Page 86 - Organic Electronics in Sensors and Biotechnology

Or ganic Thin-Film Transistors for Inor ganic Substance Monitoring 63

• The several available synthetic methods permit the construc-
tion of a plethora of extended π-systems. This allows the fine
tuning of the electronic properties.
• The synthesis of extended π-systems may enhance the π−π
interactions which are crucial for efficient interchain charge
transport.

Due to the higher oxidation potential and the more accessible
synthetic protocols, anthracene is fast becoming a very deeply inves-
tigated moiety for use as active layer in OTFT devices. Historically,
anthracene has been widely studied as an organic photoconductor
and for OLED devices 108–112 while little attention has been paid to its appli-
cation in field-effect transistors. Hole mobilities in anthracene single
crystal were measured by the time of flight technique and were
113
found to reach up to 3 cm /(V · s) at 300 K. While in single crystal
2
2
OTFT devices the higher mobility was 0.02 cm /(V · s) measured at
170 K. 114
In the last few years a considerable number of anthracene deriva-
tives were reported. The best results for thermal evaporated thin
films were obtained by Meng and coworkers reporting for a 2,6-bis
[2-(4-pentylphenyl)vinyl] anthracene a hole mobility of 1.28 cm /(V · s)
2
and on/off ratio greater than 10 . The observed high charge mobili-
7 115
ties have been attributed to the densely packed crystal structure that
in principle would ensure a high transfer integral between the adjacent
molecules.
For solution deposited thin films, the best mobility was reported
recently by Park et al. for a 9,10-bis(triisopropylsilylethynyl) substi-
tuted anthracene-thiophene oligomers. A hole mobility of 4.0 ×
116
−3
10 cm /(V · s) and on/off ratio of 10 were observed for a chloroform
2
6
spin-coated OTFT. Remarkably the introduction of the bulky TIPS
substituents led to a π-stacked crystal structure with an interplanar
distance of 3.49 Å, similar to the value observed for functionalized
pentacene.
Here we report on synthesis, characterization, and NO gas
131
x
sensing properties of a new p-type semiconductor based on a 9,10-
ter-anthryleneethynylene bearing decyl alkyl chains as side groups,
namely, D3ANT. To the best of our knowledge, no example has been
provided so far of 9,10 substituted anthracenes exhibiting field-effect
modulation properties and high selectivity toward NO gases.
x
In the ter-anthrylene ethynylene structure, three neighboring anthra-
cenes are chemically linked by two ethynylene bonds, hence facilitating
the effective charge transport to be extended beyond a single anthra-
cene unit. With respect to 9,10-anthrylenes, the introduction of ethy-
nylene moieties between the anthracene units was conceived to build
a planar π-framework potentially endowed with good intermolecular
interactions also in a disordered film.