Diphenylamino-substituted tristyryl: Vs. triphenyl isocyanurates: Improved conjugation has minimal impact on two-photon absorption

Article abstract of DOI:10.1039/c8nj01904e

This contribution reports the synthesis of C₈₇H₆₀N₆O₃ (3-NPh₂), the tristyryl analogue of the triphenylisocyanurate C₈₁H₅₄N₆O₃ (2-NPh₂) which was previously demonstrated to be an active two-photon absorber. Contrary to expectation, planarization and extension of the central π-system does not lead to a marked improvement of the two-photon absorption cross-section.

Full text of DOI:10.1039/c8nj01904e

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Diphenylamino-substituted tristyryl vs. triphenyl
isocyanurates: improved conjugation has minimal
impact on two-photon absorption†
Cite this:DOI: 10.1039/c8nj01904e
Received 19th April 2018,
Accepted 14th June 2018
ab
ab
a
c
Amedee Triadon, Alphonsine Ngo Ndimba, Nicolas Richy, Anissa Amar,
´ ´
a
a
b
b
Abdou Boucekkine,
Mireille Blanchard-Desce, Olivier Mongin * and Frederic Paul*
Thierry Roisnel, Marie P. Cifuentes, Mark G. Humphrey,
*
DOI: 10.1039/c8nj01904e
d
a
a
´
´
rsc.li/njc
This contribution reports the synthesis of C87
H
60
N O
6 3
2
(3-NPh ), the
tristyryl analogue of the triphenylisocyanurate C81
H N O
54 6 3
(2-NPh )
2
which was previously demonstrated to be an active two-photon
absorber. Contrary to expectation, planarization and extension of
the central p-system does not lead to a marked improvement of the
two-photon absorption cross-section.
1
,2
Since the seminal work of Cho, planar octupolar molecules
have attracted sustained interest for their two-photon absorption
properties; this is because of the increasing attention given to
this third-order nonlinear optical (NLO) property for applications
Scheme 1 Known (1-X and 2-X; X = NH
3-NPh
for selected 2-X compounds in G o¨ ppert-Mayer (GM) units.
2
, NMe
2 2
, NPh ) and targeted
(
2
, 4-X; X = Br) molecular structures. 2PA cross-sections are given
2
–5
in diverse fields ranging from microfabrication to bioimaging.
In this respect, we recently identified extended triazinane-2,4,6- could be improved by inserting 1,2-ethylene groups between the
triones such as 2-X (Scheme 1), more commonly known as central isocyanurate core and the appended phenyl rings in the
6
,7
isocyanurates,
molecules of this size when functionalized by peripheral donor should planarize and slightly extend the p-manifold on each arm
as exhibiting large hyperpolarizabilities for most active derivative 2-NPh
2
. Such a chemical modification
8
,9
groups (X = NH , NMe , NPh ).
2
at the same time. To this aim, we targeted the derivative 3-NPh ,
2
2
2
9
As previously pointed out, because of steric interactions using a synthetic approach requiring the preliminary isolation
between the oxygen atoms of the central ring and the ortho of 4-Br. This molecule accessed following a workup inspired
hydrogens of the peripheral phenyl groups of the molecule, the from that used by Mormann et al. to isolate its analogue 4-H in a
latter adopt a twisted conformation which results in a partial completely different context.
disruption of the p-manifold connecting the terminal electron-
Access to 4-Br was achieved in one step by cyclotrimerization
1
2
releasing groups to the central electron-deficient core. Given of the corresponding styryl isocyanate 5-Br, itself generated
that the NLO properties are often strongly correlated with the from its acryloyl azide precursor 6-Br using a Curtius reaction
spatial extension and good overlap of the conjugated p-manifold (Scheme 2) and engaged without purification in the cyclo-
1
0,11
between donor and acceptor groups,
we logically wondered trimerization step. The acryloyl azide precursor 6-Br was isolated in
if the two-photon absorption (2PA) performance of such molecules good yields (93%), in two steps, from commercial 4-bromocinammic
acid and characterized by NMR.
a
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes), UMR 6226,
F-35000 Rennes, France. E-mail: olivier.mongin@univ-rennes1.fr,
frederic.paul@univ-rennes1.fr
b
Research School of Chemistry, Australian National University, Canberra,
ACT 2601, Australia. E-mail: Mark.Humphrey@anu.edu.au
c
D ´e partement de Chimie, Facult ´e des Sciences, Universit ´e Mouloud Mammeri,
1
5000 Tizi-Ouzou and Facult ´e de chimie, USTHB, Alger, Algeria
d
Univ. Bordeaux, ISM (CNRS-UMR 5255), 33405 Talence, France
†
Electronic supplementary information (ESI) available. CCDC 1511480. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c8nj01904e
Scheme 2 Synthesis of 4-Br.
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Fig. 2 Absorption and normalized emission spectra of 2-NPh
-NPh (green) in CH Cl (20 1C).
2
(black) and
3
2
2
2
Fig. 1 ORTEP representation of 4-Br at the 50% probability level with
selected bond lengths indicated. Hydrogen atoms have been omitted for
clarity.
dipole moment. The relative weakness of this stabilization means
that several rotamers are likely to co-exist in solution, while no
p-stacking could be evidenced experimentally by absorption
spectroscopy (ESI†).
The new compound 4-Br was characterized by the usual
techniques and by X-ray diffraction,‡ providing definitive structural
evidence for this intermediate (Fig. 1). In line with this solid-state
The UV-visible absorption and emission spectra of 4-Br and
3
-NPh
corresponding analogues without a double bond in each arm
i.e. 1-Br and 2-NPh ), their first electronic transitions take
2
were subsequently recorded. When compared to their
1
structure, the H NMR spectrum reveals the presence of only one
isomer in solution with the classic AB pattern of trans-substituted
(
2
3
double bonds in an E configuration ( JHH = 14.8 Hz). A striking
place at slightly lower energies, in line with the extension and
difference with the triaryl isocyanurate derivatives previously
crystallized is the overall coplanarity between the peripheral
double bonds and the central heterocycle. One branch of the
three presents a dihedral angle of ca. 451, whereas the two
others are nearly coplanar with dihedral angles of ca. 51 and 101.
This enforced coplanarity is certainly driven by the weak intra-
molecular hydrogen bonding existing between the carbonyl
groups and the a- and b-hydrogen atoms on the trans-alkenyl
spacers (and resulting in intramolecular OÁÁÁH distances o2.50 Å).
improved conjugation of their p-manifold. For instance, a
À1
10 nm (ca. 735 cm ) red-shift is seen for the first absorption
of 3-NPh relative to that of 2-NPh (Fig. 2). While 4-Br, similar
2
2
to 1-Br (F
-NPh possesses a fluorescence quantum yield (F
lower than that of 2-NPh
emission (31 nm, ca. 1515 cm ) that is attributable to the
extension/planarization of the p-manifold in the former.
F
= 0.0006), is nearly non-emissive in solution (F
F
= 0.0005),
3
2
F
= 0.61) slightly
2
(F
F
= 0.73), with again a red shift in
À1
9
Similar to what had been previously established for 2-NPh2,
2
The extended derivative 3-NPh was then obtained in modest
DFT calculations confirm that the first electronic transition in
yield (18%) from 4-Br by a Sonogashira coupling (Scheme 3), and
was also fully characterized by the usual means. The presence of
additional 1,4-phenylene-ethynylene units in the arms is clearly
3
-NPh corresponds to a LUMO/LUMO+1 ’ HOMO/HOMOÀ1
2
(
p–p*) transition, implying some charge-transfer (CT) from the
electron-rich periphery toward the central isocyanurate core
Fig. 3). According to DFT (see ESI†), this charge-transfer on the
central ring is however less pronounced than in the shorter
derivative 4-NPh . The shift to lower energy and the increase in
1
13
established by H and C NMR spectroscopy, and also by IR
(
À1
spectroscopy (nCRC at 2205 cm ).
The enforced planarity of these two new tristyryl derivatives
relative to their known triaryl analogues is confirmed by the
2
transition moment when progressing from 2-NPh to 3-NPh2
2
DFT optimizations of these compounds. In CH
symmetric C3h structure is often slightly less stable than one
with a tilted arm (C symmetry), whereas they have nearly the
2 2
Cl , a fully
are qualitatively confirmed by TD-DFT simulations (ESI†).
We then determined the two-photon absorption (2PA) of 3-NPh2
in the near-infrared (NIR) range (700–1000 nm) by investigating its
two-photon excited fluorescence (TPEF) behavior. Contrary to
s
same energy in vacuum. This can be explained by the fact that
the dipole moment of the fully symmetric (C ) structure is close
3
10
our expectations based on previous examples, it possesses a
to zero, so the compound is not stabilized at all by the surrounding
dielectric, in contrast to the C structure which presents a non-zero
s
maximum 2PA cross-section of similar magnitude (ca. 410 GM),
2
Fig. 3 Plots of the frontier molecular orbitals for 3-NPh primarily involved
in the main excitation underlying the first allowed transition. Contour values
À3 1/2
Scheme 3 Synthesis of 3-NPh
2
.
are Æ0.03 (e Bohr
)
.
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evaporated under reduced pressure to yield the crude isocyanate
(5-Br). The latter was then solubilized in nitrobenzene (8.50 mL)
and 2 mol% of cesium fluoride (33 mg, 0.21 mmol) was added.
The reaction mixture was stirred 48 h at room temperature giving
in some cases a pale precipitate. A mixture of diethyl ether/hexane
(
1/1) was then added and the crude solid that formed was collected
by filtration on a sintered glass filter funnel, before being purified
by flash chromatography on silica gel (CH Cl /heptane = 1 : 1, v/v).
Yield: 3.10 g (81%). HRMS (EI): m/z = 669.8971 [M + H] (calc. for
: 669.8971). IR (neat): n = 1760 (CQO, vw), 1704
CQO, s), 1655 (CQC, w). Raman (neat): n = 1764 (CQO, m),
2
2
+
Fig. 4 Two-photon absorption spectra of 2-NPh
methane (20 1C) in the near-IR range.
2 2
and 3-NPh in dichloro-
27 3 3 3
C H19Br N O
(
1
1
705 (CQO, vw), 1649 (CQC, vs). H NMR (300 MHz, DMSO-d )
6
but slightly bathochromically-shifted and broadened compared d = 7.59 (d, J = 8.7 Hz, 6H), 7.51 (d, J = 8.7 Hz, 6H), 7.15 (s, 6H,
1
3
to that of its non-styryl analogue 2-NPh (Fig. 4). The comparison CQCH). C NMR (75 MHz, DMSO-d
6
) d = 147.5, 134.4, 132.3,
2
of this band with its rescaled one-photon spectrum shows that, 129.0, 127.8, 121.8, 121.5. X-ray-quality crystals were grown by
11
analogous to 2-NPh
2
and in spite of the octupolar symmetry,
3
slow diffusion of pentane into a CDCl solution of 4-Br.
the 2PA takes essentially place in the first allowed 1PA excited
state (see ESI†).
1
,3,5-Tri(4-((4-(diphenylamino)phenyl)ethynyl)styryl)-1,3,5-
triazinane-2,4,6-trione (3-NPh
,3,5-Tri((E)-4-bromostyryl)-1,3,5-triazinane-2,4,6-trione (4-Br; 0.237 g,
.35 mmol) and 4-ethynyl-N,N-diphenylaniline (7; 0.426 g,
.58 mmol) were introduced into a flask under argon. Deoxygenated
triethylamine (2.5 mL) was added, and then copper iodide (8.30 mg,
3.6 mmol) and bis(triphenylphosphine)palladium(II) dichloride
15.20 mg, 21.60 mmol). The reaction was heated at 85 1C for
0 h. After cooling to room temperature, the mixture was filtered
2
)
1
0
1
Conclusions
This work reports the synthesis, full characterization and study
of two new tristyryl isocyanurates 4-Br and 3-NPh , the latter
2
4
(
2
being an extended version of 2-NPh , the corresponding triphenyl
2
analogue presenting remarkable two-photon absorption properties.
As indicated by X-ray structural data, electronic spectroscopy and
DFT calculations, the structure of 3-NPh allows now for better
2
conjugation between the three donor groups and the central
isocyanurate core through the p-manifold of the peripheral arms.
through a pad of celite and the filtrate evaporated to dryness. The
crude product was purified by column chromatography (silica gel,
CH Cl /heptane = 70 : 30, v/v). A dark yellow-green compound was
obtained. Yield: 80 mg (18%). HRMS (EI): m/z = 1236.4706 [M] (calc.
for C87 : 1236.4721). IR (neat): n = 2204 (CRC, m), 1772
2
2
+
2
However, in spite of these changes, this new octupole (3-NPh ) does
not present a higher two-photon absorption cross-section than that
60 6 3
H N O
1
(
(
CQO, vw), 1707 (CQO, s), 1653 (sh, CQC, w). H NMR
300 MHz, CDCl ): d = 7.52 (d, J = 8.4 Hz, 6H), 7.44 (d, J = 8.4
of 2-NPh , at odds with what happened for related examples cited in
2
3
the literature. This unexpected (and currently unexplained)
statement warrants now further studies of these tristyryl iso-
cyanurate derivatives to definitively settle that point and to under-
stand better the origin of that rather uncommon phenomenon.
However, on the practical side, the broader 2PA band found for
Hz, 6H), 7.40 (d, J = 8.6 Hz, 6H), 7.33 (d, J = 14.8 Hz, 3H), 7.34–
7.27 (m, 12H), 7.21 (d, J = 14.8 Hz, 3H), 7.16–7.12 (m, 12H), 7.12–
1
3
7
.06 (m, 6H), 7.03 (d, J = 8.6 Hz, 6H). C NMR (75 MHz, CDCl3):
d = 148.0, 147.2, 146.5, 134.2, 132.6, 131.8, 129.4, 128.6, 126.6,
25.0, 123.8, 123.6, 122.2, 119.7, 115.9, 91.1, 88.5.
1
2
3-NPh will allow excitation to be performed further in the near-
IR range.
Luminescence measurements
Luminescence measurements in solution were performed in
dilute air-equilibrated solutions contained in quartz cells of 1 cm
Experimental
À6
pathlength (ca. 10 M, optical density o0.1) at room temperature
The reactions were carried out under an inert atmosphere using
Schlenk techniques. Solvents were freshly distilled under argon
using standard procedures. The 3-(4-bromophenyl)-acryloyl
azide 6-Br and the 4-ethynyl-N,N-diphenylaniline 7 are known
(20 1C), using an Edinburgh Instruments (FLS920) fluorimeter in
photon-counting mode. Luminescence quantum yields were
1
4,15
measured according to literature procedures.
1
3
Two-photon excited fluorescence measurements
compounds (see ESI† for further details).
TPEF cross-sections were measured relative to fluorescein in 0.01 M
1
,3,5-Tri(4-bromostyryl)-1,3,5-triazinane-2,4,6-trione (4-Br).
16
aqueous NaOH using the well-established method described by
1
7
A solution of 3-(4-bromophenyl)acryloyl azide (6-Br; 4.32 g, Xu and Webb and the appropriate solvent-related refractive
1
8
1
7.1 mmol) in anhydrous toluene (20 mL) was heated at 68 1C. index corrections. Reference values between 700 and 715 nm
1
9
To measure the progress of the reaction, tubing was attached to for fluorescein were taken from the literature. The quadratic
the top of the condenser, and connected to an inverted test tube dependence of the fluorescence intensity on the excitation power
filled with water, to collect the volume of nitrogen evolved during was checked for each sample and all wavelengths. A Chameleon
the reaction. After completion of the reaction (12 h) the solvent was Ultra II (Coherent) laser was used, generating 140 fs pulses at a
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80 MHz repetition rate. The excitation was focused into the de Calcul Intensif). We also wish to thank Hugo Coupevent and
cuvette through a microscope objective (10Â, NA 0.25). The Axel Lehmann for assistance in the synthesis.
fluorescence was detected in epifluorescence mode via a dichroic
mirror (Chroma 675dcxru) and a barrier filter (Chroma e650sp-2p)
by a compact CCD spectrometer module BWTek BTC112E. Total
Notes and references
‡
Crystal data: C27
1
H18Br N O , M = 672.17, monoclinic, space group
3 3 3
fluorescence intensities were obtained by integrating the corrected
emission.
3
P2 /n, a = 19.931(3) Å, b = 6.4376(9) Å, c = 21.314(3) Å, U = 2684.8(6) Å ,
Z = 4, R = 0. 0978 (see ESI† for details).
X-ray crystallography
1 B. R. Cho, K. H. Son, S. H. Lee, Y. S. Song, Y. K. Lee,
S. J. Jeon, J. H. Choi, H. Lee and M. Cho, J. Am. Chem. Soc.,
Data collection of crystals of 4-Br was performed on a D8
VENTURE AXS diffractometer at 150 K, with graphite mono-
2001, 123, 9412–9417.
2
W. H. Lee, S. H. Lee, J.-A. Kim, J. H. Choi, M. Cho, S.-J. Jeon
and B. R. Cho, J. Am. Chem. Soc., 2001, 123, 10658–10667.
3 F. Terenziani, C. Katan, E. Badaeva, S. Tretiak and M. Blanchard-
Desce, Adv. Mater., 2008, 20, 4641–4678.
G. S. He, L.-S. Tan, Q. Zheng and P. N. Prasad, Chem. Rev.,
2008, 108, 1245–1330.
H. M. Kim and B. R. Cho, Chem. Commun., 2009, 153–164.
R. G. Arnold, J. A. Nelson and J. J. Verbanc, Chem. Rev., 1957,
chromatized MoK
methods using the SIR97 program and subsequently refined
with full-matrix least-square methods based on F (SHELXL-97).
a
radiation. The structure was solved by direct
2
0
2
21
The contribution of the disordered solvents to the calculated
structure factors was estimated following the BYPASS algo-
4
2
2
23
rithm, implemented as the SQUEEZE option in PLATON.
5
6
A new data set, free of solvent contribution, was then used in
the final refinement. All non-hydrogen atoms were refined with
anisotropic atomic displacement parameters. H atoms were
included in the final cycle of refinement in their calculated
57, 47–76.
7
H. Ulrich, The Chemistry and Technology of Isocyanates,
J. Wiley & Sons, New York, 1996.
8 G. Argouarch, R. Veillard, T. Roisnel, A. Amar, A. Boucekkine,
A. Singh, I. Ledoux and F. Paul, New J. Chem., 2011, 35,
2
positions. A final refinement on F with 6191 unique intensities
2
and 295 parameters converged at oR(F ) = 0.1884 (R(F) =
0.0978) for 4555 observed reflections with I 4 2s(I). The data
2409–2411.
have been deposited at the Cambridge Crystallographic Data
Centre (CCDC 1511480).†
9
G. Argouarch, R. Veillard, T. Roisnel, A. Amar, H. Meghezzi,
A. Boucekkine, V. Hugues, O. Mongin, M. Blanchard-Desce
and F. Paul, Chem. – Eur. J., 2012, 18, 11811–11826.
0 Y. Z. Cui, Q. Fang, G. Xue, G. B. Xu, L. Yin and W. T. Yu,
Chem. Lett., 2005, 34, 644–645.
1 J. C. Collings, S.-Y. Poon, C. Le Droumaguet, M. Charlot,
C. Katan, L.-O. Pålsson, A. Beeby, J. A. Mosely, H. M. Kaiser,
D. Kaufmann, W.-Y. Wong, M. Blanchard-Desce and
T. B. Marder, Chem. – Eur. J., 2009, 15, 198–208.
2 C. Irle and W. Mormann, Liq. Cryst., 1996, 21, 295–305.
3 T. Terai, M. Kohno, G. Boncompain, S. Sugiyama, N. Saito,
R. Fujikake, T. Ueno, T. Komatsu, K. Hanaoka, T. Okabe,
Y. Urano, F. Perez and T. Nagano, J. Am. Chem. Soc., 2015,
Computational details
1
1
The DFT calculations reported in this work have been per-
2
4
formed using the Gaussian09 program. The geometries of all
the compounds have been optimized without symmetry con-
2
5
straints using the MPW1PW91 functional and the 6-31G*
basis set. The solvent effects were taken into account (Polariz-
2
6
able Continuum Model). Calculation of the frequencies of
normal modes of vibration were carried out to confirm the true
minima character of the optimized geometries. TD-DFT calcu-
lations were performed at the same level of theory using the
1
1
2
7,28
previously optimized geometries. Swizard
was used for
137, 10464–10467.
2
9
plotting the simulated spectra and GaussView was employed
for the MO plots.
1
1
1
4 N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991–1024.
5 G. R. Eaton, Pure Appl. Chem., 1988, 60, 1107–1114.
6 M. A. Albota, C. Xu and W. W. Webb, Appl. Opt., 1998, 37,
7
352–7356.
7 C. Xu and W. W. Webb, J. Opt. Soc. Am. B, 1996, 13,
81–491.
Conflicts of interest
1
1
4
There are no conflicts of interest to declare.
8 M. H. V. Werts, N. Nerambourg, D. P ´e l ´e gry, Y. Le Grand and
M. Blanchard-Desce, Photochem. Photobiol. Sci., 2005, 4,
5
31–538.
Acknowledgements
1
9 C. Katan, S. Tretiak, M. H. V. Werts, A. J. Bain, R. J. Marsh,
N. Leonczek, N. Nicolaou, E. Badaeva, O. Mongin and
M. Blanchard-Desce, J. Phys. Chem. B, 2007, 111, 9468–9483.
The CNRS (PICS program No. 7106 and LIA No. 1194) and ANR
(Isogate Project) are acknowledged for financial support. O. M.
and A. T. thank the Region Bretagne for a PhD grant. M. G. H. 20 A. Altomare, M. C. Burla, M. Camalli, G. Cascarano,
thanks the Australian Research Council (ARC) for financial
support. We acknowledge the HPC resources of CINES and of
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
IDRIS under the allocations 2016-[x2015080649] and 2017- 21 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
[x2016080649] made by GENCI (Grand Equipement National
2008, 64, 112–122.
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Letter
22 P. v. d. Sluis and A. L. Spek, Acta Crystallogr., 1990, A46, 26 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005,
194–201.
105, 2999–3093.
2
2
2
3 A. L. Spek, Appl. Crystallogr., 2003, 36, 7–13.
4 M. J. Frisch, et al., Gaussian09, 2015.
5 C. Adamo and V. Barone, J. Chem. Phys., 1998, 108,
27 S. I. Gorelsky, SWizard program, Revision 4.5, 2013.
28 S. I. Gorelsky and A. B. P. Lever, J. Organomet. Chem., 2001,
635, 187–196.
664–675.
29 R. Dennington, T. Keith and J. Millam, GaussView version 5, 2003.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.