The precipitate was filtered, and washed with water and methanol. The
resulting off-white solid was dissolved in reflux toluene 450 mL, filtered
through a silica-gel pad (50 cc) and washed with toluene (50 mL). After
the clear filtrate was concentrated to 50 mL, the precipitate was collected,
washed with hexane, dried in vacuo to afford 3 (7.4 g, 81%) as a white
solid: 1H NMR (400 MHz, CDCl3) δ = 8.02 (d, 4H, J = 2.0 Hz), 7.77 (s, 1H),
7.51 (t, 2H, J = 2.0 Hz), 2.86 (s, 3H) ppm; MS: m/z 384 [M]+.
Synthesis of B3PyMPM: 3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-
2-yl)pyridine (4) (4.7 g, 22.9 mmol) and 3 (2.0 g, 5.2 mmol) were added
to a round bottom flask. 1,4-Dioxane (220 mL) and aqueous K3PO4
(1.35 M, 60 mL) were added and nitrogen bubbled through the mixture for
1 hour. Then, Pd2(dba)3 (0.19 g, 0.21 mmol) and PCy3 (0.14 g, 0.50 mmol)
were added and the resultant mixture was vigorously stirred for 30 hours at
reflux temperature under N2 fl ow. The precipitate was filtered, and washed
with water and methanol. The resulting off-white solid was purified by
chromatography on silica gel (eluent: CHCl3/CH3OH = 50:1 to 30:1 v/v)
to afford B3PyMPM (2.9 g, 77%) as a white solid: 1H NMR (400 MHz,
CDCl3): δ = 8.99 (d, 4H, J = 2.8 Hz), 8.68–8.67 (m, 4H), 8.37–8.36 (m,
4H), 8.06 (s, 1H), 8.03–8.02 (m, 4H), 7.91 (s, 2H), 7.45 (dd, 4H, J = 4.8,
8.0 Hz), 2.94 (s, 3H) ppm; MS: m/z 555 [M]+; Anal. Calcd for C37H26N6: C,
80.12; H, 4.72; N, 15.15%. Found: C, 80.22; H, 4.69; N, 15.22%.
Synthesis of B4PyMPM: B4PyMPM was synthesized by the same
procedure using 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (5)
instead of 4. For B4PyMPM: 1H NMR (400 MHz, CDCl3): δ = 8.77–8.75 (m,
8H), 8.44 (d, 4H, J = 2.0 Hz), 8.04 (s, 1H), 8.00 (t, 2H, J = 1.6 Hz), 7.66–7.64
(m, 8H), 2.95 (s, 3H) ppm; MS: m/z 555 [M]+; Anal. Calcd for C37H26N6: C,
80.12; H, 4.72; N, 15.15%. Found: C, 80.28; H, 4.66; N, 15.20%.
Synthesis of Tetraboronate Ester ( 7): Bis(pinacolato)diboron (6) (19.8 g,
78.1 mmol), 3 (6.00 g, 15.6 mmol) and KOAc (18.4 g, 187.2 mmol) were
added to a round bottom flask. Anhydrous 1,4-dioxane (300 mL) were
added and nitrogen bubbled through the mixture for 1 hour. Then,
Pd2(dba)3 (1.70 g, 1.87 mmol) and PCy3 (2.50 g, 8.98 mmol) were
added and the resultant mixture was vigorously stirred for 18 hours at
reflux temperature under N2 fl ow. The resulting mixture was cooled to
room temperature, and the precipitate was filtered off. To the resulting
solution, 300 mL chloroform was added, washed with water and brine,
dried over anhydrous MgSO4, filtered, and evaporated to dryness. The
resulting solid was purified by chromatography on silica gel (eluent:
CHCl3/EtOAc = 3:1 v/v) to afford 7 (7.1 g, 61%) as a white solid: 1H
NMR (400 MHz, CDCl3) δ = 8.59 (s, 4H), 8.40 (s, 2H), 7.99 (s, 1H),
2.88 (s, 3H), 1.37 (s, 48H) ppm; MS: m/z 751 [M]+.
3. Conclusions
A
series of 2-methylpyrimidine skeleton-based ETMs,
B2PyMPM, B3PyMPM and B4PyMPM, were designed and syn-
thesized. The only structural difference is the position of substi-
tuted pyridine rings. DFT calculations predicted that BPyMPM
derivatives had different Ip and Ea values depending on the
position of the substituted pyridine rings. As predicted from
the calculations, the Ips were observed using UPS to increase
in the order B2PyMPM (6.62 eV) < B3PyMPM (6.97 eV)
< B4PyMPM (7.30 eV). From both TLC and DSC analyses, the
degree of the H-bonding interactions is considered to increase
in the order B2PyMPM << B3PyMPM < B4PyMPM. Moreover,
TOF measurements of vacuum-deposited films were carried
out to determine the μe at 298 K: the μe of B4PyMPM was
on the order of 10−4 cm−2 V−1 s−1 at an electric field of 6.4 ×
10−5 V cm−1 . The μe of B4PyMPM was measured to be
10 times higher than that of B3PyMPM and 100 times
higher than that of B2PyMPM. Furthermore, the tem-
perature and field dependencies of μewere investigated to
extract the charge-transport parameters. Using Bässler’s
disorder formalism, the degree of
σ was estimated to
decrease in the order B2PyMPM (91 meV) > B3PyMPM
(88 meV) > B4PyMPM (76 meV) due to the number of con-
formers and intermolecular H-bonding interactions. Similarly,
the Σ was evaluated to be 2.7 for B2PyMPM, and Σ < 1.5 for
B3PyMPM and B4PyMPM. Considering the relatively high
μ0 of B4PyMPM, the intermolecular distance are shorter and
well-ordered molecular orientations are assumed due to the
H-bonding interactions occurring in the vacuum-deposited
B4PyMPM film. These results clearly indicate that the position
of substituted pyridine rings is critically important to adjust
the fundamental physical properties and the μe. Our findings
provide not only a powerful guideline to design ETMs but
also a new way to control the molecular aggregation states of
vacuum-deposited films using the weak intermolecular CH–N
hydrogen-bonding interactions.
Synthesis of B2PyMPM: 2-Bromopyridine (8) (5.3 g, 33.3 mmol) and 7
(5.0 g, 6.7 mmol) were added to a round bottom flask. Toluene (200 mL),
ethanol (100 mL) and aqueous Na2CO3 (1.0 M, 80 mL) were added
and nitrogen bubbled through the mixture for 1 hour. Then, Pd(PPh3)4
(1.54 g, 1.33 mmol) was added and the resultant mixture was vigorously
stirred for 12 hours at reflux temperature under N2 fl ow. The resulting
mixture was cooled to room temperature, washed with water, dried over
anhydrous MgSO4, filtered, and evaporated to dryness. The resulting
yellow solid was purified by chromatography on silica gel (eluent:
CHCl3) to afford B2PyMPM (3.1 g, 84%) as a white solid: 1H NMR
(400 MHz, CDCl3): δ = 8.86 (d, 4H, J = 1.4 Hz), 8.80 (t, 2H, J = 1.4 Hz),
8.76 (d, 4H, J = 4.6 Hz), 8.28 (s, 1H), 7.99 (d, 4H, J = 8.2 Hz), 7.83 (ddd,
4H, J = 8.2, 8.2, 2.0 Hz), 7.30 (dd, 4H, J = 4.6, 8.2 Hz), 2.95 (s, 3H)
ppm; MS: m/z 555 [M]+; Anal. Calcd for C37H26N6: C, 80.12; H, 4.72; N,
15.15%. Found: C, 80.14; H, 4.54; N, 15.17%.
4. Experimental Section
General Procedures: The optimized structures and single-point
energies were calculated by Gaussian03[22] at the B3LYP 6–31G(d) and
6–311+G(d,p) levels, respectively. 1H NMR spectra were recorded on a
JEOL 400 (400 MHz) spectrometer. Mass spectra were obtained using a
JEOL JMS-K9 mass spectrometer. Differential scanning calorimetry was
performed using a Perkin-Elmer Diamond DSC Pyris instrument under
nitrogen atmosphere at a heating rate of 10 °C min−1 . Thermogravimetric
analysis was undertaken using a SEIKO EXSTAR 6000 TG/DTA 6200 unit
under nitrogen atmosphere at a heating rate of 10 °C min−1 . UV–vis
spectra were measured using a Shimadzu UV-3150 UV–vis–near-infrared
(NIR) spectrophotometer. Photoluminescence spectra were measured
using
a FluroMax-2 (Jobin-Yvon-Spex) luminescence spectrometer.
Supporting Information
The ionization potentials were determined by ultraviolet photoelectron
spectroscopy (UPS). The phosphorescent spectra were measured using
a streak camera (C4334 from Hamamatsu Photonics) at 4.2 K.
Supporting Information is available from the Wiley Online Library or
from the author.
Synthesis of Tetrachloride (3) : 4,6-Dichloro-2-methylpyrimidine (1) (3.14 g,
19.2 mmol) and 3,5-dichlorophenyl boronic acid (8.08 g, 42.3 mmol)
were added to a round bottom flask. Acetonitrile (300 mL) and aqueous
Na2CO3 (1 M, 100 mL) were added and nitrogen bubbled through the
mixture for 1 hour. Then, PdCl2(PPh3)2 (0.67 g, 0.60 mmol) was added
and the resultant mixture was stirred for 6 hours at 60 °C under N2 fl ow.
Acknowledgements
We greatly acknowledge the financial support in part by the New Energy
and Industrial Technology Development Organization (NEDO) through the
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2011, 21, 336–342
2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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