7.57–7.52 (m, 4H), 7.52–7.47 (m, 2H), 7.40–7.37 (m, 1H), 7.30–7.25
(m, 4H), 7.22–7.19 (m, 1H), 7.17–7.11 (m, 7H), 7.06–7.01 (m, 2H).13C
NMR (150 MHz, CDCl3, δ [ppm]): 151.11, 147.63, 147.38, 141.05, 140.39,
139.96, 138.87, 138.41, 134.28, 131.65, 130.72, 130.27, 129.90, 129.70,
129.41, 129.32, 129.16, 129.06, 127.64, 127.33, 126.98, 126.63, 125.62,
124.57, 124.51, 124.25, 123.82, 123.04, 122.11, 120.20, 119.76.
(150 MHz, CDCl3, δ [ppm]): 149.27, 138.51, 136.75, 133.47, 131.61,
130.82, 130.75, 130.08, 129.18, 128.96, 128.47, 127.47, 126.92, 126.72,
124.91, 124.67, 123.63, 122.10, 110.91.
Synthesis of 2-(4-bromophenyl)-1-phenyl-1H-naphtho[1,2-d]imidazole
(NI-2-Br): NI-2-Br was synthesized according to the same procedure
as described above for the synthesis of NI-1-Br, starting from 4–2, and
yielding giving a white solid in 77% yield (two steps). MS (ESI+, m/Z):
Device Fabrication and Characterization: The devices were fabricated
by vacuum deposition of the materials at 5 × 10−4 Pa or below onto the
indium tin oxide (ITO) coated glass substrates with a sheet resistance
of 20 Ω per square. Before the fabrication of the devices, the NI
compounds were further purified by train sublimation. All the organic
layers were deposited at a rate of 1.0–2.0 Å s−1. The cathode was
deposited with LiF (1 nm) at a deposition rate of 0.1 Å s−1 and then
capping with Al metal (100 nm) through thermal evaporation at a rate
of 4.0 Å s−1. The electroluminescence (EL) spectra were measured using
a PR705 spectra scan spectrometer. The luminance and current density
versus driving-voltage characteristics were recorded simultaneously
with measuring of the Commission Internationale de L’Eclairage (CIE)
coordinates by combining the spectrometer CS200 with a Keithley model
2420 programmable voltage–current source meter. All measurements
were carried out at room temperature and under ambient conditions.
Ultraviolet and X-Ray Photoelectron Spectroscopy: Experiments
were carried out in a Kratos AXIS UltraDLD ultrahigh vacuum (UHV)
surface analysis system, consisting of a multiport carousel chamber, a
deposition chamber, and an analysis chamber. The base pressures in
the three chambers were better than 5 × 10−9, 2 × 10−9, and 3 × 10−9
Torr, respectively. All organic materials were carefully sublimed twice
and entirely out-gassed to ensure a good material purity and to be able
to study the intrinsic behavior. The film thickness was monitored by a
quartz-crystal microbalance. Prior to film deposition, the ITO-coated
glass substrates were subjected to a routine cleaning process and ex
situ treated by UV-ozone exposure. The organic materials, including
NI-1-PhTPA, NI-2-PhTPA, and LiF were evaporated in situ in steps
onto the ITO substrates from resistively heated tantalum boats in the
deposition chamber at a rate of 1–2 Å s−1. The samples were transferred
to the analysis chamber without breaking vacuum for the UPS and XPS
measurements after each deposition step. The UPS measurements
were carried out using an unfiltered He I (21.2 eV) gas discharge lamp
to characterize the valence states and the vacuum level (VL). There
was no sign of sample charging in all measurements, even when the
thickness of the organic films reached several hundreds of Angstroms.
A monochromatic aluminum Kα source (1486.6 eV) was used in the
XPS measurements to study the interfacial chemical reactions and the
development of possible molecular level bending across the interface.
For the collection of secondary electrons, the samples were negatively
biased at 4 V. All measurements were performed at room temperature.
The photoelectrons were collected by a hemispherical analyzer with a
total instrumental energy resolution of 0.1 eV for the UPS measurements
and 0.5 eV for the XPS measurements. In all the UPS and XPS spectra,
the Fermi level (EF) is referred to as the zero binding energy (BE).
1
calcd. for C23H15BrN2, 398.0; found, 398.0. H NMR (600 MHz, CDCl3,
δ [ppm]): 7.95 (t, J = 7.7 Hz, 2H), 7.75 (d, J = 8.8 Hz, 1H), 7.67–7.63
(m, 1H), 7.63–7.58 (m, 2H), 7.50–7.46 (m, 2H), 7.41 (m, 4H), 7.38 (m,
1H), 7.20 (m, 1H), 7.13 (d, J = 8.5 Hz, 1H).13C NMR (150 MHz, CDCl3,
δ [ppm]): 150.30, 140.31, 138.55, 131.70, 131.48 130.75, 130.70, 130.31,
130.02, 129.40, 129.26, 129.00, 125.69, 124.70, 124.39, 123.63, 122.06,
120.15, 119.71.
Synthesis of NI-1-TPA:
tetramethyl-1,3,2-dioxaborolan-2-yl)aniline (2.3 g,
A
mixture of N,N-diphenyl-4-(4,4,5,5-
mmol), NI-1-Br
6
(2.0 g, 5 mmol), 100 mg of Pd(PPh3)4, potassium carbonate (2.8 g,
20 mmol), THF (15 mL), toluene (30 mL), and distilled water (20 mL)
was refluxed for 24 h under argon protection. Then the mixture was
extracted with dichloromethane. The organic phases were combined
and dried over magnesium sulfate. After the solvent was removed, the
product was further purified by column chromatography on silica gel
to afford a yellow powder (2.2 g, 78%). MALDI-TOF (m/Z): calcd. for
C41H29N3, 563.24; found, 563.19. Anal. calcd. for C41H29N3: C 87.36,
H 5.19, N 7.45; found: C 87.52, H 5.12, N 7.31. 1H NMR (600 MHz,
CDCl3, δ [ppm]): 8.82 (d, J = 7.7 Hz, 1H), 7.93 (d, J = 7.8 Hz, 1H),
7.66 (d, J = 7.8 Hz, 4H), 7.52–7.47 (m, 8H), 7.39 (d, J = 6.8 Hz, 2H),
7.34 (d, J = 8.6 Hz, 1H), 7.26–7.23 (m, 4H), 7.14–7.11 (m, 6H), 7.03 (t,
J = 6.8 Hz, 2H). 13C NMR (150 MHz, CDCl3, δ [ppm]): 150.32, 147.62,
147.58, 141.03, 138.64, 137.10, 133.86, 133.47, 130.73, 129.98, 129.77,
129.34, 128.75, 128.55, 128.44, 127.63, 127.59, 126.96, 126.60, 126.36,
124.78, 124.56, 124.32, 123.72, 123.12, 122.21, 110.96.
Synthesis of NI-2-TPA: NI-2-TPA was synthesized according to the
same procedure as described above for the synthesis of NI-1-TPA, but
using NI-2-Br, which yielded a yellow solid in 79% yield. MALDI-TOF
(m/Z): calcd. for C41H29N3, 563.24; found, 563.18. Anal. calcd. for
1
C41H29N3: C 87.36, H 5.19, N 7.45; found: C 87.48, H 5.04, N 7.37. H
NMR (600 MHz, CDCl3, δ [ppm]): 7.99 (d, J = 8.8 Hz, 1H), 7.95 (d,
J = 8.1 Hz, 1H), 7.75 (d, J = 8.7 Hz, 1H), 7.67–7.57 (m, 5H), 7.55–7.51
(m, 2H), 7.51–7.47 (m, 2H), 7.47–7.42 (m, 2H), 7.39–7.36 (m, 1H),
7.28–7.23 (m, 4H), 7.21–7.19 (m, 1H), 7.15 (d, J = 8.1 Hz, 1H), 7.13–
7.08 (m, 6H), 7.05–7.01 (m, 2H). 13C NMR (150 MHz, CDCl3, δ [ppm]):
151.27, 147.62, 147.57, 140.95, 140.44, 138.92, 133.79, 131.64, 130.69,
130.20, 129.81, 129.66, 129.38, 129.31, 129.16, 128.60, 127.64, 126.20,
125.56, 124.54, 124.50, 124.19, 123.69, 123.09, 122.12, 120.18, 119.77.
Synthesis of NI-1-PhTPA: NI-1-PhTPA was synthesized according
to the procedure as described above for the synthesis of NI-1-TPA by
combining NI-1-Br and N,N-diphenyl-4′-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-[1,1'-biphenyl]-4-amine, giving a green-yellow solid
in 79% yield. MALDI-TOF (m/Z): calcd. for C47H33N3, 639.27; found,
639.22. Anal. calcd. for C47H33N3: C 88.23, H 5.20, N 6.57; found:
1
C 88.14, H 5.34, N 6.39. H NMR (600 MHz, CDCl3, δ [ppm]): 8.83 (d,
Supporting Information
J = 8.2 Hz, 1H), 7.94 (d, J = 8.1 Hz, 1H), 7.70 (d, J = 8.4 Hz, 2H), 7.68–
7.65 (m, 2H), 7.64–7.60 (m, 4H), 7.58 (d, J = 8.4 Hz, 2H), 7.56–7.47 (m,
6H), 7.39 (dd, J = 5.2, 3.2 Hz, 2H), 7.34 (d, J = 8.8 Hz, 1H), 7.26 (dd,
J = 11.2, 4.6 Hz, 4H), 7.13 (d, J = 8.5 Hz, 6H), 7.03 (t, J = 7.3 Hz, 2H).
13C NMR (150 MHz, CDCl3, δ [ppm]): 150.20, 147.65, 147.40, 141.11,
139.96, 138.68, 138.51, 137.13, 137.09, 134.29, 133.52, 130.75, 130.01,
129.79, 129.34, 129.08, 128.79, 128.45, 127.65, 127.61, 127.35, 127.00,
126.77, 126.63, 124.80, 124.53, 124.38, 123.83, 123.05, 122.21, 110.97.
Synthesis of NI-2-PhTPA: NI-2-PhTPA was synthesized according to
the same procedure as described above for the synthesis of NI-1-TPA
by combining NI-2-Br and N,N-diphenyl-4′-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-[1,1'-biphenyl]-4-amine, giving a green-yellow solid
in 79% yield. MALDI-TOF (m/Z): calcd. for C47H33N3, 639.27; found,
639.22. Anal. calcd. for C47H33N3: C 88.23, H 5.20, N 6.57; found: C 88.29,
H 5.07, N 6.43.1H NMR (600 MHz, CDCl3, δ [ppm]): 8.00 (d, J = 8.7 Hz,
1H), 7.96 (d, J = 8.1 Hz, 1H), 7.77 (d, J = 8.7 Hz, 1H), 7.68–7.59 (m, 9H),
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
M.L. and X.L.L. contributed equally to this work. The authors greatly
appreciate the financial support from the Ministry of Science and
Technology (2015CB655003 and 2014DFA52030), the National Natural
Science Foundation of China (91233116 and 51073057), the Ministry
of Education (NCET-11–0159), and the Guangdong Natural Science
Foundation (S2012030006232).
Received: May 27, 2015
Revised: June 18, 2015
Published online: July 14, 2015
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2015, 25, 5190–5198
2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
5197