Trinaphthylamines as robust organic materials for two-photon-induced fluorescence

Article abstract of DOI:10.1021/ja8055112

The synthesis of a novel π-conjugated trinaphthylamines series is described. These original push?pull octupolar systems exhibit large two-photon action cross section (σφ up to 510 GM) increased by a factor of 2?3 as compared to their triphenylamines analogues. This substantial improvement of the two-photon absorption properties is attributed to the stronger donor character of the trinaphthyl core. Copyright

Full text of DOI:10.1021/ja8055112

Published on Web 11/19/2008
Trinaphthylamines as Robust Organic Materials for Two-Photon-Induced
Fluorescence
Guillaume Bordeau,† Rémy Lartia,† Germain Metge,‡ Céline Fiorini-Debuisschert,‡ Fabrice Charra,‡
and Marie-Paule Teulade-Fichou*,†
Institut Curie, CNRS UMR-176, Centre UniVersitaire, 91405 Orsay Cedex, France, and CEA- Saclay, DSM/
DRECAM/SPCSI, 91191 Gif-sur-YVette, France
Received July 24, 2008; E-mail: marie-paule.teulade-fichou@curie.fr
Scheme 1. Synthesis of the New Trinaphthylamine Derivatives
Two-photon absorption (2PA) has recently attracted considerable
interest due to its potential applications in a number of areas,
including two-photon fluorescence imaging,1 3D optical data
storage,2 optical power limiting,3 and photodynamic therapy.4 A
broad variety of donor-π-conjugated bridge-acceptor compounds
of dipolar-,5 quadripolar-,6 and octupolar-7type has been studied.
In particular acceptor-terminated triphenylamines (TP) have been
shown to be excellent materials for 2PA7 because of strong
intramolecular charge-transfer (ICT), additional coherent coupling
between branches, in the case of multibranched systems, resulting
in a further increase of the 2PA cross-section.6-8 TP is an electron-
rich, propeller-shaped molecule with C3 symmetry displaying an
octupolar feature and which can be linked to different electron-
withdrawing end groups via π-conjugated units. Many studies have
explored this design, developing efficient fluorescent TP derivatives
with high 2PA cross-sections.7 In all these studies, the strength of
the acceptor end groups and the size of the bridges were varied to
increase the ICT. Comparatively, the reverse strategy, that is,
structural variation of the C3-symmetry core to enhance its electron-
donating property, has never been considered presumably because
of the lack of a synthetic pathway to other appropriate triarylamine
cores. Hence we speculated that extending triphenyl to the
trinaphthyl motif would strongly enrich the electron-donating
property of the three-branched core. Herein, we would like to report
on the simple synthesis and on the photophysical properties of three
tris(2-naphthyl)amine derivatives (TN) π-conjugated with different
acceptor groups. We show that switching from a classical TP core
to a more electron-rich TN (displaying a larger electronic π-cloud)
leads to a substantial increase in 2PA cross-section as compared to
their TP counterparts. Additionally, to our knowledge, examples
of trinaphthylamines are very scarce9 and in particular tris(2-
naphthyl)amines have never been reported.
The synthesis of the TN derivatives (Scheme 1) was straight-
forward (four steps) and efficient (30-37% overall yields). The
commercially available 6-bromo-2-naphtho¨ıc acid (100%) and
6-amino-2-naphtho¨ıc acid (92%) were transformed to their ester
derivatives and coupled via a Pd-catalyzed Buchwald-Hartwig to
give 1 (79%). The subsequent ester reduction carried out via the
classical two-step procedure (reduction to alcohol followed by
smooth oxidation to aldehyde) led to an intractable mixture of
under- and over-reduced products. Hence we developed an alterna-
tive one-step synthesis to the key trialdehyde intermediate 2, via
the concomitant triple reduction of the compound 1 with a modified
Red-Al reagent10 (74% yield). Then 4-pyridinyl, 2-benzothiazolyl,
and 2-benzoxazolyl moieties were introduced via vinylation because
these are efficient electron-withdrawing groups frequently incor-
porated into push-pull NLO materials.11 This was achieved by
Wittig-Horner reaction between the trialdehyde 2 and the corre-
sponding phosphonate affording the three TN derivatives TN-3BZo,
TN-3Bzt, and TN-3Py (60-73%).
The photophysical properties of TN derivatives were studied in
toluene and dichloromethane and the results are summarized in
Table 1. All the TN compounds show a broad and intense absorption
band (ꢀ ) 90 000-115 000 L ·mol-1 ·cm-1) with maximum absorp-
tion wavelength between 400 and 440 nm slightly red-shifted
compared to that of their TP counterparts11 (Table 1). Importantly
a strong increase of the one-photon absorption efficiency was
observed (ca. 20-30%) in correlation with the increased π-con-
jugated surface. All compounds display high fluorescence quantum
yields in dichloromethane (0.5 < Φ < 0.65) and large Stokes shifts
(95-125 nm, Table 1). These large Stokes shifts, that are important
to avoid reabsorption, are close to those of the corresponding TP
with a slight increase due to a red shift of the fluorescence. The
Figure 1. Two-photon excitation spectra of compounds in CH2Cl2: Bzt
series (9), Bzo series (À), Py series (]); TN (plain lines), TP (dashed
lines). Values are average of three independent experiments.
† Institut Curie, CNRS UMR-176.
‡ CEA- Saclay, DSM/DRECAM/SPCSI.
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16836 J. AM. CHEM. SOC. 2008, 130, 16836–16837
10.1021/ja8055112 CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
Table 1. 1PA and 2PA Photophysical Properties of TN and TP Derivatives
λabs (nm) λem (nm)
2PA σa
max
compound
toluene
CH2Cl2
ꢀa (L.mol-1.cm-1
)
toluene
CH2Cl2
Φa,b
σΦ (GM)
σ/MW (GM·g-1 ·mol)
[λmax] (GM) [nm]
TN Series
528
TN-3Py
TN-3Bzt
TN-3Bzo
415
440
434
414
434
431
79400
114900
111100
465
485
478
0.58
0.65
0.63
320[740]
640[740]
810[740]
185
415
510
0.45
0.73
0.98
559
542
TP Series
511
TP-3Py
TP-3Bzt
TP-3Bzo
402
435
431
406
432
424
59500
97300
89000
462
479
469
0.51
0.50
0.52
130[720]
510[740]
540[720]
65
255
280
0.23
0.70
0.80
534
518
a Measurements were performed in CH2Cl2 b Fluorescence emission quantum yield, measured using quinine bisulphate in 1 N H2SO4 as a reference.
quantum yields are also enhanced by 20%, likely due to higher
π-delocalization and additional rigidity. All the derivatives show a
large bathochromism shift in their fluorescence emission along with
the increase of the solvent polarity but no red shift of the absorption
band. This solvatochromism behavior is characteristic of an internal
charge transfer upon excitation12 between the triarylamine core and
peripheral acceptor groups. Moreover, this solvatochromism is more
pronounced in the TN series than in the TP series, reflecting an
increase of ICT (Table S1).
2PA spectra of the dyes were obtained after two-photon-induced
fluorescence (TPIF) measurements, using a femtosecond Ti:sapphire
laser source. The TPIF intensities of the samples were measured
and compared with a reference solution of fluorescein, the ratio of
the fluorescent signals enabling determination of the 2PA cross-
section (Figure 1).13
derivatives. Given the straightforward synthesis of the derivatizable
trisformyl TN key intermediate 2 proposed herein, this work opens
broad perspectives for new molecular design of fluorescent 2PA-
organic materials based on the trinaphthylamine core.
Acknowledgment. This research was supported by MENRT
(Ministe`re Education Nationale, Recherche et Technologie, Ph.D.
fellowship to G.B.), C’nano IdF (Nanosciences Ile de France, Ph.D.
fellowship to G.M.) and EU-FP6-NMP4-2003-505-669 (post doc-
toral fellowship to R.L.)
Supporting Information Available: Complete ref 6a,b. Experi-
mental details and characterization data for all new compounds. This
material is available free of charge via the Internet at http://pubs.acs.org.
References
Importantly, the three TN show high 2PA cross-sections that
were strongly enhanced (up to 810 GM) as compared to that of the
TP counterparts. Additionally, as a consequence of both enhance-
ment of 2PA cross section and quantum yield, the TN derivatives
exhibit a two to 3-fold increase of the action cross-section defined
by the product of the 2PA cross-section and emission quantum yield
(σΦ). This enhancement effect is modulated by the strength of the
acceptor since it is particularly emphasized in the case of the weaker
acceptor Py (σΦ increasing from 65 to 185), whereas slightly
attenuated for the Bzt and Bzo series (from 255-280 GM to
415-510 GM, respectively). This result is however difficult to
rationalize given the dispersion inherent to measurements of 2PA
cross sections.14 Nonetheless the ranking order of the σΦ values
observed in the TN series is still reflecting the strength of the
terminal acceptor (Py < Bzt ∼ Bzo). Altogether, these results fully
validate our hypothesis that increasing the donor character of the
triarylamine core leads to a stronger ICT.
Another way to increase 2PA cross section is to extend the
π-bridge linking donor and acceptor groups, but this inevitably
results in large-sized systems that may limit applications such as
bioimaging. Interestingly, the high 2PA performances of the TN
compounds are accompanied by only a slight increase in molecular
weight (4 carbons/branch). To compare the 2PA performances of
different series, the two-photon absorption/molecular weight ratio
(σ/MW) is shown to be a relevant figure of merit.7d In this regard,
our compounds fall in the range of the best large-sized 2PA
chromophores reported to date15 with a σ/MW ratio up to 0.98
GM·g-1 ·mol for TN-3Bzo (Table 1).
(1) (a) Denk, W.; Strickler, J. H.; Webb, W. W. Science 1990, 248, 73–76. (b)
Xu, C.; Zipfel, W.; Shear, J. B.; Williams, R. M.; Webb, W. W. Proc.
Natl. Acad. Sci. U.S.A. 1996, 93, 10763–10768.
(2) (a) Parthenopoulos, D. A.; Rentzepis, P. M. Science 1989, 245, 843–845.
(3) Ehrlich, J. E.; Wu, X. L.; Lee, I.-Y. S.; Hu, Z.-Y.; Ro¨ckel, H.; Marder,
S. R.; Perry, J. W. Opt. Lett. 1997, 22, 1843–1845.
(4) Bhawalkar, J. D.; Kumar, N. D.; Zhao, C. F.; Prasad, P. N. J. Clin. Laser
Med. Surg. 1997, 15, 201–204.
(5) (a) Reinhardt, B. A.; Brott, L. L.; Clarson, S. J.; Dillard, A. G.; Bhatt,
J. C.; Kannan, R.; Yuan, L.; He, G. S.; Prasad, P. N. Chem. Mater. 1998,
10, 1863–1874. (b) Abbotto, A.; Beverina, L.; Bozio, R.; Bradamante, S.;
Ferrante, C.; Pagani, G. A.; Signorini, R. AdV. Mater. 2000, 12, 1963–
1967.
(6) (a) Albota, M.; et al. Science 1998, 281, 1653–1656. (b) Zheng, S.; et al.
Chem. Mater. 2007, 19, 432–442.
(7) (a) Porres, L.; Mongin, O.; Katan, C.; Charlot, M.; Pons, T.; Mertz, J.;
Blanchard-Desce, M. Org. Lett. 2004, 6, 47–50. (b) Lee, W.-H.; Lee, H.;
Kim, J.-A.; Choi, J.-H.; Cho, M.; Jeon, S.-J.; Cho, B. R. J. Am. Chem.
Soc. 2001, 123, 10658. (c) He, G. S.; Swiatkiewicz, J.; Jiang, Y.; Prasad,
P. N.; Reinhardt, B. A.; Tan, L. S.; Kannan, R. J. Phys. Chem. A 2000,
104, 4805–4810. (d) Katan, C.; Terenziani, F.; Mongin, O.; Werts, M. H. V.;
Porres, L.; Pons, T.; Mertz, J.; Tretiak, S.; Blanchard-Desce, M. J. Phys.
Chem A 2005, 109, 3024–3037.
(8) Drobizhev, M.; Karotki, A.; Dzenis, Y.; Rebane, A.; Suo, Z.; Spangler,
C. W. J. Phys. Chem. B 2003, 107, 7540–7543.
(9) Alameddine, B.; Savary, S.; Aebisher, O.; Jenny, T. A. Synthesis 2007, 2,
271–276, and patents cited herein.
(10) Hagiya, K.; Mitsui, S.; Taguchi, H. Synthesis 2003, 823–828.
(11) (a) Allain, C.; Schmidt, F.; Lartia, R.; Bordeau, G.; Fiorini-Debuisschert,
C.; Charra, F.; Tauc, P.; Teulade-Fichou, M.-P. ChemBioChem 2007, 8,
424–433. (b) Lartia, R.; Allain, C.; Bordeau, G.; Schmidt, F.; Fiorini-
Debuisschert, C.; Charra, F.; Tauc, P.; Teulade-Fichou, M.-P. J. Org. Chem.
2008, 73, 1732–1744. (c) Nielsen, C. B.; Johnsen, M.; Arnbjerg, J.;
Pittelkow, M.; McIlroy, S. P.; Ogilby, P. R.; Jorgensen, M. J. Org. Chem.
2005, 70, 7065–7079.
(12) Diwu, Z.; Zhang, C.; Klaubert, R. P.; Haughland, J. J. Photochem.
Photobiol., A 2000, 131, 95–100.
(13) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481–491.
(14) Jha, P. C.; Wang, Y.; Agren, H. Chemphyschem 2008, 9, 111–116.
(15) (a) Yang, W. J.; Kim, D. Y.; Kim, C. H.; Jeong, M.-Y.; Lee, S. K.; Jeon,
S.-J.; Cho, B. R. Org. Lett. 2004, 6, 1389–1392. (b) Bhaskar, A.;
Ramakrishna, G.; Lu, Z.; Twieg, R.; Hales, J. M.; Hagan, D. J.;
VanStryland, E.; Goodson, T. J. Am. Chem. Soc. 2006, 128, 11840–11849.
In conclusion, we described an original new family of trinaph-
thylamine derivatives which are very efficient fluorophores for 2PA
absorption. Their high 2PA cross-sections represent an interesting
improvement as compared to the widely explored triphenylamine
JA8055112
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