6
162
V. S. Vyas et al. / Tetrahedron Letters 50 (2009) 6159–6162
around the C@C bond.12 Interestingly, however, T2–T4 showed an
invariant) emission band centered at 520 nm, and the emission
Supplementary data
(
intensity linearly increased with the increasing number of pheny-
lene moieties from T2 to T4 (see Fig. 5B). The fluorescence
quantum yields for T2–T4 were also determined using 9,10-
Synthetic details, spectral data, and NMR spectra/mass spectra
of various compounds in Scheme 1 are available. Supplementary
diphenylanthracene (
U
= 0.91)13 as a standard (see the Supple-
mentary data for the experimental details) and the values are
compiled in Table 1. The quantum yield data in Table 1 show that
there is a modest increase in the fluorescence quantum yield from
References and notes
1.
(a) Introduction to Molecular Electronics; Petty, M. C., Bryce, M. R., Bloor, D., Eds.;
Oxford University Press: New York, 1995; (b) Organic Electronics; Klauk, H., Ed.;
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Scherf, U.; Neher, D.; Brauchle., C.; Meerholz, K. Nature 2000, 405, 661.
(a) Gale, D. M. J. Appl. Polym. Sci. 1978, 22, 1971; (b) Irvine, P. A.; Wu, D. C.;
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A. V.; Resch, T.; Knachel, H. C.; Adams, W. W.; Socci, E. P.; Farmer, B. L. Polymer
1993, 34, 1571.
T2 (U = 0.01) to T3 (U = 0.02) to T4 (U = 0.04).
As such, the observation of relatively weak emission from T2–
T4 suggests that the emission largely arises from a reorganization
of the ethylenic-centered exciton to the poly-p-phenylene groups
2.
1
4
of the T2–T4. Indeed, a comparison of the emission spectra of
3
poly-p-phenylenes with that of T2–T4 show a reasonable spectral
similarity, however, at this juncture, we are unable to reconcile
the invariance of the emission bands of T2–T4. Further studies
using time-resolved spectroscopy as well as theoretical calcula-
tions will be required to pinpoint the origin of the observed emis-
sion of T2–T4.
3. Banerjee, M.; Shukla, R.; Rathore, R. J. Am. Chem. Soc. 2009, 131, 1780.
4
.
(a) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350 and
references cited therein; (b) Zade, S. S.; Bendikov, M. Org. Lett. 2006, 8, 5243.
(a) Suzuki, A. Chem. Commun. 2005, 4759; (b) Hassan, J.; Sevignon, M.; Gozzi,
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5.
6.
7.
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Buckles, R. E.; Hausman, E. A.; Wheeler, N. G. J. Am. Chem. Soc. 1950, 72, 2494.
McMurry, J. E. Acc. Chem. Res. 1983, 16, 405. and references therein.
(a) The first oxidation wave of TPEs (i.e., TPE?TPE ) is completely reversible
In summary, we have developed an efficient synthesis of solu-
ble tetrakis(poly-p-phenylene)ethylenes (TPEs), where poly-p-
phenylene units contain up to 4 phenylene moieties, from easily
available precursors. Various TPEs undergo reversible electro-
chemical oxidations and form stable cation-radical salts in solu-
tion which are stabilized by charge delocalization onto the
poly-p-phenylene arms. The evaluation of absorption/emission
properties of various TPEs showed that the intramolecular reorga-
nization of exciton energy from the non-emissive tetraphenyleth-
ylene core to the poly-p-phenylene arms allows them to emit.
Efforts are underway to develop more effective emitters based
on tetrakis(poly-p-phenylene) derivatives in which C@C bond
rotations, responsible for the radiation-less deactivation of the
excited state, are hampered.
+Å
if the scanning is terminated before the start of second oxidation event as
judged by the almost unity anodic/cathodic peak current ratios, I
theoretical), at room temperature.; (b) Bashkin, J. K.; Kinlen, P. J. Inorg. Chem.
990, 29, 4507 and references cited therein.
a c
/I = 1.0
(
1
9. (a) Bell, F. A.; Ledwith, A.; Sherrington, D. C. J. Chem. Soc. C 1969, 13, 2719; (b)
Bell, F. A.; Ledwith, A.; Sherrington, D. C. J. Org. Chem. 1976, 13, 155.
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13. Momicchioli, F.; Bruni, M. C.; Baraldi, I. J. Phys. Chem. 1972, 76, 3983.
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Chem. 2007, 72, 8054; (b) Debroy, P.; Lindeman, S. V.; Rathore, R. J. Org. Chem.
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Acknowledgment
We thank the National Science Foundation for the financial
support.