DIARYLETHENE-CONTAINING TERPYRIDINE
+
spectrometry (MS) (m/z): 652.6 [(M + H) ]; Anal. Calcd. for C39
H
32
N
4
O
2
S
2
:
in toluene and then coordinated with different metal ions to
C, 71.75; H, 4.94; N, 8.58; S, 9.82. Found: C, 71.48; H, 5.11; N, 8.65; S, 9.97.
give L–M–L complexes 4–6. All the synthesized complexes
1
were fully characterized by ESI-MS, H NMR, UV–vis spectra,
1
and elemental analysis. In H NMR spectra of the complexes,
Complex L–Zn–L (4)
signals of the protons attached to the TPY moieties appeared
at lower magnetic fields than those of the free ligand because
of the strong electron-withdrawing effects of the metal
centers.
Zn(CH
3
COO)
10 mL) and then added drop-wise to the solution of ligand 3
32.6 mg, 0.05 mmol) in C OH (10 mL) and CHCl (1.5 mL). The
2 2 2 5
2H O (4.8 mg, 0.022 mmol) was dissolved in C H OH
(
(
2
H
5
3
mixture was stirred at room temperature for 30 min. Then, an excess
of KPF (160 mg) was added. After 1 h, the solid was centrifuged,
washed with ethanol, water, and Et O, and dried in vacuum to give
a yellow product (Yield: 84%). m.p. > 300 C; H NMR (400 MHz, DMSO-d
d (ppm): 9.46 (s, 4H), 9.16 (d, J = 7.59 Hz, 4H), 8.58 (d, J = 7.49 Hz, 4H), 8.32
s, 4H), 8.00 (s, 4H), 7.91 (d, J = 7.25Hz, 4H), 7.53 (s, 4H), 2.28 (d, J= 8.86 Hz,
6
2
ꢀ
1
Electronic absorption and photochromic behaviors
6
)
The absorption spectra of ligand
3 in n-hexane and
(
1
ꢁ4
2+
complexes 4–6 in dilute (10 mmol/L) THF solution were
recorded. Their photochromic behaviors were investigated
by monitoring the changes in the absorption spectra upon
irradiation at a specific wavelength capable of triggering the
open/closed isomerization in the DTE units. The results are
summarized in Table 1.
2H), 2.16 (s, 6H), 2.01 (s, 12H), 1.85 (s, 6H); ESI-MS (m/z): 684.5 [M ꢁ 2PF
6
] ;
64 12 8 4 2 4
Anal. Calcd. for C78H F N O P S Zn: C, 56.40; H, 3.88; N, 6.75; S, 7.72. Found:
C, 56.15; H, 3.99; N, 6.91; S, 7.53.
Complex L–Co–L (5)
The photocyclization of ligand 3 was studied in different-
CoCl
and then added drop-wise to the solution of ligand 3 (32.6 mg,
.05 mmol) in OH (10 mL)/CHCl (1.5 mL). The mixture was
refluxed for 3 h under nitrogen atmosphere. After filtration, an excess
of KPF (160 mg) was added, and the yielding solid was centrifuged,
washed with ethanol, water, and Et O, and dried in vacuum to give
a brown product (Yield: 86%). m.p. > 300 C; H NMR (400 MHz,
DMSO-d ) d (ppm): 85.69 (br, 4H), 50.29 (s, 4H), 35.82 (s, 4H), 31.04
s, 4H), 13.55 (s, 4H), 10.09 (s, 4H), 8.96 (s, 4H). The C–H peaks of
2
ꢂ6H
2 2 5
O (5.2 mg, 0.022 mmol) was dissolved in C H OH (10 mL)
polarity solvents including CH CN, THF, and n-hexane by irradi-
3
0
C
2
H
5
3
ation at 254 nm (Fig. 1). Remarkable solvent dependence of
the photochromic reaction was observed. The conversion of
ligand 3 from an open-ring to a closed-ring isomer in the
photostationary state (PSS) under irradiation with UV light
decreased with increasing solvent polarity, in good agreement
with the previous report, which presumed that it was due to
6
2
ꢀ
1
6
(
[
19]
1
the contribution of twisted intramolecular charge transfer.
the thienyl rings in the H NMR spectrum were overlapped with
2
+
In acetonitrile, no appreciable color change was observed
upon irradiation with UV light, as shown in Fig. 1(c).
the solvent residual peak of DMSO; ESI-MS (m/z): 681.3 [M ꢁ 2PF
6
] ;
Anal. Calcd. for C78 Co: C, 56.62; H, 3.90; N, 6.77;
64 12 8 4 2 4
H F N O P S
S, 7.75. Found: C, 56.34; H, 4.08; N, 6.92; S, 7.96.
As shown in Fig. 1(a), the starting open form of ligand 3 in
n-hexane solution showed two peaks at 282 and 375 nm. The
former peak was assigned to the TPY-based transition, and
Complex L–Ru–L (6)
1
the peak at 375 nm was responsible for the S ! S ( IL)
0
1
RuCl
added drop-wise to the solution of ligand 3 (32.6 mg, 0.05 mmol) in
OH (10 mL)/CHCl (1.5 mL). The mixture was refluxed for 4 h under
nitrogen atmosphere. After filtration, an excess of KPF (160 mg) was
added, and the yielding solid was centrifuged, washed with ethanol,
water, and Et O, and dried in vacuum to give a brown product (Yield:
2%). m.p. > 300 C; H NMR (400 MHz, DMSO-d
3 2 5
(4.6 mg, 0.022 mmol) was dissolved in C H OH (10 mL) and then
transition of the DTE unit. Upon irradiation with 254 nm light,
the yellowish solution turned reddish, the peak at 282 nm
gradually decreased, and new absorption bands appeared at
C
2
H
5
3
6
3
78 and 532 nm, which were assigned to S
0
! S
2
and S
0
! S
1
transitions, respectively. Such behavior was characteristic of
the formation of the closed form of DTE derivatives, because
2
ꢀ
1
8
6
) d (ppm): 9.54
(
(
s, 4H), 9.11 (d, J = 8.17 Hz, 4H), 8.57 (d, J = 8.27 Hz, 4H), 8.10
t, J = 7.60 Hz, 4H), 7.91 (d, J = 7.90 Hz, 4H), 7.59 (d, J = 5.33 Hz, 4H),
7
.31 (d, J = 6.58 Hz, 4H), 2.28 (d, J = 9.02 Hz, 12H), 2.16 (s, 6H), 2.01
Table 1. UVvis absorption maxima of all compounds studied
2
+
(
d, J = 4.33 Hz, 12H), 1.85 (s, 6H); ESI-MS (m/z): 702.6 [M ꢁ 2PF
6
] ;
Anal. Calcd. for C78
H
64
F
12
N
8
O
4
P
2
S
4
Ru: C, 55.22; H, 3.80; N, 6.60; S,
max/nm (c = 2 ꢃ 10ꢁ4 mmol/L)
l
7
.56. Found: C, 55.49; H, 3.57; N, 6.51; S, 7.80.
b
b
Compound
(O)
TPY-based
S
0
! S
2
S
0
! S
1
MLCT
3
282
280
344
344
285
—
378
—
380
—
378
—
378
375
532
410
532
320
522
380
567
—
—
—
—
—
—
491
491
RESULTS AND DISCUSSION
3(PSS)
4
4
(O)
(PSS)
Synthesis and characterization
The particular type of diarylethene unit was chosen to be
incorporated into our molecule for its good photochromic
property and ease of functionalization at the maleic anhy-
dride oxygen. Scheme 1 outlines the synthetic route for the
chemically modified dithienylethene maleic anhydride, allow-
ing a fine tune of its photochromic and thermal properties.
5(O)
5(PSS)
6(O)
286
285,310
286,309
6(PSS)
TPY, terpyridine; MLCT, metal-to-ligand charge transfer; PSS,
photostationary state.
0
0
4
′-(4-nitrophenyl)-2,2′:6′,2 -terpyridine was synthesized follow-
a
All spectra were recorded in a conventional 1.0 cm quartz
ing a facile one-pot reaction by the previously reported proce-
dure.
by using SnCl /HCl. Ligand 3 was prepared from DTE by a con-
ventional thermal imidization with the amino TPY compound 2
ꢁ4
cell at a concentration of 2 ꢃ 10 M in tetrahydrofuran
[16]
The nitro group was reduced to amino compound
except L in n-hexane.
2
b
Dithienylethene-based transitions.
J. Phys. Org. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc