Synthesis and electrochemical and theoretical studies of V-shaped donor-acceptor hexaazatriphenylene derivatives for second harmonic generation

Article abstract of DOI:10.1021/jo101311v

In this article we describe novel synthetic strategies toward well-defined disubstituted conjugated hexaazatriphenylene (HAT) derivatives. The systems are designed as novel V-shaped chromophores displaying C₂ symmetry suitable for nonlinear optical investigations. Different donor moieties and linkers have been used in order to tune the electrochemical properties as well as the absorption spectra of the novel HAT derivatives. μβ values as high as 1010 × 10^-48 esu have been obtained for a derivative containing the electron-rich dibutylamino moiety. Theoretical calculations have been performed showing a reasonable agreement with the experimental results and supporting the two-dimensional NLO character of these chromophores.

Full text of DOI:10.1021/jo101311v

pubs.acs.org/joc
Synthesis and Electrochemical and Theoretical Studies of V-Shaped
Donor-Acceptor Hexaazatriphenylene Derivatives for Second
Harmonic Generation
†,‡
Rafael Juarez, Mar Ramos, Jose L. Segura,* Jesus Orduna,* Belen Villacampa, and
†
,‡
,§
^
ꢀ
ꢀ
ꢀ
ꢀ
Raquel Alicante^
†
´
´
ꢀ
ꢀ
Departamento de Tecnologıa Quımica y Ambiental, Universidad Rey Juan Carlos, C/Tulipan s/n, Mostoles,
´
‡
28933, Spain, Departamento de Quımica Organica I, Universidad Complutense de Madrid,
ꢀ
§
´
ꢀ
Avda. Complutense s/n, Madrid, 28040, Spain, ^Departamento de Quımica Organica, ICMA,Universidad de
´
Zaragoza-CSIC, 50009 Zaragoza, Spain, and Departamento de Fısica de la Materia Condensada, ICMA,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
segura@quim.ucm.es; jorduna@unizar.es
Received July 4, 2010
In this article we describe novel synthetic strategies toward well-defined disubstituted conjugated hexaaza-
triphenylene (HAT) derivatives. The systems are designed as novel V-shaped chromophores displaying C2
symmetry suitable for nonlinear optical investigations. Different donor moieties and linkers have been used in
order to tune the electrochemical properties as well as the absorption spectra of the novel HAT derivatives.
μβ values as high as 1010 ꢀ 10-48 esuhavebeenobtainedforaderivativecontaining the electron-rich dibutyl-
amino moiety. Theoretical calculations have been performed showing a reasonable agreement with the
experimental results and supporting the two-dimensional NLO character of these chromophores.
1. Introduction
with DNA in different ways.3,4 Although most of the literature
concerned with the HAT system deals with its coordination
properties and the properties of the corresponding complexes, in
the last years some work has also been done to study its proper-
ties and applications in the absence of metals.
1,4,5,8,9,12-Hexaazatriphenylene (HAT) was first synthe-
sized in 19811 as a novel metal ligand for coordination chemistry.
The six nitrogen atoms allow HAT to act as a triple bidentate
ligand that can bond up to three metal atoms. This property
has been widely used for the construction of metal-organic
frameworks of different complexity.2 The photophysical and
photochemical properties of some HAT complexes have also
demanded interest today due to their capability of interaction
Theoretical investigations have been reported5-7 as well as
numerous contributions involving experimental properties
(4) Blasius, R.; Moucheron, C.; Kirsch-De Mesmaeker, A. Eur. J. Inorg.
Chem. 2004, 3971–3979.
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Geerts, Y.; Piris, J.; Debije, M. G.; Van de Craats, A. M.; Senthilkumar, K.;
Siebbeles, L. D. A.; Warman, J. M.; Bredas, J. L.; Cornil, J. J. Am. Chem.
Soc. 2004, 126, 3271–3279.
ꢀ
(6) Cornil, J.; Lemaur, V.; Calbert, J.-P.; Bredas, J.-L. Adv. Mater. 2002,
14, 726–729.
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J. J. Organomet. Chem. 1981, 217, 179–82.
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1627–1641.
7542 J. Org. Chem. 2010, 75, 7542–7549
Published on Web 10/25/2010
DOI: 10.1021/jo101311v
r
2010 American Chemical Society

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Juarez et al.
JOCArticle
like liquid crystal behavior,8-16 electron mobility,17-20 self-
assembling,21-28 and redox properties.29-31 HATs have also
been used to modify and control the color of mesoporous
silica32 and have been included in organic light emitting
devices (OLEDs).33,34
CHART 1. HATs Studied in the Present Paper
Nonlinear optical (NLO) properties of HAT derivatives
have been treated only once in the literature and only refer to
some completely symmetric (trigonal) derivatives and its
metal complexes with Cuþ.35 These molecules showed an
octupolar NLO response.
Most of the HAT derivatives in the previous references
involve trigonal molecules and only a few papers describe
(7) Lozman, O. R.; Bushby, R. J.; Vinter, J. G. J. Chem. Soc., Perkin
Trans. 2 2001, 1446–1452.
(8) Lehmann, M.; Kestemont, G.; Aspe, R. G.; Buess-Herman, C.; Koch,
M. H. J.; Debije, M. G.; Piris, J.; Haas, M. P. d.; Warman, J. M.; Watson,
M. D.; Lemaur, V.; Cornil, J.; Geerts, Y. H.; Gearba, R.; Ivanov, D. A.
Chem.;Eur. J. 2005, 11, 3349–3362.
(9) Ong, C. W.; Liao, S.-C.; Chang, T. H.; Hsu, H.-F. J. Org. Chem. 2004,
69, 3181–3185.
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(10) Lehmann, M.; Lemaur, V.; Cornil, J.; Bredas, J.-L.; Goddard, S.;
Grizzi, I.; Geerts, Y. Tetrahedron 2004, 60, 3283–3291.
(11) Ong, C. W.; Liao, S.-C.; Chang, T. H.; Hsu, H.-F. Tetrahedron Lett.
2003, 44, 1477–1480.
(12) Gearba, R. I.; Lehmann, M.; Levin, J.; Ivanov, D. A.; Koch,
ꢀ
M. H. J.; Barbera, J.; Debije, M. G.; Piris, J.; Geerts, Y. H. Adv. Mater.
2003, 15, 1614–1618.
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R. A. J.; Meijer, E. W. Chem. Mater. 2001, 13, 2675–2679.
(14) Kestemont, G.; Halleux, V. d.; Lehmann, M.; Ivanov, D. A.;
Watson, M.; Geerts, Y. H. Chem. Commun. 2001, 2074–2075.
(15) Boden, N.; Bushby, R. J.; Cooke, G.; Lozman, O. R.; Lu, Z. J. Am.
Chem. Soc. 2001, 123, 7915–7916.
(16) Arikainen, E. O.; Boden, N.; Bushby, R. J.; Lozman, O. R.; Vinter,
J. G.; Wood, A. Angew. Chem., Int. Ed. 2000, 39, 2333–2336.
(17) Zhao, W.; Salomon, E.; Zhang, Q.; Barlow, S.; Marder, S. R.; Kahn,
A. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 165336/1–165336/6.
(18) Chan, C. K.; Kahn, A.; Zhang, Q.; Barlow, S.; Marder, S. R. J. Appl.
Phys. 2007, 102, 014906/1–014906/6.
non-trigonal HAT derivatives.36-38 All the properties of
known HATs and the existence of very few synthetic routes to
derivatives of nontrigonal HATs led us to propose new synthetic
routes for molecules 1-4 (Chart 1). The aim of the present work
is to provide full synthetic details to complete the previous
preliminary communication39 and describe new products to offer
a wider scope of the properties of donor-acceptor nontrigonal
HATs including their dipolar nonlinear optical properties.
SCHEME 1. Synthesis of Hexaaminobenzene (8) and Diamine 9
(19) Chan, C. K.; Amy, F.; Zhang, Q.; Barlow, S.; Marder, S.; Kahn, A.
Chem. Phys. Lett. 2006, 431, 67–71.
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C.; Jones, S. C.; Barlow, S.; Domercq, B.; Amy, F.; Kahn, A.; Bredas, J.-L.;
Kippelen, B.; Marder, S. R. J. Am. Chem. Soc. 2005, 127, 16358–16359.
(21) Ha, S. D.; Zhang, Q.; Barlow, S.; Marder, S. R.; Kahn, A. Phys. Rev.
B: Condens. Matter Mater. Phys. 2008, 77, 085433/1–085433/7.
(22) Xu, Q.-M.; Ma, H.; Tucker, N.; Bardecker, J. A.; Jen, A. K. Y.
Nanotechnology 2007, 18, 335302/1–335302/9.
(23) Salomon, E.; Zhang, Q.; Barlow, S.; Marder, S. R.; Kahn, A. J. Phys.
Chem. C 2008, 112, 9803–9807.
(24) Ha, S. D.; Kaafarani, B. R.; Barlow, S.; Marder, S. R.; Kahn, A.
J. Phys. Chem. C 2007, 111, 10493–10497.
(25) Palma, M.; Levin, J.; Lemaur, V.; Liscio, A.; Palermo, V.; Cornil, J.;
Geerts, Y.; Lehmann, M.; Samori, P. Adv. Mater. 2006, 18, 3313–3317.
(26) Ishi-i, T.; Yaguma, K.; Kuwahara, R.; Taguri, Y.; Mataka, S. Org.
Lett. 2006, 8, 585–588.
2. Results and Discussion
ꢁ
2.1. Synthesis. In the present work we present an experi-
mental and theoretical study of V-shaped donor-acceptor
HATs 1-4 (Chart 1) focusing on the NLO properties of
the compounds. The molecules contain an HAT electron-
deficient nucleus and two electron-donor peripherical sub-
tituents joined by an alkenyl (1, 2) or alkynyl moiety (3, 4).
This design was adopted in order to generate a dipolar
moment benefitial for a NLO response. In the preliminary
communication we reported the synthesis of V-shaped HAT
derivatives 1 and 2 starting from 9 (Scheme 1).39 Diamine 9
could be obtained starting with the nitration of 5,40 substitu-
tion of chlorine atoms with ammonia to form 7,41 reduction
of the nitro groups to yield hexaaminobenzene (8),42 and
finally condensation of 8 with two molecules of glyoxal.43
(27) Ishi-i, T.; Murakami, K.-i.; Imai, Y.; Mataka, S. J. Org. Chem. 2006,
71, 5752–5760.
(28) Salomon, E.; Kahn, A. Surf. Sci. 2008, 602, L79–L83.
(29) Furukawa, S.; Okubo, T.; Masaoka, S.; Tanaka, D.; Chang, H. C.;
Kitagawa, S. Angew. Chem., Int. Ed. 2005, 44, 2700–2704.
(30) Wang, R.; Ramaraj, R.; Okajima, T.; Kitamura, F.; Matsumoto,
N.; Thiemann, T.; Mataka, S.; Ohsaka, T. J. Electroanal. Chem. 2004,
567, 85–94.
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T.; Mataka, S.; Ohsaka, T. J. Phys. Chem. B 2003, 107, 9452–9458.
(32) Okabe, A.; Fukushima, T.; Ariga, K.; Aida, T. Angew. Chem., Int.
Ed. 2002, 41, 3414–3417.
(33) Liao, L.-S.; Slusarek, W. K.; Hatwar, T. K.; Ricks, M. L.; Comfort,
D. L. Adv. Mater. 2008, 20, 324–329.
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223311/3.
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Tetrahedron Lett. 1998, 39, 9205–9208.
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1997, 36, 584–592.
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8829–8833.
(38) Nasielski, J.; Moucheron, C.; Verhoeven, C.; Nasielski-Hinkens, R.
Tetrahedron Lett. 1990, 31, 2573–2576.
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J. Org. Chem. Vol. 75, No. 22, 2010 7543

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SCHEME 2. Synthesis of Key Products 11 and 12 and Final
Obtention of Alkenyl-Linked Compounds 1 and 2
SCHEME 4. Final Obtention of Alkynyl-Linked HATs 3 and 4
TABLE 1. Electrochemical Behavior of 1-4a
compd
technique
Ered 1
Ered 2
Ered 3
Eox 1
Eox 2
1
CV
DPV
CV
DPV
CV
DPV
CV
DPV
-1.38
-1.36
-1.39
-1.39
-1.27
-1.20
-1.29
-1.27
-1.94
-1.87
-1.81
-1.90
0.93
0.96
0.57
0.59
1.52
1.93
0.81
0.86
-2.39
1.26
0.78
2
3
4
-1.81
-1.85
SCHEME 3. Synthesis of Alkynyl R-Diketones 21 and 22
1.03
aAll measurements were obtained in dichloromethane solutions. Condi-
tions: concentrations of 2 mM of sample and 0.1 M of HFPTBA. Pt work-
ing and auxiliary electrodes. Ag/Agþ reference electrode. Scan rate 100 mV/s.
Values referenced to Fc/Fcþ. All values are given in volts (V). In CV experi-
ments Ered refers to E1/2 (half-wave potential) and Eox to the onset of the
process. In DPV all the values refer to the maximum of each redox signal.
The free terminal alkynes 19 and 20 have been previously
reported starting from trimethylsilylacetylene precursors.44,45
However, we preferred to use triisopropylsilyl as a protecting
group due to its higher stability allowing us to store 17 and 18
for a long time without degradation when necessary. Alkynes
19 and 20 were then treated first with butyllithium, CuBr,
and LiBr to effect the in situ formation of a dialkylcuprate
intermediate that is immediately treated with oxalyl chloride
to yield the R-diketones 21 and 22. Finally, condensation
of diamine 9 and the corresponding diketone afforded the
alkynyl-linked HATs 3 (63%) and 4 (36%) (Scheme 4).
NMR spectra show the HAT protons as a not solved
multiplet at >9.2 ppm. The rest of the signals at high field
correspond to the hexyloxy or dibutylaminobenzene termi-
nal moieties. Alkyne groups appear clearly in the IR spectra.
Both molecules show an intense and sharp signal at 2206 and
2186 cm-1 for 3 and 4, respectively, corresponding to the
stretch of the triple bond.
Diamine 9 can be condensed with 1,4-dibromobutadione
(10) to obtain the HAT derivative 11 (Scheme 2). 11 is
transformed into the diphosphonate 12 by heating in the
presence of trimethylphosphite. Finally a Wittig-Horner
reaction with the corresponding aldehyde (13 or 14) leads to
the desired products 1 and 2 with yields of 60% and 25%,
respectively. NMR spectra of the compounds show the all-
trans configuration of the double bonds. Alkenyl protons
appear like two doublets with a coupling constant of 15.2 Hz
for compound 1 and 15.5 Hz for compound 2. HAT moiety
protons appear as two doublets at >9 ppm with a small
coupling constant of 2.0 Hz. The rest of the signals can be
assigned to the hexyloxybenzene or dibutylaminobenzene
periphery.
For the synthesis of alkynyl-linked HATs 3 and 4 we have
developed a different synthetic route that requires the prep-
aration of diketones 21 and 22 (Scheme 3). The route starts
with a Sonogashira cross-coupling reaction between 15 or 16
and triisopropylsilyl acetylene followed by deprotection in
the presence of fluoride salts.
2.2. Electrochemistry. The electrochemical behavior of the
molecules was studied by cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) in dichloromethane.
All molecules showed a donor-acceptor character with
quasireversible reduction waves and irreversible oxidation
processes (Table 1).
Alkynyl-linked HATs 3 and 4 showed better acceptor
properties than alkenyl-linked HATs 1 and 2.
The oxidation potentials obtained by CV showed that the
molecules with the hexyloxyphenyl groups were weaker elec-
tron donors (onset of 0.93 and 1.52 V for 1 and 3, respec-
tively) than the dibutylaminobenzene-substituted ones (onset of
0.57 and 0.81 V for 2and 4, respectively). In the cathodic regime,
(42) Rogers, D. Z. J. Org. Chem. 1986, 51, 3904–3905.
(43) Moucheron, C.; Mesmaeker, A. K. D.; Choua, S. Inorg. Chem. 1997,
36, 584–592.
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Howard, J. A. K.; Marder, T. B.; Low, P. J. Liq. Cryst. 2008, 35, 119–132.
(45) Miller, J. J.; Marsden, J. A.; Haley, M. M. Synlett 2004, 165–168.
7544 J. Org. Chem. Vol. 75, No. 22, 2010

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TABLE 2. UV-via Absorption and Emission Maximaa
absorption
emission
compd
λmax
ε
λexc
λem
1
2
3
4
420
490
404
473
18 046
54 511
158 482
144 066
420
490
404
473
513
633
469
624
aAll measurements were recorded in dichloromethane with a sample
concentration of 0.001 mM. Wavelengths are given in nm and molar
extinction coefficients in M-1 cm-1
.
FIGURE 1. Electrochemistry of molecule 1. Top: Cyclic voltam-
metry showing two quasireversible reduction waves. Bottom: Dif-
ferential pulse voltammetry showing three reduction signals.
Measurement conditions: see Table 1.
alkynyl molecules 3 and 4 showed first reduction potentials of
-1.27 and -1.29 V, respectively, around 100 mV less negative
than alkenyl-linked 1 (Figure 1, top), and 2, which showed first
reduction potentials of -1.38 and -1.39 V, respectively.
In CV only two of the three reduction waves for the HAT
moiety46 could be detected for molecules 1 and 2 and only the
first one was observed for 3 and 4. DPV experiments allowed
the detection of the third reduction process for 1 (Figure 1,
bottom). Probably this process was very near or beyond the
solvent window for molecules 2, 3, and 4. DPV studies also
showed that the oxidation process for HATs 1, 2, and 4 consists
of at least two different processes. Only one oxidation signal
was observed for compound 3. In this case again more pro-
cesses could be located outside the solvent window.
FIGURE 2. Top: Absorption (left) and emission spectra (right) of
molecules 1 (solid line: excitation wavelength 420 nm) and 3 (dashed
line: excitation wavelength 404 nm). Bottom: Absorption and
emission spectra of molecules 2 (solid line: excitation wavelength
490 nm) and 4 (dashed line: excitation wavelength 473 nm). Spectra
were recorded in 0.001 mM solutions in dichloromethane.
2.3. Photophysical Studies. Basic photophysical properties
of the four molecules were investigated using absorption
and emission spectroscopy. Absorption spectra showed that
alkynyl-linked HATs 3 and 4 have larger extinction coeffi-
cients (Table 2) than alkenyl-linked HATs 1 and 2 although
the shapes of the spectra are very similar (Figure 2).
If 1 and 3 are compared (Figure 2, top) it can be seen that
the lowest energy absorption of 1 is red-shifted (420 nm) com-
pared with 3 (404 nm). The same behavior can be seen for
dibutylaminobenzene-substituted HATs (Figure 2, bottom).
The lowest energy transition of 2 is bathochromically shifted
(490 nm) compared with 4 (473 nm). When the lowest energy
transition is excited the fluorescence spectra can be collected.
Again emission of alkenyl-linked HATs is red-shifted (513 and
633 nm for 1 and 2, respectively) compared to that of alkynyl-
linked HATs (469 and 624 nm for 3 and 4, respectively). It can
be observed that the 2 and 4 emission maxima differ only by 9
nm but the difference for the emission maxima of 1 and 3 is 44
nm (Figure 2, Table 2).
(46) Jia, C.; Liu, S.-X.; Tanner, C.; Leiggener, C.; Sanguinet, L.;
Levillain, E.; Leutwyler, S.; Hauser, A.; Decurtins, S. Chem. Commun.
2006, 1878–1880.
The nonlinear optical properties of compounds 1-4
were studied with the EFISH technique at 1.907 nm in
J. Org. Chem. Vol. 75, No. 22, 2010 7545

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FIGURE 3. Side view of the B3P86/6-31G*optimized C2 geometry (the optimization was constrained) of compound 3.
TABLE 3. Results of Theoretical Calculations
TD-DFTa
sym.
CPHFb
compd
EHOMO
ELUMO
E01
μ01
Δμ01
βzzz(0)
βzyy(0)
μβ(0)
1
-5.81
-2.73
A
B
B
A
A
B
B
A
B
A
B
A
B
A
B
A
2.71
2.87
3.18
3.40
2.48
2.59
2.80
3.02
2.97
2.97
3.35
3.34
2.64
2.68
2.94
3.04
5.8
7.3
4.6
8.2
5.8
7.2
5.7
8.5
5.5
5.4
2.4
8.3
5.6
4.9
3.4
9.8
11.9
10.3
10.3
11.3
9.6
12.7
12.5
14.4
12.0
10.1
12.0
11.3
15.4
13.9
16.5
17.1
30
26
114
2
3
4
-5.31
-6.12
-5.55
-2.49
-2.78
-2.56
51
39
66
46
16
28
596
201
731
aB3P86/6-31G*, energies are in eV, dipoles in Debye. bHF/6-31G*, hyperpolarizabilities β in 10-30 esu and μβ in 10-48 esu.
dichloromethane. Similar μβ values, around 1000 ꢀ 10-48
esu, were obtained for dibutylamino derivatives 2 and 4
(1010(50) ꢀ 10-48 and 970(50)ꢀ10-48 esu, respectively).
As expected from the relative donor strength of substitu-
ents, much lower response was observed for hexyloxy
benzene derivatives. μβ=200(30)ꢀ10-48 esu was obtained
for compound 3 whereas the nonlinear optical response of
1 was too small to be reliably determined. For the sake of
comparison, Disperse Red 1, a common benchmark of
organic NLO-Chromophores, gives a μβ(0) value of ca.
480 ꢀ 10-48 esu in the same experimental conditions.
2.4. Theoretical Calculations. The molecular geometries of
compounds 1-4 have been optimized constrained to C2
symmetry by using the hybrid B3P86 DFT (density func-
tional theory) method and the 6-31G* basis set. The π sys-
tems in ethylenic compounds 1 and 2 are completely planar,
but this is not the case for acetylenic chromophores 3 and 4
(see Figure 3): The folding angle defined by one of the sub-
stituents, the HAT moiety, and the other substituent is 3.6ꢀ.
Furthermore, the substituted phenyl rings are twisted by 15ꢀ
(3) or 13.4ꢀ (4) with respect to the HAT moiety. On the basis
of structural parameters, a better π delocalization is expected
for ethylenic than for acetylenic compounds.
The properties of compounds 1-4 studied by theoretical
methods are gathered in Table 3. While it is not possible to
match precisely theoretical calculations performed on iso-
lated molecules in the gas phase to experimental measure-
ments performed in solution, the results of the calculations
allow a qualitative description of the observed trends. It can
be seen that the HOMO energy is higher for dialkylamino
compounds than for their analogous alkoxy compounds
by 0.50-0.57 eV thus explaining the less positive oxida-
tion potential of the former. In a similar way the HOMO
and LUMO energies of ethylenic compounds are higher
than that of their acetylenic analogues (compare 1 to 3
and 2 to 4) in good agreement with the lower oxidation and
more negative reduction potential of 1 compared to 3 and
2 compared to 4.
The absorption spectra calculated by TD-DFT (time-
dependent density functional theory) predict the lowest
excitation energies with an error of 0.24 eV for compound
1 and less than 0.1 eV for 2-4, which is a reasonable error
for this method. We have previously mentioned that re-
placement of a double by a triple bond decreases the energy
of both the HOMO and the LUMO; according to our
calculations this effect is more important on the HOMO
and therefore causes an increased HOMO-LUMO gap
that results in a hypsochromic shift. In a similar way,
on passing from hexyloxy to dibutylamino substituent the
HOMO energy increases by 0.50 eV (from 1 to 2) or 0.57 eV
(from3to 4) while the LUMO energy increases by 0.24 and 0.22
eV, respectively, and therefore there is a decreased HOMO-
-LUMO gap and the absorption of dibuthylamino derivatives
is red-shifted with respect to their hexyloxy analogues.
Molecules 1-4 belong to the so-called V-shaped (or
Λ-shaped) chromophores47 displaying C2 symmetry. Making
use of the standard orientation, we assume that the mole-
cule lies on the yz plane with z along the symmetry axis (see
Figure 4). The molecular hyperpolarizability is dominated
by two tensor components: βzzz and βzyy (the off-diagonal
component) and the EFISH technique samples μβ values
contributed from both tensor components:
μβ ¼ μβz ¼ μðβzzz þ βzyy
Þ
A simple model to study the NLO properties describes
C2 chromophores as the combination of two isolated
(47) Wolff, J. J.; Wortmann, R. J. Prakt. Chem. 1998, 340, 99–111.
7546 J. Org. Chem. Vol. 75, No. 22, 2010

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component is found for ethylenic compounds compared to
their acetylenic analogues.
A commonly used48-52 intuitive explanation to the origin
of the nonlinear optical response in V-shaped chromophores
assumes that it mainly arises from transitions from the
ground to excited states (in other words that the contribution
of transitions between excited states to the hyperpolarizabil-
ity is negligible). Making use of a “simplified multistate two-
level treatment”, the contribution of each excited state to the
hyperpolarizability can be calculated as:
2
β0e f μ0e2Δμ0e=ΔE0e
where μ0e is the transition dipole, Δμ0e the dipole moment
difference between ground and excited state, and ΔΕ0e the
excitation energy.
Figure 4 shows the molecular orbitals involved in the
lowest energy transitions of compound 2. Transitions be-
tween orbitals with the same symmetry (HOMO f LUMO
and HOMO-1 f LUMOþ1) have A symmetry, are therefore
polarized along the z axis, and contribute to βzzz. On the
other hand, transitions between orbitals with different sym-
metry (HOMO f LUMOþ1 and HOMO-1 f LUMO) have
B symmetry, are polarized along the y axis, and contribute to
FIGURE 4. A 0.04 contour plot of the molecular orbitals of 2
involved in the four lowest energy electronic transitions.
chromophores in one molecule.48 Using this approach, the
above-mentioned tensor components can be calculated as:
βzzz ¼ 2 cos3 ðR=2Þβ1
βzyy ¼ 2 cos ðR=2Þ sin2 ðR=2Þβ1
β
zyy. The calculated parameters contributing to this multiple
two-state approach are gathered in Table 3. It can be seen
that, for each electronic transition, there is a close-in-energy
transition with a different symmetry but similar μ0e and Δμ0e.
This fact explains the analogous values obtained for the two
tensor components (βzzz and βzyy) in each of the studied
compounds. The enhanced NLO response of amino deriva-
tives 2 and 4 compared to 1 and 3 can be explained on the
basis of the lower ΔE0e calculated for dibutylamino deriva-
tives that is experimentally confirmed by their absorption
spectra.
where β1 is the hyperpolarizability of a single chromo-
phore and R is the angle formed by the two chromophores
in the molecule. It can be concluded that the ratio of the
two tensor components depends on the angle formed by
the two chromophores (βzyy /βzzz=tan2 (R/2)) and there-
fore the two-dimensional character of a given molecule
increases with the angle formed by the two chromophores.
The angle described by the heteroatom substituting the
phenyl ring (O in 1 and 3, N in 2 and 4), the center of the
HAT moiety, and the heteroatom substituting the other
phenyl ring is 71ꢀ in ethylenic compounds 1 and 2 and 49ꢀ in
derivatives 3 and 4. Therefore, on only the basis of the molec-
ular geometries, it is expected that βzyy should be smaller than
βzzz for all the studied compounds and that ethylenic com-
pounds should have a larger two-dimensional character than
their acetylenic analogues.
To get further insight into the nonlinear optical properties
of these compounds the zero frequency molecular hyperpo-
larizability was calculated as the analytical second derivative
of the dipole moment with respect to the electric field using
the Coupled Perturbed Hartree-Fock (CPHF) method.
Experimental μβ values cannot be easily extrapolated to zero
frequency due to the two-dimensional character of these
chromophores that gives rise to several excited states close
in energy. However, a reasonable agreement between theo-
retical and experimental data can be found if we assume that
compound 2 having lower excitation energies than 4 displays
a larger resonance enhancement when measuring the NLO
properties at 1.9 nm and therefore while the μβ(0) value is
somewhat larger for 4, the μβ values measured for these
compounds are similar.
3. Conclusions
In conclusion, we have developed a new series of hexaaza-
triphenylene derivatives as novel V-shaped chromophores
displaying C2 symmetry suitable for nonlinear optical inves-
tigations. By varying the type of linker and the nature of the
donor moiety, the electrochemical properties as well as the
absorption spectra of the well-defined asymmetric do-
nor-acceptor conjugated systems can facilely be tuned. By
using the EFISH technique high μβ values have been
obtained for the systems containing the more electron-rich
dibutylamino moiety. To get further insight on the nonlinear
optical properties of these compounds we have performed
theoretical calculations and found that there is a reasonable
qualitative agreement between experimental and calculated
hyperpolarizabilities. Additionally, the theoretical calcula-
tions support the two-dimensional NLO character of these
chromophores. The versatility of the synthetic routes de-
scribed above paves the way for the functionalization of the
ꢀ
(49) Andreu, R.; Galan, E.; Garı
J.; Alicante, R.; Villacampa, B. J. Org. Chem. 2010, 75, 1684–1692.
(50) Andreu, R.; Carrasquer, L.; Garın, J.; Modrego, M. J.; Orduna, J.;
´
n, J.; Herrero, V.; Lacarra, E.; Orduna,
As expected from molecular geometries, the CPHF-calcu-
lated βzzz is always larger than βzyy and a larger off-diagonal
´
Alicante, R.; Villacampa, B.; Allain, M. Tetrahedron Lett. 2009, 50, 2920–
2924.
(51) Coe, B. J.; Harris, J. A.; Jones, L. A.; Brunschwig, B. S.; Song, K.;
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Swanson, C. A.; Brunschwig, B. S.; Clays, K.; Franz, E.; Garın, J.; Orduna,
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J.; Horton, P. N.; Hursthouse, M. B. J. Am. Chem. Soc. 2010, 132, 1706–
1723.
Clays, K.; Garı
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n, J.; Orduna, J.; Coles, S. J.; Hursthouse, M. B. J. Am. Chem.
Soc. 2005, 127, 4845–4859.
(52) Coe, B. J.; Harris, J. A.; Brunschwig, B. S.; Garın, J.; Orduna, J. J.
´
Am. Chem. Soc. 2005, 127, 3284–3285.
J. Org. Chem. Vol. 75, No. 22, 2010 7547

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Juarez et al.
JOCArticle
HAT moiety with different moieties to further tune their
nonlinear optical response.
CDCl3) δ (ppm) 160.4, 150.9, 146.7, 154.8, 142.6, 141.9, 139.7,
139.3, 129.4, 128.9, 119.5, 114.8, 68.1, 31.6, 29.2, 25.7, 22.6, 14.0.
FTIR (KBr) ν (cm-1) 2929, 2858, 1602, 1509, 1249, 1172, 754.
MS (EI) m/z (%) 638 [M]•þ (100), 553 (25). Elemental Anal.
Calcd: C (75.21), H (6.63), N (13.16). Found: C (75.32), H (6.58),
N (13.18). Mp 237-239 ꢀC.
HAT-Alkene(NBu2)2 (2): A red solid was obtained (29 mg,
25%). 1H NMR (400 MHz, CDCl3) δ (ppm) 9.25 (d, 2H, J = 2.2
Hz), 9.17 (d, 2H, J = 2.2 Hz), 8.24 (d, 2H, J = 15.5 Hz), 7.63
(d, 4H, J = 9.0 Hz), 7.53 (d, 2H, J = 15.5 Hz), 6.67 (d, 4H, J =
9.0 Hz), 3.34 (t, 8H, J = 8.3 Hz), 1.70-1.52 (m, 8H), 1.49-1.22
(m, 8H), 0.98 (t, 12H, J = 7 Hz). 13C NMR (100 MHz, CDCl3)
δ (ppm) 151.6, 149.1, 146.6, 145.4, 142.9, 141.7, 140.2, 138.8,
133.3, 129.7, 123.6, 116.5, 111.4, 50.8, 29.5, 20.3, 13.9. FTIR
(KBr) ν (cm-1) 2958, 2931, 1598, 1522, 1502, 1368, 1183. MS
(EI) m/z (%) 692 [M]•þ (21), 640 (88), 368 (62), 449 (91), 107
(100). Elemental Anal. Calcd: C (76.27), H (7.56), N (16.17).
Found: C (76.18), H (7.63), N (16.23). Mp 184 ꢀC.
General Procedure for the Synthesis of 17 and 18. To a solution
under argon atmosphere of the corresponding iododerivative
(15 or 16) (6.58 mmol) and triisopropylsilylacetylene (6.58 mmol)
in diisopropylamine (20 mL) were added [PdCl2(PPh3)2] (230 mg,
0.33 mmol) and CuI (106 mg, 0.56 mmol). The suspension was
stirred at room temperature for 16 h. After this time 50 mL of
hexane was added and the reaction was filtered over a plug of
silica with dichloromethane as eluent. The solvent was then
removed and the residue purified by column chromatography
(silica gel, hexane).
((4-(Hexyloxy)phenyl)ethynyl)triisopropylsilane (17): The prod-
uct was obtained as a colorless oil (1.975 g, 84%). 1H NMR (400
MHz, CDCl3) δ (ppm) 7.40 (d, 2H, J = 9.1 Hz), 6.80 (d, 2H, J=
9.1 Hz), 3.94 (t, 2H, J=6.6 Hz), 1.77 (quint, 2H, J=6.6 Hz), 1.45
(m, 2H), 1.33 (m, 4H), 1.12 (s, 18H), 1.09 (s, 3H), 0.9 (t, 3H, J=
7.0 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm) 159.1, 133.4,
115.4, 114.2, 107.16, 88.4, 68.0, 31.5, 29.1, 25.6, 18.7, 14.0, 11.3.
FTIR (CH2Cl2) ν (cm-1) 2938, 2864, 2153, 1605, 1506, 1246, 882,
831, 782. MS(ESI)m/z 381.3 [M þ Na]•þ. ElementalAnal. Calcd:
C (77.03), H (10.68). Found: C (76.99), H (10.75).
4. Experimental Section
2,3-Bis(bromomethyl)hexaazatriphenylene (11). To a stirred
suspension of diamine (9) (673 mg, 3.17 mmol) in absolute
ethanol (70 mL) at 0 ꢀC under argon atmosphere was added
1,4-dibromobutanedione (10) (1.161 g, 4.76 mmol). The suspen-
sion was stirred for 5 h at that temperature, then the solvent was
removed under vacuum. The crude product was purified by
column chromatography (CH2Cl2 until unchanged butanedione
was eluted then CH2Cl2 with 2% MeOH). A pale-yellow solid
were isolated (1.265 g, 95%). 1H NMR (200 MHz, CDCl3)
δ (ppm) 9.33 (d, 2H, J = 2.0 Hz), 2.29 (d, 2H, J = 2.0 Hz), 5.18
(s, 4H). 13C NMR (50 MHz, CDCl3) δ (ppm) 154.1, 147.2, 147.1,
142.5, 141.7, 140.8, 29.6. FTIR (KBr) ν (cm-1) 3030, 2970, 2923,
1631, 1380, 1092. MS (EI) m/z (%) 418 [M]•þ (3), 262 (100), 221
(64). Elemental Anal. Calcd: C (40.03), H (1.92), N (20.01).
Found: C (40.19), H (2.05), N (19.87). Mp >170 ꢀC dec.
2,3-Bis((dimethylphosphonate)methyl)hexaazatriphenylene (12).
A suspension of 11 (161 mg, 0.38 mmol) in trimethylphosphite
(15 mL) under Argon atmosphere was heated to reflux for 3 h.
After this time an excess of solvent was distilled and the residue was
purified by column chromatography (CH2Cl2: MeOH 9:1). The
1
product was obtained as a pale-brown solid (102 mg, 56%). H
NMR (400 MHz, CDCl3) δ (ppm) 9.28 (d, 2H, J = 2.0 Hz), 9.25
(d, 2H, J = 2.0 Hz), 4.30 (d, 4H, J = 22.0 Hz), 3.80 (d, 12H, J =
11.0 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm) 151.5, 146.9,
146.6, 142.2, 142.0, 140.1, 53.2, 34.2 (d, CH2-P, J = 132.0). FTIR
(KBr) ν (cm-1) 2958, 1635, 1542, 1239, 1030. MS (EI) m/z (%) 478
[M]•þ (100), 384 (30), 275 (33), 94 (36). Elemental Anal. Calcd: C
(45.20), H (4.21), N (17.57). Found: C (45.02), H (3.98), N (17.65).
Mp >220 ꢀC dec.
4-Hexyloxybenzaldehyde (13). In a round-bottomed flask
p-hydroxybenzaldehyde (2 g, 16 mmol), hexyl bromide (3.46 g,
21 mmol), and K2CO3 (2.94 g, 21 mmol) were dissolved in DMF
(50 mL). The solution was heated to reflux for 16 h and then
allowed to cool to room temperature. The reaction was poured
into water and extracted with dichloromethane. The organic
phase was dried over MgSO4 and filtered and the solvent was
removed in vacuo. The oil obtained was purified by column
chromatography (silica gel), using a mixture of hexane:ethyl
acetate (7: 3) as eluent, to yield 2.877 g of product as a pale
N,N-Dibutyl-4-((triisopropylsilyl)ethynyl)aniline (18): The
product was obtained as a light yellow oil (2.32 g, quantitative).
1H NMR (400 MHz, CDCl3) δ (ppm)=7.31 (d, 2H, J=9.0 Hz),
6.52 (d, 2H, J=9.0 Hz), 3.26 (t, 4H, J=7.6 Hz), 1.54 (quint, 4H,
J=7.6 Hz), 1.33 (sext, 4H, J=7.7 Hz), 1.16 - 1.06 (m, 21H),
0.94 (t, 6H, J=7.3 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm)
147.9, 133.3, 111.1, 109.3, 108.7, 86.8, 50.7, 29.4, 20.3, 18.7,
13.9, 11.5. FTIR (CH2Cl2) ν (cm-1) 2939, 2863, 2144, 1605,
1
yellow oil (87%). H NMR (400 MHz, CDCl3) δ (ppm) 9.87
(s. 1H), 7.82 (d, 2H, J = 8.4 Hz), 6.99 (d, 2H, J = 8.4 Hz), 4.04
(t, 2H, J = 6.5 Hz), 1.81 (m, 2H), 1.47 (m, 2H), 1.34 (m, 4H),
0.91 (t, 3H, J = 6.9 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm)
190.8, 164.2, 131.9, 129.7, 114.7, 68.4, 31.5, 29.0, 25.6, 22.6, 14.0.
FTIR (CH2Cl2) ν (cm-1) 2931, 2863, 2733, 1691, 1601, 1509,
1514, 1461, 1366, 1184. MS (ESI) m/z 408.3 [M þ Na]•þ
.
Elemental Anal. Calcd: C (77.85), H (11.24), N (3.63). Found:
C (78.02), H (11.11), N (3.51).
General Procedure for the Synthesis of 21 and 2253. Under
argon atmosphere the corresponding unprotected alkyne (19 or
20) (3.96 mmol) was dissolved in anhydrous THF (15 mL) at
0 ꢀC. To this solution was added butyllithium (3.96 mmol, 1.6 M
in hexanes) slowly and the resulting solution was stirred for
30 min. Meanwhile a second solution was prepared dissolving LiBr
(688 mg, 7.92 mmol) and CuBr (568 mg, 3.96 mmol) under argon
atmosphere in anhydrous THF (50 mL) at 0 ꢀC. The first solution
was slowly added to the second and then the resulting mixture was
stirred. After 10 min oxalyl chloride (226 mg, 1.78 mmol) was added
slowly. The mixture was stirred at 0 ꢀC for 1 h and then allowed to
warm to room temperature. The solution was then poured into a
saturated solution of NH4Cl. The organic phase was separated and
the aqueous phase extracted with two portions of ether. The organic
extracts were dried with MgSO4 and filtered and the solvent was
removed.
1310, 1256, 1159, 1015, 832. MS (ESI) m/z 229.0 [M þ Na]•þ
.
Elemental Anal. Calcd: C (75.69), H (8.80). Found: C (75.75),
H (8.63).
General Procedure for the Synthesis of 1 and 2. A suspension of
phosphonate (12) (80 mg, 0.17 mmol) and the corresponding
aldehyde (13 or 14) (0.37 mmol) in dry THF (10 mL) under argon
atmosphere was heated to reflux, then potassium tert-butoxide
(56 mg, 0.50 mmol) was added. The solution was refluxed for 3 h
and then allowed to cool to room temperature and methanol
(5 mL) was added. After the solvent was removed the residue was
purified by column chromatography (CH2Cl2 until elution of
unchanged aldehyde and then CH2Cl2 with 2% MeOH).
HAT-Alkene(OHex)2 (1): A yellow-orange solid was isolated
(64 mg, 60%). 1H NMR (400 MHz, CDCl3) δ (ppm) 9.22 (d, 2H,
J = 2.1 Hz), 9.21 (d, 2H, J = 2.1 Hz), 8.23 (d, 2H, J = 15.2 Hz),
7.67 (d, 4H, J = 9.0 Hz), 7.59 (d, 2H, J = 15.2 Hz), 6.95 (d, 4H,
J=9.0 Hz), 4.01 (t, 4H, J=7.3 Hz), 1.90-1.70 (m, 4H), 1.57-
1.2 (m, 12H), 0.92 (t, 6H, J = 7.0 Hz). 13C NMR (100 MHz,
(53) Faust, R.; Weber, C.; Fiandanese, V.; Marchese, G.; Punzi, A.
Tetrahedron 1997, 53, 14655–14670.
7548 J. Org. Chem. Vol. 75, No. 22, 2010

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Juarez et al.
JOCArticle
1,6-Bis(4-(hexyloxy)phenyl)hexa-1,5-diyne-3,4-dione (21):
The solid obtained was purified by column chromatography
(silica gel), using a mixture of hexane:dichloromethane (6.5:3.5).
The product was isolated as a yellow solid (53%). 1H NMR (400
MHz, CDCl3) δ (ppm) 7.64 (d, 4H, J = 8.8 Hz), 6.91 (d, 4H, J =
8.8 Hz), 4.00 (t, 4H, J = 6.5 Hz), 1.79 (q, 4H, J = 6.7 Hz),
HAT-Alkyne(OHex)2 (3): The product was isolated as a yellow
solid (63%). 1H NMR (400 MHz, CDCl3) δ (ppm) 9.18 (m, 4H),
7.57 (d, 4H, J = 8.3 Hz), 6.84 (d, 4H, J = 8.3 Hz), 3.93 (t, 4H, J =
6.5 Hz), 1.73 (m, 4H), 1.39 (m, 4H), 1.28 (m, 8H), 0.84 (t, 6H, J =
6.7 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm) 160.6, 146.5, 143.5,
141.7, 138.9, 134.1, 128.2, 114.7, 113.1, 99.7, 86.5, 68.1, 31.4, 29.0,
25.6, 22.5, 13.9. FTIR (KBr) ν (cm-1) 3047, 2929, 2862, 2206, 1602,
1.46 (m, 4H), 1.38-1.29 (m, 8H), 0.90 (t, 6H, J = 5.0 Hz). 13
C
NMR (100 MHz, CDCl3) δ (ppm) 172.7, 162.2, 136.2, 115.0,
110.6, 101.8, 86.9, 68.3, 31.5, 29.0, 25.6, 22.6, 14.0. FTIR
(CH2Cl2) ν (cm-1) 2933, 2863, 2187, 1661, 1600, 1509, 1255,
1174, 999, 835. MS (ESI) m/z 481.3 [M þ Na]•þ. Elemental Anal.
Calcd: C (78.57), H (7.47). Found: C (78.39), H (7.55). Mp
103-105 ꢀC
1511, 1244, 1126, 831. MS (MALDI/TOF) m/z 635.2 [M þ H]•þ
.
Elemental Anal. Calcd: C (75.69), H (6.03), N (13.24). Found: C
(75.83), H (5.85), N (13.25). Mp 210 ꢀC.
HAT-Alkyne(NBu2)2 (4): The product was isolated as a red
solid (36%). 1H NMR (400 MHz, CDCl3) δ (ppm) 9.22 (m, 4H),
7.56 (d, 4H, J = 8.3 Hz), 6.59 (d, 4H, J = 8.3 Hz), 3.30 (t, 8H,
J = 7.5 Hz), 1.59 (m, 8H), 1.37 (m, 8H), 0.96 (t, 12H, J=7.2
Hz). 13C NMR (100 MHz, CDCl3) δ (ppm) 149.1, 146.8, 146.1,
143.8, 141.8, 138.3, 134.3, 111.0, 106.6, 102.4, 87.2, 50.6, 29.2,
20.2, 13.9. FTIR (KBr) ν (cm-1) 2956, 2927, 2865, 2186, 1603,
1523, 1368, 1182, 812. MS (MALDI/TOF) m/z 689.3 [M þ H]•þ
Elemental Anal. Calcd: C (76.71), H (7.02), N (16.27). Found:
C (76.82), H (7.09), N(16.42). Mp 240-242 ꢀC.
1,6-Bis(4-(dibutylamino)phenyl)hexa-1,5-diyne-3,4-dione (22):
The solid obtained was purified by column chromatography
(Et3N deactivated silica gel, light exclusion) with a mixture of
hexane:dichloromethane (5:5). The product was isolated as a red
solid (16%). 1H NMR (400 MHz, CDCl3) δ (ppm) 7.54 (d, 4H,
J = 9.1 Hz), 6.58 (d, 4H, J = 9.1 Hz), 3.32 (t, 8H, J = 7.6 Hz),
1.59 (quint, 8H, J = 7.7 Hz), 1.36 (sext, 8H, J = 7.6 Hz), 0.97
(t, 12H, J = 7.3 Hz). 13C NMR (100 MHz, CDCl3) δ (ppm)
173.0, 150.6, 136.4, 111.3, 105.4, 103.9, 89.5, 50.7, 29.3, 20.2,
13.9. FTIR (CH2Cl2) ν (cm-1) 2957, 2867, 2159, 1645, 1589,
ꢀ
Acknowledgment. We thank Comunidad Autonoma de
Madrid (project S2009/MAT-1467), Gobierno de Aragon-
ꢀ
1522, 1365, 1189, 983. MS (MALDI/TOF) m/z 513.2 [M þ H]•þ
.
Fondo Social Europeo (Project E39), the UCM-BSCH joint
project (GR58/08), and the MCyT of Spain (CTQ2007-
60459, CTQ2008-02942, CTQ2010-14982, MAT2008-06522-
C02-02) for financial support. R.J. and R.A. are indebted
to the “Universidad Rey Juan Carlos” and the Spanish
Government (FPI program, No. BES2006-12104), respec-
tively, for predoctoral fellowships.
Elemental Anal. Calcd: C (79.65), H (8.65), N (5.46). Found:
C (79.48), H (8.64), N (5.59). Mp 104-106 ꢀC
General Procedure for the Synthesis of 3 and 4. A solution of
diamine (9) (0.47 mmol) and the corresponding diketone (21 or
22) (0.56 mmol) in chloroform (10 mL), ethanol (10 mL), and
acetic acid (1 mL) was heated to reflux for 2 h. After this time the
solution was allowed to cool to room temperature. The reaction
was treated with a saturated solution of NaHCO3 and brine. The
organic phase was dried over MgSO4 and filtered and the
solvent was removed under vacuum. The residue was purified
Supporting Information Available: Experimental and
theoretical details and 1H NMR and 13C NMR spectra. This
material is available free of charge via the Internet at http://
pubs.acs.org.
´
by column chromatography (sılica gel) with dichloromethane
(2% methanol) as solvent.
J. Org. Chem. Vol. 75, No. 22, 2010 7549