Unexpected one-pot method to synthesize spiro[fluorene-9,9′-xanthene] building blocks for blue-light-emitting materials

Article abstract of DOI:10.1021/ol060871z

An unexpected one-pot synthetic approach toward spiro[fluorene-9,9′- xanthene] (SFX) under excessive MeSO₃H conditions has been developed. The key step involves a thermodynamically controlled cyclization reaction. Blue-light-emitting materials based on SFX building blocks that exhibit high thermal stability have also been synthesized.

Full text of DOI:10.1021/ol060871z

ORGANIC
LETTERS
2006
Vol. 8, No. 13
2787-2790
Unexpected One-Pot Method to
Synthesize Spiro[fluorene-9,9 -xanthene]
′
Building Blocks for Blue-Light-Emitting
Materials
Ling-Hai Xie,†,‡ Feng Liu,† Chao Tang,†,‡ Xiao-Ya Hou,† Yu-Ran Hua,†
Qu-Li Fan,†,‡ and Wei Huang*,†,‡,§
Institute of AdVanced Materials (IAM), Fudan UniVersity, 220 Handan Road, Shanghai
200433, People’s Republic of China, Institute of AdVanced Materials (IAM), Nanjing
UniVersity, 22 Hankou Road, Nanjing 210093, People’s Republic of China, and
Faculty of Engineering, National UniVersity of Singapore, 9 Engineering DriVe 1,
Singapore 117576, Republic of Singapore
wei-huang@fudan.edu.cn; chehw@nus.edu.sg
Received April 10, 2006
ABSTRACT
An unexpected one-pot synthetic approach toward spiro[fluorene-9,9′-xanthene] (SFX) under excessive MeSO3H conditions has been developed.
The key step involves a thermodynamically controlled cyclization reaction. Blue-light-emitting materials based on SFX building blocks that
exhibit high thermal stability have also been synthesized.
In recent years, spiro compounds have attracted much
attention because of their promising applications in the fields
of molecular tectonics,1 enantioselective molecular recogni-
tion,2 molecular electronics,3 and optoelectronic devices.4 For
example, supramolecular tectons and synthons based on
spirobifluorene have been used to construct porous hydrogen-
bonded networks and linear polymeric metal-organic frame-
works with square cavities.1 Spiro homopolymers exhibit
excellent spectrum stability even in air-annealing experi-
(2) (a) Smith, D. K.; Diederich, F. J. Chem. Soc., Chem. Commun. 1998,
2501-2502. (b) Lustenberger, P.; Martinborough, E.; Denti, T. M.;
Diederich, F. J. Chem. Soc., Perkin Trans. 2 1998, 747-762. (c) Smith, D.
K.; Zingg, A.; Diederich, F. HelV. Chim. Acta 1999, 82, 1225-1241. (d)
Tejeda, A.; Oliva, A. I.; Simo´n, L.; Grande, M.; Caballero, M.-C.; Mora´n,
J. R. Tetrahedron Lett. 2000, 41, 4563-4566.
(3) (a) Tour, J. M.; Wu, R.-L.; Schumm, J. S. J. Am. Chem. Soc. 1990,
112, 5662-5663. (b) Pei, J.; Ni, J.; Zhou, X.-H.; Cao, X.-Y.; Lai, Y.-H. J.
Org. Chem. 2002, 67, 8104-8113.
(4) (a) Yu, W.-L.; Pei, J.; Huang, W.; Heeger, A. J. AdV. Mater. 2000,
12, 828-831. (b) Zeng, G.; Yu, W.-L.; Chua, S.-J.; Huang, W. Macro-
molecules 2002, 35, 6907-6914.
† Fudan University.
‡ Nanjing University.
§ National University of Singapore.
(1) (a) Wong, K.-T.; Liao, Y.-L.; Peng, Y.-C.; Wang, C.-C.; Lin, S.-Y.;
Yang, C.-H.; Tseng, S.-M.; Lee, G.-H.; Peng, S.-M. Cryst. Growth Des.
2005, 5 (2), 667-671. (b) Fournier, J.-H.; Maris, T.; Wuest, J. D. J. Org.
Chem. 2004, 69, 1762-1775. (c) Fournier, J.-H.; Maris, T.; Wuest, J. D. J.
Org. Chem. 2003, 68, 240-246.
10.1021/ol060871z CCC: $33.50
© 2006 American Chemical Society
Published on Web 05/26/2006

Scheme 1. Typical Synthetic Route to SFX9a
Scheme 2. Additional Synthetic Route to SFX9b
One method starts from two different kinds of o-halobiaryls,
as shown in Scheme 1. The other involves dichlorofluorene
and was patented in 1995, as shown in Scheme 2. However,
SFX has not previously been prepared with a one-step route
as of yet.
ments.5 Spiro compounds also possess other interesting
properties, including high solubility, high fluorescent quan-
tum efficiency, nondispersive hole-transporting ability, and
ambipolar carrier transporting properties.6 Although spiro
compounds are becoming an important class of building
blocks in materials and supramolecular science, much effort
has been devoted to exploring spirobifluorene derivatives
instead of other spiro compounds, e.g. spiro[fluorene-9,9′-
xanthene]. This is partially because of the lack of convenient
and efficient synthetic routes. Therefore, developing efficient
synthetic methodologies of spiro structures is critical to
further expanding the scope of applications of spiro com-
pounds.
Unexpectedly, we discovered a novel one-pot route to
synthesize SFX, as shown in Scheme 3. Originally, we
Scheme 3. One-Pot Approach for the Synthesis of SFX and
Its Derivatives
To date, to the best of our knowledge, there have been
few examples for the development of spiro compounds via
a one-pot route.7 A one-pot approach is appealing because
of its inherent simplicity. Recently, Shu et al. repeatedly
conducted a one-step condensation reaction of 2,7-dibromo-
9-fluorenone with resorcinol to form spiro frameworks
directly, using ZnCl2/HCl as a condensing reagent.8 To
expand the scope of preparation and facilitate the develop-
ment of spiro compounds, a one-pot synthetic route utilizing
readily available reagents has been developed in our labora-
tory and is described in the present letter, to produce a series
of spiro[fluorene-9,9′-xanthene]s (SFXs). To explain this
process theoretically, a thermodynamically controlled mech-
anism has been hypothesized. In addition, an SFX building
block has been exploited to construct blue-light-emitting
materials with high thermal stability.
intended to prepare 4,4′-(9-fluorenylidene)diphenol (FDPO)
starting from commercially available fluorenone according
to the procedure reported in the literature10 (Scheme 4).
Scheme 4. Synthesis of 4,4′-(9-Fluorenylidene)diphenol
In the literature, SFX has been arduously synthesized by
However, the Eaton’s reagent was replaced by the excessive
mixture of MeSO3H and P2O5 (3:1), and the reaction time
was lengthened to 24 h. An unknown compound was
obtained with the molecular mass (M+) of 322 amu, as
determined by GC-MS. TLC demonstrated that its polarity
was lower than that of fluorenone. Thus, it was confirmed
means of two multistep routes with complicated procedures.9
(5) (a) Vak, D.; Chun, C.; Lee, C. L.; Kim, J.-J.; Kim, D-Y. J. Mater.
Chem. 2004, 14, 1342-1346. (b) Wu, Y.; Li, J.; Fu, Y.; Bo, Z. Org. Lett.
2004, 6, 3485-3487. (c) Vak, D.; Lim, B.; Lee, S.-H.; Kim, D.-Y. Org.
Lett. 2005, 7, 4229-4232. (d) Tseng, Y.-H.; Shih, P.-I.; Chien, C.-H.; Dixit,
A. K.; Shu, C.-F.; Liu, Y.-H.; Lee, G.-H. Macromolecules 2005, 38, 10055-
10060.
(6) Wong, K.-T.; Chien, Y.-Y.; Chen, R.-T.; Wang, C.-F.; Lin, Y.-T.;
Chiang, H.-H.; Hsieh, P.-Y.; Wu, C.-C.; Chou, C. H.; Su, Y. O.; Lee, G.-
H.; Peng, S.-M. J. Am. Chem. Soc. 2002, 124, 11576-11577.
(7) Bischoff, F.; Adkins, H. J. Am. Chem. Soc. 1923, 45, 1030-1033.
(8) Tseng, Y.-H.; Shih, P.-I.; Chien, C.-H.; Dixit, A. K.; Shu, C.-F.; Liu,
Y.-H.; Lee, G.-H. Macromolecules 2005, 38, 10055-10060.
(9) (a) Clarkson, R. G.; Gomberg, M. J. Am. Chem. Soc. 1930, 52, 2881-
2891. (b) Walters, M. E.; Richey, W. F.; Clement, K. S.; Brewster, S. L.;
Tasset, E. L.; Puckett, P. M.; Durvasula, V. R.; Nguyen, H. A. U.S. Patent
789 232, 1995.
(10) (a) Morgan, P. W. Macromolecules 1970, 3, 536-544. (b) Chou,
C.-H.; Shu, C.-F. Macromolecules 2002, 35, 9673-9677.
2788
Org. Lett., Vol. 8, No. 13, 2006

Scheme 5. Plausible Mechanism of the One-Pot Method
Figure 1. ORTEP drawing of SFX. The ellipsoid probability is
30%.
mediates and the o,p-substituted or p,p-substituted intermedi-
ates. Because the last ring-closure step is not reversible, the
equilibrium moves forward when the ether bond is formed
with the loss of H2O. As the reaction time lengthens, the
yield of SFX increases. Compared with the reaction time of
6 h with a yield of 40%, a reaction time of 24 h results in
higher yields of up to 80% for SFX. In the meantime, FDPO
in a reaction mixture can be separated by silicon gel
chromatography if the reaction time is shorter than 6 h.
Therefore, SFX is a thermodynamic-controlled product and
FDPO is a kinetic-controlled product. Following the mech-
anism, we deduce that FDPO can be transformed into SFX
under MeSO3H conditions, which is similar to the transfor-
mation of 3,4-dimethylphenol into 9,9-dimethylxanthenes in
the literature.12 The conclusion is confirmed by the efficient
transformation experiment of FDPO into SFX under MeSO3H/
phenol conditions in a high yield of 55%. It should be noted
that an important factor for this reaction is the amount of
MeSO3H acid used because the formation of the ether bond
needs an excessive acid catalyst, which leads to the move-
ment of the equilibrium. Nevertheless, theoretical elucidation
is needed to confirm this hypothesis; however, this is beyond
the scope of the present work.
that the unknown compound was not FDPO. Finally, its
structure was determined to be SFX by single-crystal X-ray
diffraction,11 as shown in Figure 1.
To confirm the process, the reaction was replicated several
times following the same conditions. To expand the scope
of this preparation, we attempted to synthesize dibromo-
substituted SFX which is a useful building block for the
construction of optoelectronic materials, under the same
conditions as SFX. However, a complicated mixture was
obtained that could not be well characterized. Thus, the
excess P2O5/MeSO3H mixture was not efficient for the
development of dibromo-substituted SFX. However, we
occasionally attempted to synthesize the monobromo-SFX
using only MeSO3H as the catalyst. Surprisingly, the
monobromo-SFX was obtained with a high yield of 72%
and determined by GC-MS, 1H, and 13C NMR. Thus, excess
P2O5 was not essential in this one-pot ring-closure reaction.
The repeated experiments also confirmed the course, and the
dibromo-substituted SFX was also successfully prepared with
a high yield of 78%.
Scheme 5 describes a plausible reaction pathway of the
ring-closure process in the one-pot method. First, an elec-
trophilic attack of protonized fluorenone to the o- or
p-position of phenol and the loss of equivalent water give a
carbon cation, which then attacks the o- or p-position of
another phenol to afford diphenol. Subsequently, intramo-
lecular cyclization through the loss of H2O produces the SFX
product in the presence of an acid catalyst if diphenol is the
o,o-substituted intermediate. Meanwhile, the equilibrium
should be hypothesized between the o,o-substituted inter-
Finally, we made use of SFX to construct a blue-light-
emitting model compound with high morphological stability
by means of the Suzuki coupling reaction, as shown in
Scheme 6. The reactions of monobromo-SFX with 2,7-bis-
(4,4,5,5-tetramethyl-[1,3,2]dioxaborolane-2-yl)-9,9-dioctylflu-
orene under Pd(PPh3)4/K2CO3 catalytic conditions gave 2,7-
bis[spiro[fluorene-9,9′-xanthene]-2-yl]-9,9-dioctylfluorene
(BSFXF) with a yield of 90%.
BSFXF is soluble in common organic solvents such as
dichloromethane, toluene, and tetrahydrofuran. The absorp-
tion spectrum of BSFXF in dilute chloroform with an
absorption peak at 361 nm is shown in Figure 2. The
(11) Crystal data for SFX: Crystals were grown from CH2Cl2/alcohol.
The structure was solved on a Bruker SMART CCD diffractometer using
Mo KR radiation. C25H16O (Mr ) 332.38); orthorhombic, space group
P212121, Dc ) 1.293 g cm-3, a ) 10.699(2), b ) 16.752(3), c ) 9.5269-
(18) Å, R ) 90, â ) 90, γ ) 90°, V ) 1707.5(6) Å3, Z ) 4, λ ) 0.71073
Å, µ ) 0.077 mm-1, T ) 293(2) K, R ) 0.0338 for 8370 observed
reflections [I > 2σI] and Rw ) 0.0882 for all 3344 unique reflections.
(12) Caruso, A. J.; Lee, J. L. J. Org. Chem. 1997, 62, 1058-1063.
Org. Lett., Vol. 8, No. 13, 2006
2789

Scheme 6. Synthesis of a Blue-Light-Emitting Model
Compound
emission spectrum exhibits a typical feature of terfluorene
with the maximum emission peaks at 398 and 417 nm and
a high quantum yield of 87%. PL in the solid state shows a
red shift of about 20 nm by comparison with that in solution,
which could be attributed to different dielectric environments.
The annealing experiments exhibited no red shift and low-
energy green emission bands in PL spectra, which reveals
that no excimer or keto defect is formed. The thermal
properties of BSFXF were investigated using differential
scanning calorimetry (DSC) and thermogravimetric analysis
(TGA) under a nitrogen atmosphere at the scan rate of 10
°C/min. BSFXF exhibits a high decomposition temperature
up to 380 °C (5% weight loss temperature) and a Tg up to
154 °C, which is higher than that of polyfluorene (Tg ) 75
°C).13 The above results indicate that BSFXF based on the
SFX building block has high thermal stability and spectral
stability similar to that for the materials based on the
spirobifluorene building block.5b
Figure 2. UV-vis and photoluminescence (PL) spectra of BSFXF
in chloroform (1 µM) and as solid films and annealing PL at 150
°C for 12 h under a nitrogen and air atmosphere.
building blocks have been created. The development of a
one-pot procedure for the preparation of other xanthene
derivatives is currently being pursued.
Acknowledgment. This work was financially supported
by the NNSFC under Grants 60325412, 90406021, and
50428303, the Shanghai Commission of Science and Tech-
nology under Grants 03DZ11016 and 04XD14002, and the
Shanghai Commission of Education under Grant 03SG03.
L.H.X. appreciates technical support from Ms. Zhi-Pei Qin
with the University of Waterloo, Canada.
In conclusion, an efficient and convenient one-pot ap-
proach for the preparation of SFX has been developed, which
is a thermodynamic-controlled process under excessive acid
catalyst. Blue-light-emitting materials based on the SFX
Supporting Information Available: The experimental
1
procedures for the new compounds, H and 13C NMR, MS
spectra, TGA, DSC thermograms, and an X-ray crystal-
lographic file (CIF) for SFX. This material is available free
of charge via the Internet at http://pubs.acs.org.
(13) Grell, M.; Bradley, D. D. C.; Inbasekaran, M.; Woo, E. P. AdV.
Mater. 1997, 9, 798.
OL060871Z
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Org. Lett., Vol. 8, No. 13, 2006