Fluorescent ethenyl- and ethynyl-dimesitylboranes derived from 5-(dimethylamino)-N-(prop-2-ynyl)naphthalene-1-sulfonamide

Article abstract of DOI:10.1071/CH07242

Two new fluorescent ethenyl- and ethynyl-dimesitylboranes functionalized with a dansyl group 1 and 2 have been synthesized in good yields. Compound 1 was prepared by the hydroboration of 5-(dimethylamino)-N-(prop-2-ynyl)naphthalene- 1-sulfonamide I with d

Full text of DOI:10.1071/CH07242

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2007, 60, 915–922
Fluorescent Ethenyl- and Ethynyl-dimesitylboranes Derived
from 5-(Dimethylamino)-N-(prop-2-ynyl)naphthalene-
1-sulfonamide
Wai-Yeung Wong,A,B Suk-Yue Poon,A Mei-Fang Lin,A and Wai-Kwok WongA
ADepartment of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong
Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, ROC.
BCorresponding author. Email: rwywong@hkbu.edu.hk
Two new fluorescent ethenyl- and ethynyl-dimesitylboranes functionalized with a dansyl group 1 and 2 have been synthe-
sized in good yields. Compound 1 was prepared by the hydroboration of 5-(dimethylamino)-N-(prop-2-ynyl)naphthalene-
1-sulfonamide I with dimesitylborane (HB(Mes)2) in dry tetrahydrofuran at room temperature, and compound 2 was
synthesized by Pd-catalyzed cross-coupling of I with 4-I-C6H4B(Mes)2. Both organoborane compounds 1 and 2 have
been characterized by infrared spectroscopy, NMR spectroscopy, and mass spectrometry.The molecular structures of I and
1 were confirmed by X-ray crystallography. The electronic absorption and redox properties of 1 and 2 were investigated.
They both exhibit large positive solvatochromism and their emission spectra have been recorded in a range of organic
solvents with the fluorescence maxima exhibiting large bathochromic shifts in highly polar solvents, indicative of charge
transfer which leads to large dipole moments in the excited state. The application of 1 as a blue fluorescent dopant in
doped guest–host organic light-emitting diodes is also described.
Manuscript received: 16 July 2007.
Final version: Accepted without change.
Introduction
particularly effective, as steric congestion around boron results
in the formation of propeller-like structures where the ortho-
substituents on the aryl ligands form a cage around the vacant
pz orbital.
The current search for new luminescent materials is a result
in part of their potential for use in electroluminescent (EL)
displays.[1] In recent years, there has been considerable interest
in both academia and industry in developing blue organic light-
emitting devices (OLEDs), and the realisation of blue electro-
luminescence is an important step for possible application of
these materials in flat-panel full-colour displays.[2] It is well
known that the EL efficiency, colour, and operational stability
of blue OLEDs can be significantly improved with the use of
a guest–host doped emitter.[3] There have been several recent
developments in blue-doped emitter systems, including the uti-
lization of 2-methyl-9,10-di(2-napthyl)anthracene (MADN) as
a blue host.[4]
Electronic and electro-optical materials that contain electron-
rich organic molecules have attracted much attention.[5] New
routes to electron-deficient systems have also been devel-
oped, taking advantage of the fact that three-coordinate boron
is isoelectronic and isostructural with a carbocation.[6] These
organoboroncompoundshaveinterestingoptical, electronic, and
structural properties with a wide range of applications,[6] includ-
ing fluoride ion sensors,[7] non-linear optical materials,[8] and
both single and two-photon fluorescence.[9] They can also serve
as emissive and/or electron-transport layers in OLEDs.[10] As
with many other low-coordinate systems, a common strategy in
the synthesis of three-coordinate boranes is to provide kinetic
stability by blocking the approach of nucleophiles with ster-
ically demanding substituents while maintaining conjugation
with other unsaturated hydrocarbon substituents.[6,10] Bulky aryl
moieties such as the mesityl (2,4,6-trimethylphenyl) group are
Many endeavours have been made to employ fluorescent
labels such as anthracene,[8b,9c,11] acridone,[12] and fluorene[13]
for the design of various novel optoelectronic materials.
However, the 5-(dimethylamino)naphthalene-1-sulfonyl (dan-
syl) chromophore has been less explored.[14] In view of the high
luminescence quantum yield and high photochemical resistance
to bleaching of the auxiliary dansyl unit,[14] we expect that a
properly derivatized molecule, such as 5-(dimethylamino)-N-
(prop-2-ynyl)naphthalene-1-sulfonamide I could be employed
to attach a fluorescent label to the B(Mes)2 moiety through an
acetylide linkage, which is likely to exhibit rich photophysical
and optoelectronic properties. In the present article, we describe
the synthesis, spectroscopic, structural, and photophysical prop-
erties of two new fluorescent compounds that incorporate the
dansyl and dimesitylborane moieties. Preliminary studies of
such compounds as dopants in a guest–host blue-doped emitter
system will be discussed.
Results and Discussion
Synthesis and Characterization
Scheme 1 summarizes the reaction pathways to all the com-
pounds in this study. Ligand I was prepared by reacting
dansyl chloride and propargylamine in a NEt3/CH2Cl2 sol-
vent mixture according to the literature method.[14a] The
terminal acetylene was hydroborated using HB(Mes)2 in
THF to obtain the trans-ethenyldimesitylborane 1 in 60%
© CSIRO 2007
10.1071/CH07242
0004-9425/07/120915

916
W.-Y. Wong et al.
H3C
H3C
CH3
CH3
N
N
Et3N
ϩ
H
CH2NH2
O
S
O
O
S
O
HN
Cl
H
Dansyl chloride
Propargylamine
HB(Mes)2
I
Me
Me
Me
B(Mes)2
N
N
N
THF
O
O
ϩ
Me
N
H
S
N
H
S
O
O
1 (60%)
B(Mes)2
Me
Me
O
S
Pd(PPh3)2Cl2
CuI, Et3N
Me
Me
B(Mes)2
ϩ
I
N
H
N
O
O
N
H
S
O
2 (46%)
Scheme 1. Synthetic routes to compounds I, 1, and 2.
yield.[15] (p-Iodophenyl)dimesitylborane, prepared by reacting
1,4-diiodobenzene with BunLi followed by reaction with dime-
sitylboron fluoride, was used in a Pd-catalyzed cross-coupling
reaction with I to yield the dimesitylborylalkynyl compound
2 in moderate yield (46%).[16] Compound 1 was purified by
repeated recrystallization and compound 2 was purified by
preparative TLC on silica plates followed by recrystalliza-
tion. Both mesitylboranes are organic soluble and have been
fully characterized by NMR and infrared (IR) spectroscopies
and matrix-assisted laser desorption–ionization time-of-flight
(MALDI-TOF) high-resolution mass spectrometry (MS). Com-
pounds 1 and 2 are thermally stable solids with onset decom-
position temperatures of 296 and 328◦C, respectively, as shown
by thermogravimetric analysis (TGA).The crystalline borane, 1,
did not exhibit a discernable glass transition. When 2 was heated,
an endotherm as a result of melting was observed at 181◦C, and
upon cooling and re-heating, a glass transition was observed
at 72◦C.
structurally similar molecules in the unit cell. The propynyl
group is attached to N(2) by a CH2 bridge in I and has a typ-
ical C≡C bond length of 1.163(5) Å. The B–C bond lengths
of 1 are 1.573(5) and 1.574(5) Å for the B–mesityl bonds and
1.577(5) Å for the boron–vinyl bond.
Photophysical and Redox Properties
The photophysical properties of boranes 1 and 2 have been
studied in toluene at room temperature and the results are
summarized in Table 2. Both 1 and 2 show similar struc-
tured absorption bands (∼322–324 nm).The absorption maxima
exhibit negligible bathochromic solvatochromic shifts in sol-
vents of increasing polarity, which is consistent with very small
ground-state dipole moments. Fluorescence occurs in the blue
region for compounds 1 and 2. Excitation of 1 and 2 in toluene
solutions gave strong emission peaks located at 477 and 487 nm,
respectively. The emission wavelengths of 1 and 2 are slightly
red-shifted with respect to that of I (454 nm in toluene). These
featureless luminescence spectra are independent of the excita-
tion wavelength used. Because of their similar emission pattern,
it is considered that the emission features in I and the dansy-
lated boranes should have the same origin. In contrast to their
absorption behaviour, 1 and 2 exhibit pronounced positive sol-
vatochromism in their fluorescence spectra (Table 3), which can
be attributed to highly polarized excited states. In other words,
their emission spectra shift towards longer wavelengths with
increasing polarity of the solvents. Solvent-dependent emission
in solution has been frequently observed for three-coordinate
organoboron compounds.[15] As shown in Fig. 2, the shift of the
emission maximum with solvents is dramatic in each case. For
example, in the non-polar solvent, hexane, the emission maxima
of 1 and 2 are located at 448 and 450 nm, while in dimethyl sul-
foxide (DMSO), the emission maxima appear at 515 and 516 nm,
respectively (Table 3). The fluorescence lifetimes of 1 and 2 are
14 and 12 ns, respectively.
Spectroscopic data (IR, 1H and 13C NMR, and MS) for these
newfluorophore-anchoredmesitylboranesareinagreementwith
their formulation. The disappearance of the IR ν(C≡C) and
ν(≡C–H) bands in 1 confirms that hydroboration of the alkyne
unit occurred to give a vinyl boron compound. The IR spectrum
of 2 displays a strong ν(C≡C) absorption band at 2238 cm−1
,
but absorption as a result of the terminal acetylenic C–H group
1
of the ligand is absent. The H NMR spectra of the new com-
pounds show resonances that stem from the coordinated dansyl
group, but the signals attributable to −C≡CH for I (∼1.92 ppm)
are not observed. The 13C NMR spectroscopic data also give
precise information about the structure of the compounds. In
each case, the carbon resonances of the mesityl methyl group
are clearly identified at ∼21 and 23 ppm for both compounds.
Notably, there are two distinct 13C NMR signals for the indi-
vidual sp carbons in 2, in accordance with the formulation. The
MALDI-TOF MS and elemental analytical data further support
the formulation of these compounds. For 1 and 2, molecular ion
peaks are observed at m/z 537 and 611 amu, respectively.
Single-crystal X-ray diffraction studies for I and 1 confirm
their structures (Fig. 1). Important bond parameters are listed
in Table 1. For both I and 1, there are two independent but
The electrochemical properties of 1 and 2 were inves-
tigated by cyclic voltammetry in THF. The potentials were
measured against Ag/AgCl as the reference electrode and each
measurement was calibrated with the ferrocene/ferrocenium
(Fc/Fc+) redox system as an internal standard. The reduction

Fluorescent Substituted Dimesitylboranes
917
(a)
(b)
C(1)
C(1)
C(2)
C(9)
N(1)
N(1)
C(4)
C(5)
C(6)
C(2)
C(24)
C(3)
C(12)
C(11)
C(10)
C(19)
C(18)
C(20)
C(21)
C(3)
C(8)
C(22)
C(7)
C(8)
C(16)
C(15)
C(4)
C(5)
C(10)
C(11)
C(17)
C(23)
C(13)
C(15)
C(14)
B(1)
O(2)
C(14)
C(31)
N(2)
C(9)
C(25)
S(1)
C(7)
C(6)
C(12)
N(2)
C(26)
C(27)
C(28)
C(33)
O(1)
C(30)
C(29)
C(13)
S(1)
O(2)
O(1)
C(32)
Fig. 1. Molecular structures of one of the two independent molecules of I (left) and 1 (right).
Table 1. Selected bond lengths [Å] and angles [◦] for compounds I
and 1
Table 3. Absorption and emission maxima of 1 and 2 in different
solvents
Solvent
Compound 1
λmax
Compound 2
λmax
Bond length [Å]
Bond angle [◦]
λem
λem
Compound I
O(1)–S(1)–O(2)
S(1)–O(1)
1.428(2)
1.428(2)
1.615(3)
1.452(4)
1.473(5)
1.163(5)
119.7(2)
107.5(1)
121.1(2)
114.2(3)
178.7(4)
Hexane
CCl4
Toluene
CH2Cl2
Ethanol
DMSO
320
318
318
318
318
325
448
464
477
503
510
515
321
323
323
321
321
324
450
462
481
500
510
516
S(1)–O(2)
C(12)–S(1)–N(2)
S(1)–N(2)–C(13)
N(2)–C(13)–C(14)
C(13)–C(14)–C(15)
S(1)–N(2)
N(2)–C(13)
C(13)–C(14)
C(14)–C(15)
Compound 1
S(1)–O(1)
S(1)–O(2)
S(1)–N(2)
B(1)–C(15)
B(1)–C(16)
B(1)–C(25)
C(14)–C(15)
1.431(3)
1.436(3)
1.614(3)
1.577(5)
1.573(5)
1.574(5)
1.312(5)
O(1)–S(1)–O(2)
C(8)–S(1)–N(2)
118.9(2)
106.8(2)
124.7(3)
110.9(3)
123.6(3)
120.5(3)
115.8(3)
and this can be attributed to the reduction of the boron cen-
tre. Hence, the calculated highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
energies for 1 (2) are −5.64 (−5.54) and −2.25 eV (−2.26 eV),
respectively.
S(1)–N(2)–C(13)
N(2)–C(13)–C(14)
C(16)–B(1)–C(25)
C(15)–B(1)–C(16)
C(15)–B(1)–C(25)
Electroluminescent Behaviour
Table 2. Photophysical data for 1 and 2
Initially, it was noted that a blue-emitting OLED device
based on a neat emissive layer of 1 showed a poor EL effi-
ciency with luminance yield ηL = 0.83 cdA−1 and power effi-
ciency ηP = 0.21 lmW−1. From the similar photoluminescence
(PL)/electroluminescence (EL) spectra (Fig. 3), it is concluded
that the emissive states of both EL and solid PL are identical
and the absence of aggregation or π-stacking is apparent. In
the present study, blue-doped devices A–E were used instead.
Typical multilayer EL devices A–C were constructed using
dopant 1 with indium tin oxide (ITO) as the anode, 4,4ꢀ,4ꢀ-tris[2-
N-naphthyl-N-phenylamino]triphenylamine (2-TNATA, 60 nm)
as the hole-injection material, 4,4ꢀ-bis[N-(1-naphthyl)-N-
phenylamino]biphenyl (NPB, 10 nm) as the hole-transporting
material, and MADN (40 nm) as the host material for blue
dopants. Tris[8-hydroxyquinolinato]aluminum (Alq3) was used
as the electron-transporting layer and LiF/Al as the bi-layer
cathode (Fig. 4). Devices D,E were similarly fabricated using
1,3,5-tris[N-(phenyl)benzimidazole]benzene (TPBI)[18] as the
hole blocker and electron transporter instead of Alq3. Different
Compound
λmax [nm]A
Toluene
322 (5.8)
287 (2.0), 324 (2.7) 287, 324
Eg [eV]B
λem [nm]C
Film
322
1
2
3.39
3.28
477 (20, 14)
487 (18, 12)
AExtinction coefficients (104 M−1 cm−1) are shown in parentheses.
BEstimated from the onset wavelength of the solid-state optical absorption.
CToluene (290 K). Fluorescence quantum yields [%] and lifetimes [ns]
shown in parentheses (ΦF, τF) were measured in toluene relative to quinine
sulfate in 1.0 N H2SO4 and 9,10-diphenylanthracene in cyclohexane.
potentials (Ered) and optical bandgaps (Eg) were used to deter-
mine the HOMO and LUMO energy levels using the equations
ELUMO = −(Ered + 4.8) and EHOMO = −(Eox − Ered) eV, which
were calculated using the internal standard ferrocene value of
−4.8 eVwithrespecttothevacuumlevel.[17] Eachofthemshows
an irreversible reduction peak at −2.55 and 2.54V, respectively,

918
W.-Y. Wong et al.
for device A. The turn-on voltages (Vturn-on) observed for such
devicesare∼4.0V.Therearenoundesirableemissionpeaksfrom
Alq3 in each case but a slight blue-shift in the EL maximum was
noted for the blue-doped devices relative to the one without the
MADN host. The pertinent EL characteristics of devices A–E
are summarized in Table 4. The maximum blue EL efficiency of
device A can reach 2.5 cdA−1 and 1.2 lmW−1 at 20 mA cm−2
and 6.7V at 3 wt.-% doping concentration with Commission
Internationale de L’Eclairage colour coordinates of (0.17, 0.12).
The corresponding external quantum efficiency is ∼2.4%. Fig. 6
depicts the EL performance of device D. The EL performance
of devices A and B is slightly lower than that of devices D and
E at the same doping level. Optimization of the device efficien-
cies using other host systems and the applicability of 1 for the
electron-transport layer warrants further examination.
(a)
Toluene
CCl4
Ethanol
CH2Cl2
Hexane
DMSO
1.0
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
Conclusions
Wavelength [nm]
We have studied the chemistry and optoelectronic properties of
two new mesitylborane compounds anchored with fluorescent
dansyl termini through the hydroboration and cross-coupling
reactions based on the dansylated alkyne unit.The spectroscopic,
structural, and electrochemical properties of these compounds
were examined and interestingly, their emission spectra display
significant solvent-induced shifts characteristic of highly polar
excited states. These fluorescent materials hold promise for blue
light generation and have also found potential applications in
dopant-based blue OLEDs.
(b)
Toluene
CCl4
Ethanol
CH2Cl2
DMSO
Hexane
1.0
0.8
0.6
0.4
0.2
0.0
Experimental
General Procedures
The preparations of organoborane compounds were carried out
under a nitrogen atmosphere with the use of standard inert
atmosphere and Schlenk techniques, but no special precau-
tions were taken to exclude oxygen during workup. Solvents
were predried and distilled from appropriate drying agents.
All chemicals, unless otherwise stated, were obtained from
commercial sources and used as received. Preparative TLC
was performed on 0.7 mm silica plates (Merck Kieselgel 60
GF254) prepared in our laboratory. The starting compounds
(p-iodophenyl)dimesitylborane[15] and 5-(dimethylamino)-N-
(prop-2-ynyl)naphthalene-1-sulfonamide[14a] were prepared by
the reported procedures. Infrared spectra were recorded as
CH2Cl2 solutions in a CaF2 cell (0.5 mm path length) on a
Nicolet Magna 550 Series II FTIR spectrometer. NMR spectra
were measured in CDCl3 on aVarian INOVA 400 MHz FT NMR
spectrometer. ChemicalshiftswerequotedrelativetoSiMe4 (δ0)
400
450
500
550
600
650
700
Wavelength [nm]
Fig. 2. Photoluminescence spectra of (a) 1 and (b) 2 in different solvents.
1.0
EL
PL
0.8
0.6
0.4
0.2
0.0
1
for both H and 13C nuclei. The MALDI-TOF high-resolution
mass spectra were recorded on an Autoflex Bruker MALDI-
TOF system. Electronic absorption spectra were obtained with
a Hewlett Packard 8453 diode array UV-vis spectrometer. The
solution emission spectra and lifetimes of the compounds were
measured on a Photon Technology International Fluorescence
QuantaMaster Series QM1 spectrophotometer. The fluores-
cence quantum yields were determined in toluene solutions
at 293 K against quinine sulfate in 0.1 N H2SO4 and 9,10-
diphenylanthracene in cyclohexane.[19] The decay curves were
analyzed using a Marquardt-based non-linear least-squares fit-
ting routine and were shown to follow a single-exponential func-
tion in each case according to I = I0 + A exp(−t/τ). For solid-
state emission, the photoluminescence measurement system
consisted of a monochromator (Acton SpectraPro 500i) attached
300
400
500
600
700
800
Wavelength [nm]
Fig. 3. Solid-state PL and neat-emissive layer electroluminescent (EL)
spectra of 1.
dopant concentrations were used to obtain the optimum weight
percentages for devices with the highest efficiencies. Fig. 5
depicts the current–voltage–luminance (I–V–L) characteristics
of devicesA–C and EL efficiency versus current density curves

Fluorescent Substituted Dimesitylboranes
919
Al (100 nm)
LiF (1 nm)
Al (100 nm)
LiF (1 nm)
N
N
TPBI (15 nm)
x% 1:MADN (40 nm)
NPB (10 nm)
2-TNATA (60 nm)
ITO
Alq3 (15 nm)
x% 1:MADN (40 nm)
NPB (10 nm)
2-TNATA (60 nm)
ITO
N
N
N
N
Glass
Glass
A–C
D–E
TPBI
CH3
N
N
N
N
NPB
MADN
N
N
N
O
O
Al
N
N
N
2-TNATA
N
O
CBP
Alq3
Fig. 4. Thegeneral structuresof theblue-doped blueorganiclight-emitting devices(OLED)devicesand themolecular structures
of the relevant compounds used in these devices.
to a photomultiplier tube (PMT) (Hamamatsu R636-10) as the
detector. The signal from the PMT was first pre-amplified by the
pre-amplifier(PrincetonAppliedResearch5182), andthenitwas
processed by the lock-in amplifier (Stanford Research Systems
SR830 DSP Lock-in Amplifier) and recorded by the computer.
The excitation source used was a N2 pulse 337 nm contin-
uous laser (Spectra-Physics 337201-01). The excitation light
source was directed to the sample by optics and the emission
from the sample was collected and focussed by a lens onto the
input slit of the monochromator system. Cyclic voltammetry
experiments were performed with a PrincetonApplied Research
model 273A potentiostat. A conventional three-electrode con-
figuration consisting of a glassy carbon working electrode, a
Pt-wire counter electrode, and an Ag/AgCl reference electrode
(0.1 M in acetonitrile) was used. The solvent in all measure-
ments was deoxygenated THF and the supporting electrolyte
was 0.1 M [Bu4N]PF6. Ferrocene was added as a calibrant
after each set of measurements and all potentials reported were
quoted with reference to the Fc/Fc+ couple. Thermal analyses
were performed with Perkin–Elmer Pyris Diamond DSC and
Perkin–Elmer TGA6 thermal analyzers at a scanning rate of
hexane/CH2Cl2 (1/1, v/v) to yield white crystals of 1 (320 mg,
60%) (Found: C 71.8, H 7.2, N 5.2. C33H39BN2O2S·H2O
requires C 71.2, H 7.4, N 5.0%). δH (400 MHz, CDCl3) 8.52–
8.56 (m, 2H, Ar), 8.23–8.34 (m, 2H, Ar), 7.46–7.58 (m, 2H,
CH vinyl), 7.15–7.19 (m, 1H, Ar), 6.76 (s, 4H, Mes), 6.67 (m,
1H, Ar), 4.95 (m, 1H, NH), 3.75 (m, 2H, NHCH2), 2.90 (s,
6H, N(CH3)2), 2.28 (s, 6H, p-Mes), 2.04 (s, 12H, o-Mes). δC
(100.3 MHz, CDCl3) 151.98, 149.55, 140.51, 133.70, 130.54,
129.85, 129.55, 128.54 (Ar + vinyl), 141.51, 140.34, 138.68,
128.16 (Mes), 46.85 (NHCH2), 45.37 (N(CH3)2), 23.15, 21.11
(Mes). m/z (MALDI-TOF) 537.2756 (calc. 537.2753) (M+).
Preparation of Compound 2
Ligand I (100 mg, 0.35 mmol), (p-iodophenyl)dimesitylborane
(157 mg, 0.35 mmol), Pd(PPh3)2Cl2 (5 mg), and CuI (1.3 mg)
were added to a nitrogen-purged flask and then NEt3 (50 mL)
was added to the mixture through a cannula. The reaction mix-
ture was stirred at room temperature. After 1 day, the mixture
was refluxed at 80◦C for 6 h. The solvent was then removed
under vacuum. The crude product was dissolved in CH2Cl2
and purified on preparative silica TLC plates with CH2Cl2 as
eluent. From the yellow band (RF 0.60) 2 was obtained as an
off-white solid (98 mg, 46%) (Found: C 74.5, H 6.7, N 4.3.
C39H41BN2O2S·H2O requires C 74.3, H 6.9, N 4.4%). νmax
(CH2Cl2)/cm−1 2238 (C≡C). δH (400 MHz, CDCl3) 8.43 (d,
J 8.4, 1H, Ar), 8.33–8.28 (m, 2H, Ar), 7.56 (t, J 8, 1H, Ar), 7.46
(t, J 8, 1H, Ar), 7.29 (d, J 8, 2H, Ar), 7.13 (d, J 8, 1H, Ar),
6.85 (d, J 8, 2H, Ar), 6.81 (s, 4H, Mes), 5.11 (t, J 6.4, 1H, NH),
4.04 (d, J 6.4, 2H, NHCH2), 2.78 (s, 6H, N(CH3)2), 2.30 (s, 6H,
p-Mes), 1.95 (s, 12H, o-Mes). δC (100.3 MHz, CDCl3) 152.05,
20◦C min−1
.
Preparation of Compound 1
In a glove box, a solution of dimesitylborane[20] (1.0 mmol,
260 mg) in THF (20 mL) was added dropwise to a flask that
contained a solution of ligand I (1.0 mmol, 288 mg) in THF
(20 mL) and the mixture was stirred for 3 days. The solvent
was removed under vacuum, and Et2O (2 × 20 mL) was added
to extract the product.The crude product was recrystallized from

920
W.-Y. Wong et al.
135.60, 134.50, 130.78, 129.92, 128.51, 125.05, 123.18, 118.51,
115.08 (Ar), 141.35, 140.66, 138.83, 128.17 (Mes), 85.00, 84.57
(C≡C), 45.26 (N(CH3)2), 33.85 (NHCH2), 23.32, 21.16 (Mes).
m/z (MALDI-TOF) 611.2944 (calc. 611.2910) (M+).
2.5
2.0
1.5
1.0
0.5
0.0
4
3
2
1
0
X-Ray Crystallography
Single crystals of 1 suitable for X-ray crystallographic analyses
weregrownbyslowevaporationofitssolutioninCH2Cl2/hexane
at room temperature. The crystals were chosen and mounted on
a glass fibre using epoxy resin. Crystal data, data collection
parameters, and results of the analyses are listed in Table 5.
Ϫ1
0
100
200
300
(a)
Current density [mA cmϪ2
]
500
3%
5%
7%
5000
4000
3000
2000
1000
Fig. 6. Luminance (ꢀ) and power (•) efficiencies versus current density
curves of blue organic light-emitting devices (OLED) device D.
400
300
200
100
0
3%
5%
7%
Table 5. Summary of crystal data for compounds I and 1
Parameter
Compound I
Compound 1
Empirical formula
Molecular weight
Crystal size [mm3]
Crystal system
Space group
a [Å]
C15H16N2O2S
288.36
C33H39BN2O2S
538.53
0
0.30 × 0.25 × 0.21 0.26 × 0.24 × 0.10
0
2
4
6
8
10
12
Monoclinic
P 21/c
25.017(5)
8.020(2)
15.193(3)
90
Triclinic
¯
P 1
Voltage [V]
11.478(2)
11.792(2)
21.952(4)
99.480(3)
91.102(4)
90.351(3)
2929.9(9)
0.143
b [Å]
(b)
c [Å]
α [◦]
2.5
2.0
1.5
1.0
0.5
0.0
4
β [◦]
107.08(3)
90
2913(1)
0.225
1.315
8
γ [◦]
3
U [Å3]
µ (MoKα) [mm−1
]
Dcalc [g cm−3
Z
]
1.221
4
2
F(000)
1216
1152
1.88–25.00
14066
9965
0.0408
1
θ range [◦]
1.70–25.00
14021
5111
Reflections collected
Unique reflections
Rint
0
0.0396
Ϫ1
Observed reflections [I > 2σ(I)] 3758
6246
No. of parameters
365
711
0
100
200
300
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0620, 0.1758
0.0798, 0.1874
1.050
0.636 to −0.382
0.0716, 0.1674
0.1217, 0.1955
1.035
0.836 to −0.424
Current density [mA cmϪ2
]
Goodness-of-fit on F2
Residual extrema in final
Fig. 5. (a) Current–voltage–luminance characteristics of blue organic
light-emitting devices (OLED) devices A–C and (b) luminance (ꢀ) and
power (•) efficiencies versus current density curves of OLED device A.
diff. map [e Å−3
]
Table 4. EL performance of the doped blue-emitting devices at 20 mA cm−2
CIE, Commission Internationale de L’Eclairage; EL, electroluminescent; EQE, external quantum efficiency
Device
Vturn-on
[V]
x
[%]
Voltage
[V]
Luminance
Luminance
yield
Power
efficiency
[lmW−1
]
EQE
[%]
CIE(x)
CIE(y)
EL λem
[nm]
[cd m−2
]
[cdA−1
]
A
B
C
D
E
4.0
4.0
4.0
4.1
4.7
3
5
7
3
5
6.7
6.8
6.8
7.3
6.6
494
483
436
434
422
2.5
2.4
2.2
2.2
2.1
1.2
1.1
1.0
0.9
1.0
2.35
2.17
2.05
2.82
2.14
0.17
0.17
0.17
0.16
0.17
0.12
0.13
0.12
0.08
0.11
439
440
440
436
438

Fluorescent Substituted Dimesitylboranes
921
The diffraction experiments were carried out at 293 K on a
Bruker Axs SMART 1000 CCD area-detector diffractometer
using graphite-monochromated MoKα radiation (λ 0.71073 Å).
The raw intensity data frames were integrated with the SAINT+
program using a narrow-frame integration algorithm.[21] Cor-
rections for Lorentz and polarization effects were also applied
by SAINT+. For each analysis an empirical absorption correc-
tion based on the multiple measurement of equivalent reflections
was applied by using the program SADABS.[22] The structures
were solved by direct methods, and expanded by difference
Fourier syntheses using the software SHELTXL.[23] Structure
refinements were made on F2 by the full-matrix least-squares
technique. In each case, all the non-hydrogen atoms were
refined with anisotropic displacement parameters. The hydro-
gen atoms were placed in their ideal positions but not refined.
CCDC-654097 and CCDC-654098 contain the supplementary
crystallographic data for this paper.
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OLED Device Fabrication and Testing
Commercial ITO-coated glass with a sheet resistance of 20–
30 ꢀ sq−1 was used as the starting substrate. Before device
fabrication, the ITO glass substrates were cleaned by ultra-
sonication in organic solvents followed by ozone treatment for
20 min.[24] The device was fabricated layer by layer in a stan-
dard vacuum coater under a base vacuum of ∼10−6 torr. The
deposition of the entire device was carried out without a vac-
uum break. The MADN:dopant emissive layer was co-deposited
simultaneously with a series of controlled ratios.The layer thick-
ness was monitored in situ using a quartz crystal oscillator.
The characteristics of the I–V–L of the devices were measured
with a PR650 spectrophotometer with a direct current source
controlled by a computer in a dark room under ambient air con-
ditions at room temperature. All measurements were completed
within 20 min after the device was unloaded from the vacuum
chamber.
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Acknowledgements
[8] (a) Z. Yuan, J. C. Collings, N. J. Taylor, T. B. Marder, C. Jardin,
J.-F. Halet, J. Solid State Chem. 2000, 154, 5. doi:10.1006/JSSC.
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Financial support from a CERG Grant from the Hong Kong Research Grants
Council (HKBU 202005P) and a Faculty Research Grant from the Hong
Kong Baptist University (FRG/05-06/II-71) is gratefully acknowledged. We
thank Dr J. C. Collings and Professor T. B. Marder (Durham University) for
assistance with the syntheses of the compounds.
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