C O M M U N I C A T I O N S
proton peaks in the 6-6.3 region is that oxygen bridges can form
at different positions of 1 (for example, the 5-18, 6-17, or 7-16
positions).
In summary, irradiation of 2 in the PMMA matrix at 395 nm
produced 1, which showed a long wavelength absorption band
(600-825 nm), having a maximum at 760 nm. Compound 1 was
found to be stable up to 4 h in the PMMA matrix. However, it was
not stable in solution and immediately produces oxygen adducts
in the presence of air.
Acknowledgment. We thank Dr. T. H. Kinstle and Dr. J. R.
Cable for helpful discussions. R.M. is thankful to the McMaster
Endowment for providing a fellowship. Support from Navy Office
of Research (Grant No. N00014-05-1-0372) is greatly acknowl-
edged.
Figure 1. Absorption spectra recorded during and after irradiation of 2 in
a PMMA film (inset: enlarged portion from 600 to 850 nm).
Table 1. Theoretical and Experimental S0-S1 Values of Acenes
TDDFT/6-31G*
a
experimental S0
−S1
S0−S1
S0(OS)−S1
Supporting Information Available: Synthesis and characterization
of 2 and 8, results of photolysis of 2 and 8 in solution and in the thin
films of PMMA, MALDI-MS of 1, and H NMR of oxygen adducts
of 1. This material is available free of charge via the Internet at http://
pubs.acs.org.
compound
nm
eV
eV
eV
1
pentacene
hexacene
heptacene
582
695
825
2.14
1.79
1.50
1.95
1.54
1.24
1.57
1.36
a S0(OS)-S1 values were calculated considering an open shell (OS)
ground state, using the stabilization energy from ref 19b.
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The only difference between 2 and 8 is that the former did not
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1
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by H NMR. The protons of the bridged C atoms of 2 appear at
5.4 ppm. Three additional peaks appeared between 6 and 6.3 ppm
1
in the H NMR of an irradiated solution of 2 in CDCl3 purged
with oxygen. These peaks can be assigned to the protons at the
carbon atoms attached to the oxygen bridge. The reason for many
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