Photochromism of Fluorescent Diarylethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5423
(200 MHz, CDCl3) δ 2.08 (s, 3H), 2.10 (s, 3H), 2.36 (s, 6H),
6.73 (s, 1H), 7.26-7.96 (m, 14H); MS m/z 690 (M+). Anal. Calcd
for C38H28F6N2S2: C, 66.07; H, 4.09; N, 4.06. Found: C, 65.99;
H, 3.87; N, 3.98.
Anal. Calcd for C38H28F6N2S2: C, 66.07; H, 4.09; N, 4.06.
Found: C, 65.62; H, 4.22; N, 3.97.
1-(3,5-Dim et h yl-2-t h ien yl)-2-[2,4-d im et h yl-5-(2′′,4′′,5′′-
t r ip h en ylim id a zol-4′-yl)-3-t h ien yl]p er flu or ocyclop en -
ten e (3a ). To the solution of 2,4-dimethylthiphene (13; 71 mg,
0.3 mmol) and TMEDA (0.2 mL) in anhydrous ether (7 mL)
was added dropwise n-BuLi (1.6 M in hexane, 0.2 mL, 0.33
mmol) at 0 °C under argon atmosphere. The reaction mixture
was stirred for 30 min at -78 °C, and then perfluorocyclopen-
tene derivative (11; 60 mg, 0.1 mmol) in anhydrous THF (4
mL) was added. The reaction mixture was stirred for 1 h at
-78 °C, and then methanol was added. The product was
extracted with chloroform, dried with magnesium sulfate, and
concentrated. Purification was performed by column chroma-
tography (SiO2, chloroform) followed by GPC. 3a was obtained
as a yellow powder (38 mg, 42%): 1H NMR (200 MHz, CDCl3)
δ 2.06 (s, 3H), 2.01 (s, 3H), 2.28 (s, 3H), 2.39 (s, 3H), 2.37 (s,
3H), 6.52 (s, 1H), 7.30-7.98 (m, 14H); MS m/z 690 (M+).
3-Br om o-2,4-d im eth yl-5-(2′′,4′′,5′′-tr ip h en ylim id a zolyl)]-
th iop h en e (9). To the solution of 4′-bromo-triphenylimidazole
(2.0 g, 5.2 mmol), Pd(PPh3)4 (200 mg), and aqueous Na2CO3
(6.5 mL; 20% w/w) in THF (200 mL) was added 4-bromo-3,5-
dimethyl-2-thiopheneboronic acid8 (8; 2.75 g; 12 mmol) under
argon atmosphere. The solution was refluxed for 48 h at 70
°C. 2 N HCl was poured into the reaction mixture, and then
the product was extracted with chloroform, dried with mag-
nesium sulfate, and concentrated. Purification was performed
by column chromatography (SiO2; chloroform). 9 was obtained
1
as a yellow powder (1.38 g, 54%): mp. 202-204 °C; H NMR
(200 MHz, CDCl3) δ 2.31 (s, 3H), 2.46 (s, 3H), 7.20-7.97 (m,
14H); MS m/z 484 (M+), 486 (M + 2)+. Anal. Calcd for C C27H21
-
BrN2S: C, 66.80; H, 4.36; N, 5.77. Found: C, 66.47; H, 4.46;
N, 5.43.
C
38H28F6N2S2: C, 66.07; H, 4.09; N, 4.06. Found: C, 66.32; H,
2,4-Dim eth yl-5-[4′-(2′′,4′′,5′′-tr ip h en ylim id a zolyl)]th io-
p h en e (10). To the solution of bromothiophene (9; 200 mg,
0.41 mmol) in anhydrous THF (8 mL) was added dropwise
n-BuLi (1.6 M in hexane, 0.5 mL, 0.82 mmol) at -78 °C under
argon atmosphere. The reaction mixture was stirred for 1 h
at -78 °C, and then methanol was added. The product was
extracted with chloroform, dried with magnesium sulfate, and
concentrated. Purification was performed by column chroma-
tography (SiO2, chloroform) followed by GPC. 10 was obtained
4.33; N, 4.02.
1-(2,5-Dim et h yl-3-t h ien yl)-2-[2,4-d im et h yl-5-(2′′,4′′,5′′-
t r ip h en ylim id a zol-4′-yl)-3-t h ien yl]p er flu or ocyclop en -
ten e (4a ). To the solution of 3-bromo-1,2-dimethylindole (14;
227 mg, 1.0 mmol) in anhydrous THF (8 mL) was added
dropwise n-BuLi (1.6 M in hexane, 0.68 mL, 1.1 mmol) at 0
°C under argon atmosphere. The reaction mixture was stirred
for 1 h at 0 °C. The solution was cooled at -78 °C, and then
perfluorocyclopentene derivative (11; 77 mg, 0.12 mmol) in
anhydrous THF (5 mL) was added. The reaction mixture was
stirred for 1 h at -78 °C and then methanol was added. The
product was extracted with chloroform, dried with magnesium
sulfate, and concentrated. Purification was performed by
column chromatography (SiO2, chloroform) followed by GPC.
4a was obtained as a yellow powder (33 mg, 38%): 1H NMR
(200 MHz, CDCl3) δ 1.71 (s, 1H), 1.77 (s, 2H), 1.83 (s, 2H),
1.90 (s, 1H), 2.57 (s, 3H), 2.46 (s, 3H), 6.70-7.87 (m, 18H);
MS m/z 723 (M+). Anal. Calcd for C42H31F6N3S: C, 69.70; H,
4.32; N, 5.81. Found: C, 70.09; H, 4.66; N, 5.97.
P h otoch r om ic Qu a n tu m Yield s. The cyclization quantum
yields were determined by comparing the photocyclization rate
of furyl flugide in n-hexane by using a normal procedure.20
The cycloreversion quantum yields were also measured using
furyl flugide in toluene as a reference.21
F lu or escen ce Qu a n tu m Yield s. The fluorescence quan-
tum yields were determined using anthracene in cyclohexane
(Φf ) 0.31; excitation wavelength 366 nm) as a reference.22
1
as a yellow powder (38 mg, 23%): mp 207-208 °C; H NMR
(200 MHz, CDCl3) δ 2.28 (s, 3H), 2.48 (s, 3H), 6.61 (s, 1H),
7.30-7.98 (m, 14H); MS m/z 406 (M+). Anal. Calcd for
C
27H22N2S: C, 79.77; H, 5.45; N, 6.89. Found: 80.01; H, 5.60;
N, 7.02.
1-[2,4-Dim eth yl-5-(2′′,4′′,5′′-tr ip h en ylim id a zol-4′-yl)-3-
th ien yl]p er flu or ocyclop en ten e (11). To the solution of
bromothiophene (9; 300 mg, 0.62 mmol) in anhydrous THF
(20 mL) was added dropwise n-BuLi (1.6 M in hexane, 1.12
mL, 1.86 mmol) at -78 °C under argon atmosphere. The
reaction mixture was stirred for 1.5 h at -78 °C, and then
perfluorocyclopentene (0.25 mL, 1.86 mmol) was added in one
portion. The reaction mixture was stirred for 1 h at -78 °C,
and then methanol was added. The product was extracted with
chloroform, dried with magnesium sulfate, and concentrated.
Purification was performed by column chromatography (SiO2,
chloroform) followed by GPC. 11 was obtained as a yellow
powder (77 mg, 20%): 1H NMR (200 MHz, CDCl3) δ 2.15 (s,
3H), 2.40 (s, 3H), 7.27-7.99 (m, 14H); MS m/z 598 (M+). Anal.
Calcd for C32H27F7N2S: C, 63.57; H, 4.50; N, 4.63. Found: C,
63.25; H, 4.11; N, 4.25.
1-(2,5-Dim et h yl-3-t h ien yl)-2-[2,4-d im et h yl-5-(2′′,4′′,5′′-
t r ip h en ylim id a zol-4′-yl)-3-t h ien yl]p er flu or ocyclop en -
ten e (2a ). To the solution of 3-iodo-2,5-dimethylthiphene (12;
90 mg, 0.38 mmol) in anhydrous THF (8 mL) was added
dropwise n-BuLi (1.6 M in hexane, 0.25 mL, 0.42 mmol) at
-78 °C under argon atmosphere. The reaction mixture was
stirred for 30 min at -78 °C, and then perfluorocyclopentene
derivative (11; 77 mg, 0.13 mmol) in anhydrous THF (5 mL)
was added. The reaction mixture was stirred for 1 h at -78
°C, and then methanol was added. The product was extracted
with chloroform, dried with magnesium sulfate, and concen-
trated. The product was extracted with chloroform, dried with
magnesium sulfate, and concentrated. Purification was per-
formed by column chromatography (SiO2, chloroform) followed
by GPC. 2a was obtained as a colorless powder (52 mg, 58%):
1H NMR (200 MHz, CDCl3) δ 2.04 (s, 6H), 2.27 (s, 3H), 2.39
(s, 3H), 6.63 (s, 1H), 7.26-7.96 (m, 14H); MS m/z 690 (M+).
Ack n ow led gm en t. This work was supported by
CREST (Core Research for Evolutional Science and
Technology) of J apan Science and Technology Corp.
(J ST).
Su p p or tin g In for m a tion Ava ila ble: UV/visible absorp-
tion spectra of photochromic reaction in THF upon irradiation
with 366-nm light: 2a , 3a , and 4a . This material is available
J O010267W
(19) (a) Irie, M.; Sakemura, K.; Okinaka, M.; Uchida, K. J . Org.
Chem. 1995, 60, 8305. (b) Uchida, K.; Nakayama, Y.; Irie, M. Bull.
Chem. Soc. J pn. 1990, 63, 1311.
(20) Yokoyama, Y.; Kurita, Y. J . Synth. Org. Chem. J pn. 1991, 49.
364.
(21) Heller. H. G.; Langan, J . R. J . Chem. Soc., Perkin Trans. 2 1981,
341.
(22) Handbook of fluorescence spectra of aromatic molecules; Ber-
lman, I. B., Ed.; Academic Press: New York and London, 1971.