Concise synthesis and two-photon-excited deep-blue emission of 1,8-diazapyrenes

Article abstract of DOI:10.1002/asia.201200192

Efficient violet-blue-emitting molecules are especially useful for applications in full-color displays, solid-state lighting, as well as in two-photon absorption (TPA) excited frequency-upconverted violet-blue lasing. However, the reported violet-blue-emitting molecules generally possess small TPA cross sections. In this work, new 1,8-diazapyrenes derivatives 3 with blue two-photon-excited fluorescence emission were concisely synthesized by the coupling reaction of readily available 1,4-naphthoquinone O,O-diacetyl dioxime (1) with internal alkynes 2 under the [{RhCl₂Cp*} ₂]-Cu(OAc)₂ (Cp=pentamethylcyclopentadienyl ligand) bimetallic catalytic system. Elongation of the π-conjugated length of 1,8-diazapyrenes 3 led to the increase of TPA cross sections without the expense of a redshift of the emission wavelength, probably due to the rigid planar structure of chromophores. It is especially noteworthy that 2,3,6,7-tetra(4- bromophenyl)-1,8-diazapyrene (3 c) has a larger TPA cross section than those of other molecules reported so far. These experimental results are explained in terms of the effects of extension of the π-conjugated system, intramolecular charge transfer, and reduced detuning energy. Copyright

Full text of DOI:10.1002/asia.201200192

DOI: 10.1002/asia.201200192
Concise Synthesis and Two-Photon-Excited Deep-Blue Emission of 1,8-
Diazapyrenes
Tingchao He,[a] Pei Chui Too,[b] Rui Chen,[a] Shunsuke Chiba,*[b] and Handong Sun*[a]
Abstract: Efficient violet–blue-emitting
molecules are especially useful for ap-
plications in full-color displays, solid-
state lighting, as well as in two-photon
absorption (TPA) excited frequency-
upconverted violet–blue lasing. Howev-
er, the reported violet–blue-emitting
molecules generally possess small TPA
cross sections. In this work, new 1,8-di-
azapyrenes derivatives 3 with blue two-
photon-excited fluorescence emission
were concisely synthesized by the cou-
pling reaction of readily available 1,4-
naphthoquinone O,O-diacetyl dioxime
(1) with internal alkynes 2 under the
[{RhCl2Cp*}2]–CuACTHNUGRTENUNG(OAc)2 (Cp*=pen-
tamethylcyclopentadienyl ligand) bi-
metallic catalytic system. Elongation of
the p-conjugated length of 1,8-diaza-
pyrenes 3 led to the increase of TPA
cross sections without the expense of
a redshift of the emission wavelength,
probably due to the rigid planar struc-
ture of chromophores. It is especially
noteworthy that 2,3,6,7-tetra(4-bromo-
phenyl)-1,8-diazapyrene
(3c)
has
a larger TPA cross section than those
of other molecules reported so far.
These experimental results are ex-
plained in terms of the effects of exten-
sion of the p-conjugated system, intra-
molecular charge transfer, and reduced
detuning energy.
Keywords: diazapyrenes
blue emission fluorescence
two-photon
·
deep-
·
·
nonlinear optics
absorption
·
Introduction
tracted much attention for their important applications, such
as in full-color displays and solid-state lighting.[8] However,
to the best of our knowledge, there have been only a few
papers reporting the efficient two-photon-excited blue emis-
sion of organic molecules.[1]
The development of efficient two-photon absorption (TPA)
materials have recently been expedited by their potential
applications in multiphoton microscopy, optical limiting, fre-
quency-upconversion lasing, pulse stabilization, and reshap-
ing.[1] To achieve large TPA cross sections, various molecular
structures have been designed, such as donor–bridge–accept-
or (D–p–A) dipoles,[2] donor–bridge–donor (D–p–D) quad-
rupoles,[3] octupoles,[4] oligomeric porphyrin derivatives,[5]
and others.[6]
In addition to the aforementioned applications, TPA-in-
duced frequency-upconverted violet–blue lasing, which can
be used to generate low-cost, high-energy, coherent light
sources, offers new views in various laser-based applica-
tions.[7] Moreover, violet–blue-emitting molecules have at-
It is generally accepted that the increase in donor–accept-
or strength, the conjugation length, and the planarity of the
p system will lead to large TPA cross sections.[1,9] However,
the structural guidelines for enlarging TPA cross sections
with violet–blue emission are extremely rare. The lack of ef-
ficient design strategies for these molecules might be a seri-
ous obstacle for their related applications. One of the struc-
tural requirements for violet–blue-emission molecules is
short p conjugation, but it usually results in smaller TPA
cross sections. On the other hand, elongation of p conjuga-
tion for enhancement of TPA cross section causes a redshift
of the emission wavelength and decreases the fluorescence
quantum yield and photostability.[10] Moreover, the TPA
cross sections of violet–blue-emission molecules reported so
far are very small, usually in the range of tens of GM
(1 GM=10ꢀ50 cm4 s).[11] Moreover, synthetic processes for
such violet–blue-emission molecules generally require multi-
step routes. Based on these backgrounds, the development
of concise synthetic methods for p-conjugated molecules
possessing efficient two-photon-excited violet–blue emission
has remained a significant challenge.
[a] Dr. T. He, Dr. R. Chen, Prof. H. Sun
Division of Physics and Applied Physics
School of Physical and Mathematical Sciences
Nanyang Technological University
Singapore 637371 (Singapore)
Fax : (+65)65138086
E-mail: hdsun@ntu.edu.sg
[b] P. C. Too, Prof. S. Chiba
Division of chemistry and Biological Chemistry
School of Physical and Mathematical Sciences
Nanyang Technological University
Singapore 637371 (Singapore)
Herein, we utilize newly and concisely synthesized 1,8-di-
azapyrenes[12] to build up new TPA chromophores, which
can efficiently emit deep-blue light. TPA cross sections,
measured with femtosecond pulses by the Z-scan tech-
nique,[13] are in the range of (1–15), (6–120), (54–298), and
Fax : (+65) 67911961
E-mail: shunsuke@ntu.edu.sg
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200192.
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(5–82) GM for the four 1,8-diazapyrenes 3a, 3b, 3c, and 3d,
respectively (see below). Although the TPA cross sections
are smaller than those of several molecules emitting at
wavelengths between 500 and 700 nm, they are larger than
those of most molecules with deep-blue emission.[11] More-
over, by taking the present simple preparation into consider-
ation, 1,8-diazapyrenes 3 could be valuable for applications
related to deep-blue emission. It is also found that elonga-
tion of the p-conjugated length could result in increased
TPA cross sections, without a dramatic redshift of emission
wavelength and low fluorescence quantum yield, probably
due to the rigid planar structure of the chromophores.
Figure 1. UV-visible and photoluminescence (PL) spectra of 1,8-diazapyr-
enes 3.
Results and Discussion
Preparation of 1,8-Diazapyrenes
One-Photon-Absorption and -Emission Properties
Synthesis of 1,8-diazapyrenes was concisely achieved by the
coupling reaction of readily available 1,4-naphthoquinone
O,O-diacetyl dioxime (1) with internal alkynes 2 under the
Figure 1 shows the UV-visible molar absorptivity spectra of
chromophores 3a, 3b, 3c, and 3d in tetrahydrofuran (THF)
at a concentration of 1.0ꢁ10ꢀ5 mLꢀ1. From the results shown
in Figure 1, it can be observed that the one-photon-absorp-
tion and -emission spectra for chromophore 3a exhibit a vi-
bronic structure with the progression of several peaks; this
indicates that there is a coupling with vibrational modes in
[{RhCl2Cp*}2]–Cu
G
(Cp*=pentamethylcyclopenta-
dienyl ligand) bimetallic catalytic system, which has recently
been developed in our group.[14] Treatment of a mixture of
1
and internal alkynes (2 equiv) with 5 mol% of
[{RhCl2Cp*}2] and 20 mol% of Cu(OAc)2 in N,N-dimethyl-
AHCTUNGTRENNUNG
ꢀ
formamide (DMF) at 608C resulted in concurrent formation
chromophore 3a that corresponds to C C and/or C=C
ꢀ
of two pyridine rings through the sequence of ortho-aryl C
stretching during excitation from the ground state to the ex-
cited state, or the emission from the excited state down to
the ground state. The absorption maximum of 3b and 3c is
larger than those of 3a and 3d due to greater p conjugation.
All of compounds 3 also show strong one-photon-excited
PL spectra, which are comparatively shown in Figure 1. The
emission peaks for chromophores 3a, 3b, 3c, and 3d are
405, 421, 442, and 410 nm, respectively, which are also in
agreement with the order of the degree of p conjugation.
The PL lifetime is an important parameter for organic emit-
ting molecules, so we have also measured time-resolved PL
(TRPL) decay curves for the four molecules (Figure 2).
Compounds 3a, 3b, and 3d have single-exponential PL
emission decay behavior with lifetimes of 2.35, 3.55, and
ꢀ
H bond cleavage, insertion of alkynes, and C N bond for-
mation, thereby giving the corresponding 1,8-diazapyrenes 3
(Table 1). While the reaction with 4-octyne (2a) gave 1,8-di-
Table 1. One-step synthesis of 1,8-diazapyrenes 3.[a]
Entry
Alkynes
R1
R2
Yield of 3[b] [%]
1
2
3
4
2a
2b
2c
2d
nPr
Ph
4-Br-C6H4
Me
nPr
Ph
4-Br-C6H4
Ph
33 (3a)
72 (3b)
71 (3c)
59 (3d)
[a] All reactions were carried out on a 0.5 mmol scale of oxime 1 with
2 equivalents of alkyne 2 under a nitrogen atmosphere. [b] Isolated yields
based on oxime 1.
azapyrene 3a in the moderate yield (Table 1, entry 1), aryl
alkynes such as 2b and 2c made the reactions smooth and
afforded 1,8-diazapyrenes 3b and 3c in good yields (Table 1,
entries 2 and 3). In the reaction with the asymmetrical
alkyne 1-phenyl-1-propyne (2d) regioselective formation of
1,8-diazapyrene 3d was observed in 59% yield (Table 1,
entry 4). These 1,8-diazapyrenes are stable to air and mois-
ture.
Figure 2. Room-temperature TRPL measurements of 3.
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Synthesis and Emission of 1,8-Diazapyrenes
Table 2. The lifetimes (t) and fluorescence quantum yields (FPL) for 1,8-
diazapyrenes 3.
lecular solutions were freshly prepared at a concentration of
10ꢀ4 mLꢀ1 in THF. In addition, the laser beam was focused
as close as possible to the wall of the quartz cell and the PL
signal was collected in back-scattering geometry, so that
only the emission from the edge of the solution was collect-
ed. It was also found that TPA excited PL spectra for all of
the compounds in THF were essentially the same as their
one-photon-excited PL spectra, as shown in Figure 3a, thus
implying that both one- and two-photon emissions were ob-
served from the same excited state.
3a
3b
3c
3d
t[a] [ns]
2.35
3.55
t2 =1.57
t1 =0.48
1.9
3.62
[b]
FPL [%]
4.5
2.7
4.5
[a] PL lifetime obtained from time-correlated single-photon counting
(TCSPC). [b] Obtained by using quinine sulfate monohydrate (F=0.58)
as a standard.
3.62 ns, respectively, whereas the 4-bromophenyl adduct 3c
exhibits double-exponential PL decay behavior and a much
faster decay rate, thus indicating a much stronger intermo-
lecular interaction for 3c in solution.[15] The shorter lifetime
of 3a can be attributed to a facile nonradiative decay path-
way for this molecule, but this is much longer than that of
many other organic molecules.[8,16,17] The long excited-state
lifetimes of the compounds provide a major advantage for
PL applications, such as diagnostics and optical amplifica-
To fully realize the potential application of two-photon
excitation of the fluorescent molecules, it is important to
know their TPA spectra. The TPA cross sections at a discrete
wavelength for 3 were determined by the Z-scan method
(Figure 4). By repeating the open-aperture Z-scan measure-
ments for each laser wavelength, we can obtain the TPA
spectra shown in Figure 5. Although chromophore 3a exhib-
ited small s2 values at excitation wavelengths, chromophores
3b–d displayed much larger TPA cross sections. For exam-
ple, the maximum s2 value of 3a was 15 GM at 680 nm,
whereas that of 3b was around 120 GM at 680 nm. With the
installation of 4-bromophenyl substituents (for 3c), the max-
imum TPA cross section could be up to 298 GM at 800 nm,
which was about 20 times larger than the maximum s2 of
3a. Note that this value is even larger than all of the organic
molecules reported in the literature.[11]
Although the quantum yields of 3 are lower than those of
other compounds reported in the literature,[11] the TPA
brightness values (the products of the peak TPA cross sec-
tion and the fluorescence quantum yields) are still moderate
due to their larger TPA cross sections, which are important
for fluorescent molecule applications. It is known that the
TPA process is a third-order nonlinear process, which is
tion. The lifetimes (t) and fluorescence quantum yield (FPL
)
for the four compounds are summarized in Table 2.
TPA and Emission Properties
Note that all experimental results presented from here on
correspond to intrinsic TPA cross sections measured in the
femtosecond regime, and thereby, prevent contributions
from linear nonresonant absorption or from excited-state
absorption that may result in artificially enhanced TPA
cross sections when the molecules are excited in the nano-
second regime.[18] It was found that 3a, 3b, 3c, and 3d
showed strong two-photon-excited PL emission, which can
be easily observed by the naked eye, as shown in Figure 3c.
Figure 3b logarithmically shows the PL integrated intensity
versus the excitation power of a 780 nm laser. All the plots
have slopes near two, which coincides with the requirement
for two-photon-excited PL.[1] To avoid the reabsorption
effect due to high concentration of the molecules, the mo-
Figure 4. Open aperture Z-scan results for solutions of 3 obtained by
using 680 or 800 nm femtosecond pulses (experimental data (open cir-
cles), theoretical fitted data (solid line)). The concentration of 3a was 2ꢁ
10ꢀ2 m and for the other three molecules was 2ꢁ10ꢀ3 m, excited with
power densities of 277.1, 459.9, 226.0, and 411.5 GWcmꢀ2, giving a TPA
coefficient of 0.0064, 0.0051, 0.0150, and 0.0035 cmGWꢀ1 for 3a, 3b, 3c,
and 3d, respectively.
Figure 3. a) TPA excited PL spectra for 3; b) PL integrated intensity
versus power density at 780 nm. The log–log plots with slope values of
around two indicate the nature of TPA in all of the compounds.
c) Images of TPA excited PL emission for 3 under excitation at 780 nm.
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Figure 6. Geometry-optimized structural analyses of 3 for their HOMO
and LUMO energies.
in which M01 and M12 are the transition dipole moments
from S0 to S1 and S1 to S2, respectively; ꢀhw ¼ ðE2 ꢀ E0Þ=2;
and the damping factor, G, can be set to 0.1 V in almost all
cases for the centrosymmetric molecules. The denominator
is the square of the detuning energy between the ground
and TPA states.[3,20] A smaller detuning energy will lead to
a larger TPA cross section. From the TPA spectra presented
in Figure 5, the detuning energy for 3c is smaller than those
for 3a, 3b, and 3d. It is consistent with the much larger
TPA cross sections for 3c.
To evaluate the photostability of 3, photobleaching ex-
periments were performed for a solution of 3 in THF by
using a power density of 100.01 GWcmꢀ2 for 100 fs pulses
at 780 nm. The emission intensities monitored at PL spectra
peaks were recorded at time intervals of 5 s for a period of
1200 s. It was found that the emission intensities for all of
the compounds decreased by less than 5%, which indicated
the high photostability of 3.
To gain an insight into the electronic structure of 3, quan-
tum chemical calculations were carried out by using the
hybrid Hartree–Fock/DFT at the B3LYP/6-31G level.[21] The
TPA cross section is related to the extent of intramolecular
charge transfer through the p bridge in the molecule.[22] The
HOMOs and LUMOs are depicted in Figure 6. From the
calculated frontier orbitals, for 3a, there are no changes on
the localization of LUMO and HOMO. However, compared
with the localization of HOMOs on the diazapyrene core,
the LUMOs of 3b, 3c, and 3d are delocalized on both the
core and substituent, indicating an increase in intramolecu-
Figure 5. TPA spectra of 1,8-diazapyrenes 3 under the femtosecond pulse
excitation.
strongly dependent on intramolecular charge transfer. The
p-electron-rich substituents will induce an increase in charge
transfer from the ends of the molecules to the center, result-
ing in larger s2 values. Therefore, compounds 3b, 3c, and 3d
exhibit much larger s2 values than those of 3a. Note also
that the maximum TPA coefficient of 3d was five times
larger than that of 3a, without suffering from a dramatic
redshift of emission wavelength and low fluorescence quan-
tum yield. For 3a, 3b, and 3d, the monotonic increase in
TPA cross-section spectra at wavelengths below 800 nm in-
dicates that the optimal excitation at wavelengths is shorter
than the estimation based only on the linear absorption
properties. This can be attributed to the higher electronic
transition (S0–Sn) for TPA excitation.[19] For centrosymmetric
molecules, a three-level model can be utilized to describe
their TPA properties, in which TPA into high-lying states is
not dipole coupled to the ground state. It can be written as
Equation (1):
M021M122
ð1Þ
s2 ¼
2
ðE1 ꢀ E0 ꢀ ꢀhwÞ G
Table 3. The comparison of TPA cross-sectional values for 3 and other organic molecules with deep-blue emission.
Materials[a]
Methods[b] lex [nm] s2 [GM] labs [nm]
lem [nm]
References
M-OPP(4)-SOR
calix-OPP(4)-SOR
TPEF, fs
TPEF, fs
NLT, fs
NLT, fs
NLT, fs
NLT, fs
NLT, fs
TPEF, fs
600
600
800
800
800
800
800
750
710
710
680
680
800
680
31
169
7
319
319
276
275
376
357
367
407
425
483
460
461
463
434
470
497
494
[11a]
[11a]
[11b]
[11b]
[11b]
[11b]
[11b]
[11d]
[11d]
[11d]
1,4-bis(5,6-diphenyl-1,2,4-triazin-3-yl)benzene
1,3-bis(5,6-diphenyl-1,2,4-triazin-3-yl)benzene
2-[4-(1H-phenanthro
2-[4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl]benzoxazole
2-styryl-1H-phenanthro[9,10-d]imidazole
trans-2-(p-formylstyryl)benzimidazole
5
[9,10-d]imidazol-2-yl)phenyl]benzoxazole
21
16
7
180
40
59
15
120
298
82
E
270, 360
282, 336, 469
278, 336, 458
340, 356, 383,
272, 296, 362
278, 300, 365, 403
3,7-bis
3,7-bis
3a
ACHTUNGTRENNUNG[5’-(trifluoromethyl)-1’H-pyrazole-3’-yl]10-ethylphenothiazine TPEF, fs
[5’-
(phenyl)-10H-pyrazole-3’-yl]10-ethylphenothiazine
TPEF, fs
Z scan
Z scan
Z scan
Z scan
386, 405[d] this work
3b
3c
3d
421[d]
this work
this work
this work
442 nm[d]
266, 286, 344, 359, 392 410[d]
[a] The abbreviation of the materials is directly used from the corresponding reference. [b] PEF=two-photon-excited fluorescence method, NLT=non-
linear transmittance method. [d] Excited at 325 nm by using a continuous wave HeCd laser.
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Synthesis and Emission of 1,8-Diazapyrenes
flash column chromatography (n-hexane/ethyl acetate=60:40) to yield
oxime 1 as a reddish brown solid (0.51 g, 1.89 mmol, 30%). M.p. 146–
1488C; 1H NMR (400 MHz, CDCl3): d=2.36 (6H, s), 7.55 (2H, s), 7.56
(2H, dd, J=3.6, 6.4 Hz), 8.37 ppm (2H, dd, J=3.6, 6.0 Hz); 13C NMR
(100 MHz, CDCl3): d=19.8, 122.2, 124.3, 128.5, 130.9, 150.8, 168.2 ppm;
IR (NaCl) 1773, 1620, 1574, 1539, 1520, 1368, 1188, 939 cmꢀ1; HRMS
(ESI): m/z calcd for C14H13N2O4: 273.0875 [M+H]+; found: 273.0884.
lar charge transfer and favoring the enhancement of their
TPA cross sections. To facilitate the comparison, molecules
reported with TPA cross sections with blue emission are
listed in Table 3. Clearly, compounds 3b, 3c, and 3d have
larger TPA cross sections. In particular, compound 3c has
the largest maximum s2 of all other molecules in Table 3.
Synthesis of 1,8-Diazapyrene 3
A typical procedure for the reaction of 1 and 2b (Table 1, entry 2):
[{RhCl2Cp*}2] (15.5 mg, 0.025 mmol) and CuACTHNUTRGEN(UNG OAc)2 (18.2 mg, 0.20 mmol)
Conclusion
were added to a solution of 1 (136.1 mg, 0.50 mmol) and 2b (178.2 mg,
1.00 mmol) in DMF (1.5 mL) and the reaction mixture was stirred at
608C under a nitrogen atmosphere for 18 h. After being cooled to room
temperature, the reaction was quenched with pH 9 buffer and organic
materials were extracted with CH2Cl2 (3ꢁ). The combined extracts were
washed with water (3ꢁ) and brine and dried over MgSO4. The solvents
were removed under reduced pressure and the crude was purified by
silica-gel flash column chromatography (n-hexane/ethyl acetate=80:20)
to afford 3b as an orange solid (92.4 mg, 0.286 mmol, 72%). M.p. 275–
2778C; 1H NMR (400 MHz, CDCl3): d=7.28–7.34 (m, 10H), 7.36–7.41
(m, 6H), 7.51–7.54 (m, 4H), 8.04 (s, 2H), 8.70 ppm (s, 2H); 13C NMR
(100 MHz, CDCl3): d=117.2, 127.58, 127.60, 127.8, 128.2, 129.0, 130.5,
130.7, 131.6, 133.0, 134.4, 136.9, 140.9, 147.3, 156.2 ppm; IR (NaCl): n˜ =
1557, 1445, 1381, 1074, 1030 cmꢀ1; HRMS (ESI): m/z calcd for C38H25N2:
509.2018 [M+H]+; found: 509.2018.
Efficient two-photon-excited emission in the deep-blue
region has been demonstrated on newly synthesized 1,8-dia-
zapyrenes 3 by pumping with femtosecond pulses. It was
shown that the TPA cross section could be increased by
elongation of the p conjugation of the 1,8-diazapyrenes 3
without a large redshift of the emission wavelength, which
implied that varying the donors (or acceptors) linked to the
1,8-diazapyrene core was an effective way to tailor TPA
properties for applications related to deep-blue emission.
Our findings may open a new avenue to design highly effi-
cient TPA molecules for blue PL emission and lasing as well
as provide a novel series of organic molecules that can be
used in nonlinear optical applications and fundamental stud-
ies.
2,3,6,7-TetrapropylbenzoACTHNUGRTENNUG[lmn]ACHTUNTGREN[NUNG 2,9]phenanthroline (3a)
Brownish red solid; M.p. 77–788C; 1H NMR (400 MHz, CDCl3): d=1.13
(t, J=7.2 Hz, 6H), 1.16 (t, J=7.2 Hz, 6H), 1.76–1.85 (m, 4H), 1.92–2.01
(m, 4H), 3.23–3.27 (m, 4H), 3.28–3.33 (m, 4H), 8.39 ppm (s, 4H);
13C NMR (100 MHz, CDCl3): d=14.5, 14.6, 24.0, 25.2, 30.2, 38.3, 117.3,
126.4, 128.8, 131.3, 133.1, 145.7, 158.4 ppm; IR (NaCl): n˜ =2961, 2932,
Experimental Section
2872, 1562, 1477, 1456, 1391, 1263 cmꢀ1; HRMS
ACTHNUTRGNEUNG(ESI): m/z calcd for
General
C26H33N2: 373.2644 [M+H]+; found: 373.2645.
1H NMR (400 MHz) spectra were recorded on a Bruker Avance 400
spectrometer in CDCl3 (with (CH3)4Si (d=0.00 ppm) as an internal stan-
dard). 13C NMR (100 MHz) spectra were recorded on a Bruker Avance
400 spectrometer in CDCl3 (with residual CHCl3 (d=77.00 ppm) as an
internal standard). The following abbreviations are used to explain the
multiplicities: s=singlet, d=doublet, t=triplet, q=quartet, m=multip-
let. IR spectra were recorded on a Shimazu IR Prestige-21 FTIR spec-
trometer. High-resolution mass spectra were obtained with a Finnigan
MAT 95 XP mass spectrometer (Thermo Electron Corporation). Melting
points were recorded on a Buchi B-54 melting-point apparatus. Flash
column chromatography was performed by using Merck silica gel 60 with
2,3,6,7-Tetrakis(4-bromophenyl)benzoACTHNUTRGENN[GU lmn]ACHTUGNTREN[NUGN 2,9]phenanthroline (3c)
Yellowish green solid; M.p. 191–1938C; 1H NMR (400 MHz, CDCl3): d=
7.20 (d, J=8.0 Hz, 4H), 7.39 (d, J=8.4 Hz, 4H), 7.47 (d, J=8.4 Hz, 4H),
7.58 (d, J=8.0 Hz, 4H), 8.01 (s, 2H), 8.67 ppm (s, 2H); 13C NMR
(100 MHz, CDCl3): d=117.1, 122.4, 122.6, 128.9, 129.3, 131.3, 131.8,
132.1, 133.1, 133.3, 134.2, 135.5, 139.5, 147.7, 154.9 ppm; IR (NaCl): n˜ =
1587, 1549, 1491, 1377, 1126, 1070, 1011, 833 cmꢀ1; HRMS (ESI): m/z
calcd for C38H21N279Br281Br2: 824.8397 [M+H]+; found: 824.8403.
3,6-Dimethyl-2,7-diphenylbenzoACHTNUTRGENNUG[lmn]ACHTUNGTRNE[NUGN 2,9]phenanthroline (3d)
Yellow solid; M.p. 234–2368C; 1H NMR (400 MHz, CDCl3): d=2.94 (s,
6H), 7.48–7.52 (m, 2H), 7.56–7.60 (m, 4H), 7.71–7.74 (m, 4H), 8.52 (s,
2H), 8.53 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=16.1, 117.2,
124.3, 126.9, 128.0, 128.3, 129.8, 132.1, 134.2, 141.5, 146.0, 157.5 ppm; IR
(NaCl): n˜ =3057, 2968, 1558, 1474, 1379, 1362, 1016, 833 cmꢀ1; HRMS
(ESI): m/z calcd for C28H21N2: 385.1705 [M+H]+; found: 385.1705.
distilled solvents. Anhydrous DMF (99.8%), Cu
ACHTUNGRTEN(NUNG OAc)2 (98% trace
metal basis), Cu(OAc) (97%), and [{RhCl2Cp*}2] (97%) were purchased
ACHTUNGTRENNUNG
from Sigma–Aldrich.
Preparation of (1E,4E)-Naphthalene-1,4-dione O,O-diacetyl dioxime (1)
NH2OH·HCl (1.32 g, 18.9 mmol) was added in one portion to a solution
of naphthalene-1,4-dione (1.0 g, 6.3 mmol) and pyridine (2.5 mL,
31.5 mmol) in EtOH (6 mL) and the reaction mixture was stirred at 608C
for 2 h. The reaction was quenched by adding water and the organic ma-
terials were extracted with CH2Cl2 (4ꢁ). The combined extracts were
washed with 1n aqueous HCl and brine, and dried over MgSO4. Volatile
materials were removed in vacuo to give (1E, 4E)-naphthalene-1,4-dione
dioxime, which was used for the next acetylation step without further pu-
rification.
Optical Absorption and Emission Spectra
Linear absorption spectra for compounds 3 were recorded on a Shimadzu
UV-3101 PC spectrophotometer. For the one-photon-excited PL, a contin-
uous wave HeCd laser emitting at 325 nm was used as the excitation
source and the signal was dispersed by a 750 mm monochromator com-
bined with suitable filters, and detected by a photomultiplier using the
standard lock-in amplifier technique.
The crude residue obtained above was treated with Ac2O (1.2 mL,
12.6 mmol) and a catalytic amount of 4-dimethylaminopyridine (DMAP;
5 mg) in pyridine (3 mL) and the reaction mixture was stirred at room
temperature for 4 h. After the volatile materials were evaporated, the re-
sulting residue was treated with water and organic materials were ex-
tracted in CH2Cl2 (4ꢁ). The combined extracts were washed with 1n
aqueous HCl and brine and dried over MgSO4. The solvents were re-
moved under reduced pressure and the crude was purified by silica-gel
TPA Cross-Sectional Measurements
TPA coefficients of molecules were measured by using the Z-scan tech-
nique.[13] The compounds were dissolved in THF and placed in 1 mm
quartz cuvettes. The laser source is a Ti:sapphire system that produced
100 fs (HW1/e) pulses at a repetition of 80 MHz. Measurements were
carried out in the wavelength range of 680–820 nm for TPA excitation. In
the measuring process, the input laser beam was first passed though
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Shunsuke Chiba, Handong Sun et al.
FULL PAPER
a beam chopper with an open ratio of 1/10 and a rotating speed of 315
rounds per second. Then the Gaussian beam was tightly focused onto the
samples by a convex lens (f=10 cm). The transmitted beam was detected
by a silicon photodiode using the standard lock-in amplifier technique.
The measured curves were symmetric with respect to the focal point (z=
0), where they exhibit a minimum transmittance in the case of TPA. The
TPA coefficient, b, can be estimated from the normalized transmittance
given by Equation (2):
A. Mawatari, K. Nakao, H. Enozawa, T. Nishinaga, M. Iyoda, J.
Am. Chem. Soc. 2008, 130, 3252–3253; c) A. Fukazawa, H. Yamada,
Y. Sasaki, S. Akiyama, S. Yamaguchi, Chem. Asian J. 2010, 5, 466–
469.
[7] Y. Zhang, S. L. Lai, Q. X. Tong, M. F. Lo, T. W. Ng, M. Y. Chan,
Chem. Mater. 2012, 24, 61–70.
[8] a) D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, M. Krçger, E.
Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, P.
Hinze, A. Gerhard, P. Stçssel, H. Vestweber, Adv. Mater. 2005, 17,
31–34; b) T. C. He, R. Chen, W. W. Lin, F. Huang, H. D. Sun, Appl.
Phys. Lett. 2011, 99, 081902–081904.
[9] Z. Zeng, Z. Guan, Q. Xu, J. Wu, Chem. Eur. J. 2011, 17, 3837–3841.
[10] Q. Zheng, S. K. Gupta, G. S. He, L. S. Tan, P. N. Prasad, Adv. Funct.
Mater. 2008, 18, 2770–2779.
[11] a) H. H. Fan, K. F. Li, X. L. Zhang, W. Yang, M. S. Wong, K. W.
Cheah, Chem. Commun. 2011, 47, 3879–3881; b) Y. Sun, W. Huang,
C. Lu, Y. Cui, Dyes Pigm. 2009, 81, 10–17; c) Z. L. Huang, N. Li, H.
Lei, Z. R. Qiu, H. Z. Wang, Z. P. Zhong, Z. H. Zhou, Chem.
Commun. 2002, 2400–2401; d) D. M. Li, L. Lv, P. Sun, W. Zhou, P.
Wang, J. Wu, Y. Kan, H. Zhou, Y. Tian, Dyes Pigm. 2009, 83, 180–
186.
1
TOAðTPAÞ
¼
ð2Þ
2
1 þ bLeff½I00=ð1 þ ðz=z0Þ Þꢁ
in which I00 is the peak intensity, z is the sample position, z0 ¼ pw20=l is
the diffraction length of the beam, w0 is the beam waist radius at the
focus point, and Leff =[1ꢀexp(ꢀa0L)]/a0 is the effective thickness of the
G
sample. As a macroscopic parameter that depends on the concentration
of the TPA molecules, b (in units of cmGWꢀ1) can be further expressed
as b=s2’N0 =s2’NAd0 ꢁ10ꢀ3, in which s02 is the molecular TPA cross sec-
tion (in units of cm4 GWꢀ1), N0 is the molecular density (in units of
cmꢀ3), NA is Avogadroꢂs number, and d0 is the molar concentration of the
absorbing molecules (in units of MLꢀ1). Moreover, one can also use an-
other parallel expression for the TPA cross section, defined as s2 ¼ hns02,
in which hn is the photon energy of the input light beam. According to
this definition, s2 can be calculated in units of GM.[23]
[12] H. C. Becker, A. Broo, B. Norden, J. Phys. Chem. A 1997, 101,
8853–8860.
[13] M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Haga, E. W. Van Stry-
land, IEEE J. Quantum Electron. 1990, 26, 760–769.
[14] a) P. C. Too, S. H. Chua, S. H. Wong, S. Chiba, J. Org. Chem. 2011,
76, 6159–6168; b) Y. F. Wang, K. K. Toh, J. Y. Lee, S. Chiba, Angew.
Chem. 2011, 123, 6049–6053; Angew. Chem. Int. Ed. 2011, 50, 5927–
5931; c) P. C. Too, T. Noji, Y. J. Lim, X. Li, S. Chiba, Synlett 2011,
2789–2794; d) P. C. Too, Y. F. Wang, S. Chiba, Org. Lett. 2010, 12,
5688–5691.
[15] G. S. He, Q. Zheng, C. Lu, P. N. Prasad, IEEE J. Quantum Electron.
2005, 41, 1037–1043>.
[16] B. Xu, H. Fang, F. Chen, H. Lu, J. He, Y. Li, Q. Chen, H. Sun, W.
Tian, New J. Chem. 2009, 33, 2457–2464.
[17] T. B. Clark, M. E. Orr, D. C. Flynn, T. Goodson III, J. Phys. Chem.
C 2011, 115, 7331–7338.
[18] R. L. Sutherland, M. C. Brant, J. Heinrichs, J. E. Rogers, J. E. Slagle,
D. G. McLean, P. A. Fleitz, J. Opt. Soc. Am. B 2005, 22, 1939–1948.
[19] M. Drobizhev, N. S. Makarov, S. E. Tillo, T. E. Hughes, A. Rebane,
Nat. Methods 2011, 8, 393–399.
[20] S. Chung, S. Zheng, T. Odani, L. Beverina, J. Fu, L. A. Padilha, A.
Biesso, J. M. Hales, X. Zhan, K. Schmidt, A. Ye, E. Zojer, S.
Barlow, D. J. Hagan, E. W. Van Stryland, Y. Yi, Z. Shuai, G. A.
Pagani, J. Brꢃdas, J. W. Perry, S. R. Marder, J. Am. Chem. Soc. 2006,
128, 14444–14445.
[21] Gaussian 98, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuse-
ria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Mont-
gomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J.
Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli,
C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q.
Cui, K. Morokuma, P. Salvador, J. J. Dannenberg, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V.
Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W.
Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez,
M. Head-Gordon, E. S. Replogle, J. A. Pople, Gaussian, Inc., Pitts-
burgh, PA, 1998.
Acknowledgements
Support from the Singapore Ministry of Education through the Academic
Research Fund (Tier 1) under Project No. RG63/10 (for S.H.D.), from
the Singapore National Research Foundation through the Competitive
Research Programme (CRP) under Project No. NRF-CRP5-2009-04 (for
S.H.D.), and from the Science & Engineering Research Council for
A*STAR Grant No. 082 101 0019 (for C.S.) is gratefully acknowledged.
We thank Prof. Changshun Wang from Shanghai Jiao Tong University
for providing us with the Z-scan measurement system and for helpful dis-
cussions.
[1] G. S. He, L. Tan, Q. Zheng, P. N. Prasad, Chem. Rev. 2008, 108,
1245–1330.
[2] a) B. A. Reinhardt, L. L. Brott, S. J. Clarson, A. G. Dillard, J. C.
Bhatt, R. Kannan, L. Yuan, G. S. He, P. N. Prasad, Chem. Mater.
1998, 10, 1863–1874; b) R. Kannan, G. S. He, L. Yuan, F. Xu, P. N.
Prasad, A. G. Dombroskie, B. A. Reinhardt, J. W. Baur, R. A. Vaia,
L.-S. Tan, Chem. Mater. 2001, 13, 1896–1904; c) L. Beverina, J. Fu,
A. Leclercq, E. Zojer, P. Pacher, S. Barlow, E. W. Van Stryland, D. J.
Hagan, J. L. Brꢃdas, S. R. Marder, J. Am. Chem. Soc. 2005, 127,
7282–7283.
[3] M. Albota, D. Beljonne, J. L. Brꢃdas, J. E. Ehrlich, J. Y. Fu, A. A.
Heikal, S. E. Hess, T. Kogej, M. D. Levin, S. R. Marder, D. McCord-
Maughon, J. W. Perry, H. Rçckel, M. Rumi, G. Subramaniam, W. W.
Webb, X. L. Wu, C. Xu, Science 1998, 281, 1653–1656.
[4] D. Beljonne, W. Wenseleers, E. Zojer, Z. Shuai, H. Vogel, S. J. K.
Pond, J. W. Perry, S. R. Marder, J. L. Brꢃdas, Adv. Funct. Mater.
2002, 12, 631–641.
[5] a) K. Ogawa, A. Ohashi, Y. Kobuke, K. Kamada, K. Ohta, J. Am.
Chem. Soc. 2003, 125, 13356–13357; b) T. K. Ahn, K. S. Kim, D. Y.
Kim, S. B. Noh, N. Aratani, C. Ikeda, A. Osuka, D. Kim, J. Am.
Chem. Soc. 2006, 128, 1700–1704; c) S. Saito, J. Y. Shin, J. M. Lim,
K. S. Kim, D. Kim, A. Osuka, Angew. Chem. 2008, 120, 9803–9806;
Angew. Chem. Int. Ed. 2008, 47, 9657–9660.
[22] V. Chandrasekhar, M. D. Pandey, S. K. Maurya, P. Sen, D. Goswami,
Chem. Asian J. 2011, 6, 2246–2250.
[23] G. S. He, C. Xu, P. N. Prasad, B. A. Reinhardt, J. C. Bhatt, A. G. Dil-
lard, Opt. Lett. 1995, 20, 435–437.
[6] a) C. Katan, S. Tretiak, M. H. V. Werts, A. J. Bain, R. J. Marsh, N.
Leonczek, N. Nicolaou, E. Badaeva, O. Mongin, M. Blanchard-
Desce, J. Phys. Chem. B 2007, 111, 9468–9483; b) M. Williams-
Harry, A. Bhaskar, G. Ramakrishna, T. Goodson III, M. Imamura,
Received: February 21, 2012
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Nonlinear Optics
Tingchao He, Pei Chui Too, Rui Chen,
Shunsuke Chiba,*
Handong Sun*
&&&& — &&&&
Concise Synthesis and Two-Photon-
Excited Deep-Blue Emission of 1,8-
Diazapyrenes
Cause and effect: Efficient two-photon
excited deep-blue emission has been
demonstrated for newly synthesized
1,8-diazapyrene derivatives (see
sections can be greatly increased by
elongation of p conjugation in the 1,8-
diazapyrenes without a large redshift
in the emission wavelength.
scheme). Two-photon-absorption cross
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