Synthesis and photophysical studies of silylene-spaced divinylarene copolymers. Molecular weight dependent fluorescence of alternating silylene-divinylbenzene copolymers

Full text of DOI:10.1021/ja971373b

J. Am. Chem. Soc. 1997, 119, 11321-11322
11321
syntheses are normally limited by using alkynyl silyl hydrides
as starting materials. We recently developed a convenient
procedure to prepare vinylsilanes from the corresponding aryl-
or vinyl-substituted dithioacetals.13 It was felt that conjugated
silyl hydride precursors can be efficiently obtained by this
method. In this paper, we report a convenient synthesis and
the photophysical investigations of alternating silylene-
divinylarene copolymers 1.
Synthesis and Photophysical Studies of
Silylene-Spaced Divinylarene Copolymers.
Molecular Weight Dependent Fluorescence of
Alternating Silylene-Divinylbenzene Copolymers
Ruey-Min Chen, Kuo-Ming Chien, Ken-Tsung Wong,
Bih-Yaw Jin, and Tien-Yau Luh*
Department of Chemistry, National Taiwan UniVersity
Taipei, Taiwan 106, Republic of China
Jui-Hung Hsu and Wunshain Fann
Institute of Atomic and Molecular Sciences
Academia Sinica, and Department of Physics
National Taiwan UniVersity
Treatment of 2 with Me2(iPrO)SiCH2MgCl in the presence
of 5 mol % of NiCl2(PPh3)2 in refluxing benzene gave 3 in good
yield. Reduction of the Si-O bond in 3 with LAH yielded 4
(eq 1).13 Bissilylhydrides 7 were prepared similarly (eq 2).
Treatment of 4 with 8b in the presence of 0.5 mol % of RhCl-
(PPh3)3 gave 10b in 76% yield. Alternatively, 9 was allowed
Taipei, Taiwan 106, Republic of China
ReceiVed April 30, 1997
Introduction of spacers between well-defined chromophores
in the polymeric chain can occasionally increase the processi-
bility, and in the mean time, the emission wavelength can be
predicted.1-7 There has been an increasing use of tetrahedral
silylene moiety as a bridge connecting chromophores in
polymers.3-7 Recent study indicates that a silylene spacer
between two conjugated moieties facilitates the intramolecular
photoinduced charge transfer process.8 When the polymer
contains a silicon linkage, it is envisaged that the polymer could
be highly folded such that the two π-conjugated moieties may
be located in close proximity and interaction between these
chromophores may result in interesting photophysical behav-
iors.9 Hydrosilylation, inter alia,5-7,10 provides a useful entry
for the synthesis of σ,π-conjugate organosilicon polymers.3,4,11,12
However, owing to the accessibility of silane monomers,
(1) (a) Yang, Z.; Sokolik, I.; Karasz, F. E. Macromolecules 1993, 26,
1188. (b) Kim, D. J.; Kim. S. H.; Lee, J. H.; Kang, S. J.; Kim, H. K.;
Zyung, T.; Cho, I.; Choi, S. K. Mol. Cryst. Liq. Cryst. 1996, 280, 391.
(2) Brouwer, H. J.; Krasnikov, V. V.; Hilberer, A.; Hadziioannou, G.
AdV. Mater. 1996, 8, 935 and references therein.
to react with 7a,c under the same conditions to afford the
monomers 10a,c in 85 and 78% yields, respectively. Monomers
10 were used as reference compounds for photophysical studies.
In a similar manner, the rhodium-catalyzed hydrosilylation of
8 with 7 yielded polymers 1 (eq 3). It is noteworthy that the
average molecular weight (Mn) of 1 depends on the reaction
conditions. Higher concentration and longer reaction times
favor the formation of 1 with a higher molecular weight.
The absorption spectra for 1 and 10 are compared in Figure
1. No significant shifts between the polymers 1 and the
corresponding monomer 10 were observed. However, there
appeared a weak absorption in the region of 340-400 nm for
1a, and the intesitity slightly increases with the molecular weight
of 1a (Figure 1a).
(3) (a) Hu, S. S.; Weber, W. P. Polym. Bull. 1989, 21, 133. (b) Ohshita,
J.; Matsuguchi, A.; Furumori, K.; Hong, R.-F.; Ishikawa, M. Macromol-
ecules 1992, 25, 2134. (c) Ohshita, J.; Kanaya, D.; Watanabe, T.; Ishikawa,
M. J. Organomet. Chem. 1995, 489, 165.
(4) (a) Corriu, R. J. P.; Gerbler, P.; Gue´rin, C.; Henner, B. J. L.; Jean,
A.; Mutin, P. H. Organometallics 1992, 11, 2507. (b) Wu, H. J.; Interrante,
L. V. Macromolecules 1992, 25, 1840. (c) Pang, Y.; Ijadi-Maghsoodi, S.;
Barton, T. J. Macromolecules 1993, 26, 5671.
(5) Kim, H. K.; Ryu, M.-K.; Lee, S.-M. Macromolecules 1997, 30, 1236
and references therein.
(6) (a) Ohshita, J.; Kanaya, D.; Ishikawa, M.; Koike; T.; Yamanaka, T.
Macromolecules 1991, 24, 2106. (b) Corriu, R. J. P.; Guerin, C.; Henner,
B.; Kuhlmann, T.; Jean, A.; Garnier, F.; Yassar, A. Chem. Mater. 1990, 2,
351. (c) Yuan, C.-H.; West, R. Appl. Organomet. Chem. 1994, 8, 423.
(7) Corriu, R. J. P.; Douglas, W. E.; Yang, Z. X.; Karakus, Y.; Cross,
G. H.; Bloor, D. J. Organomet. Chem. 1993, 455, 69.
Polymer 1a exhibited dual fluorescence spectra (Figure 2a).
The higher energy emission at ca. 340 and 360 nm for 1a is
compatible with those for 10a. The relative intensity of the
emission in the blue light region increases with the molecular
weight of 1a, and vibronic fine structures were observed in this
region. The emission profiles remained essentially unchanged
with concentration (5-100-fold) and with solvents (<8 nm, in
MeCy, benzene, or CHCl3). Time-resolved fluorescence spectra
of 1a3 and 10a in CHCl3 were monitored at 341 and 414 nm.
The fluorescence of 1a3 at 414 nm showed a slow decay with
τ ) 1.1 ns. On the other hand, both 1a3 and 10a exhibited a
fast fluorescence decay (τ ≈ 120 ps) at 341 nm. An additional
slow decay for 10a was also observed at 341 nm, and its lifetime
(8) van Walree, C. A.; Roest, M. R.; Schuddeboom, W.; Jenneskens, L.
W.; Verhoeven, J. W.; Warman, J. M.; Kooijman, H.; Spek, A. L. J. Am.
Chem. Soc. 1996, 118, 8395.
(9) (a) Miao, Y.-J.; Herkstroeter, W. G.; Sun, B. J.; Wong-Foy, A. G.;
Bazan, G. C. J. Am. Chem. Soc. 1995, 117, 11407 and references therein.
(b) For a review, see: Solaro, R.; Galli, G.; Ledwith, A.; Chiellini, E. In
Polymer Photophysics; Phillips, D., Ed.; Chapman & Hall: London, 1985;
pp 377-430.
(10) (a) Corriu, R. J. P.; Douglas, W. E.; Yang, Z.-X. J. Polym. Sci., C:
Polym. Lett. 1990, 28, 431. (b) Ijadi-Maghsoodi, S.; Barton, T. J.
Macromolecules 1990, 23, 4485. (c) Corriu, R. J. P.; Douglas, W. D.; Yang,
Z.-X. J. Organomet. Chem. 1991, 417, C50. (d) Fang, M.-C.; Watanabe,
A.; Matsuda, M. Chem. Lett. 1994, 13. (e) Mao, S. S. H.; Tilley, T. D. J.
Am. Chem. Soc. 1995, 117, 5365.
(11) (a) Son, D, Y.; Bucca, D.; Keller, T. M. Tetrahedron Lett. 1996,
37, 1579. (b) Kunai, A.; Toyoda, E.; Nagamoto, I.; Horio, T.; Ishikawa,
M. Organometallics 1996, 15, 75.
(12) For a recent review on hydrosilylation, see: Ojima, I. In The
Chemistry of Organosilicon Compounds; Rappoport, Z., Apeloig, Y., Eds.;
Wiley: Chicester, 1997; Vol. 2, in press.
(13) (a) Ni, Z.-J.; Yang, P.-F.; Ng, D. K. P.; Tzeng, Y.-L.; Luh, T.-Y. J.
Am. Chem. Soc. 1990, 112, 9356. (b) For reviews, see: Luh, T.-Y. Acc.
Chem. Res. 1991, 24, 257; Pure Appl. Chem. 1996, 68, 105.
S0002-7863(97)01373-5 CCC: $14.00 © 1997 American Chemical Society

11322 J. Am. Chem. Soc., Vol. 119, No. 46, 1997
Communications to the Editor
Figure 1. Absorption specta for (a) 1a and 10a, (b) 1b and 10b, and
(c) 1c and 10c.
was compatible with that fitted for the decay at 414 nm. When
the fluorescence spectum of 1a3 was monitored at 1 ns delay
time after laser excitation, only low-energy emission was
observed (see the Supporting Information). These data indicated
that the emission of 1a at these two wavelengths may be arised
from different species.
Figure 2. Emission spectra for (a) 1a of different molecular weights
and 10a and (b) 1b,c and 10b,c.
In the excitation spectra for 1a (Figure 3), the intensity at
375 nm increases with the molecular weight, and such enhance-
ment is substantial in comparison with those in the absorption
spectra. These observations suggested that significant intra-
molecular interactions between lumophores in 1a both at the
ground and at the excited states might occur, and this interaction
seemed to be more important as the polymer becomes larger. It
is noteworthy that intrachain aggregation of chromophores has
also been observed in the block copolymers obtained by ring-
opening metathesis polymerization (ROMP) of [2,2]paracyclo-
phanene and norbornene.9a AM1 and Hartree-Fock (3-21G*)
calculations on divinyl- and distyrylsilanes suggested that the
molecules are quite flexible. Accordingly, the opportunity for
one chromophore unit in 1a located proximal to the other in
space would increase with the molecular weight.
In contrast to the emission properties of 1a, there was not
much difference in the fluorescence spectra between polymers
1b,c and the corresponding monomers 10b,c (Figure 2b). This
implies that the above-mentioned intramolecular interaction may
not exist in these polymers. These polymers contain either the
bulky alkoxy moiety in 1b or ter-aryl unit in 1c as part of the
backbone. The steric hindrance of the alkoxy group and the
rigidity of the ter-aryl moiety might prohibit the chromophores
in these polymers in close proximity. It is interesting to note
that the emission frequencies of the alkoxy-substituted 1b also
fall within the blue light region (Figure 2b).
Figure 3. Excitation spectra for 1a at different molecular weights and
10a.
that significant intramolecular interaction between lumophores
occurs in 1a. Our system involving a simple divinylarene
moiety in these silylene-spaced copolymers could result in the
emission to occur in the blue light region.
Acknowledgment. This work was supported by the National
Science Council of the Republic of China.
Supporting Information Available: Spectral data and experimental
procedures for synthesis and spectrophometric measurements of 1 and
10, Hartree-Fock (3-21G*) calculations on divinylsilanes, and time-
resolved fluorescence spectra of 1a3 and 10a (9 pages). See any current
masthead page for ordering and Internet access instructions.
In summary, we have demonstrated that a new versatile
approach toward the synthesis of a variety of co-silylene-
conjugated polymers. The photophysical studies have shown
JA971373B