaces (a-carbon atoms of hexyl groups are
disordered in the crystal structure); (c) top view of offset stacked
macrocycles of 1b from the crystal structure highlighting the distance
between diacetylene subunits of neighboring molecules with alkoxyl
groups and hydrogen atoms omitted for clarity.
a Department of Chemistry, the Chinese University of Hong Kong,
Shatin, New Territories, Hong Kong, China
b Department of Electronic Engineering, the Chinese University of
Hong Kong, Shatin, New Territories, Hong Kong, China
w Electronic supplementary information (ESI) available: Synthesis of
1a and 1b, device fabrication and characterization. CCDC 689532
(1b). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b806601a
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Scheme 1 Synthesis of macrocycles: (a) NaBH4, i-PrOH, then
HCl, (b) K2CO3, C6H13Br, DMF; (c) (i) trimethylsilylacetylene,
CH3MgBr, Ni(acac)2, PPh3, THF; (ii) KOH aq., THF; (d) Cu(OAc)2,
pyridine–CH3OH.
as shown in Fig. 1(b) and (c). The a-carbon atoms of the hexyl
groups are disordered in the crystal structure, and the hydrogen
atoms on a- and b-carbon atoms are not included due to such
disorder. The molecules of 1b stack in one direction with
overlap between anthracene subunits of neighboring macro-
cycles and a distance of 3.56 A between aromatic planes of
neighboring macrocycles. Such molecular packing should allow
charge transport along the direction of p-stacking. The closet
contacts between diacetylene subunits of two macrocycles are
observed between neighboring stacks rather than in one stack.
As shown in Fig. 1(c), the two diacetylene subunits in neighbor-
ing stacks are placed in a parallel arrangement with a distance d
between the diyne centers of 5.85 A and a declination angle +
of 52.21 between the molecular and stacking axes. It is well
established that diacetylenes undergo topochemical photopoly-
merization to form trans-polybutadiyne when diacetylene
monomers are arranged in tilted stacks in crystals with d of
4.7–5.2 A, and + of ca. 451.15 Thus the observed stability of
macrocycle molecules to photoirradiation can be attributed to
the molecular packing because the diyne-diyne separation (d)
between diacetylene subunits of 1b is too large to allow this type
of topochemical photopolymerization.
Fig. 2 (a) Absorption spectrum of 1a in a film of 150 nm thick
overlapped with color bars, which show the wavelength and half-peak
width of the illumination tested in the study of phototransistors. (b)
Drain current vs. drain voltage for the thin film transistor of 1a
deposited on OTS-treated SiO2 at a substrate temperature of 110 1C
with channel dimension of W = 2 mm and L = 100 mm tested in dark
and under violet light (l = 408 nm) of 1.0 mW cmꢀ2, respectively.
(c and d) Drain current vs. gate voltage for the above device tested at a
drain voltage of ꢀ50 V in the dark and under violet light (l = 408 nm)
of 3.9 mW cmꢀ2, respectively.
crystals rather than continuous films possibly because of the
relatively low solubility of 1b at room temperature.
Thin-film transistors of 1a in a top-contact configuration
were fabricated by thermal evaporation in vacuum using gold
as source and drain electrodes, highly n-doped silicon as a gate
electrode and a 300 nm thick layer of SiO2 as dielectric. The
thin film of 1a performs as a p-channel field effect transistor
with its field effect mobility dependent on the surface treat-
ment with a self-assembled monolayer of octadecyl trichloro-
silane (OTS) and the substrate temperature during deposition.
Deposition of 1a on OTS-treated SiO2 at a substrate tempera-
ture of ca. 110 1C was found to yield the best device perfor-
mance with field effect mobility of 0.02–0.07 cm2 Vꢀ1 sꢀ1 in
our studies. Fig. 2(b)–(d) shows typical I–V curves for such
devices, from which a field-effect mobility of 0.05 cm2 Vꢀ1 sꢀ1
Thin films of 1a were deposited on oxidized silicon sub-
strates by thermal evaporation in vacuum. X-Ray diffraction
from the film (shown in Fig. S2 of ESIw) shows a primary
diffraction peak at 2y = 8.801 (d-spacing: 10.04 A) with a
second-order peak at 2y = 17.751 (d-spacing: 5.02 A) indicat-
ing a polycrystalline film. The relatively weak diffractions
suggest low long-range orders of molecules in the thin film.
The p–p interaction between molecules of 1a was revealed by
comparing the absorption spectra from a dilute solution of 1a
in 1,2,4-trichlorobenzene (3 ꢂ 10ꢀ5 M) and from a thermal
evaporated film of 150 nm thick on glass (shown in Fig. S2 in
ESIw). The longest wavelength absorption for 1a shifts to the
red by ca. 25 nm on going from solution (468 nm) to the thin
film (493 nm). This type of red shift can be attributed to the
delocalization of the excited state due to p-stacking and is
common in many p-stacked systems.16 Deposition of 1b by
thermal evaporation was not successful due to polymerization
of 1b prior to sublimation. On the other hand, casting a
solution of 1b on an oxidized silicon substrate yielded isolated
is measured in the saturation regime using the equation: IDS
=
(mWCi/2L)(VG ꢀ VT)2 and Ci of 11 nF cmꢀ2 for 300 nm
SiO2.17,18 The on/off ratio of the drain current obtained
between 0 and ꢀ50 V gate bias from the output I–V curves
is 41 ꢂ 104.
Interestingly thin film transistors of 1a also show a photo
effect, which was first noticed when the I–V characteristics were
measured under white light from a halogen lamp. To test the
photo effect, five LED lamps were used as sources of visible
light with varied colors, which are shown in Fig. 2(a) with the
absorption spectrum of 1a in a thin film. It is found that
irradiation with violet, blue and green light, which have photon
energy higher than the HOMO–LUMO gap of 1a in the solid
state (about 550 nm as estimated from the edge of longest
wavelength absorption), causes the threshold voltage to shift
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without apparently changing the charge carrier mobility. Such
effect indicates that light functions as an additional parameter
to control the number of mobile charges. As shown in Fig. 2(d),
upon irradiation with violet light (l = 408 nm) of 3.9 mW cmꢀ2
the threshold voltage shifts from ꢀ29 V to ꢀ9 V. A ratio of
photo-current and dark-current (Iph/Idark) as high as 4 ꢂ 103 is
measured from the transfer curves shown in Fig. 2(c). In
contrast, transistors of 1a do not show response to orange
and red light. Such photo effect can be attributed to charges
generated by dissociation of photo-induced excitons.8,9 The
relatively large threshold voltage (ꢀ29 V) suggests high density
of charge carrier traps in the transistor.17 Photo irradiation
shifts the threshold voltage to less negative values because some
of the traps are filled with the photo-induced charges.
6 S. Toyota, M. Goichi and M. Kotani, Angew. Chem., Int. Ed.,
2004, 43, 2248–2251.
7 (a) J. E. Anthony, Chem. Rev., 2006, 106, 5028–5048; (b) K. Ito, T.
Suzuki, Y. Sakamoto, D. Kubota, Y. Inoue, F. Sato and S. Tokito,
Angew. Chem., Int. Ed., 2003, 42, 1159; (c) H. Meng, F. Sun, M. B.
Goldfinger, F. Gao, D. J. Londono, W. J. Marshal, G. S.
Blackman, K. D. Dobbs and D. E. Keys, J. Am. Chem. Soc.,
2006, 128, 9304–9305; (d) H. Meng, F. Sun, M. B. Goldfinger, G.
D. Jaycox, Z. Li, W. J. Marshal and G. S. Blackman, J. Am. Chem.
Soc., 2005, 127, 2406–2407; (e) S. Ando, J. I. Nishida, E. Fujiwara,
H. Tada, Y. Inoue, S. Tokito and Y. Yamashita, Chem. Mater.,
2005, 17, 1261; (f) J. A. Merlo, C. R. Newman, C. P. Gerlach, T.
W. Kelley, D. V. Muyres, S. E. Fritz, M. F. Toney and C. D.
Frisbie, J. Am. Chem. Soc., 2005, 127, 3997; (g) Z. Wang, C. Kim,
A. Facchetti and T. J. Marks, J. Am. Chem. Soc., 2007, 129,
13362–13363; (h) A. Dell’Aquila, F. Marinelli, J. Tey, P. Keg, Y.-
M. Lam, O. L. Kapitanchuk, P. Mastrorilli, C. F. Nobile, P.
Cosma, A. Marchenko, D. Fichou, S. G. Mhaisalkar, G. P.
Suranna and L. Torsi, J. Mater. Chem., 2008, 18, 786–791.
8 Organic phototransistors showing response to UV light: (a) Y.-Y.
Noh, D.-Y. Kim, Y. Yoshida, Y. Yase, B. J. Jung, E. Lim and H.
K. Shim, Appl. Phys. Lett., 2005, 86, 043501; (b) T. P. I. Saragi, R.
Pudzich, T. Fuhrmann and J. Salbeck, Appl. Phys. Lett., 2004, 84,
2334–2336; (c) Y.-Y. Noh, J. Ghim, S.-J. Kang, K.-J. Baeg, D.-Y.
Kim and K. Yase, J. Appl. Phys., 2006, 100, 094501.
In summary, the studies above demonstrate that the thin
films of macrocycle 1a function as phototransistors combining
light detection and signal magnification in a single device. The
photo response suggests potential applications of this family of
conjugated macrocycle molecules in organic optoelectronics,
such as photodetectors and solar cells. The success of using
conjugated macrocycle molecules as organic semiconductors in
OFETs19 also suggests a new strategy to design electronic
materials for OFET-based chemical sensors since the intrinsic
cavity from a macrocyclic structure may selectively bind a guest
molecule. For such application, the cavity inside the conjugated
macrocycle should be enlarged to accommodate a guest mole-
cule. Investigations on conjugated macrocycles with larger
cavities are in progress in our laboratory.
9 Organic phototransistors showing response to visible light:
(a) Y.-Y. Noh, D.-Y. Kim and K. Yase, J. Appl. Phys., 2005, 98,
074505; (b) R. M. Meixner, H. Gobel, F. A. Yildirim, W. Bauhofer
¨
and W. Krautschneider, Appl. Phys. Lett., 2006, 89, 092110;
(c) M. Mas-Torrent, P. Hadley, N. Crivillers, J. Veciana and C.
Rovira, ChemPhysChem, 2006, 7, 86–88; (d) Q. Tang, L. Li, Y.
Song, Y. Liu, H. Li, W. Xu, Y. Liu, W. Hu and D. Zhu, Adv.
Mater., 2007, 19, 2624–2628; (e) Y. Hu, G. Dong, C. Liu, L. Wang
and Y. Qiu, Appl. Phys. Lett., 2006, 89, 072108.
10 (a) S. Akiyama, S. Misumi and M. Nakagawa, Bull. Chem. Soc.
Jpn., 1960, 1293–1298; (b) S. Akiyama and M. Nakagawa, Chem.
Ind., 1960, 346–347.
11 H. E. Katz, J. Org. Chem., 1989, 54, 2179–2183.
12 F. Diederich and H. Staab, Angew. Chem., Int. Ed. Engl., 1978, 17,
372–374.
This work is financially supported by the Chinese University
of Hong Kong. The authors would like to thank Prof. Jimmy
C. Yu, Prof. Jianfang Wang (the Chinese University of Hong
Kong) and Prof. Feng Yan (the Hong Kong Polytechnic
University) for help on thin film and device characterization.
We thank Dr A. L. Briseno (University of Washington) for
helpful discussion.
13 S. Akiyama, K. Nakashima, S. Nakatsuji and M. Nakagawa, Dyes
Pigm., 1990, 13, 117–122.
14 (a) Q. Zhou, P. J. Carroll and T. M. Swager, J. Org. Chem., 1994,
59, 1294–1301; (b) U. H. F. Bunz and V. Enkelmann, Chem.–Eur.
J., 1999, 5, 263–266; (c) T. Nishinaga, Y. Miyata, N. Nodera and
K. Komatsu, Tetrahedron, 2004, 60, 3375–3382; (d) T. Nishinaga,
N. Nodera, Y. Miyata and K. Komatsu, J. Org. Chem., 2002, 67,
6091–6096; (e) M. L. Bell, R. C. Chiechi, C. A. Johnson, D. B.
Kimball, A. J. Matzger, W. B. Wan, T. J. R. Weakley and M. M.
Haley, Tetrahedron, 2001, 57, 3507–3520; (f) J. J. Pak, T. J. R.
Weakley and M. M. Haley, J. Am. Chem. Soc., 1999, 121,
8182–8192.
15 (a) A. Sun, J. W. Lauher and N. S. Goroff, Science, 2006, 312,
1030–1034; (b) G. W. Coates, A. R. Dunn, L. M. Henling, D. A.
Dougherty and R. H. Grubbs, Angew. Chem., Int. Ed. Engl., 1997,
36, 248–251; (c) R. Xu, V. Gramilish and H. Frauenrath, J. Am.
Chem. Soc., 2006, 128, 5541–5547.
Notes and references
z Crystal data for 1b: C48H40O2: M = 648.80, triclinic, space group
ꢀ
P1, a = 8.9279(8), b = 10.0248(9), c = 11.7180(10) A, a = 75.067(2),
b = 67.838(2), g = 69.165(2), V = 894.48(14) A3, Z = 1, 7913
reflections collected, 3059 unique (Rint = 0.0247). The final R was
0.1624 (all data) and wR was 0.3683 (all data).
1 Recent reviews: (a) W. Zhang and J. S. Moore, Angew. Chem., Int.
Ed., 2006, 45, 4416–4439; (b) S. Hoger, Angew. Chem., Int. Ed.,
¨
2005, 44, 3806–3808; (c) S. Hoger, Chem.–Eur. J., 2004, 10, 1320;
16 (a) U. Rohr, P. Schilichting, A. Bohm, M. Gross, K. Meerholz, C.
¨
Brauchle and K. Mullen, Angew. Chem., Int. Ed., 1998, 37,
¨
¨
¨
(d) U. H. F. Bunz, Y. Rubin and Y. Tobe, Chem. Soc. Rev., 1999,
28, 107; (e) M. M. Haley, J. J. Pak and S. C. Brand, Top. Curr.
Chem., 1999, 201, 81–130.
2 D. Venkataraman, S. Lee, J. Zhang and J. S. Moore, Nature, 1994,
371, 591–593.
3 (a) R. Boese, A. J. Matzger and K. P. C. Vollhardt, J. Am. Chem.
Soc., 1997, 119, 2052–2053; (b) P. I. Dosa, C. Erben, V. S. Iyer, K.
P. C. Vollhardt and I. M. Wasser, J. Am. Chem. Soc., 1999, 121,
10430–10431.
4 T. Naddo, Y. Che, W. Zhang, K. Balakrishnan, X. Yang, M. Yen,
J. Zhao, J. S. Moore and L. Zang, J. Am. Chem. Soc., 2007, 129,
6978–6979.
1434–1437; (b) Q. Miao, X. Chi, S. Xiao, R. Zeiss, M. Lefenfeld,
C. Kloc, M. L. Steigerwald, T. Siegrist and C. Nuckolls, J. Am.
Chem. Soc., 2006, 128, 1340–1345; (c) S.-H. Lim, T. G. Bjorklund,
F. C. Spano and C. J. Bardeen, Phys. Rev. Lett., 2004, 92, 107402.
17 C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater., 2002,
14, 99–117.
18 The capacitance of OTS-treated 300 nm thick SiO2 was reported to
be 11.3 nF cmꢀ2 and is close to the capacitance of untreated
300 nm thick SiO2. See: Q. Miao, M. Lefenfeld, T.-Q. Nguyen, T.
Siegrist, C. Kloc and C. Nuckolls, Adv. Mater., 2005, 17, 407–412.
19 For examples of organic field effect transistors from conjugated
macrocycle molecules, see: (a) H. Xu, G. Yu, W. Xu, Y. Xu, G.
Cui, D. Zhang, Y. Liu and D. Zhu, Langmuir, 2005, 21, 5391–5395;
(b) T. Zhao, Z. Wei, Y. Song, W. Xu, W. Hu and D. Zhu, J. Mater.
Chem., 2007, 17, 4377–4381.
5 (a) K. P. Baldwin, A. J. Matzger, D. A. Scheiman, C. A. Tesier, K.
P. C. Vollhardt and W. J. Youngs, Synlett, 1995, 000, 1215–1218;
(b) J. J. Pak, T. J. R. Weakley, M. M. Haley, D. Y. K. Lau and J.
F. Stoddart, Synthesis, 2002, 9, 1256–1260.
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