Synthesis, Characterization and Photochromic Studies of Spirooxazine-Containing 2,2′-Bipyridine Ligands and Their Rhenium(I) Tricarbonyl Complexes

Article abstract of DOI:10.1002/chem.200305485

A series of spirooxazine-containing 2,2′-bipyridine ligands and their rhenium(I) tricarbonyl complexes has been designed and synthesized, and their photophysical, photochromic and electrochemical properties have been studied. The X-ray crystal structures

Full text of DOI:10.1002/chem.200305485

FULL PAPER
Synthesis, Characterization and Photochromic Studies of Spirooxazine-
Containing 2,2’-Bipyridine Ligands and Their Rhenium(i) Tricarbonyl
Complexes
Chi-Chiu Ko, Li-Xin Wu, Keith Man-Chung Wong, Nianyong Zhu, and
[
a]
Vivian Wing-Wah Yam*
Abstract: A series of spirooxazine-containing 2,2’-bipyridine ligands and their rhe-
nium(i) tricarbonyl complexes has been designed and synthesized, and their photo-
physical, photochromic and electrochemical properties have been studied. The X-
ray crystal structures of two of the complexes have been determined. Detailed
studies showed that the emission properties of the complexes could readily be
switched through photochromic reactions.
Keywords: luminescence
gands ¥ photochromism ¥ rhenium ¥
spirooxazine
¥ N li-
Introduction
fined to the organic system, and it has not been until recent-
ly that increasing study of the incorporation of these organic
spirooxazines/spiropyrans into transition metal complex sys-
The rapid expansion in the development of new optical
memory and storage devices has inspired research into pho-
tochromic compounds, which are promising candidates as
[9]
tems has been pursued. The incorporation of such photo-
chromic moieties into transition metal complex systems
would be expected to give rise to perturbation of the photo-
chromic behavior. Gust et al., for example, showed that a
spiropyran could be photosensitized by the excited state of a
[1]
optical recording and storage materials, and as materials
[2]
for ophthalmic and sunglass lenses. In addition to their po-
tential applications utilizing their different absorption prop-
erties, the changes in electron delocalization have also been
employed for the design of photoswitchable non-linear opti-
[9a]
zinc±porphyrin system.
In our previous communication,
we have demonstrated the photosensitization of a pyridine-
[
3]
[4]
[5]
cal devices, enzymatic systems, host±guest systems and
containing spirooxazine by the rhenium(i) tricarbonyl dii-
[6]
[9b]
luminescent devices. Spirooxazines are one of the most
popular classes of photochromic materials, and have been
shown to possess high fatigue resistance and excellent pho-
tostability. The photochromism of spirooxazines is attribut-
able to the photochemical cleavage of the spiro-CꢀO bond,
which results in the extension of p-conjugation in the col-
ored photomerocyanine conformer and thus shifts the ab-
sorption to the visible region. It has been extensively studied
mine complex system.
As an extension of this work, a
series of spirooxazine-containing 2,2’-bipyridine ligands and
their rhenium(i) tricarbonyl complexes has been synthesized
and characterized. The switching of their emission proper-
ties through photochromic reactions is also reported.
[
7]
Results and Discussion
[7b,8]
and reviewed.
Most studies of this class have been con-
Synthesis: The synthetic routes for the formation of the spi-
rooxazine-containing ligands are summarized in Scheme 1.
Esterification of 1,3,3-trimethyl-9’-hydroxyspiroindoline-
naphthoxazine (SO) with 2,2’-bipyridine-4,4’-dicarboxylic
[
a] Dr. C.-C. Ko, Dr. L.-X. Wu, Dr. K. M.-C. Wong, Dr. N. Zhu,
Prof. Dr. V. W.-W. Yam
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based
Materials Research
[10]
acid
and the unsymmetrically substituted 2,2’-bipyridine,
Department of Chemistry, and HKU-CAS Joint Laboratory on New
Materials
The University of Hong Kong, Pokfulam Road, Hong Kong SAR
4’-methyl-2,2’-bipyridine-4-carboxylic acid (prepared by the
stepwise oxidation of 4,4’-dimethyl-2,2’-bipyridine with sele-
nium(iv) dioxide and silver(i) oxide without isolation of the
intermediates, as described by McCafferty et al. ) in the
presence of triethylamine in anhydrous benzene at room
temperature gave L1 and L2, respectively. Substitution reac-
tions of mono- or di(bromomethyl)-substituted 2,2’-bipyri-
(
P. R. China)
[11]
Fax : (+852)2857-1586
E-mail: wwyam@hku.hk
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
766
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200305485
Chem. Eur. J. 2004, 10, 766 ± 776

7
66 ± 776
ing diimine ligands in anhy-
drous benzene at 508C afforded
complexes 1±4, which were iso-
lated as yellow to red crystals,
depending on the nature of the
diimine ligands, after purifica-
tion by column chromatography
on silica gel and subsequent re-
crystallization from CH Cl /
2
2
Et O. The identities of the li-
2
gands L1±L4 and complexes 1±
4
were confirmed by satisfacto-
1
ry elemental analyses, H NMR
spectroscopy, IR spectroscopy
and FAB mass spectrometry,
and for complexes 1 and 2 also
by X-ray crystallography.
X-ray crystalstructure determi-
nation: Perspective drawings of
complexes 1 and 2 are depicted
in Figure 1 and Figure 2, respec-
tively, the structure determina-
tion data are collected in
Table 1, and selected bond
lengths and angles are summar-
ized in Table 2. The rhenium
atom adopted a distorted octa-
hedral geometry with the three
carbonyl groups in a facial ar-
rangement. The angles subtend-
ed by the nitrogen atoms of L1
and L2 at the rhenium centre,
N1-Re1-N2, were 74.78 and
7
4.88, respectively, which are
much smaller than the ideal
angle of 908 adopted in octahe-
dral geometry. The deviation
from the ideal angle is due to
the steric requirement of the
chelating ligands L1 and L2,
which is commonly observed in
other related complex sys-
[13]
tems.
The average bond length of
the spiro CꢀO moiety in 1 and
2
was about 1.47 ä, slightly
longer than the typical length
[
14]
of a CꢀO bond (1.43 ä)
in
other oxazine systems. This in-
dicates the relative weakness of
the bond and is also consistent
with the rationale for the pho-
tochromic reaction to involve
the cleavage of this spiro car-
Scheme 1. Synthetic routes to spirooxazine-containing ligands and their rhenium(i) tricarbonyl complexes.
dines (prepared by bromination of 4,4’-dimethyl-2,2’-bipyri-
dine with N-bromosuccinimide ) with SO in the presence
bon±oxygen bond. In addition, the average interplanar angle
between the indoline and naphthoxazine planes of 1 and 2
was found to be 88.28, indicative of an essentially orthogonal
arrangement. The orthogonal interplanar angle and the rela-
[12]
of K CO in DMF at room temperature gave L3 and L4.
2
3
Substitution reactions of [Re(CO) Cl] with the correspond-
5
Chem. Eur. J. 2004, 10, 766 ± 776
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
767

V. W.-W. Yam et al.
FULL PAPER
Figure 1. Structure of complex 1 with atomic numbering. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown at the 30% proba-
bility level.
values of the molar extinction
coefficients from 330±380 nm in
the ligands with two spirooxa-
zine moieties (L1 and L3) are
nearly twice those of ligands
with one spirooxazine moiety
(
L2 and L4). Complexes 1±4,
on the other hand, in addition
to the very intense IL absorp-
tions at 300±365 nm, also each
show
band at about 400±440 nm in
electronic absorption
spectra. This absorption band,
with molar extinction coeffi-
a
moderately intense
Figure 2. Structure of complex 2 with atomic numbering. Hydrogen atoms have been omitted for clarity. Ther- their
mal ellipsoids are shown at the 30% probability level.
cients
in
the
order
of
3
3
ꢀ1
ꢀ1
tively longer spiro CꢀO bond length are also commonly ob-
[14c±f]
10 dm mol cm , is ascribed to the metal-to-ligand charge
[14a,b]
served in other related spiropyran
systems.
and spirooxazine
transfer (MLCT) [dp(Re)!p*(diimine)] transition, typical
[13,16]
of rhenium(i) tricarbonyl diimine systems,
probably with
some mixing of a ligand-centered character. An absorption
energy dependence of this band, inversely related to the p-
accepting ability of the bipyridine ligands, is observed (3ꢁ
4>2>1), in agreement with the MLCT assignment. The ob-
servation of a very weak band at about 604 nm, both in the
ligands and in the complexes, is attributable to the absorp-
tion of the open form, which is present in trace amounts and
in thermal equilibrium with the closed form, as typically
Electronic absorption spectroscopy: The photophysical data
for all the ligands and complexes are collected in Table 3.
The electronic absorption spectra of the free ligands in di-
chloromethane show very intense absorption bands, with
molar
extinction
coefficients
in
the
order
of
4
3
ꢀ1
ꢀ1
10 dm mol cm at about 280 and 300 nm, which are ten-
tatively assigned as intraligand (IL) p!p* transitions of the
bipyridine and indoline moieties. The additional moderately
intense bands and shoulders at about 330, 348 and 368 nm
are most likely to be IL p!p* transitions of the naphthoxa-
zine moiety, similar to those observed in other related sys-
[7a,17]
found in these systems.
Excitation of the ligands in solution in CH Cl at room
2
2
temperature at l>350 nm produces weak luminescence. Li-
gands L1 and L2 each show two emission bands at 438 and
530 nm, with the low-energy band being more prominent,
while ligands L3 and L4 each show only one emission band,
[15]
tems.
The assignments of these low-energy absorptions
have been further supported by the observation that the
768
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2004, 10, 766 ± 776

Spirooxazine-Containing 2,2’-Bipyridine Ligands and Their Rhenium(i) Tricarbonyl Complexes
766 ± 776
Table 1. Crystal and structure determination data for complexes 1 and 2.
at 450 nm. With reference to previous related spectroscopic
[9c,d]
1
2
works,
the low-energy emission band at about 530 nm,
only observed in ligands L1 and L2, is tentatively assigned
as ligand-centered phosphorescence while the high-energy
band at about 440±450 nm found in all the ligands studied is
tentatively assigned as ligand-centered fluorescence. On the
formula
C
59
H
44ClN
6
O
9
Re¥2CH
2
Cl
2
¥2H
2
O
C
965.65
301
37 4 6 3
H28ClN O Re¥CHCl
M
r
1408.54
301
T [K]
a [ä]
c [ä]
c [ä]
a [8]
b [8]
13.899(3)
14.209(3)
16.749(3)
105.64(3)
90.26(3)
98.44(3)
3147.3(11)
red
triclinic
P1 (no. 2)
2
1416
1.486
0.50î0.30î0.20
12.039(2)
12.503(3)
13.461(3)
94.26(3)
95.68(3)
110.43(3)
1876.5(6)
yellowish orange
triclinic
P1 (no. 2)
other hand, excitation of complexes 1±4 in CH Cl solutions
2
2
at l>400 nm at room temperature resulted in strong lumi-
nescence (Figure 3), with emission maxima at about 633±
g [8]
V [ä ]
7
22 nm, depending on the nature of the diimine ligand. This
3
3
emission band is assigned as deriving from a MLCT
dp(Re)!p*(diimine)] origin, probably mixed with some
crystal color
crystal system
space group
Z
[
3
≈
≈
LC character. The emission energy dependence–3ꢁ4
2
952
(
633 nm)>2 (695 nm)>1 (722 nm)–is inversely related to
F(000)
the p-accepting ability of the diimine ligands–L1>L2>
ꢀ
3
1
calcd [gcm
]
1.709
0.50î0.20î0.10
3
L4ꢁL3–and in agreement with such a MLCT origin. The
crystal dimen-
sions [mm]
MLCT emission energy of 1 was found to be the lowest of
the complexes studied, and is in accord with the strongest p-
accepting ability of L1 in complex 1. Similarly, with poorer
p-accepting diimine ligands, such as L3 and L4 in complexes
l [ä (graphite-
monochromated,
MoKa)]
0.71073
0.71073
ꢀ
1
m [cm
]
22.05
2
100
35.75
2
77
3
and 4, higher-energy emission bands were observed. Com-
oscillation [8]
no. of images
collected
distance [mm]
exposure time
plexes 1 and 2 also display strong photoluminescence in
EtOH/MeOH/CH Cl (4:1:1 v/v/v) glass at 77 K, while com-
2
2
120
300
120
600
plexes 3 and 4 are found to be non-emissive in this medium.
3
These emissions are also tentatively assigned as MLCT
[
s]
3
no. of data col-
lected
no. of unique
data
no. of data used 6026
in refinement
15856
8143
9405
5848
4878
phosphorescence, probably mixed with some LC character,
similar to that observed in solution at room temperature.
Upon excitation at 365 nm, the ligands and the complexes
exhibit photochromism, with a growth in intensity of the
band at 604 nm, corresponding to the generation of the
open form. The open form generated is thermally unstable
and readily undergoes thermal bleaching, which follows first
order kinetics, to the closed form. Unlike the previously re-
[
m]
no. of parame-
ters refined [p]
R
751
478
0.0539
0.1430
0.0428
0.1213
+0.563, ꢀ1.004
[9c]
+
[
a]
ported
(SOPY
rhenium complexes–[Re(NꢀN)(CO) (SOPY)]
wR
3
residual extrema +0.958, ꢀ0.928
=
1,3,3-trimethylspiroindolinenaphthoxazine-9’-yl
in final differ-
nicotinate)–however, complexes 1±4 did not show photo-
ꢀ
3
ence map [eä
]
chromism with MLCT (400±440 nm) excitation. This is prob-
2
2
2
2
c
2
0
3
[
a] w = 1/[s (F
o
)+(aP) +bP], where P = [2F ¥Max(F , 0)]/3
ably because the energies of the MLCT excited state of the
complexes, which are estimated to be about 166±
ꢀ
1
1
(
88 kJmol from the phosphorescence of the complexes
633±722 nm), are insufficient for sensitization when com-
pared to the triplet excited state energies of spirooxazines
Table 2. Selected bond lengths [ä] and bond angles [8] with estimated
standard deviations (esds) in parentheses for 1 and 2.
ꢀ
1
[18]
(
ꢁ210±225 kJmol ).
Excitation of L1±L4 and complexes 1±4 at 365 nm in dry
1
ice/acetone baths at 195 K converted the closed forms of the
ligands and their complexes to the open forms, photomero-
cyanine, and slowed down the thermal bleaching reactions.
Figure 4 shows the emission spectra of complexes 1 and 2 as
well as their open forms in EtOH/MeOH/CH Cl (4:1:1 v/v/v)
at 77 K. The original emission band associated with the
closed forms of complexes 1 and 2 disappeared, with the
evolution of a new emission band, peaking at 705±710 nm,
corresponding to the emission of the open forms of the com-
plexes. On the other hand, excitation of the open forms of
L1±L4 and complexes 3 and 4, which, unlike their closed
forms, are non-emissive in this medium, shows emission
bands at 705±710 nm. In view of the close resemblance of
the emissions of the open forms of the complexes to those
of the free ligands and the relative insensitivity of the emis-
Re1ꢀC1
Re1ꢀC2
Re1ꢀC3
Re1ꢀN1
1.905(10)
1.916(11)
2.031(10)
2.163(6)
Re1ꢀN2
O6ꢀC37
O9ꢀC46
2.168(6)
1.440(12)
1.459(12)
2
2
C1-Re1-C2
C1-Re1-C3
C2-Re1-C3
N1-Re1-N2
88.4(4)
93.0(4)
93.1(4)
74.7(2)
O6-C37-C38
N4-C37-C38
O9-C46-C47
N6-C46-C47
107.7(9)
102.9(8)
111.2(8)
102.3(8)
2
Re1ꢀC3
Re1ꢀC2
Re1ꢀC1
1.928(10)
1.942(9)
2.071(12)
Re1ꢀN1
Re1ꢀN2
O6ꢀC27
2.164(6)
2.175(5)
1.455(9)
C3-Re1-C2
C3-Re1-C1
C2-Re1-C1
88.8(3)
92.5(4)
88.9(4)
N1-Re1-N2
O6-C27-C26
N4-C27-C28
74.7(2)
111.0(6)
101.5(6)
Chem. Eur. J. 2004, 10, 766 ± 776
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769

V. W.-W. Yam et al.
FULL PAPER
Table 3. Photophysical data for the ligands and the complexes.
Absorption
Medium
(T [K])
Emission
lem [nm] (t [ms])
o
[
a]
3
ꢀ1
ꢀ1
[b]
l
abs [nm] (e [dm mol cm ])
L1
302(30880), 316(26960), 346(10310), 368(5620)
284(19590), 304(16260), 316(14370), 346(5170), 368(2810)
276(28310), 334(15660), 348(13720)
CH
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
glass (77)
CH Cl (298)
glass (77)
2
Cl
2
(298)
438 (<0.1), 530 (<0.1)
±
710 (0.5)
[
c]
[d]
[
c]
L1(PMC)
L2
2
2
438 (<0.1), 530 (<0.1)
[
c]
[d]
±
[
c]
L2(PMC)
L3
710 (0.8)
2
2
445 (<0.1)
[
c]
[d]
±
[
c]
L3(PMC)
L4
705 (0.8)
280(22230), 334(8720), 348(7670)
2
2
445 (<0.1)
[
c]
[d]
±
[
c]
L4(PMC)
1
705 (0.9)
722 (<0.1)
642 (1.9)
710 (1.8)
695 (<0.1)
600 (3.5)
710 (2.7)
633 (<0.1)
320(22920), 344(12590), 360(8780), 374(5280), 440(3900)
306(21750), 316(21080), 346(7790), 364(5770), 416(4760)
294(33820), 316(19690), 334(14660), 346(13120), 400(4690)
294(22650), 316(13260), 334(9930), 346(8920), 398(3310)
2
2
[
c]
[
c]
1
2
(PMC)
(PMC)
(PMC)
(PMC)
2
2
[
c]
[
c]
2
3
2
2
[
c]
[d]
±
[
c]
3
4
705 (<0.1)
633 (<0.1)
2
2
[
c]
[d]
±
[
c]
4
glass (77)
705 (<0.1)
[
2 2
a] In dichloromethane at 298 K. [b] Excitation wavelength at ca. 420 nm. Emission maxima are corrected values. [c] EtOH/MeOH/CH Cl (4:1:1, v/v/v).
PMC: photomerocyanine form. [d] Non-emissive.
Figure 3. Normalized solution emission spectra of 1 (d), 2 (b), 3
(
c) and 4 (g) in dichloromethane at 298 K.
sion energies to the nature of the bipyridine ligands, the
emission is assigned as LC emission, probably originating
from the LC phosphorescence of the photomerocyanine
form of the spironaphthoxazine moiety. Similar assignments
Figure 4. Normalized emission spectra of the closed forms (c) and the
open forms (g) of 1 (a) and 2 (b) in EtOH/MeOH/CH Cl (4:1:1 v/v/v)
2 2
at 77 K.
[18b]
have also been reported in the literature.
[
19]
ture,
while their activation entropies vary much more
°
ꢀ1
ꢀ1
Bleaching reaction kinetics: The kinetics for the bleaching
reactions of the photomerocyanines of the ligands L1, L2
and L4 and complexes 1±4, after excitation at 365 nm, were
investigated in acetonitrile solution. Figure 5 shows repre-
sentative UV/Vis spectral changes in the photomerocyanines
drastically, from ꢀ17.7 Jmol
K
when DH is large to
ꢀ
1
ꢀ1
°
ꢀ100.3 Jmol
K
when DH is small, as has been discussed
[15,19]
in the literature.
The positive values for the activation
enthalpies indicated that the bleaching reaction is an activat-
ed process. The orderness in the activated complex in the
transition state in relation to the open form is decreased, as
reflected in the negative values of the activation entropies.
The activation enthalpies and entropies for the reactions
with time, together with the absorbance trace at lmax
=
604 nm as a function of time. The thermodynamic activation
parameters are collected in Table 4. The activation enthal-
pies for the reactions of the ligands L1, L2, and L4 are
ꢀ
1
in complexes 1±4 range from 54.8 to 60.5 kJmol and from
ꢀ
1
ꢀ1 ꢀ1
found to be 45±70 kJmol , which are in a range typical of
those reported for this type of compounds in the litera-
ꢀ47.8 to ꢀ66.9 Jmol K , respectively. The variations in
the activation enthalpy and entropy in these complexes are
770
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2004, 10, 766 ± 776

Spirooxazine-Containing 2,2’-Bipyridine Ligands and Their Rhenium(i) Tricarbonyl Complexes
766 ± 776
ence of the heavy rhenium
atom, which enhances the spin±
orbit coupling and hence im-
proves the intersystem crossing
efficiency through the relaxa-
tion of spin-forbidden process-
es, resulting in a more allowed
and efficient ring-opening reac-
tion to produce the photomero-
cyanine via the triplet state. Al-
though the triplet pathway
would be much enhanced in the
presence of the heavy atom, the
quantum efficiencies for com-
plexes 1 and 2 in relation to
those of their free ligands L1
and L2, respectively, are found
to be decreased. It is likely that
the lower quantum efficiencies
of 1 and 2 than those of their
free ligands are attributable to
the presence of low-lying
Figure 5. Time-dependent UV/Vis absorption spectral changes in the open form of complex 3 in CH
3
CN at
5
.68C after excitation at 365 nm. The inserts show the overlaid UV/Vis absorption spectra at different decay
times and the decay trace at the absorption maximum at 604 nm with time.
Table 4. Activation parameters for the bleaching reaction of the ligands
and the complexes in solution in acetonitrile.
°
ꢀ1
°
ꢀ1
ꢀ1
ꢀ1
ꢀ1
DH [kJmol
]
DS [J mol
K
]
a
E [kJmol ]
L1
L2
L3
L4
1
2
3
4
45.0Æ0.9
69.1Æ2.8
ꢀ100.3Æ3.3
ꢀ17.7Æ9.1
47.3Æ0.9
71.5Æ2.8
[
a]
[a]
[a]
±
±
±
57.3Æ3.3
60.5Æ3.2
54.8Æ2.2
58.5Æ1.7
57.6Æ3.2
ꢀ57.3Æ11.6
ꢀ47.8Æ11.1
ꢀ66.9Æ7.7
ꢀ51.5Æ5.9
ꢀ53.6Æ11.3
59.6Æ3.3
62.9 Æ 3.2
57.1Æ2.2
60.9Æ1.7
59.0Æ3.2
[
a] Data not obtained, due to the insolubility of the compound.
much smaller than those in their free ligands. A relationship
°
°
between DH and DS similar to that seen in the free li-
Figure 6. A plot of activation enthalpy against activation entropy for the
bleaching reactions of the open forms of the ligands L1, L2 and L4 and
the complexes 1±4.
[15,19]
gands and discussed in the literature,
served in the complexes, although the extent of the variation
has also been ob-
is much smaller. The range of activation energies (E ) for
a
these complexes also changes much less significantly, from
ꢀ
1
3
5
7.1 to 62.9 kJmol , as compared to those of the free li-
MLCT states in these complexes, which would provide an
ꢀ
1
gands, which range from 47.3 to 71.5 kJmol . A careful in-
efficient quenching pathway for the triplet state of the spi-
rooxazine moiety, and thus decrease the efficiency for the
photochromic reaction via the triplet pathway.
°
°
vestigation on the variation between DH and DS in the
whole series of complexes 1±4 and their free ligands L1, L2
and L4 has been performed. An isokinetic relationship–
°
°
that is, a linear proportionality between DH and DS , as
Table 5. A summary of the estimated photochemical quantum yields of
the photochromic forward reactions of the ligands and the complexes in
acetonitrile with excitation at l = 365 nm.
°
°
shown in the plot of DH and DS (Figure 6)–has been ob-
tained. This is indicative of a common bleaching reaction
mechanism for the whole series of complexes and the li-
gands. From the slope of the plot, an isokinetic temperature
of 285.0Æ3.9 K for the bleaching reaction is obtained.
f
365
L1
L2
L3
L4
1
2
3
4
0.60Æ0.01
0.45Æ0.01
[
a]
±
0.44Æ0.01
0.15Æ0.01
0.18Æ0.01
0.48Æ0.01
0.65Æ0.01
Photochemicalquantum yie dl for the photochromic reaction
(
Table 5): The quantum yields for the spirooxazine-contain-
ing bipyridine ligands with excitation at l = 365 nm are in
the range of 0.36±0.60. The increased efficiency of complex
4
in relation to its free ligand L4 may be a result of the pres-
[a] Data were not obtained, due to the insolubility of the compound.
Chem. Eur. J. 2004, 10, 766 ± 776
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
771

V. W.-W. Yam et al.
FULL PAPER
The quantum efficiencies for the photochromic reactions
of the complexes are in the order 4 (0.65)>3 (0.48)>2
0.18)>1 (0.15), in accord with the energies of the MLCT
excited states. This trend is supportive of the quenching
mechanism (from the triplet state of spirooxazine to
L2>L3>L4. In general, the better the p-accepting ability
of the diimine ligand, the more stable the dp(Re) orbital
will be, and hence the more difficult the oxidation process.
(
I
II
Similar oxidation couples ascribed to a Re Re oxidation
have been reported in other related systems, Re(CO) -
3
3
[22]
MLCT), in which the efficiency of the quenching pathway
(NꢀN)Cl.
3
increases as the MLCT excited state energy decreases.
The third irreversible oxidation wave, which occurs at
about +1.76 V, is only observable in complexes 3 and 4.
The close resemblance of this oxidation wave to that ob-
served in the free ligand L4 is suggestive of a ligand-cen-
tered oxidation. The slightly more positive potential in com-
plex 4 than in its free ligand L4 is probably attributable to
the electron-withdrawing effect of the rhenium metal centre
upon coordination.
Electrochemical studies: Complexes 1±4 each display an ir-
reversible oxidation wave at about +0.91 to +0.99 V, and a
quasi-reversible oxidation couple at about +1.28 to
+
1.40 V in the oxidative scan of their cyclic voltammograms
ꢀ
3
in acetonitrile (0.1 moldm nBu NPF ), while two to three
4
6
quasi-reversible reduction couples and one irreversible re-
duction wave at ꢀ0.90 to ꢀ2.02 V versus SCE are observed
in the reductive scan. Complexes 3 and 4 also each show an
irreversible oxidation wave at about +1.76 V. The electro-
chemical data for the free ligands and their rhenium(i) com-
plexes are summarized in Table 6.
The first two reduction couples are tentatively assigned to
the bipyridyl ligand-centered reductions, as they are com-
[20,21]
monly observed in related systems.
The trends of these
reduction potentials are also in line with the electron-rich-
ness and p-accepting ability of the diimine ligands as dis-
cussed earlier, while the other two, more negative reduc-
tions are assigned to the ligand-centered reduction of the
spirooxazine moiety, as similar waves are observed in the
free ligand reductions. In general, coordination of the li-
gands to the rhenium metal centre should render the ligand
less electron-rich and thus make the ligand-centered reduc-
tions in the complexes more ready to occur. As a result, po-
tentials less negative than seen in the free ligands are com-
monly observed in the complexes.
Table 6. Electrochemical data for the ligands and the complexes in aceto-
ꢀ
3
[a]
nitrile solution (0.1 moldm nBu
4
NPF
6
) at 298 K .
[
b]
[b]
Compound Oxidation
E
1
=
[V] vs. SCE Reduction
1
=
2
E [V] vs. SCE
2
(E
pa [V] vs. SCE)
(Epc [V] vs. SCE)
[
c]
[c]
L1
L2
L3
L4
1
2
3
4
±
±
(+1.03)
±
ꢀ1.68, ꢀ2.12
[
c]
[c]
±
(+0.93), +1.70
(+0.99), +1.40
(+0.99), +1.34
(+0.91), +1.29, (+1.76)
(+0.91), +1.28, (+1.76)
(ꢀ2.06), (ꢀ2.19)
ꢀ0.92, (ꢀ1.28), ꢀ1.44, ꢀ1.96
ꢀ1.08, ꢀ1.55, ꢀ1.99
ꢀ1.33, ꢀ1.59, (ꢀ1.85), ꢀ2.01
(ꢀ1.44), ꢀ1.49, (ꢀ1.81),
Conclusion
ꢀ
2.02
ꢀ
1
[
a] Working electrode, glassy carbon; scan rate, 100 mVs . [b ]E 1/2 is
pa + Epc)/2; Epa and Epc are peak anodic and peak cathodic potentials,
respectively. [c] Data could not be obtained, due to the low solubility of
A series of spirooxazine-containing 2,2’-bipyridine ligands
has been successfully synthesized and incorporated into rhe-
nium(i) tricarbonyl diimine complex systems. The moderate-
ly intense absorption at 400±440 nm in the complexes, which
is absent in the absorption spectra of the free ligands, is as-
signed as the MLCT [dp(Re)!p*(diimine)] transition,
probably mixed with some LC character. All complexes ex-
(
E
ꢀ
3
4 6
the compound in acetonitrile solution (0.1 moldm nBu NPF ).
With reference to previous electrochemical studies on re-
[20]
[21]
lated indolinespiropyrans and indolinespirooxazines, as
well as the close resemblance of the potentials of the first ir-
reversible oxidation wave to those of the corresponding free
ligands, the first oxidative wave is assigned to the oxidation
of the spirooxazine moiety, probably arising from the re-
moval of a lone-pair electron on the nitrogen atom of the in-
doline moiety. The more positive potential of this oxidation
wave in complexes 1 and 2 (ca. +0.99 V vs. SCE) and L2
3
hibit strong MLCT phosphorescence at 633±722 nm in
CH Cl at 298 K. However, in EtOH/MeOH/CH Cl glass at
2
2
2
2
3
77 K, only complexes 1 and 2 display strong MLCT emis-
sions at about 642 nm and 600 nm, respectively, and this
emission band would be switched to LC phosphorescence of
photomerocyanine moiety at 705±710 nm upon conversion
to the open form.
(
+
ca. +1.03 V vs. SCE) than in complexes 3 and 4 (ca.
0.91 V vs. SCE) and L4 (ca. +0.93 V vs. SCE) is suppor-
The activation parameters for the thermal bleaching reac-
tions have been determined. The activation enthalpies for li-
ꢀ
1
tive of a spirooxazine ligand-centered oxidation, since the
presence of the electron-withdrawing ester linkage in L2
and hence complexes 1 and 2 would render the oxidation
process more difficult.
The second quasi-reversible oxidation couple in the rheni-
um complexes, at about +1.28 to +1.40 V, is found to be
dependent on the nature of the diimine ligand and is as-
signed to the metal-centered oxidation of Re to Re . The
potential for the oxidation is found to follow the order: 1
(
gands L1, L2 and L4 are 45±70 kJmol and the activation
entropies for the ligands L1, L2 and L4 vary drastically from
ꢀ
1
ꢀ1
°
ꢀ1 ꢀ1
ꢀ17.7 Jmol
K
when DH is large to ꢀ100.3 Jmol
K
°
°
when DH is small. A similar relationship between DH and
DS has also been observed in the complexes, but the extent
°
of the variation is much smaller. The variations in the acti-
vation enthalpy, activation entropy and the activation
energy in all the complexes are also much smaller than
those in the free ligands. An isokinetic relationship, with an
isokinetic temperature of 285.0Æ3.9 K, has been obtained
for the bleaching reactions.
I
II
+1.40 V)>2 (+1.34 V)>3 (+1.29 V)>4 (+1.28 V), in line
with the p-accepting ability of the diimine ligands: L1>
772
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 766 ± 776

Spirooxazine-Containing 2,2’-Bipyridine Ligands and Their Rhenium(i) Tricarbonyl Complexes
766 ± 776
0
2 3
.82 mmol) and K CO (250 mg, 1.78 mmol) in DMF (20 mL), and the
ExperimentalSection
mixture was stirred for two days. The reaction mixture was poured into
deionized water (50 mL) to precipitate the crude product, which was
then filtered and washed with copious amounts of deionized water. The
crude product was then purified by column chromatography on silica gel
with dichloromethane/diethyl ether (1:1 v/v) as eluent to give 3 as an ana-
Materials and reagents: [Re(CO)
5
Cl] was obtained from Strem Chemi-
cals, Inc. 4,4’-Dimethyl-2,2’-bipyridine and N-bromosuccinimide were ob-
tained from Aldrich Chemical Co. 2,2’-Bipyridine-4,4’-dicarboxylic acid
[
10]
was prepared by a slight modification of a reported procedure.
Di(bromomethyl)-2,2’-bipyridine ((BrCH bpy)) and 4-bromomethyl-4’-
methyl-2,2’-bipyridine were prepared by slight modifications of a report-
4,4’-
1
lytically pure white powder. Yield: 70 mg, 0.08 mmol; 10%. H NMR
2 2
)
(
300 MHz, CD
2
Cl
2
, 298 K): d = 1.28 (s, 12H; ꢀMe), 2.69 (s, 6H; ꢀNMe),
5
.35 (s, 4H; ꢀMe on 2,2’-bipyridine), 6.51 (d, J = 7.7 Hz, 2H; indolinic
[
12]
ed procedure. 4’-Methyl-2,2’-bipyridine-4-carboxylic acid was prepared
proton at 7-position), 6.79±6.84 (m, 4H; naphthoxazinic proton at 5’-posi-
tion and indolinic proton at 5-position), 7.02 (d, J = 7.2 Hz, 2H; indolin-
ic proton at 4-position), 7.10±7.16 (m, 4H; naphthoxazinic proton at 8’-
position and indolinic proton at 6-position), 7.46 (d, J = 5.0 Hz, 2H; bi-
pyridyl proton at 5,5’-position), 7.57 (d, J = 8.8 Hz, 2H; naphthoxazinic
proton at 6’-position), 7.65 (d, J = 8.8 Hz, 2H; naphthoxazinic proton at
[
11]
by a slight modification of a reported procedure. 1,3,3-Trimethyl-9’-hy-
droxy-spiroindolinenaphthoxazine (SO) was synthesized by modification
[
23]
of a reported procedure. Benzene (Lab-Scan, AR) was distilled over
sodium before use for synthesis. All other reagents were of analytical
grade and were used as received.
Syntheses
7
’-position), 7.67 (s, 2H; naphthoxazinic proton at 2’-position), 7.95 (d, J
Bis(1,3,3-trimethylspiroindolinenaphthoxazine-9’-yl) 2,2’-bipyridyl-4,4’-di-
carboxylate (L1): 2,2’-Bipyridyl-4,4’-dicarboxylic acid chloride was freshly
prepared by heating 2,2’-bipyridyl-4,4’-dicarboxylic acid (130 mg,
= 2.5 Hz, 2H; naphthoxazinic proton at 10’-position), 8.57 (s, 2H; bipyr-
idyl proton at 3,3’-position), 8.66 ppm (d, J = 5.0 Hz, 2H; bipyridyl
proton at 6,6’-position); positive ion FAB-MS: m/z: 869 [M+H] ; ele-
+
0
.61 mmol) at reflux with thionyl chloride (15 mL) until a clear solution
48 6 4 2
mental analyses calcd (%) for C56H N O ¥H O (887): C 75.83, H 5.68, N
was obtained. The excess thionyl chloride was removed under reduced
pressure at room temperature to leave a white solid consisting of the acid
chloride. Benzene (20 mL), triethylamine (5 mL) and SO (2.0 equivalents,
9.47; found: C 76.10, H 5.48, N 9.21.
4
2
-(1,3,3-Trimethylspiroindolinenaphthoxazine-9’-oxymethyl)-4’-methyl-
,2’-bipyridine (L4): The title ligand was synthesized by a procedure simi-
4
20 mg, 1.22 mmol) were then added to the freshly prepared acid chlo-
lar to that used for 3, except that 4-bromomethyl-4’-methyl-2,2’-bipyri-
dine was used in place of 4,4’-di(bromomethyl)-2,2’-bipyridine, and 1
equivalent of SO (285 mg, 0.83 mmol) was used instead. Purification by
column chromatography on silica gel with dichloromethane/diethyl ether
ride. The resulting mixture was then stirred at room temperature for two
days. After removal of the solvent under reduced pressure and at room
temperature, the residue was purified by column chromatography on
silica gel with chloroform/diethyl ether (8:1 v/v) as eluent to afford 1 as a
(
5:1 to 1:3 v/v) as eluent gave 4 as an analytically pure white powder.
1
white solid. Yield: 208 mg, 0.23 mmol; 38%. H NMR (300 MHz, CDCl
3
,
1
Yield: 106 mg, 0.2 mmol; 25%. H NMR (300 MHz, CD
2 2
Cl , 298 K): d =
2
7
98 K): d = 1.37 (s, 12H; ꢀMe), 2.78 (s, 6H; ꢀNMe), 6.59 (d, J =
.6 Hz, 2H; indolinic proton at 7-position), 6.91 (t, J = 7.6 Hz, 2H; indo-
8.9 Hz, 2H; naphthoxazinic
1
.35 (s, 6H; ꢀMe), 2.45 (s, 3H; ꢀMe on bpy), 2.76 (s, 3H; ꢀNMe), 5.38
(
s, 2H; ꢀOCH ꢀ on bpy), 6.57 (d, J = 7.5 Hz, 1H; indolinic proton at 7-
2
linic proton at 5-position), 7.04 (d, J
=
position), 6.85±6.91 (m, 2H; naphthoxazinic proton at 5’-position and in-
dolinic proton at 5-position), 7.08 (d, J = 7.1 Hz, 1H; indolinic proton at
proton at 5’-position), 7.10 (d, J = 7.6 Hz, 2H; indolinic proton at 4-posi-
tion), 7.23 (t, J = 7.6 Hz, 2H; indolinic proton at 6-position), 7.32 (dd, J
4
-position), 7.19±7.25 (m, 3H; naphthoxazinic proton at 8’-position, indo-
=
2.3 Hz, 8.9 Hz, 2H; naphthoxazinic proton at 8’-position), 7.71 (d, J =
linic proton at 6-position and bipyridyl proton at 5’-position), 7.48 (d, J
= 4.9 Hz, 1H; bipyridyl proton at 5-position), 7.59 (d, J = 8.8 Hz, 1H;
naphthoxazinic proton at 6’-position), 7.68 (d, J = 8.8 Hz, 1H; naphthox-
azinic proton at 7’-position), 7.71 (s, J = 7.1 Hz, 1H; naphthoxazinic
proton at 2’-position), 7.98 (d, J = 2.1 Hz, 1H; naphthoxazinic proton at
10’-position), 8.26 (s, 1H; bipyridyl proton at 3’-position), 8.56 (m, 2H;
bipyridyl proton at 3,6’-position), 8.71 ppm (d, J = 4.9 Hz, 1H; bipyridyl
8
.9 Hz, 2H; naphthoxazinic proton at 6’-position), 7.83 (s, 2H; naphthox-
azinic proton at 2’-position), 7.85 (d, J = 8.9 Hz, 2H; naphthoxazinic
proton at 7’-position), 8.13 (d, J = 4.9 Hz, 2H; bipyridyl proton at 5,5’-
position), 8.44 (d, J = 2.3 Hz, 2H; naphthoxazinic proton at 10’-posi-
tion), 9.00 (d,
J
=
4.9 Hz, 2H; bipyridyl proton at 6,6’-position),
9
1
.24 ppm (s, 2H; bipyridyl proton at 3,3’-position); IR (KBr disc): n˜ =
750 cm (C=O); positive ion FAB-MS: m/z: 897 [M+H] ; elemental
ꢀ
1
+
+
proton at 6-position); positive ion FAB-MS: m/z: 527 [M+H] ; elemen-
analyses calcd (%) for C56
H
44
N
6
O
6
(897): C 74.98, H 4.94, N 9.34; found:
tal analyses calcd (%) for C H N O (526): C 77.54, H 5.74, N 10.64;
3
4
30
4
2
C 74.66, H 5.17, N 8.94.
found: C 77.59, H 5.89, N 10.54.
1
4
,3,3-Trimethylspiroindolinenaphthoxazine-9’-yl4 ’-methyl-2,2’-bipyridyl-
-carboxylate (L2): The title ligand was synthesized by a procedure simi-
[Re(CO) (L1)Cl] (1): The complex was prepared by a modification of a
literature method used for the related Re diimine complexes.
3
I
[24]
lar to that used for 1, except that 4’-methyl-2,2’-bipyridyl-4-carboxylic
acid was used in place of 2,2’-bipyridyl-4,4’-dicarboxylic acid, and 1
equivalent of SO (210 mg, 0.61 mmol) was used instead. Column chroma-
tography on silica gel (230±400 mesh) with chloroform/diethyl ether (3:1
[Re(CO) Cl] (150 mg, 0.42 mmol) and L1 (407 mg, 0.44 mmol) were sus-
pended in benzene (50 mL). The suspension was stirred at 45±508C
5
under nitrogen for two days, during which the starting materials dissolved
gradually to give a dark red solution, which subsequently changed to a
red suspension. After removal of the solvent under reduced pressure, the
residue was purified by column chromatography with dichloromethane/
acetone (5:2 v/v) as eluent. Red crystals of 1 were obtained by slow diffu-
sion of n-hexane vapor into a dichloromethane solution of the complex.
1
v/v) as eluent gave 2 as a white solid. Yield: 168 mg, 0.31 mmol; 51%. H
NMR (300 MHz, CDCl
3
, 298 K): d = 1.29 (s, 6H; ꢀMe), 2.42 (s, 3H;
ꢀMe on 2,2’-bpy), 2.71 (s, 3H; ꢀNMe), 6.53 (d, J = 7.8 Hz, 1H; indolinic
proton at 7-position), 6.83 (t, J = 7.4 Hz, 1H; indolinic proton at 5-posi-
tion), 6.98±7.05 (m, 2H; naphthoxazinic proton at 5’-position and indolin-
ic proton at 4-position), 7.11±7.17 (m, 2H; indolinic proton at 6-position
and bipyridyl proton at 5’-position), 7.24 (dd, J = 2.3 Hz, 8.8 Hz, 1H;
naphthoxazinic proton at 8’-position), 7.69 (d, J = 8.8 Hz, 1H; naphthox-
azinic proton at 6’-position), 7.70 (s, 1H; naphthoxazinic proton at 2’-po-
sition), 7.81 (d, J = 8.8 Hz, 1H; naphthoxazinic proton at 7’-position),
1
Yield: 167 mg, 0.14 mmol; 33%. H NMR (300 MHz, CDCl , 298 K): d
3
= 1.35 (s, 12H; ꢀMe), 2.76 (s, 6H; ꢀNMe), 6.58 (d, J = 7.7 Hz, 2H; in-
dolinic proton at 7-position), 6.91 (t, J = 7.5 Hz, 2H; indolinic proton at
5-position), 7.04±7.10 (m, 4H; indolinic proton at 4-position and naph-
thoxazinic proton at 5’-position), 7.19±7.30 (m, 4H; indolinic proton at 6-
position and naphthoxazinic proton at 8’-position), 7.69±7.74 (m, 4H;
naphthoxazinic proton at 2’,6’-position), 7.86 (d, J = 8.9 Hz, 2H; naph-
7
1
.98 (dd, J = 1.6 Hz, 4.9 Hz, 1H; bipyridyl proton at 5-position), 8.29 (s,
H; bipyridyl proton at 3’-position), 8.36 (d, J = 2.3 Hz, 1H; naphthoxa-
thoxazinic proton at 7’-position), 8.34 (d, J
= 5.7 Hz, 2H; bipyridyl
zinic proton at 10’-position), 8.52 (d, J = 4.9 Hz, 1H; bipyridyl proton at
’-position), 8.85 (d, J = 4.9 Hz, 1H; naphthoxazinic proton at 6-posi-
tion), 9.10 ppm (d, J = 4.9 Hz, 1H; bipyridyl proton at 3-position); IR
proton at 5,5’-position), 8.45 (d, J = 2.4 Hz, 2H; naphthoxazinic proton
at 10’-position), 9.09 (s, 2H; bipyridyl proton at 3,3’-position), 9.36 ppm
(d, J = 5.7 Hz, 2H; bipyridyl proton at 6,6’-position); IR (KBr disc): n˜
6
ꢀ
1
ꢀ1
ꢀ1
(
KBr disc): n˜
=
1750 cm (C=O); positive ion FAB-MS: m/z: 541
= 1902, 1927, 2026 cm (C=O), 1749 cm (C=O); positive ion FAB-MS:
+
1
+
[
M+H] ; elemental analyses calcd (%) for C34
H
28
N
4
O
3
¥ =
2
H
2
O (549): C
m/z: 1202 [M+H] ; elemental analyses calcd (%) for C H ClN O R-
5
9
44
6
9
1
7
4.30, H 5.32, N 10.19; found: C 74.21, H 5.25, N 10.14.
e¥ = CH Cl (1224): C 58.14, H 3.64, N 6.87; found: C 58.00, H 3.93, N
4
2
2
6
.65.
4
,4’-Bis(1,3,3-trimethylspiroindolinenaphthoxazine-9’-oxymethyl)-2,2’-bi-
pyridine (L3): SO (2.0 equivalents, 570 mg, 1.65 mmol) was added to a
stirred mixture of 4,4’-di(bromomethyl)-2,2’-bipyridine (280 mg,
[Re(CO)
3
(L2)Cl] (2): The title complex was synthesized by a procedure
similar to that used for 1, except that L2 (245 mg, 0.44 mmol) was used in
Chem. Eur. J. 2004, 10, 766 ± 776
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
773

V. W.-W. Yam et al.
FULL PAPER
place of L1 in the substitution reaction and dichloromethane/acetone
was the 355 nm output (third harmonic, 8 ns) of a Spectra-Physics
Quanta-Ray Q-switched GCR-150 pulsed Nd-YAG laser (10 Hz). Lumi-
nescence decay traces were recorded on a Tektronix Model TDS 620A
digital oscilloscope and the lifetime (t) determination was accomplished
by single exponential fitting of the luminescence decay traces with the
(
9:1 v/v) was used as eluent in the column chromatography. Slow diffu-
sion of diethyl ether vapor into a concentrated CHCl solution of the
complex gave 2, isolated as bright orange crystals. Yield: 181 mg,
3
1
0
.21 mmol; 51%. H NMR (500 MHz, CD
Me), 2.62 (s, 3H; ꢀMe on bpy), 2.77 (s, 3H; ꢀNMe), 6.59 (d, J =
.8 Hz, 1H; indolinic proton at 7-position), 6.89 (t, J = 7.6 Hz, 1H; indo-
linic proton at 5-position), 7.08±7.11 (m, 2H; naphthoxazinic proton at
’-position and indolinic proton at 4-position), 7.21 (t, J = 7.6 Hz, 1H;
indolinic proton at 6-position), 7.31 (dd, J = 2.4 Hz, 8.8 Hz, 1H; naph-
thoxazinic proton at 8’-position), 7.45 (d, J 5.6 Hz, 1H; bipyridyl
proton at 5’-position), 7.76 (d, J = 7.2 Hz, 1H; naphthoxazinic proton at
’-position), 7.78 (s, 1H; naphthoxazinic proton at 2’-position), 7.89 (d, J
8.8 Hz, 1H; naphthoxazinic proton at 7’-position), 8.26±8.27 (m, 2H;
2 2
Cl , 298 K): d = 1.36 (s, 6H;
ꢀ
model I(t) = I
o
exp(ꢀt/t), where I(t) and I
o
stand for the luminescence in-
7
tensities at time = t and time = 0, respectively. Solution samples for lu-
minescence lifetime measurements were degassed by use of at least four
1
5
freeze-pump-thaw cycles. H NMR spectra were recorded on Bruker
DPX 300 (300 MHz), Bruker DPX 400 (400 MHz) or Bruker DRX 500
(500 MHz) FT-NMR spectrometers. Chemical shifts (d, ppm) are report-
ed relative to tetramethylsilane (Me Si). All positive ion FAB mass spec-
4
tra were recorded on a Finnigan MAT95 mass spectrometer. Elemental
analyses of all the metal complexes were performed on a Carlo Erba
1106 elemental analyzer by the Institute of Chemistry at the Chinese
Academy of Sciences in Beijing.
=
6
=
bipyridyl proton at 5,3’-position), 8.45 (d, J = 2.4 Hz, 1H; naphthoxazin-
ic proton at 10’-position), 8.90 (d, J = 5.6 Hz, 1H; bipyridyl proton at 6’-
position), 8.94 (s, 1H; bipyridyl proton at 3-position), 9.28 ppm (d, J =
The thermal bleaching reaction of spirooxazines is known to follow first-
order kinetics at various temperatures. The kinetics for the bleaching re-
action were determined by measurement of the UV/Vis spectral changes
at various temperatures by use of a Hewlett±Packard 8452A diode array
spectrophotometer, with temperature controlled by a Lauda RM6 com-
pact low-temperature thermostat. The first-order rate constants were ob-
tained by taking the negative value of the slope of a linear least-squares
5
1
8
.6 Hz, 1H; bipyridyl proton at 6-position); IR (KBr disc): n˜ = 1881,
ꢀ
1
ꢀ1
926, 2024 cm (C=O), 1747 cm (C=O); positive ion FAB-MS: m/z:
+
+
47 [M+H] , 811 [MꢀCl]
; elemental analyses calcd (%) for
37 4 6 3
C H28ClN O Re¥CHCl (966): C 47.25, H 3.03, N 5.80; found: C 47.33, H
3
.03, N 5.80.
[
Re(CO) (L3)Cl] (3): The title complex was synthesized by a procedure
3
similar to that used for 1, except that L3 (394 mg, 0.44 mmol) was used in
place of L1 in the substitution reaction and dichloromethane/acetone
fit of ln [(AꢀA
¥
)/(A
o
ꢀA
¥
)] against time according to Equation (1),
(
10:1 v/v) was used as eluent in the column chromatography. Slow diffu-
ln ½ðAꢀA Þ=ðA ꢀA ފ ¼ ꢀkt
ð1Þ
1
0
1
sion of diethyl ether vapor into a concentrated acetone solution of the
complex gave 3, isolated as a yellow powder. Yield: 271 mg, 0.23 mmol;
where A, A
o
, and A
¥
are the absorbances at the absorption wavelength
1
5
5%. H NMR (400 MHz, CD
2
Cl
2
, 298 K): d = 1.34 (s, 12H; ꢀMe), 2.75
maximum of the photomerocyanine at times t, 0, and infinity, respectively
and k is the rate constant of the reaction.
(
s, 6H; ꢀNMe), 5.46 (s, 4H; ꢀOCH ꢀ on bpy), 6.56 (d, J = 7.7 Hz, 2H;
2
indolinic proton at 7-position), 6.87±6.92 (m, 4H; naphthoxazinic proton
The kinetics parameters were obtained by a linear least-squares fitting of
ln(k/T) against 1/T according to the linear expression of the Eyring equa-
tion (2),
at 5’-position and indolinic proton at 5-position), 7.07 (d, J = 7.2 Hz,
2
H; indolinic proton at 4-position), 7.19±7.23 (m, 4H; naphthoxazinic
proton at 8’-position and indolinic proton at 6-position), 7.61 (d, J =
8
2
.8 Hz, 2H; naphthoxazinic proton at 6’-position), 7.66 (d, J = 5.6 Hz,
H; bipyridyl proton at 5,5’-position), 7.71±7.74 (m, 4H; naphthoxazinic
°
ꢀ1
°
ln ðk=TÞ ¼ ꢀðDH =RÞð1=TÞ þ ln ðk
B
h
Þ þ ðDS =RÞ
ð2Þ
proton at 7’-position), 7.98 (d, J = 2.5 Hz, 2H; naphthoxazinic proton at
0’-position), 8.41 (s, 2H; naphthoxazinic proton at 2’-position), 9.06 ppm
d, J = 5.6 Hz, 2H; bipyridyl proton at 6,6’-position); IR (KBr disc): n˜
°
°
where DH and DS are the changes in activation enthalpy and entropy,
respectively, T is the temperature, and k , R and h are Boltzmann×s con-
1
(
B
ꢀ
1
stant, the universal gas constant and the Planck constant, respectively.
=
1896, 1919, 2023 cm (C=O); positive ion FAB-MS: m/z: 1176
+
+
[
M+H] , 1140 [MꢀCl]
Re¥1/2CH Cl
8.88, H 4.04, N 6.95.
Re(CO) (L4)Cl] (4): The title complex was synthesized by a procedure
;
elemental analyses calcd (%) for
The photochemical quantum yields of the photochromic forward reaction
were obtained by a linear least-squares fitting of Equation (3),
C
59
H
48ClN
6
O
7
2
2
(1217): C 58.71, H 4.03, N 6.90; found: C
5
ꢀ
kt
[
3
½kVðAꢀA
0
e
ފ
ꢀ
¼
ð3Þ
½eIð1ꢀeꢀ ފ
kt
similar to that used for 1, except that L4 (238 mg, 0.44 mmol) was used in
place of L1 in the substitution reaction and chloroform/acetone (2:1 v/v)
was used as eluent in the column chromatography. Slow diffusion of di-
ethyl ether vapor into a concentrated acetone solution of the complex
where f is the photochemical quantum yield, V is the volume of irradiat-
ed sample solution, e is the extinction coefficient of the photomerocya-
nine, and I is the intensity of the light of excitation in Einsteins per
second.
1
gave 4, isolated as a yellow powder. Yield: 209 mg, 0.25 mmol; 60%. H
NMR (400 MHz, CD
2
Cl
2
, 298 K): d = 1.36 (s, 6H; ꢀMe), 2.60 (s, 3H; ꢀ
Me on bpy), 2.77 (s, 3H; ꢀNMe), 5.45 (s, 2H; ꢀOCH ꢀ on bpy), 6.58 (d,
2
Crystalstructure determination : All the experimental details are given in
Table 1. Crystals of 1 suitable for X-ray studies were obtained by slow
diffusion of n-hexane vapor into a dichloromethane solution of 1. A red
crystal of dimensions 0.5î0.3î0.2 mm mounted on a glass capillary was
used for data collection at 288C on a MAR diffractometer with a
J = 7.7 Hz, 1H; indolinic proton at 7-position), 6.89±6.94 (m, 2H; naph-
thoxazinic proton at 5’-position and indolinic proton at 5-position), 7.09
(
d, J = 6.6 Hz, 1H; indolinic proton at 4-position), 7.18±7.25 (m, 2H;
naphthoxazinic proton at 8’-position, indolinic proton at 6-position), 7.36
d, J = 5.6 Hz, 1H; bipyridyl proton at 5’-position), 7.61±7.65 (m, 2H;
naphthoxazinic proton at 6’-position and bipyridyl proton at 5-position),
(
3
00 mm image plate detector with use of graphite-monochromated MoKa
radiation (l = 0.71073 ä). Data collection was made with 28 oscillation
of f, 300 s exposure time and a scanner distance of 120 mm. The images
were collected and interpreted, and intensities were integrated by use of
the program DENZO. The structure was solved by direct methods by
employment of the SIR-97 program on a PC. Almost all atoms, other
than atoms of solvent molecules, were located by direct methods and suc-
cessive least-squares Fourier cycles. The positions of the other non-hydro-
gen atoms were found after successful refinement by full-matrix, least-
7
2
.73±7.75 (m, 2H; naphthoxazinic proton at 2’,7’-position), 7.98 (d, J =
.4 Hz, 1H; naphthoxazinic proton at 10’-position), 8.06 (s, 1H; bipyridyl
proton at 3’-position), 8.35 (s, 1H; bipyridyl proton at 3-position), 8.90
d, J = 5.6 Hz, 1H; bipyridyl proton at 6’-position), 9.06 ppm (d, J =
[26]
(
[27]
5
1
.6 Hz, 1H; bipyridyl proton at 6-position); IR (KBr disc): n˜ = 1888,
ꢀ
1
+
913, 2022 cm (C=O); positive ion FAB-MS: m/z: 834 [M+H] , 798
+
[
(
MꢀCl] ; elemental analyses calcd (%) for C37
H
30ClN
4
O
5
2 2
Re¥1/4CH Cl
853): C 52.42, H 3.60, N 6.56; found: C 52.40, H 3.59, N 6.32.
[28]
squares by use of the SHELXL-97
program on a PC. The methyl
Physicalmeasurements and instrumentation : Electronic absorption spec-
tra were recorded on a Hewlett±Packard 8452A diode array spectropho-
tometer. Steady-state emission and excitation spectra at room tempera-
ture and at 77 K were recorded on a Spex Fluorolog-2 Model F 111 fluo-
rescence spectrophotometer. Excited state lifetimes of solution samples
were measured with a conventional laser system. The excitation source
groups near both ends of the ligand were disordered due to site symme-
try as were the related bound N (N4, N6) and C (C38, C47) atoms. Since
C and N atoms have very similar scattering factors, disorder of C and N
atoms sharing the same positions were not treated. Instead, their posi-
tions were located correspondingly. One crystallographic asymmetric unit
consisted of one formula unit: that is, a complex molecule, two solvent
774
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 766 ± 776

Spirooxazine-Containing 2,2’-Bipyridine Ligands and Their Rhenium(i) Tricarbonyl Complexes
766 ± 776
molecules of CH
2
Cl
2
and two solvent molecules H
2
O. In the final stage of
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(
except those of water molecule) were generated by use of the
[
28]
SHELXL-97 program. Positions of H atoms were calculated based on
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ꢀ
3
maximum residual peaks and holes of 0.958 and ꢀ0.928 eä , respective-
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orange crystal of dimensions 0.5î0.2î0.1 mm mounted on a glass capil-
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a 300 mm image plate detector with use of graphite-monochromated
MoKa radiation (l = 0.71073 ä). Data collection was made with 28 oscil-
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non-hydrogen atoms were refined anisotropically. H atoms were generat-
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. In the final stage of least-squares refinement, all
[
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3
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V. W.-W. Y. acknowledges support from The University of Hong Kong
Foundation for Educational Development and Research Limited and
The University of Hong Kong. The work described in this paper was sup-
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ministrative Region, China (Project HKU7097/01P). C.-C. K. acknowl-
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[
[
25] Derivation of Equation 3, please refer to Supporting Information.
26] DENZO (version 1.3.0): ™The HKL Manual - A description of pro-
grams DENZO, XDISPLAYF, and SCALEPACK∫ written by D.
Gewirth, with the co-operation of the program authors Z. Otwinow-
ski, W. Minor, (1995), Yale University, New Haven, U.S.A.
Received: August 27, 2003 [F5485]
776
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 766 ± 776