Fig. 3 Crystal structure and stacking pattern of 12a (H atoms are
omitted for clarity).
Fig. 4 AFM images of 50 nm thick films deposited on an OTS
modified SiO2/Si substrate of 12a (5 mm  5 mm) at 25 1C (a), 60 1C
(b) and 100 1C (c) and 12b (2 mm  2 mm) at 25 1C (d), 60 1C (e) and
100 1C (f).
Table 1 Detailed performance of OFETs based on 12a and 12b thin
films on octadecyltrichlorosilane (OTS) or PMMA (polymethyl
methacrylate) treated SiO2/Si substrates at different substrate
temperatures (Tsub
)
0.40 cm2 VÀ1 sÀ1 was observed on thin films of 12a deposited
on OTS modified SiO2 at the substrate temperature of 60 1C
(Table 1). The more positive value12 of VT, observed for the
OTS modified devices, may arise from the assembling of
charge on the OTS surface during the operation, while the
device of 12a based on a PMMA surface modified SiO2/Si
substrate yielded a rather higher on/off ratio and a favorable VT.
In summary, this work is a desolate example of the synthesis,
structure and application of new meso-aryl substituted air-
stable oxygen bridged neutral annulenes as promising active
materials for OFETs.
Compound
Ts/1C
m/cm2 VÀ1 sÀ1
Ion/Ioff
VT/V
12a
20
20
60
100
20
60
100
0.10
0.02a
0.8 Â 103
1.2 Â 104
3.51 Â 103
1 Â 103
28
20.3
6.0
0.35 (0.40)b
0.14
20.0
15.7
24.8
24.8
24.4
12b
0.28 Â 10À3
0.1
0.11
1.6 Â 102
102
a
b
PMMA surface modified SiO2/Si substrate (25 nm). The maximum
value of mobility is presented in brackets beside the average value.
This is in contrast to the almost square shape in
tetrathia[22]annulene where the two SÁ Á ÁS distances were
3.110 A and 3.018 A.4 This is presumably because of the
trans-geometry of the ethylenic bridge connecting the two
neighboring furan rings, compared to cis-geometry in the
tetrathia[22]annulene. (iii) As expected, bond alternation is
not evident, consistent with a planar aromatic system with
electron delocalization. This fact has also been verified from
the NICS(1) values, which, in contrast to the that of isolated
furan (À10.35), are considerably negative (À20.01, À18.65,
À15.15 and À16.61) for the four furans of the fully conjugated
12a (Fig. S28 and S32, ESIw). Changing the meso substituent
from phenyl in 12a to p-tolyl in 12b does not induce any ring
puckering of the annulene core and/or affect aromaticity. In
the packing diagrams, the molecules of both 12a and 12b
stacked in a standard layer-by-layer herringbone fashion. In
12a the molecules stacked into layers along the bc-plane with a
tilt angle of 52.791 between the annulene core and the bc-plane.
This is significantly different from their sulfur analogues, where a
shifted face-to-face pattern was observed.4
KS thanks DST, New Delhi, for the Research grant SR/S1/
OC-27/2009 and UGC (SAP), New Delhi and National single
crystal X-ray facility, IIT Mumbai.
Notes and references
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Electrical transport properties of 12a and 12b were
characterized on vacuum deposited thin films, both of these
compounds displayed p-type semiconductor behavior. Thin-film
transistors were fabricated on OTS or PMMA/SiO2/Si substrates
in a top-contact configuration using Au as source and drain
electrodes. The transfer and output curves for the devices of 12a
and 12b are shown in Fig. S49 (ESI) and detailed performance is
given in Table 1.
The morphology of the thin films (Fig. 4) changed with
temperature (20 1C to 100 1C). While changing the temperature
from 20 1C to 60 1C increased the grain size as well as yielded
more ordered films, at 100 1C, the films developed cracks.
The highest performance with
a mobility as high as
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 121–123 123