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photon-counting spectrofluorimeter from Edinburgh Analytical In-
struments (FL/FS 900) with a photomultiplier tube in a Peltier-
cooled housing. The excitation sources used were the same
375 nm laser diode from PicoQuant (LDH-d-C-375B) and the
355 nm laser diode from Crystal Laser (QC 355–050). The lifetimes
of the samples that needed blue light as the excitation source
were measured in a LifeSpec II time-correlated single-photon-
counting spectrometer from Edinburgh Instruments, the excitation
source used was a Ti:Sapphire laser (Chameleon Ultra II, Coherent),
the pulses were picked at 4 MHz for the repetition rate, and the ex-
citation wavelengths were selected between 440 nm and 480 nm
by a frequency-doubling unit (APE-GmbH SHG). Cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) were carried out on
a CH instruments Electrochemical Workstation CHI430. Tetrabuty-
lammonium perchlorate (TBAP; 0.1m) in argon-purged CH2Cl2 was
used as the supporting electrolyte at room temperature. The con-
ventional three-electrode configuration consisted of a platinum or
an indium tin oxide (ITO) working electrode, a platinum wire auxili-
ary electrode, and an Ag/AgNO3 reference electrode. Each mea-
surement was calibrated using ferrocene/ferrocenium (Fc/Fc+) as
a standard. Cyclic voltammograms were obtained at a scan rate of
100 mVsÀ1. The elemental analysis was performed with a PerkinElm-
er 2400 Series II CHNS/O system (Waltham, MA) equipped with Per-
kinElmer EA Data Manager software. The purification was carried
out in a three-zone sublimation apparatus (Lindberg/Blue Thermo
Electron Corporation). X-ray diffraction data were collected on
a Nonius Kappa CCD diffractometer, Rigaku SCX-Mini with Mercury
CCD diffractometer, and Rigaku AFC-12 with Saturn 724+ CCD dif-
fractometer with MoKa radiation (l=0.71075 ꢃ). Single crystals suit-
able for X-ray analysis were grown by slow sublimation.
yields and some products could not be isolated owing to the
high sublimation temperature used for purification. As expect-
ed, the electronic nature of the substituents enabled tuning of
the UV/Vis absorption and emission maxima. In several instan-
ces, the limited solubility of the benzimidazole products led to
aggregation and corresponding redshifted absorption spectra.
Such spectra, when used to calculate HOMO–LUMO energy
gap, may provide unrealistic values of the energy levels, partic-
ularly in the cases where the oxidation peaks are not directly
accessible. In all the series of compounds discussed herein, the
absorption and emission energies tend to correlate with the
extinction coefficient and the quantum efficiency. Cyclic vol-
tammetry and differential pulse voltammetry displayed quasi-
reversible reductions for the studied compounds, suggesting
n-type behavior. This has been confirmed in experimental
field-effect transistors, where use of these materials showed n-
type transistor characteristics with the mobilities of
~10À2 cm2 VÀ1 sÀ1. Importantly, it was found that compounds
comprising fluorinated fragments derived from 1,2-diamino-
3,4,5,6-tetrafluoro-benzene showed the ability to form a large
number of C···F and N···F intermolecular interactions and short
contacts, contributing to the formation of small grains in the
films. We presume that these features enabled the relatively
high electron mobilities (~0.03 cm2 VÀ1 sÀ1). This finding will be
explored in following studies as we believe that it will enable
the design of novel n-type semiconductors for OFET applica-
tions.
General procedures for the syntheses
Experimental Section
3,4-Diaminothiophene l was synthesized according to reported
methods[25] and 4,5-diaminopyrene n was synthesized in three
steps from pyrene, with a total yield of 20%, by the modification
of the reported procedure for 9,10-diaminophenanthrene d.[26]
Instruments
Mass spectra were collected on a Shimadzu Gas Chromatography-
Mass Spectrometry (GC-MS) QP5050 A instrument equipped with
a direct probe ionization. MALDI-TOF/MS spectra were recorded by
using a Bruker Daltonics Omniflex spectrometer. FD-TOF/HRMS
spectra were obtained on a JEOL JMS-T100GC. 1H NMR and
13C NMR spectra were recorded on a Bruker DRX-300 (300 MHz) or
500 MHz Bruker instrument. Chemical shifts were calibrated to the
corresponding deuterated solvents. Melting points were obtained
on a Shimadzu DSC-60. The UV/Vis spectra were measured by
using a HP (Hewlett Packard) single-beam spectrophotometer with
a diode array or a Hitachi U-3010 double-beam spectrophotometer,
accurate to Æ0.3 nm. The light source consisted of Deuterium (D2)
and Tungsten Iodide (50W) lamps for the ultraviolet and visible re-
gions, respectively. The concentration of the solutions was adjust-
ed so that the measured absorbances would range between 0.1
and 0.3 for the optical measurements. Emission spectra were re-
corded by using a spectrofluorimeter from Edinburgh Analytical In-
struments (FL/FS 900). Compounds were dissolved in freshly dis-
tilled dichloromethane prior to measurements. The fluorescence
quantum yields of the luminophores were measured by absolute
measurement of the photoluminescence quantum yield (APLQY)
using an integrating sphere (Sphere Optics 708) and an Andor CCD
camera (DU401-FI), the spectral flux was calibrated by using a halo-
gen lamp (Sphere optics LCS-100–5W, serial number 3999). The ex-
citation sources were a 375 nm laser diode (PicoQuant, LDH-d-C-
375B) and a 355 nm laser diode (Crystal Laser, QC 355–050), the
method was modified from previous reports.[24] The steady-state
lifetime measurements were recorded in a time-correlated single-
Procedure 1—solid-state condensation catalyzed by zinc acetate
and direct sublimation (SSC-DS): A carboxylic acid anhydride and
a diamine were mixed well by using a mortar and pestle. A catalyt-
ic amount of zinc acetate (less than 0.1 molar equiv) was added to
the mixture. They were stirred and heated to a certain temperature
(220–3008C depending on the combination of anhydride and dia-
mine). After 2–3 h, the reaction mixture was allowed to cool to
room temperature. The crude material was sublimed under
vacuum (10À6–10À7 Torr), without any other purification, to give the
pure compound.
Procedure 2—aqueous condensation and direct sublimation: A
carboxylic acid anhydride and a diamine in H2O were stirred at
1008C for 2 h. The precipitate was filtered or the reaction solution
was evaporated to dryness. The solid was collected and moved to
a tube for sublimation. The solid was heated at 3008C for 1 h
under ambient pressure, then sublimed under vacuum (10À6
10À7 Torr).
–
Procedure 3—with imidazole: A carboxylic acid anhydride, a dia-
mine, and 10 equivalents of imidazole were stirred at 2008C for
3 h. The reaction mixture was washed with water and dried. The
crude material was sublimed under vacuum (10À6–10À7 Torr) with-
out any other purification.
Device fabrication: The HMDS (hexamethyldisilazane) treatment
was carried out by immersing the substrate in HMDS at room tem-
perature for >10 h. The Teflon, CYTOP, polystyrene, or PMMA
layers (ca. 20 nm) were prepared by spin-coating at 4000 rpm from
Chem. Eur. J. 2014, 20, 11835 – 11846
11844
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