Improved synthesis of 2,2′-Dibromo-9,9′-spirobifluorene and its 2,2′-bisdonor-7,7′-bisacceptor-substituted fluorescent derivatives

Article abstract of DOI:10.1021/ol0513591

(Chemical Equation Presented) Pure 2,2′-Dibromo-9,9′- spirobifluorene was synthesized by a method that did not involve troublesome dibromination of 9,9′-spirobifluorene or Sandmeyer reaction of 2,2′-diamino-9,9′-spirobifluorene. A series of donor-acceptor orthogonally substituted 9,9′-spirobifluorene was subsequently prepared showing rich variation of fluorescence in solution and in solid state.

Full text of DOI:10.1021/ol0513591

ORGANIC
LETTERS
2005
Vol. 7, No. 17
3717-3720
Improved Synthesis of
2,2
′
′
-Dibromo-9,9
-Bisdonor-7,7
′
-spirobifluorene and Its
-bisacceptor-Substituted
2,2
′
Fluorescent Derivatives
Chih-Long Chiang,†,‡ Ching-Fong Shu,*,† and Chin-Ti Chen*,‡
Department of Applied Chemistry, National Chiao Tung UniVersity, Hsin-Chu,
Taiwan 30035, and Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529
shu@cc.nctu.edu.tw; cchen@chem.sinica.edu.tw
Received June 10, 2005
ABSTRACT
Pure 2,2
Sandmeyer reaction of 2,2
prepared showing rich variation of fluorescence in solution and in solid state.
′
-Dibromo-9,9
′
-spirobifluorene was synthesized by a method that did not involve troublesome dibromination of 9,9
′-spirobifluorene or
′
-diamino-9,9 -spirobifluorene. A series of donor acceptor orthogonally substituted 9,9 -spirobifluorene was subsequently
′
−
′
Although there are abundant optical and electronic molecular
materials or polymers that are derived from 2,7-dibromo-
9,9′-spirobifluorene,1 very few materials originate from the
closely related isomer 2,2′-dibromo-9,9′-spirobifluorene.2
This drastic difference is mainly due to the easy preparation
of 2,7-dibromo-9,9′-spirobifluorene, which is readily syn-
thesized from 2,7-dibromo-9-fluorenone by reacting with a
Grinard reagent of 2-bromobiphenyl.1b According to both
literature and patent, 2,2′-dibromo-9,9′-spirofluorene can be
prepared by direct bromination of 9,9′-spirobifluorene in the
presence of a catalytic amount of ferric chloride.3 However,
in our earlier report,2a we have encountered difficulty in the
preparation and isolation of pure 2,2′-dibromo-9,9′-spirobi-
fluorene.4 Alternatively, 2,2′-dibromo-9,9′-spirofluorene can
be prepared by the replacement of amino group of 2,2′-
diamino-9,9′-spirobifluorene by cupric bromide following
conventional Sandmeyer procedure.2a In addition to biphen-
yl-, azobenzene-, and phenol-type side products, Sandmeyer
reactions are often plagued with position isomers of halide
substituent.5 In this case, 2,2′-dibromo-9,9′-spirobifluorene
was obtained together with 2,3′-dibromo-9,9′-spirobifluorene
(1) (a) Wu, R.; Schumn, J. S.; Pearson, D. L.; Tour, J. M. J. Org. Chem.
1996, 61, 6906. (b) Yu, W..-L.; Pei, J.; Hung, W.; Heeger, A. J. AdV. Mater.
2000, 12, 828. (c) 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. (d) Wu,
C. C.; Lin, Y. T.; Chiang, H. H.; Cho, T. Y.; Chen, C. W.; Wong, K. T.;
Liao, Y. L.; Lee, G. H.; Peng, S. M. Appl. Phys. Lett. 2002, 81, 577. (e)
Chien, Y.-Y.; Wong, K.-T.; Chou, P.-T.; Cheng, Y.-M. Chem. Commun.
2002, 2874. (f) Wu, C.-C.; Liu, T.-L.; Hung, W.-Y.; Lin, Y.-T.; Wong,
K.-T.; Chen, R.-T.; Chen, Y.-M.; Chien, Y.-Y. J. Am. Chem. Soc. 2003,
125, 3710. (g) Mu¨ller, C. D.; Falcou, A.; Reckefuss, N.; Rojehn, M.;
Eiederhirn, V.; Rudati, P.; Frohne, H.; Nuyken, O.; Becker, H.; Meerholtz,
K. Nature 2003 421, 829. (h) Schneider, D.; Rabe, T.; Riedl, T.; Dobbertin,
T.; Kro¨ger, M.; Becker, E.; Weimann, T.; Wang, J.; Hinze, P. Appl. Phys.
Lett. 2004, 85, 1659. (i) Wu, C.-C.; Lin, Y.-T.; Wong, K.-T.; Chen, R.-T.;
Chien, Y.-Y. AdV. Mater. 2004, 16, 61.(j) Su, H.-J.; Wu, F.-I.; Shu, C.-F.
Macromolecules 2004, 37, 7197. (k) Wu, Y.; Li, J.; Fu, Y.; Bo, Z. Org.
Lett. 2004, 6, 3485. (l) Cao, X.-Y.; Zhang, W.; Zi, H.; Pei, J. Org. Lett.
2004, 6, 4845. (m) Cheun, C. H.; Tao, Y. T.; Wu, F. I.; Shu, C. F. Appl.
Phys. Lett. 2004, 85, 4609. (n) Fungo, F.; Wong, K.-T.; Ku, S.-Y.; Hung,
Y.-Y.; Bard, A. J. J. Phys. Chem. B 2005, 109, 3984. (o) Oyston, S.; Wang,
C.; Hughes, G.; Batsanov, A. S.; Perepichka, I. F.; Bryce, M. R.; Ahn, J.
H.; Pearson, C.; Petty, M. C. J. Mater. Chem. 2005, 15, 194. (p) Wong,
K.-T.; Chen, R.-T.; Fang, F.-C.; Wu, C.-C.; Lin, Y.-T. Org. Lett. 2005, 7,
1979.
† National Chiao Tung University.
‡ Academia Sinica.
10.1021/ol0513591 CCC: $30.25
© 2005 American Chemical Society
Published on Web 07/28/2005

and 2,2,3′-tribromo-9,9′-spirobifluorene as well, and the
separation of these isomers remains difficult and greatly
hampers materials applications. Here, an improved and
reliable synthesis has been developed for the preparation of
2,2′-dibromo-9,9′-spirofluorene. We also illustrate a new
series of 2,2′-bisdonor-7,7′-bisacceptor-substituted 9,9′-spiro-
bifluorene compounds as colorful fluorescent materials
prepared from now readily accessible and pure 2,2′-dibromo-
9,9′-spirofluorene.
following bromodesilation of the disilane compound by
sodium acetate and bromine easily afforded bis-(4′-bromo-
biphenyl-2-yl)methanone. The target product was thus ob-
tained by classical Clark and Gomberg method in the present
of strong acid of methanesulfonic acid.8 The 2,2′-dibromo-
9,9′-spirobifluorene compound prepared by the new method
1
was pure (see its H NMR spectrum in Figure 1) and its
The key starting material in the preparation of 2,2′-
dibromo-9,9′-spirobifluorene is 4-(trimethylsilyl) benzenebo-
ronic acid, which is commercially available. It can be also
readily prepared in a two-step reaction from 1,4-bibromoben-
zene and chlorotrimethylsilane followed by the treatment of
n-BuLi and trimethylborate in formation of boronic acid.6
The desired 2,2′-dibromo-9,9′-spirobifluorene was prepared
in 4 steps from 4-(trimethylsilyl)benzeneboronic acid in total
overall yields near 30% (Scheme 1). The new preparation
Scheme 1
Figure 1. 1H NMR spectra (CDCl3) of 2,2′-dibromo-9.9′-spiro-
bifluorene. Please see ref 2a for the signal assignment.
chemical structure was firmly identified (see its X-ray crystal
structure in Figure 2). The new synthesis method is efficient
first involved the generation of (2′-bromobiphenyl-4-yl)-
trimethylsilane and it was easily achieved by Suzuki cross-
coupling of (trimethylsilyl)benzeneboronic acid and 1,2-
dibromobenzene. The second step of the synthesis led to the
ketone-connected dimer of (2′-bromobiphenyl-4-yl)trimeth-
ylsilane that was treated with n-BuLi and reacted with 0.5
equiv of dimethyl carbonate in a fashion similar to the
preparation of bis(3′-methoxybiphenyl-2-yl)methanone.7 The
(2) (a) Wu, F.-I.; Dodda, R.; Reddy, D. S.; Shu, C.-F. J. Mater. Chem.
2002, 12, 2893. (b) Salbeck, R. P. J. Synth. Metals 2003, 138, 21. (c) Shen,
W.-J.; Dodda, R.; Wu, C.-C.; Wu, F.-I.; Liu, T.-H.; Chen, H.-H.; Chen, C.
H.; Shu, C.-F.; Chem. Mater. 2004, 16, 930.
(3) (a) Sutcliffe, F. K.; Shahidi, H. M.; Patterson, D. J. Soc. Dyes Colors
1978, 94, 306. (b) Lupo, D.; Salbeck, J.; Schenk, H.; Stehlin, T.; Stern, R.
Wolf, A. US Patent 5840217, Nov 24, 1998.
Figure 2. Single-crystal X-ray structure of 2,2′-dibromospirobif-
luorene.
(4) (a) There is one report about 2,2′-dibromo-9, 9′-spirofluorene
synthesized from the direct bromination of 9,9′-spirobifluorene in high
yields: Pei, J.; Ni, J.; Zhou, X.-H.; Cao, X.-Y.; Lai, Y.-H. J. Org. Chem.
2002, 67, 4924. The 1H NMR spectra of 2,2′-dibromo-9,9′-spirofluorene
enclosed in the paper showed unusually broad signals indicative of the
insufficient purity or the isomer mixture of the sample. (b) Miller, R. D.;
Do¨tz, F.; Murphy, A. R.; Lee, V. Y.; Scott, J. C.; Bozano, L.; Smith, R.;
Bacilieri, C. Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Chem.) 2002,
43, 116.
(5) (a) Doyle, M. P.; Siegfried, B.; Dellaria, F., Jr. J. Org. Chem. 1977,
42, 2426. (b) Doyle, M. P.; Van Lente, M. A.; Mowat, R.; Forbare, W. F.
J. Org. Chem. 1980, 45, 2570.
(6) Kim, H.-S.; Kim, Y.-H.; Ahn, S.-K.; Kwon, S.-K. Macromolecules
2003, 36, 2327.
and reliable. Multigram quantity of 2,2′-dibromo-9,9′-spiro-
bifluorene can be prepared readily (here 4.6 g of the
analytically pure product was obtained in one round).
With a sufficient amount of pure 2,2′-dibromo-9,9′-
spirobifluorene, we quickly prepared a series of new
fluorescent 9,9′-spirobifluorene derivatives based on or-
thogonally constructed pair of donor-acceptor substituents
(7) Cheng, X.; Hou, G.-H.; Xie, J.-H.; Zhou, Q.-L. Org. Lett. 2004, 6,
2381.
(8) Clarkson, R. G.; Gomberg, M. J. Am. Chem. Soc. 1930, 52, 2881.
Org. Lett., Vol. 7, No. 17, 2005
3718

Except for BTSF, all new donor-acceptor-substituted 9,9′-
spirobifluorene compounds showed pronounced fluorescence
in solution (Figure 3). Six new spirobifluorenes exhibited
Scheme 2
Figure 3. Top: fluorescence spectra of 2,2′-bisdonor-7,7′-bisac-
captor-substituted 9,9′-spirobifluorenes in chlorobenzene. Bottom:
fluorescence images of the solution (in chlorobenzene) and spin-
coated solid films. Note that the fluorescence of BTSF (the
fourth one from the left) is hardly visible either in solution or as
solid film, although it was detectable by fluorescence spectropho-
tometer.
fluorescence with varied colors ranging from the deep blue
(λfl
401 nm) of DPASF, sky blue (λfl
480 nm) of
max
max
DPVSF, green blue of CHOSF (λfl
495 nm), yellow
max
orange (λflmax 549 nm) of BTSF, orange red (λflmax 601 nm)
of BTCNSF, to the vivid red (λflmax 620 nm) of CNSF. When
they were in the form of a solid film, red-shifting fluores-
cence generally took place. Fluorescence with different
brightness was observed for these fluorophores in solution
as well in solid state. Qualitatively, solid-state fluorescence
intensities (fluorescence quantum yields, φfls) in general
follow the same order as those in solution (Table 1). The
strongest fluorescence was found for DPVSF and CHOSF;
DPASF and CNSF showed second-rate fluorescence; weak
fluorescence or no fluorescence was observed for BTCNSF
and BTSF, respectively. Considering the strong fluorescence
in solid state, some of the fluorophores in this report are
worth further investigation for potential application of organic
(Scheme 2). DPASF was directly obtained from 2,2′-
dibromo-9,9′-spirobifluorene by Pd-catalyzed aromatic ami-
nation reaction. Similarly, CHOSF was synthesized from
2,2′-dibromo-7,7′-diformyl-9,9′-spirobifluorene, which was
easily prepared by the one-step di-formylation of 2,2′-
dibromo-9,9′-spirobifluorene carried on using CH3OCHCl2/
TiCl4 with a 83% yield.9 Using aldehyde CHOSF as the
common starting material, various acceptor bisbenzothi-
azolylvinyl-, benzothiazolylcyanovinyl-, or dicyanovinyl-
appended DPASF, i.e., BTSF, BTCNSF, and CNSF were
smoothly generated in 51-69% yields under Knoevenagel
conditions (basic Al2O3 in dry toluene). For the synthesis of
DPVSF, the efficient Horner-Wadsworth-Emmons reaction
was conducted for the formation of the C-C double to
connect DPASF and diethoxy diphenylmethylphosphonate.10
(10) Plater, M. J.; Jackson, T.; Tetrahedron 2003, 59, 4673.
(11) (a) de Mello, J. C.; Wittmann, H. F.; Friend, R. H. AdV. Mater.
1997, 9, 230. (b) Chiang, C.-L.; Wu, M.-F.; Dai, D.-C.; Wen, Y.-S.; Wang,
J.-K.; Chen, C.-T. AdV. Funct. Mater. 2005, 15, 231.
(9) Mattiello, L.; Fioravanti, G. Synth. Commun. 2001, 31, 2645.
Org. Lett., Vol. 7, No. 17, 2005
3719

Table 1. Fluorescence and Absorption Data of
2,2′-Bisdonor-7,7′-bisaccaptor-Substituted 9,9′-spirobifluorenes
λfl
λfl
solid
(nm)
φfl b
solutiona
(%)
λabmax, ꢀ
solutiona
(nm, M-1 cm-1
max
max
solutiona
(nm)
)
DPASF
DPVSF
CHOSF
BTSF
BTCNSF
CNSF
401
480
495
549
601
620
416
481
511
582
627
657
24
50
46
∼0
14
31
353, 42300
385, 84700
402, 49700
433, 59900
464, 65800
481, 66200
Figure 4. Comparison of the fluorescence intensity of BTSF as
spin-coated thin film on glass substrate (left), dispersed substance
on the surface of silica gel powders (center), and dissolved solute
in chlorobenzene (right).
a In chlorobenzene. b Fluorescence quantum yield was measured by the
integrating-sphere method described by Mello et al.11
light-emitting diodes (OLEDs). One exceptional case is
BTSF. Unlike the rest of 9,9′-spirobifluorene fluorophores,
BTSF is almost nonemissive either in solution or as solid
film. Among all new spirobifluorene compounds, the fluo-
rescence of BTSF showed largest red-shifting (1032 cm-1)
from chlorobenzene solution to solid thin film. When it was
dispersed on the surface of silica gel powder, the fluorescence
wavelength of BTSF was further red-shifted to 649 nm,
another enormous red-shifting of 2806 cm-1. Moreover,
BTSF lit up on the surface of the silica gel (see Figure 4).
Such fluorescence behavior usually indicates that there is
certain interaction of silica gel and the BTSF molecules.
Since BTSF is the only 9,9′-spirobifluorene fluorophore
showing such fluorescence changes, we can deduce that both
benzothiazolyl units of BTSF are involved in the interaction
with silica gel. Further studies are undergoing in order to
understand the intriguing fluorescence of BTSF and to
explore the possible sensor application of the material.
In summary, we have successfully demonstrated that 2,2′-
dibromo-9,9′-spirobifluorene can be prepared by a new
method that does not go through the bromination or Sand-
meyer reaction. Multigrams of pure 2,2′-dibromo-9,9′-
spirobifluorene can be readily obtained by the new synthetic
method without the contamination of bromine-substituent
position isomers. From 2,2′-dibromo-9,9′-spirobifluorene we
have also synthesized six donor-acceptor-substituted 9,9′-
spirobifluorene. These new 9,9′-spirobifluorene derivatives
show varied fluorescence color and intensity and they have
potential for light-emitting or sensing application.
Acknowledgment. We thank the National Science Coun-
cil, Academia Sinica, and National Chiao Tung University
for financial support. The assistance from Dr. Juen-Kai Wang
in the measurement of fluorescence quantum yield by the
integrating-sphere method is also acknowledged.
Supporting Information Available: Structural charac-
terization and synthetic details of 2,2′-dibromo-9,9′-spiro-
bifluorene and the new donor-acceptor-substituted 9,9′-
spirobifluorene derivatives. This material is available free
of charge via the Internet at http://pubs.acs.org.
OL0513591
3720
Org. Lett., Vol. 7, No. 17, 2005