Highly luminescent, polyaryl mesobenzanthrones

Article abstract of DOI:10.1016/j.tet.2011.07.018

Several highly luminescent, aryl-substituted mesobenzanthrones (7H-benz[de]anthracen-7-ones) were prepared by a simple, two-step synthesis: addition of a carboxylated benzyne to a cyclopentadienone followed by an intramolecular Friedel-Crafts acylation. T

Full text of DOI:10.1016/j.tet.2011.07.018

Tetrahedron 67 (2011) 7211e7216
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Highly luminescent, polyaryl mesobenzanthrones
,
Joshua P. Kurtz a, Tod Grusenmeyer a, Ling Tong b y, Gilbert Kosgei a, Russell H. Schmehl a, Joel T. Mague a,
,b,
Robert A. Pascal, Jr. a
*
a Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
b Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Several highly luminescent, aryl-substituted mesobenzanthrones (7H-benz[de]anthracen-7-ones) were
prepared by a simple, two-step synthesis: addition of a carboxylated benzyne to a cyclopentadienone
followed by an intramolecular FriedeleCrafts acylation. These compounds exhibit brilliant, yellow-green
luminescence with quantum yields ranging from 0.01 to 1, depending on the aryl substituents present,
and their photophysical behavior was elucidated by experimental and computational methods.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 May 2011
Accepted 7 July 2011
Available online 21 July 2011
Keywords:
Polycyclic aromatics
Arynes
Cyclopentadienones
Luminescent compounds
1. Introduction
fluors seemed appropriate. We now report the synthesis and
photophysics of a short series of polyaryl mesobenzanthrones.
We have previously reported the synthesis of several cleft-
containing, polyphenyl aromatic compounds, dubbed the ‘alba-
trossenes’ (1, Scheme 1),1,2 by the addition of tetraphenylbenzyne
(generated by the diazotization of tetraphenylanthranilic acid3) to
biscyclopentadienones (2). In an attempt to functionalize the clefts
with more highly polar groups, 3-aminophthalic acid (4) was
substituted as the aryne precursor, but the reaction led instead to
a complex mixture containing several highly luminescent products.
The precise identity of these materials is uncertain, but their likely
nature was illuminated by a model reaction. Diazotization of 4 in
the presence of tetracyclone (6), followed by a workup that in-
cluded an aqueous HCl wash of the organic products, led to the
formation of 1,2,3-triphenylmesobenzanthrone (8, 1,2,3-triphenyl-
7H-benz[de]anthracen-7-one), a yellow compound with a brilliant,
yellow-green luminescence.
2. Results and discussion
2.1. Synthesis and structure
In the original synthesis of 8, the addition of 3-carboxybenzyne
(derived from 4) to tetracyclone, followed by loss of carbon mon-
oxide, gives the expected intermediate 5,6,7,8-tetraphenyl-1-
naphthoic acid (7), but due to the proximity of the 1-carboxyl
and 8-phenyl groups, even aqueous acid is sufficient to catalyze
an intramolecular FriedeleCrafts acylation. However, this synthesis
suffers from extremely poor yields (typically less than 5%) due to
the interference of free carboxylic acids with aryne additions.
Fortunately, the half ester of compound 4, 2-amino-6-
(methoxycarbonyl)benzoic acid (9, Scheme 2) is known.11 Its di-
azotization yields 3-methoxycarbonylbenzyne, which adds readily
to cyclopentadienones without complications. The resulting adduct
only slowly undergoes the intramolecular FriedeleCrafts acylation
in the presence of aqueous HCl, but if the adduct is instead heated
with thionyl chloride in toluene, the desired mesobenzanthrone
forms easily. The intermediate ester need not be isolated. It is only
necessary to carry out an ordinary aqueous workup of the aryne
addition, strip the solvent from the organic extract, and heat this
material in toluene with a small amount of thionyl chloride. In this
way, 1,2,3-triphenylmesobenzanthrone (8) was prepared in 41%
yield from tetracyclone (6).
The photophysics of simple, monosubstituted mesobenzan-
thrones has been well studied,4-6 but no polyaryl mesobenzan-
thrones have been reported previously. With such a short synthesis
in hand, and encouraged by the seemingly unquenchable thirst for
new organic lumiphores with applications in biological and mate-
rials sciences,7e10 the further investigation of this new class of
* Corresponding author. Tel.: þ1 504 862 3547; fax: þ1 504 865 5596; e-mail
address: rpascal@tulane.edu (R.A. Pascal Jr.).
y
Present address: Merck Research Laboratories, Kenilworth, NJ 07033, USA.
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.07.018

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J.P. Kurtz et al. / Tetrahedron 67 (2011) 7211e7216
Scheme 1.
Mesobenzanthrones 8, 12, 13, and 15 are all yellow crystalline
solids, but compound 12 gave particularly nice needles from alco-
hol solutions, and its X-ray structure was determined. The molec-
ular structure of one of the two crystallographically independent
molecules of 12 is illustrated in Fig. 1. Notably, the anthrone core is
slightly twisted18 in these molecules due to the crowding of the aryl
groups. Thus, the torsion angles C(4)eC(5)eC(11)eC(12) (crystal-
lographic numbering) are 8.5ꢀ and 12.3ꢀ for the two independent
molecules. In addition, the various phenyl rings are twisted with
respect to the mesobenzanthrone core by 66ꢀ to 85ꢀ, but in spite of
the presumably poor conjugation of their methoxy substituents
with the core, as well as that of the nitro substituents in 13, these
groups proved to have very significant effects on the luminescence.
Scheme 2.
Polyaryl cyclopentadienones with many different aryl sub-
stituents are known,12 and provide a means to explore the effects of
electron donors and acceptors on the emission of these new lumi-
phores. Both dimethoxy (10) and dinitro (11) tetracyclones13,14 were
employed as precursors in the synthesis to give the corresponding
triarylmesobenzanthrones 12 and 13. In addition, acecyclone15 (14,
Scheme 3) and phencyclone16,17 (16)dcyclopentadienones with
larger polycyclic aromatic coresdwere also utilized in the meso-
benzanthrone synthesis. Acecyclone was readily converted to the
extremely luminescent, yellow compound 15. However, the re-
action with phencyclone gave a product with a bright orange lu-
minescence, presumably compound 17, but in several trials this
material was never isolated in pure form.
Fig. 1. Molecular structure of compound 12. Thermal ellipsoids are plotted at the 50%
probability level.
2.2. Photochemical behavior
The spectrophotometric and luminescence data for the series of
mesobenzanthones are given in Table 1. All of the compounds ab-
sorb in the blue and luminesce in the green/yellow with widely
varying efficiencies. Fig. 2 shows the absorption and fluorescence
spectra for the series in both methanol and acetonitrile. Compounds
Scheme 3.

J.P. Kurtz et al. / Tetrahedron 67 (2011) 7211e7216
7213
Table 1
Spectrophotometric and luminescence data for compounds 8, 12, 13, and 15
Compounds
8
12
13
15
Solvent
Absorbance max (nm)
Emission max (nm)
MeOH
407
521
MeCN
401
498
MeOH
407
579
MeCN
402
527
5900
0.55
MeOH
400
509
5400
0.06
MeCN
396
496
5100
0.01
MeOH
461
562
MeCN
462
519
2400
0.91
Stokes shift (
m
mꢁ1
)
5400
1.0
9.2
4900
0.04
0.6
7300
0.05
0.8
3900
0.97
9.4
Quantum yield
Lifetime (ns)
2.3
0.6
< 0.3
6.6
3
(Mꢁ1 cmꢁ1
)
1.2ꢂ104
1.1ꢂ108
0
1.6ꢂ104
6ꢂ107
1.5ꢂ109
3.6ꢂ103
6ꢂ107
1.2ꢂ109
2.5ꢂ103
2.4ꢂ108
2.0ꢂ108
6.9ꢂ103
1.0ꢂ108
1.6ꢂ109
1.1ꢂ104
6.0ꢂ103
1.0ꢂ108
3ꢂ106
8.9ꢂ103
1.4ꢂ108
1ꢂ107
kr (sꢁ1
knr (sꢁ1
)
)
8, 12, and 13 have broad, featureless UV spectra with maxima close
to 400 nm. The absorption of the fused aryl derivative 15 is signifi-
cantly red shifted (lmax w460 nm) relative to the others, and it ex-
hibits some vibronic structure, especially in acetonitrile. For all the
derivatives, only small differences exist between the absorption
maxima in methanol and acetonitrile. In contrast, the fluorescence
of all the derivatives shifts to the red upon changing the solvent
from acetonitrile to methanol. The magnitude of the solvent shift
varies with structure and is largest for the dimethoxy (12) and fused
aryl (15) derivatives. The spectra in Fig. 2 are normalized to illustrate
these differences in the fluorescence maxima.
The dinitro derivative (13) is only weakly luminescent in both
solvents. The parent compound (8) and its dimethoxy derivative
(12) exhibit large differences in emission intensity with solvent,
and 15 exhibits intense luminescence in both solvents studied.
Radiative decay rate constants were obtained from emission
quantum yield and lifetime data in both methanol and acetonitrile
for all the derivatives. The values obtained vary by only a factor of
four for all the substances; however, nonradiative relaxation rate
constants span nearly three orders of magnitude.
absorption spectra, emission spectra, and quantum yield of the
various analogs were reported. The long wavelength absorption
shifts to the red as solvent polarity increases, and absorption
maxima range from 400 to 500 nm with a typical solvent shift
(etheremethanol) of 20 nm. The fluorescence maxima also shift to
the red as the solvent polarity increases, with the most dramatic
shift in the 3-methoxy derivative with fluorescence maxima of
473 nm in hexane and 544 nm in methanol, respectively. The
fluorescence quantum yields varied greatly across the series, gen-
erally increasing with the solvent polarity; thus the 3-methoxy
derivative has a quantum yield of 0.02 in hexane and 0.76 in
methanol. Comparable effects are observed for compound 8, upon
shifting from the less polar acetonitrile to the more polar methanol,
on the absorption maxima (401 to 407 nm), emission maxima (498
to 521 nm), and quantum yield (0.04 to 1) (see Table 1).
In contrast, the addition of two methoxy groups or two nitro
groups to peripheral phenyls of compound 8 (to form 12 and 13,
respectively) dramatically changes the emissive behavior of the
system, and in quite different ways for the two derivatives. Briefly
stated, the solvent shift on the emission maxima for dimethoxy
compound 12 is substantially larger than for 8 (though in the same
direction for both), but the quantum yield for 12 is far higher in the
less polar acetonitrile (0.55) than in the more polar methanol
(0.05), a surprising inversion of the result observed for 8. For the
dinitro compound 13, the emission in very weak in both solvents
and the spectral shifts are the smallest of all the substances
reported here.
The photophysical behavior of the triphenyl compound 8 gen-
erally parallels that of simpler mesobenzanthrones. A thorough
investigation of monosubstituted mesobenzanthrones was repor-
ted in a series of papers by McKellar and colleagues.4e6 This work
examined anilino, amino, hydroxyl, and methoxy derivatives in the
3-, 4-, 6-, and 8-positions. The effects of solvent polarity on the
In order to explain these differences, produced by substituents
on phenyl rings that are essentially out of conjugation with the
main chromophore, DFT and time-dependent DFT (TDDFT) calcu-
lations were carried out for all compounds at the B3PW91/6-31G(d)
level of theory. Geometry-optimized singlet ground state structures
were employed as input for TDDFT calculations to determine sev-
eral of the lowest energy singlet and triplet electronic transitions
for each compound, both in the gas phase and with the inclusion of
acetonitrile or methanol solvent by means of a polarized contin-
uum model (see the Experimental section for additional details).
From these calculations it is clear that the nature of the lowest
allowed transition in each molecule is quite different from those in
the others.
The triphenyl compound 8 has photophysical behavior that
parallels that of the mesobenzanthrone derivatives reported by
McKellar et al. For this molecule the HOMO and LUMO of the
ground state are both largely localized on the benzanthrone ring
system (see the Supplementary data), and the lowest energy
allowed transition is of
HOMO to LUMO transition.
In contrast, for compound 12, the HOMO is localized on the two
methoxyphenyl groups while the LUMO is a * orbital of the ben-
pep* character and dominated by the
p
zanthrone (see the Supplementary data). The lowest energy tran-
sition clearly involves charge transfer from the methoxyphenyls to
the benzanthrone ring system, and this is reflected in the large
difference in emission maxima in acetonitrile and methanol. The
Fig. 2. Absorption and luminescence spectra of compounds 8, 12, 13, and 15 in
methanol (solid line) and acetonitrile (dashed line). Spectra are normalized for pre-
sentation purposes; molar absorptivities and emission quantum yields are reported in
Table 1.

7214
J.P. Kurtz et al. / Tetrahedron 67 (2011) 7211e7216
seeming anomaly that the quantum yield for 12 is lower in meth-
anol than acetonitrile is easily explained by another DFT result: the
energy gap between the excited singlet state and the triplet state is
significantly lower in methanol than in acetonitrile. This observa-
tion is unique to compound 12 among the chromophores studied,
and provides an explanation for the solvent dependence of the
emission quantum yields in that the smaller singlet-triplet gap
should result in more efficient population of the triplet state.19
For compound 13, the nitro analog, the TDDFT results indicate the
lowest energy allowed transition involves charge transfer from the
benzanthrone ring to a nitrophenyl group (see the Supplementary
data), just the opposite of the situation in 12. Thus this chromo-
phore is yet different from the others.
And what of the intensely fluorescent, fused-ring polycycle 15?
The structured absorption spectrum of compound 15, along with
the smaller Stokes shift and the very high emission yield in a rela-
tively nonpolar solvent, suggests that its photophysical behavior
more nearly parallels that of benzo[k]fluoranthene,20 a substructure
of 150s ring system, rather than that of the mesobenzanthrones. The
TDDFT analysis for 15 indicates that the lowest energy allowed
20 mL) was heated to a gentle reflux. A solution of isoamyl nitrite
(0.50 mL, 3.7 mmol) in DCE (10 mL) was added, and the heating
continued for 10 min.
A suspension of 2-amino-6-(methox-
ycarbonyl)benzoic acid (9, 0.505 g, nominally 2.60 mmol) in DCE
(30 mL) was then added in 10 equal portions, and the resulting
mixture was heated at reflux for 2 h. A 2 M NaOH solution (5 mL)
was added to quench the reaction, and it was cooled to room
temperature. The reaction mixture was then poured into 3 M HCl
(100 mL) and it was extracted with CHCl3 (50 mL). The organic layer
was dried over Na2SO4, and then the solvent was stripped off. The
remaining material was dissolved in toluene (100 mL), SOCl2 (2 mL)
was added, and the solution was heated at reflux for 16 h. After
removal of solvent, the residue was chromatographed on silica gel
(solvent, 2:1 hexaneseCH2Cl2, followed by CH2Cl2) to give a yellow
solid (104 mg). Recrystallization of this material from CHCl3eMeOH
yielded compound 8 (97.0 mg, 0.212 mmol, 40.8%). A portion of this
material (23.1 mg, 0.0504 mmol) was further purified by pre-
parative TLC (Rf 0.52; solvent, toluene) and recrystallization from
ethanol to give 8 of high purity (20.1 mg, 0.0438 mmol). 1H NMR
(CDCl3)
d 6.75 (m, 2H), 6.90 (m, 3H), 7.07e7.25 (m, 12H), 7.34 (ddd,
transition is the HOMOeLUMO transition possessing
p
e
p
* char-
J¼8.0, 6.5, 1.5 Hz, 1H), 7.68 (dd, J¼8.5, 7.5 Hz, 1H), 7.94 (dd, J¼8.5,
acter. However, while the HOMO closely resembles the HOMO of
benzo[k]fluoranthene, the LUMO has a greater orbital contribution
on the benzanthrone portion of the molecule. The strong solvent
dependence of the emission maximum suggests some degree of
charge transfer for the transition, and this is reflected in the dif-
ferential orbital occupancies of the HOMO and LUMO.
1.5 Hz, 1H), 8.46 (ddd, J¼8.0, 1.0, 1.0 Hz, 1H), 8.80 (dd, J¼7.5, 1.5 Hz,
1H); 13C NMR (CDCl3)
d 125.2, 125.6, 126.3, 126.7, 126.9, 127.0, 127.3,
127.5, 127.6, 128.3, 128.4, 128.6, 129.6, 130.1, 131.0, 131.1, 131.2, 131.6,
131.9, 132.8, 134.3, 137.4, 138.8, 139.5, 141.1, 141.7, 141.9, 184.4 (28 of
29 expected resonances observed); HRMS (ESI) m/z 459.1746
(MþH), calcd for C35H23O 459.1749.
3. Conclusion
4.2.2. 1,2-Bis(4-methoxyphenyl)-3-phenyl-7H-benz[de]anthracen-7-
one (12). 3,4-Bis(4-methoxyphenyl)-2,5-diphenylcyclopentadienone
(10, 0.201 g, 0.452 mmol) was subjected to the aryne addition and
cyclization described for the preparation of 8. The crude, concentrated
reaction mixture was chromatographed on silica gel (solvent, 7:5
hexaneseCH2Cl2, followed by 1:1 hexaneseCH2Cl2) to give a yellow
solid (35.8 mg). Recrystallization of this material from CHCl3eMeOH
yielded compound 12 of approximately 90% purity (27.2 mg,
0.0524 mmol, 11.6%). A portion of the product (19.9 mg, 0.0384 mmol)
was further purified by preparative TLC (Rf 0.34; solvent, toluene) and
The four compounds described above are just a tiny fraction of
similar lumiphores that might be prepared by using the general,
one-pot synthesis of polyaryl mesobenzanthrones from tetraar-
ylcyclopentadienones. The particular examples studied all absorb
in the blue and emit strongly in the green/yellow region of the
spectrum, but inclusion of different aryl groups will no doubt in-
crease the range of colors. Variation of the aryl substituents not
only can modify the photophysical properties of these compounds,
but also can provide convenient points of attachment of the chro-
mophores to other substrates. In sum, the polyaryl mesobenzan-
thrones are a promising new class of organic lumiphores.
1
recrystallization from ethanol to give 12 (19.2 mg, 0.0370 mmol); H
NMR (CDCl3) d
3.67 (s, 3H), 3.78 (s, 3H), 6.47 and 6.64 (AA0BB0 system,
4H), 6.71and 6.93 (AA0BB0 system, 4H), 7.11e7.26 (m, 10H), 7.34 (ddd,
J¼8, 5, 3 Hz, 1H), 7.64 (dd, J¼8.5, 7.5 Hz, 1H), 7.89 (dd, J¼8.5, 1.5 Hz,
1H), 8.45 (d, J¼7.5 Hz, 1H), 8.76 (dd, J¼6, 1.5 Hz, 1H); 13C NMR (CDCl3)
4. Experimental
d
55.0, 55.2, 112.3, 113.8, 125.3, 126.1, 126.7, 127.1, 127.4, 127.6, 128.4,
4.1. General information
128.6, 129.4, 130.1, 130.9, 131.6, 131.9, 132.2, 132.3, 132.8, 134.1, 134.2,
137.7, 139.0, 141.0, 141.4, 141.8, 157.3, 158.6, 184.5 (30 of 30 expected
resonances observed); HRMS (ESI) m/z 519.1950 (MþH), calcd for
C37H27O3 519.1960.
2-Amino-6-(methoxycarbonyl)benzoic acid (9) was prepared by
the method of Rogers and Averill.11 However, the material was of
inconsistent purity (the authors note that 9 is unstable at room
temperature), and it was always used in large excess. 3,4-Bis(4-
methoxyphenyl)-2,5-diphenylcyclopentadienone13 (10), 3,4-bis(4-
nitrophenyl)-2,5-diphenylcyclopentadienone14 (11), and acecy-
clone15 (14) were prepared as described previously. All other sol-
vents and reagents were commercial, reagent grade materials, and
they were used without further purification. 1H NMR spectra were
recorded at 400 MHz on a Varian Unity INOVA spectrometer;
samples were dissolved in CDCl3. 13C NMR spectra were recorded
on the same instrument at 101 MHz. High-resolution ESI-TOF and EI
mass spectra were recorded on Agilent 6220 and Kratos MS-50 RFA
spectrometers, respectively.
4.2.3. 1,2-Bis(4-nitrophenyl)-3-phenyl-7H-benz[de]anthracen-7-one
(13). 3,4-Bis(4-nitrophenyl)-2,5-diphenylcyclopentadienone (11,
0.200 g, 0.422 mmol) was subjected to the aryne addition and cy-
clization described for the preparation of 8. The crude, concen-
trated reaction mixture was chromatographed on silica gel (solvent,
2:1 hexaneseCH2Cl2, followed by 1:1 hexaneseCH2Cl2) to give
a yellow solid (104 mg; Rf 0.30 upon TLC; solvent, toluene). Re-
crystallization from ethanol yielded pure compound 13 (81.3 mg,
0.148 mmol, 35.1%); 1H NMR (CDCl3)
d
6.95 and 7.83 (AA0BB0 sys-
tem, 4H), 7.10 (m, 2H), 7.16 (ddd, J¼8.5, 7.0, 1.5 Hz, 1H), 7.26e7.29
(m, 4H), 7.31 and 8.08 (AA0BB0 system, 4H), 7.42 (t, J¼7.5 Hz, 1H),
7.75 (dd, J¼8.5, 7.5 Hz, 1H), 7.94 (dd, J¼8.5, 1.5 Hz, 1H), 8.50 (dd,
J¼8.0, 1.5 Hz, 1H), 8.83 (dd, J¼7.0, 1.0 Hz, 1H); 13C NMR (CDCl3)
4.2. Data for compounds
d
122.4, 123.9, 126.2, 127.4, 127.8, 128.2, 128.3, 128.9, 129.8, 130.6,
4 . 2 . 1. 1,2,3-Triphenyl-7H-benz[de]anthracen-7-one (1,2,3-
triphenylmesobenzanthrone) (8). A solution of tetraphenylcyclo-
pentadienone (6, 0.200 g, 0.520 mmol) in 1,2-dichloroethane (DCE,
131.4,132.0, 132.1,133.0,133.9,134.3,135.3,135.8,136.0,137.3,137.5,
137.8, 146.0, 146.4, 146.9, 148.4, 183.8 (27 of 29 expected resonances

J.P. Kurtz et al. / Tetrahedron 67 (2011) 7211e7216
7215
observed); HRMS (ESI) m/z 549.1447 (MþH), calcd for C35H21N2O5
model. Solvent inclusion significantly changes the location of
charge density when compared to the results of gas phase calcu-
lations, but negligible differences exist between the orbitals
obtained in the two solvents.
549.1450.
4.2.4. 9-Phenyl-5H-anthro[9,1-jk]fluoranthen-5-one (15). Acecyclone
(14, 0.100 g, 0.281 mmol) was subjected to the aryne addition and
cyclization described for the preparation of 8. The crude, concen-
trated reaction mixture was chromatographed on silica gel (solvent,
Acknowledgements
2:1 hexaneseCH2Cl2) to give
a yellow solid (22.8 mg). Re-
This work was supported by National Science Foundation Grant
CHE-0936862 to (to R.A.P.), United States Department of Energy
Grant DE-FG-02-96ER14617 (to R.H.S.), and Louisiana Board of Re-
gents Fellowship BORSF 015-GF-09 (to T.G.); all are gratefully
acknowledged.
crystallization of this material from CHCl3eMeOH yielded com-
pound 15 (21.0 mg, 0.0488 mmol, 17.3%). A portion of the product
(20.0 mg, 0.0465 mmol) was further purified by preparative TLC (Rf
0.45; solvent, toluene) and recrystallization from ethanol to give 15
of high purity (17.5 mg, 0.0407 mmol); 1H NMR (CDCl3)
d 6.57 (d,
J¼7.0 Hz, 1H), 7.36 (dd, J¼8.0, 7.0 Hz, 1H), 7.53 (m, 2H), 7.61e7.69 (m,
7H), 7.80 (d, J¼8.0 Hz, 1H), 7.90 (d, J¼7.0 Hz, 1H), 7.92 (dd, J¼8.0,
2.0 Hz, 1H), 8.52 (dd, J¼8.0, 1.5 Hz, 1H), 8.66 (dd, J¼7.5, 1.5 Hz, 1H),
Supplementary data
(1) A PDF file containing 1H and 13C NMR spectra of compounds
8,12,13, and 15, images of the calculated HOMO and LUMO for 8,12,
13, and 15, and full Refs. 24,25 and (2) an ASCII text file containing
the atomic coordinates and energies of the calculated structures of
8, 12, 13, and 15. Crystallographic data (excluding structure factors)
for the structure of 12 have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication number
CCDC 823793. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK [fax:
+44 0 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk]. Supple-
mentary data associated with this article can be found in online
version at doi:10.1016/j.tet.2011.07.018.
8.74 (d, J¼7.5 Hz, 1H), 9.19 (d, J¼7.0 Hz, 1H); 13C NMR (CDCl3)
d 122.8,
123.8, 124.9, 126.2, 126.6, 127.4, 127.7, 127.9, 128.0, 128.3, 128.4, 128.8,
128.9, 129.0, 129.3, 129.9, 130.4, 131.8, 132.2, 132.4, 133.0, 135.6, 135.8,
136.4, 136.5, 136.6, 137.3, 137.4, 137.8, 184.4 (30 of 29 expected res-
onances observed); HRMS (EI) m/z 430.1356 (Mþ), calcd for C33H19
O
430.1358.
4.3. Photochemical studies
All electronic absorption spectra were recorded on a Hew-
lettePackard 8452A diode array spectrophotometer. All fluores-
cence spectra were obtained by using an SPEX Fluorolog
spectrofluorimeter equipped with a 450-W Xe arc lamp, single
grating monochromators with fixed slits, and a thermoelectrically
cooled ANDOR CCD detector. Luminescence quantum yields were
determined from the integrated corrected emission spectra of the
mesobenzanthrone derivatives relative to anthracene as a refer-
ence. The mesobenzanthrones were absorbance matched to the
anthracene standard at 394 nm and then degassed with nitrogen
for 10 min prior to the measurement of the emission spectra. Lu-
minescence lifetimes were obtained by the time-correlated single
photon counting technique. Each sample was excited using an IBH
NanoLED pulsed diode laser source at either 377 or 440 nm. The
emitted light was collected at right angles to the excitation pulse,
filtered through bandpass filters (Andover Corporation) and col-
lected by an IBH Model TBX-04 cooled photomultiplier (PMT) de-
tector. The output of the PMT served as the input for the stop
channel of the time to amplitude converter (TAC, Tennelec TC-863).
Start pulses for the TAC were obtained from the synchronous TTL
output of the NanoLED laser source. The output from the TAC was
directed to a multichannel analyzer (Ortec, Easy MCA), where the
References and notes
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signal was accumulated. Laser light scattered from
a non-
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and the built-in default thresholds for wave function and gradient
convergence were employed. Full geometry optimizations were
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molecules. The optimized singlet geometries were used as the in-
put for TDDFT calculations at the same level of theory. These cal-
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lowest energy singlet and triplet electronic transitions for each
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nenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida,
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€