Donor-substituted triaryl-1,3,5-triazinanes-2,4,6-triones: Octupolar NLO-phores with a remarkable transparency-nonlinearity trade-off

Article abstract of DOI:10.1039/c1nj20442d

We report in this letter the measurement of the hyperpolarizabilities of a series of donor-substituted triaryl-1,3,5-triazinanes-2,4,6-triones by hyper Rayleigh scattering (HRS). A remarkable transparency-nonlinearity trade-off is evidenced for these octu

Full text of DOI:10.1039/c1nj20442d

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LETTER
Donor-substituted triaryl-1,3,5-triazinanes-2,4,6-triones: octupolar
NLO-phores with a remarkable transparency–nonlinearity trade-offw
Gilles Argouarch,a Romain Veillard,a Thierry Roisnel,a Anissa Amar,a
´ ´
Abdou Boucekkine, Anu Singh, Isabelle Ledoux* and Frederic Paul*
a
b
b
a
Received (in Montpellier, France) 25th May 2011, Accepted 12th July 2011
DOI: 10.1039/c1nj20442d
We report in this letter the measurement of the hyperpolariz-
abilities of a series of donor-substituted triaryl-1,3,5-triazinanes-
2,4,6-triones by hyper Rayleigh scattering (HRS). A remarkable
transparency–nonlinearity trade-off is evidenced for these octu-
polar NLO-phores which might be accessed in a straightforward
synthetic way and in a few steps from commercial isocyanates.
Considering their structural similarity with more widely
studied octupoles such as triazines (B) or 1,3,5-triaryl-
phenylene-based molecules (C),13 we expected that these
molecules could exhibit sizable hyperpolarizabilities, especially
if their electron-deficient core could be substituted with
electron-releasing arms. We therefore decided to synthesize
and investigate the NLO properties of derivatives such as 1–X
and 2–X or 3 by hyper Raleigh scattering (HRS) (Scheme 2).
The shorter representatives 1–X (X = OMe, NMe2, Br)
were accessed in a single step directly from the commercial
isocyanates, while the longer ones were obtained in one
additional step from 1–Br and the corresponding alkynes
using a simple Sonogashira coupling protocol (Scheme 3).14
These derivatives were characterized by mass spectrometry
and usual spectroscopies. The crystal structure of the terminal
triyne derivative 4 (R = H) could also be solved (Fig. 1). This
compound was isolated after de-silylation of its silylated
precursor 40 (R = SiMe3), which was itself obtained similarly
to 2–X or 3 using ethynyltrimethylsilane. This crystal structure
confirmed the octupolar symmetry of this new family of alkynyl-
functionalized cyclotrimers and provided useful geometrical data
for theoretical modelling of these compounds by DFT.
Since the 1980’s, molecules with nonlinear optical (NLO)
properties have attracted increasing interest in the telecommuni-
cations and signal processing domains. This interest is mostly
driven by the very promising applications expected from
materials made of such units, such as ultradense optical data
storage or ultrafast information processing.1
Among these, octupolar chromophores have attracted a
particular attention subsequent to the seminal work of Zyss
and coworkers.2–4 Indeed, the lack of permanent dipole
moment of octupolar structures, usually associated with an
improved hyperpolarizability and with a good transparency,
constitutes a strong advantage over more classic dipolar
structures for many applications.5
However, while systematic investigations regarding the
second-order NLO properties of various kinds of molecules
of D3 or D3h symmetry have been conducted,6–11 triazinane-
2,4,6-triones (Scheme 1; A), more commonly known as iso-
cyanurates, have only attracted a limited attention up to now.12
The UV-vis absorption spectra of these compounds were
recorded in dichloromethane (Table 1). In line with their
colorless nature, 1–X and 2–X present a broad transparency
range in the near-UV/visible region, their absorption at lowest
energy lying below 300 nm for the shorter derivatives 1–X.
Scheme 1
a
´
Sciences Chimiques de Rennes, UMR CNRS 6226, Universite de
Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France.
E-mail: frederic.paul@univ-rennes1.fr
b Laboratoire de Photonique Quantique et Mole´culaire,
´
UMR CNRS 8537, ENS Cachan, 61 Avenue du President Wilson,
F-94235 Cachan Cedex, France
w Electronic supplementary information (ESI) available: Details on
the procedure used for the NLO measurements. CCDC reference
number 826557 (4). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1nj20442d
Scheme 2
c
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Fig. 2 Contour surfaces of HOMO (a) and degenerated LUMO,
LUMO + 1 (b–c) of the cyclotrimer 1–NMe2.
bathochromic shift is observed for 3 which appears slightly
coloured in solution, due to a low intensity absorption
extending towards the visible range.
Scheme 3
DFT calculations reveal that the observed absorptions can
be attributed to symmetry allowed transitions corresponding
to a charge shift from peripheral arms towards the central
isocyanurate ring (Fig. 2). These transitions were computed at
220 nm for 1–OMe, 250 nm for 1–NMe2, 333 nm for 2–OMe,
375 nm for 2–NMe2 and 404 nm for 2–NPh2 in CH2Cl2,
respectively, i.e. in fair agreement with the experiment.
The hyperpolarizabilities of these compounds were subse-
quently measured in dichloromethane or chloroform using
HRS with an incident laser beam at 1907 nm or 1067 nm
(Table 1). The corresponding static hyperpolarizability values
b
HRS(0) were also derived.4,16,17 Among the organic com-
Fig. 1 ORTEP of 4 (50% probability level, one molecule of the
asymmetric unit). Hydrogen atoms have been omitted for clarity.
Selected bond lengths (A) and angles (1): C1–C2: 1.203(6); C2–C3:
1.450(6); C8–N9: 1.460(5); N9–C10: 1.398(3); C10–O10: 1.206(5);
N9–C10–O10: 122.0(3); C10–N9–C100: 123.8(4); N9–C10–N90: 115.9(4).
pounds 1–X and 2–X, increasing the donating strength of
the substituents or the length of the bridge results in an
enhancement of bHRS, which is partly attributable to disper-
sion factors, according to the corresponding bHRS(0) values.
The electronic effect of the X substituent on bHRS(0) values
appears predominant over the bridge elongation. Notably, a
sizable improvement is stated for 3 over 1–OMe, albeit a
smaller electron-releasing power is attributed to the CRC–Fc
substituent when compared to a methoxy group, based on
electronic substituent parameters.18 This suggests that the
more ‘‘polarizable’’ nature of this organometallic substituent
is also beneficial to the second-order NLO activity.
Table 1 Molecular hyperpolarizabilities and related data experimen-
tally derived for these octupolar compounds in CH2Cl2 (1.907 mm) or
in CHCl3 (1.067 mm)
a
b
c
Compound
lmax
emax
bHRS
b
HRS(0)c,d
1–OMe
1–NMe2
2–OMe
2–NMe2
2–NPh2
3
228
270
316
352
362
342
60.5
58.2
104.4
109.6
99.0
19e
55
15e
50
32e
66
19e
55
Comparison with bHRS values reported for related
octupoles13 indicates that the values obtained for the derivatives
1–X (X = OMe, NMe2) and 2–X (X = OMe, NMe2, NPh2)
are far from being negligible. First, as expected, these deriva-
tives present a much better hyperpolarizability than the
few previously examined isocyanurate derivatives featuring
electron-poorer arms and for which no conjugation was
effective with the central core.12 Then, in terms of NLO-
activity, the shorter derivatives (1–X) compare with those
reported for donor-substituted triaryl triazines (B; R = Ar;
Scheme 1),10,19 while the longer ones (2–X; X = OMe, NMe2,
NPh2) compare with those of triphenylaryl-based chromo-
phores of same size and close constitution.9 However, in both
cases, the low-energy absorption (lmax) of 1–X and 2–X is
78
49e
64
26e
11.4
a
b
c
In nm. In 103 Mꢀ1 cmꢀ1
.
In 10ꢀ30 esu (correlation between SI
units: b(SI) = 4.172 ꢁ 10ꢀ10 b(esu)). The precision of the measure-
ments is about ꢂ15%. The reported b values are given in the bX
convention as defined by Willetts et al.15 d Calculated from UV data
using the dispersion factor corresponding to a degenerate three level
model with l0=1.06 mm.4 e Measurement performed in chloroform.
As expected, this absorption is bathochromically shifted
when the para-substituents become electron-releasing and
when the unsaturated arm is extended, i.e. when progressing
from 1–X to 2–X. Among the shorter derivatives, a further
c
2410 New J. Chem., 2011, 35, 2409–2411
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blue-shifted by at least 30 nm. Actually, in terms of transparency–
activity trade-off, the shorter octupoles 1–X present performances
comparable to boroxine-based derivatives, also previously studied
by one of us.20–22
methods using the SIR97 program,24 and then refined with
full-matrix least-square methods based on F2 (SHELX-97)25
with the aid of the WINGX26 program. All non-hydrogen
atoms were refined with anisotropic thermal parameters.
H atoms were finally included in their calculated positions.
A final refinement on F2 with 1002 unique intensities and 100
parameters converged at wR(F2) = 0.1716 (R(F) = 0.0693)
for 967 observed reflections with I 4 2s(I). Crystal data:
C27H15N3O3, M = 429.42, trigonal, space group R3c,
a = 13.5264(13) A, b = 13.526 A, c = 24.608(2) A,
a = 901, b = 901, g = 1201, U = 3899.2(5) A3, Z = 6,
T = 100(2) K, Dc = 1.097 g cmꢀ3, 7587 reflections measured,
1002 unique (Rint = 0.0576) which were used in calculations.
The final wR(F2) was 0.1732 (all data). CCDC 826557.
In conclusion, the organic derivatives 1–X and 2–X, straight-
forwardly accessible from commercial reactants, present a remark-
able efficiency–transparency trade-off when compared to most
octupolar derivatives studied so far. For instance, most of them
display bDFT(0) values significantly larger than the prototypical
TIATB,20,23 while remaining blue-shifted by nearly 100 nm, at
least for the shorter derivatives 1–X. In addition, this study reveals
that a change of the terminal electron-releasing group apparently
produces a stronger effect than extending the conjugation path
with the isocyanurate core. In this connection, replacement of the
alkynylferrocenyl donor groups in 3 by more electron-releasing
organometallics might provide a simple means to increase further
the hyperpolarizability of these compounds, while maintaining a
fair transparency. Work along these lines is in progress.
Acknowledgements
CNRS is acknowledged for specific financial supports.
Notes and references
Experimental
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1,3,5-Tris(4-ethynylphenyl)-1,3,5-triazinane-2,4,6 trione (4)
In an oven-dried Schlenk tube, to a mixture of 1–Br14 (2 g;
3.37 mmol), CuI (0.128 g; 0.67 mmol, 20 mol%), PdCl2(PPh3)2
(0.236 g; 0.34 mmol, 10 mol%) in a DMF–Et3N (5 : 1) mixture
(60 mL) was added an excess of trimethylsilylacetylene
(2.90 mL, 20.20 mmol). After 2 days of stirring at 70 1C and
cooling to room temperature, the solvents were removed by
cryoscopic transfer. The reaction mixture was extracted with
CH2Cl2, washed with water and dried over MgSO4. After
filtration and evaporation to dryness, the crude product was
purified by column chromatography on silica gel (hexane/
Et2O, 1 : 1), providing 40 as a pale solid (1.37 g; 2.12 mmol;
63%). A solution of this compound (40; 820 mg, 1.27 mmol)
and TBAF (0.38 mL, 1 M solution in THF, 0.38 mmol) in
THF (30 mL) was shielded from light and stirred overnight
at room temperature. After evacuation of the solvent, the
reaction mixture was extracted with CH2Cl2, washed with
water and dried over MgSO4. After filtration and evaporation
to dryness, the crude product was purified by column chromato-
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c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 2409–2411 2411