p Topology and Spin Alignment in Photoexcited Triplet and Quintet States
FULL PAPER
was added to the solution. The organic layer was extracted with toluene,
washed with brine, and dried (MgSO4). Evaporation and crystallization
(toluene) gave 3 in 97% yield (5.45 g, 15.1 mmol) as yellow powder:
1H NMR (CDCl3): d=7.39 (t, J=9 Hz, 2H; ArH), 7.54 (d, J=8.8 Hz,
2H; ArH), 7.61 (t, J=6.9 Hz, 2H; ArH), 7.68 (d, J=7.6 Hz, 1H; ArH),
7.77 (t, J=7.6 Hz, 1H; ArH), 7.93 (s, 1H; ArH), 8.09 (d, J=7.6 Hz, 1H;
ArH), 8.63 (d, J=7.9 Hz, 2H; ArH), 10.12 ppm (s, 1H; CHO); elemental
analysis (%) calcd for C21H13BrO: C 69.82, H 3.63; found: C 70.00, H
3.62.
Experimental Section
Measurements:
A
conventional X-band ESR spectrometer (JEOL
TE300) was used without field modulation in the TRESR measurements.
TRESR signals were amplified by a wide-band preamplifier, transferred
to a high-speed digital oscilloscope (LeCroy 9350C), and accumulated,
typically 1400 times for each point. Excitation of 1 was carried out with
355 nm light from a YAG laser (Continuum Surelite II-10). The typical
laser power used in the experiments was ca. 3–5 mJ. The temperature
was controlled using an Oxford ESR 910 cold He gas flow system. All
TRESR and pulsed ESR experiments were carried in isopentane/diethyl
ether (2/3). Solvents of the highest commercially available purity were
purified by the usual procedures. Samples were degassed by repeated
freeze–pump–thaw cycles on a high-vacuum line system.
9-(3-Formylphenyl)-10-(4-formylphenyl)anthracene (4): A mixture of 3
(5.45 g, 15.1 mmol), 4-formylphenylboronic acid (3.0 g, 20 mmol), [Pd-
(PPh3)4] (0.52 g, 0.45 mmol), and K2CO3 (8.28 g, 60 mmol) in toluene
(100)/EtOH (20)/H2O (50 mL) was refluxed for 24 h under nitrogen. The
organic layer was extracted with toluene, washed with brine, and dried
with MgSO4. Evaporation, column chromatography (silica gel, benzene),
and crystallization (EtOH/toluene 9/1) gave 4 in 64% yield (3.76 g,
9.7 mmol) as slightly yellow prisms with m.p. 239–2408C: 1H NMR
(CDCl3): d=7.35–7.39 (m, 4H; ArH), 7.59–7.81 (m, 8H; ArH), 8.01 (s,
1H; ArH), 8.09–8.16 (m, 3H; ArH), 10.15 (s, 1H; CHO), 10.22 ppm (s,
1H; CHO); elemental analysis (%) calcd for C28H18O2: C 87.02, H 4.69;
found: C 87.04, H 4.55.
The echo-detected pulsed ESR measurements were performed on the X-
band TE-300 spectrometer equipped with
a pulsed microwave unit
(JEOL ES-PX1150), an arbitrary wave pattern generator (Tektronix
AWG500), a pulse buffer (JEOL PD1001), and a high-speed digital oscil-
loscope (Tektronix TDS5034). The pulsed microwaves were amplified
with a 10 W solid-state amplifier (Microwave Power Inc., Model L0809–
40). Hahnꢁs p/2–t–p pulse sequence was used for spin echo detection.
The microwave pulse was synchronized with the laser excitation using a
delay pulse generator (Stanford Research DG535). The excitation was
also carried out with 355 nm light from the YAG laser. In the echo-de-
tected nutation experiment, the pulse length of the first microwave pulse
was changed, and the second pulse was set to p pulse, as schematically
shown in Figure 9.
9-[3-(4,4,5,5-Tetramethyl-1,3-dihydroxyimidazolidin-2-yl)phenyl]-10-[4-
(4,4,5,5-tetramethyl-1,3-dihydroxyimidazolidin-2-yl)phenyl]anthracene
(5): A mixture of 4 (0.82 g, 2.1 mmol), 2,3-bis(hydroxyamino)-2,3-dime-
thylbutane (1.25 g, 8.4 mmol), and 2,3-bis(hydroxyamino)-2,3-dimethylbu-
tane monosulfate salt (0.13 g, 0.53 mmol) in MeOH (30)/CHCl3 (30 mL)
was stirred for 72 h. After evaporation under reduced pressure, MeOH
(5 mL) was added, and then H2O (20 mL) was added to the resulting ho-
mogeneous solution. The deposited powder was collected by filtration,
washed with H2O (20 mL) and MeOH (10 mL), and dried in vacuo to
give 5 as a white powder in 65% yield (0.88 g, 1.36 mmol).
9-[3-(4,4,5,5-Tetramethyl-1-yl-oxyimidazolin-2-yl)phenyl]-10-[4-(4,4,5,5-
tetramethyl-1-yl-oxyimidazolin-2-yl)phenyl]anthracene (1): A solution of
NaIO4 (0.25 g, 1.14 mmol) in H2O (40 mL) was added to a suspension of
of 5 (0.25 g, 0.38 mmol) in toluene (40 mL) and the mixture was stirred
for 2 h. The organic layer (darkblue) was separated, washed with brine,
dried (MgSO4), and evaporated. After addition of CH2Cl2 (20 mL) and
NaNO2 (0.26 g, 3.8 mmol) in H2O (20 mL) to the residue, 1n HCl was
added dropwise to the mixture at 08C until the organic layer turned
orange.[27] The organic layer was then separated, washed with brine, dried
(MgSO4), and evaporated. Column chromatography (alumina, toluene)
Figure 9. Schematic diagram of the echo-detected nutation experiment.
In the excited-state measurements, laser excitation was used. The micro-
wave pulse sequence was synchronized with the laser excitation.
The magnetic susceptibility was measured by a SQUID magnetometer
(Quantum Design MPMS2).
and recrystallization from EtOH gave
1 in 6.5% yield (0.015 g,
0.025 mmol) as red prisms with m.p. 240–2428C. Elemental analysis (%)
calcd for C40H40N2O2: C 78.92, H 6.62, N 9.20; found: C 78.76, H 6.71, N
9.01.
General methods: UV/Vis absorption spectra were measured on a Hita-
chi U-3000 absorption spectrometer at room temperature. H NMR spec-
tra were measured with a JEOL l-300 (300 MHz) spectrometer with
1
Me4Si as internal standard.
A small amount of a monoradical impurity, which was detected by ESR
spectroscopy, contaminated the product obtained by the above proce-
dures. Therefore, the product 1 was further purified by column chroma-
tography (alumina, benzene), followed by evaporation of solvent by a
freeze-dry method. The purity and biradical concentration were tested by
ESR and SQUID measurements. The biradical concentration was con-
firmed to be higher than 99%. The monoradical contaminant was not de-
tected within the sensitivity of our ESR apparatus after purification.
Materials: 2,3-Bis(hydroxyamino)-2,3-dimethylbutane was prepared ac-
cording to the literature method.[26] Other reagents were used as pur-
chased. Column chromatography was performed on silica gel (Merck
Silica-gel 60) or alumina (MerckAluminium Oxide 60). Melting points
were recorded on an As one ATM-01 micro melting-point apparatus The
stable radical 1 was synthesized according to the procedure shown in
Scheme 1.
9-(3-Formylphenyl)anthracene (2):
A mixture of 9-bromoanthracene
(4.45 g, 17.3 mmol), 3-formylphenylboronic acid (3.0 g, 20 mmol), [Pd-
(PPh3)4] (0.60 g, 0.52 mmol), and K2CO3 (9.66 g, 70 mmol) in toluene
(120)/EtOH (20)/H2O (40 mL) was refluxed for 24 h under nitrogen. The
organic layer was extracted with toluene, washed with brine, and dried
with MgSO4. Evaporation, column chromatography (silica gel, toluene),
and crystallization (EtOH) gave 2 in 90% yield (4.41 g, 15.6 mmol) as
slightly yellow prisms with m.p. 1228C: 1H NMR (CDCl3): d=7.35–7.37
(m, 2H; ArH), 7.48 (t, J=7.1 Hz, 2H, ArH), 7.56 (d, J=8.8 Hz, 2H;
ArH), 7.70–7.78 (m, 2H; ArH), 7.96 (s, 1H; ArH), 8.06–8.09 (m, 3H;
ArH), 8.54 (s, 1H; ArH), 10.12 ppm (s, 1H; CHO); elemental analysis
(%) calcd for C21H14O: C 89.34, H 5.00; found: C 89.06, H 4.97.
Acknowledgements
This workwas supported by the Grant-in-Aid for Scientific Research on
the general (No. 13440211, 16350079) and Priority Area “Application of
Molecular Spin” (Area 769, Prop. No. 15087208) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan. We also ac-
knowledge Prof. Y. Miura (OCU) for his assistance in the purification of
the sample.
9-(3-Formylphenyl)-10-bromoanthracene (3):
A mixture of 2 (4.40 g,
15.6 mmol) and N-bromosuccinimide (NBS, 2.83 g, 16 mmol) in anhy-
drous DMF (80 mL) was refluxed for 24 h under nitrogen. H2O (300 mL)
[1] Y. Teki, S. Miyamoto, K. Iimura, M. Nakatsuji, Y. Miura, J. Am.
Chem. Soc. 2000, 122, 984.
Chem. Eur. J. 2006, 12, 2329 – 2336
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2335