Organic photochromic radical compound based on a biindenylidene system

Article abstract of DOI:10.3184/030823408X360300

A novel dual functional biindenylidene derivative (4) having nitronyl nitroxide radicals on both sides of the molecules, was synthesised. Its photochromism, as well as magnetic properties were investigated. The compound 4 underwent photochromic reactions by irradiation with UV and visible light. The intermolecular magnetic interactions were measured with a SQUID susceptometer.

Full text of DOI:10.3184/030823408X360300

598 RESEARCH PAPER
OCTOBER, 598–600
JOURNAL OF CHEMICAL RESEARCH 2008
Organic photochromic radical compound based on a biindenylidene system
Xu Li*
Fundamental Department, the Chinese People's Armed Police Forces Academy, Langfang 065000, P.R. China
A novel dual functional biindenylidene derivative (4) having nitronyl nitroxide radicals on both sides of the molecules,
was synthesised. Its photochromism, as well as magnetic properties were investigated. The compound 4 underwent
photochromic reactions by irradiation with UV and visible light. The intermolecular magnetic interactions were
measured with a SQUID susceptometer.
Keywords: biindenylidene, radicals, photochromism, magnetic interactions
There is interest in the preparation of photomagnetic materials
whose magnetic properties may be controlled by using light.
Fromboththescientificandtechnologicalpointofview, toafford
examples of molecular devices as thermal or optical switching
systems correlated with spins.1-2 Several interesting example
of organic photochromic and photomagnetic compounds such
as azobenzene, diarylethene, spiropyran, terphenoquinone,
anthracene, and naphthopyran have been reported, and their
properties have been extensively investigated.3-7 Aminoxyl
radical moieties have been widely adopted in those compounds,
because of their versatility and good stability in the field of
material chemistry as building blocks for molecule-based
magnetic materials.8-10 As disclosed in recent reports,11-13 the
biindenylidene derivatives are a unique class of photochromic
organic compounds, which undergo photochromism
simultaneously with the formation of radicals in the crystalline
state. If the stable aminoxyl radical moiety is incorporated into
such a photochromic compound like biindenylidene, a new
multifunctional molecule could be designed.
On the basis of this concept, a new dual-functional
biindenylidene derivative 4 was designed by introducing two
nitroxide radicals to the biindenylidene system (Scheme 1).
Its photochromic and magnetic properties were investigated.
For the purpose of comparison, the precursors 1, 2 and 3 were
investigated accordingly as well. We report here the results
from these investigations.
In order to confirm the structure, the products were subjected
1
to spectroscopic analysis using IR, H NMR and elemental
analysis. A crystal of suitable quality for single crystal X-ray
diffraction was obtained by slow evaporation from CH2Cl2
solutions. The molecular structure of 1 is shown in the Fig. 1.
The asymmetric unit of 1 contains one half-molecule with
the other half generated by a centre of inversion (Fig. 1);
the centre of inversion lies at the mid-point of the C(9)
=C(9A) bond [symmetry code: –x + 1,–y,–z + 2 ]. The C(9)
=C(9A) bond distance of 1.342 (5) Å confirms its double-
bond character. The cyclopentenone ring adopts a flattened
envelope conformation, with atom C(9) at the flap. Two loops
CH2CH2CH2CH3
O HO
a)
H3C
CH3
OH
O
H3CH2CH2CH2C
1
OCH2CH3
OH
O
O
H3CH2CO
CH
H3C
b)
CH3
H3C
O
OH
HO
N
CH3
N
O
HC
OH
O
2
c)
O
H CH CO
CH
OCH2CH3
OH
3
2
CHO
H3C
CH3
O HO
OH
O
H3C
CH3
d)
OH
O
HC
N
N
O
4
OHC
Scheme 1 (a) n-butyl magnesium bromide in dry THF, then air oxidation H+; (b) p-benzaldehyde diethyl acetal magnesium
bromide in dry THF, then air oxidation H+; (c) p -toluenesulfonic acid in chloroform; (d) 4-amino-2,2,6,6-tetramethylpiperidino
acetate AcOH in dichloromethane.
* Correspondent. E-mail: lixu.wjxy@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2008 599
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
800
l/nm
Fig. 2 UV spectral changes of 4 (…) before and (—) after
irradiation.
and the photochromic and magnetic interactions were
investigated. The biindenylidene derived radicals underwent
photochromic reactions by irradiation with UV and visible
light in the solid state. SQUID susceptometer analysis
demonstrated that the intermolecular magnetic interactions
were antiferromagnetic interaction. These result showed that
incorporation of organic photochromism into magnetic system
could not only lead to interesting photochromic behaviour,
but also provided a new strategy to develop photomagnetic
materials.
Fig. 1 Molecular structure of 1 with atom numbering scheme.
of indanione are almost perfectly parallel, which makes the
double bond have little distortion. The two methyl groups
locate at different sides of the double bond with trans-
configuration referring to the indanone planes.
Results and discussion
Photochromic properties in the solid state
The colour of 1, 2, 3 and 4 was measured by UV-Vis absorption
in the solid state. During the reaction, no remarkable changes
were observed in the IR spectra. As expected, the precursor 1,
2, 3 showed photochromic properties. Photoirradiation of the
yellow powder 1 with UV light produced by a high pressure
Hg-lamp led to the formation of a brown powder, and the
brown powder returned slowly to yellow solid in the dark.
The new radical compound 4 showed photochromism in a
solid state too. The yellow crystals of 4 turn to brown, when
exposed to UV light for few minutes. The brown solid fade
and return to the original yellow gradually in the dark. The
UV absorption of 4 considerably increased in the wavelength
range of 500–700 nm after irradiation (Fig. 2).
Experimental
All chemicals were purchased from commercial sources, and solvents
were of analytical grade, and were dried by refluxing under N2 over
an appropriate drying agent and distilled before use. Melting points
were determined with Yanagimoto MP-35 melting point apparatus.
1H NMR spectra were recorded at 300 MHz on a Bruker-P300
instrument using tetramethylsilane as an internal reference.
Elemental analysis was performed on a YANACO CHN CORDER
MT-3 apparatus. UV–Vis spectra were recorded on TU-1901 UV–
Vis spectrophotometer. Magnetic susceptibilities were measured
by SQUID susceptometer. X-ray data collection was performed on
a Bruker SMART 1000 diffractometer with Mo-Ka radiation. The
structure was solved by direct methods (SHELXS-97)17 and non-
H atoms were refined by full-matrix least-squares method with
anisotropic temperature factors (SHELXL-97).17
Magnetic properties
Synthesis of 3,3'-dibutyl-3,3'-dihydroxy-7,7'-dimethyl-2,2'-bi-1H-
indanylidene-1,1'-dione (1): To a three-necked 250 ml round-
bottomed flask containing a stirrer bar, fitted with a pressure-
equalising dropping funnel and a reflux condenser, was added Mg
(2.4 g, 0.10 mol), anhydrous THF (15 ml) under N2 atmosphere.
A solution of CH3CH2CH2CH2Br (0.10 mol) in anhydrous ether
(60 ml) was added to this suspension from pressure-equalising
funnel. After the addition was complete, the mixture was stirred
under reflux for additional 0.5 h. The pressure-equalising funnel
was then recharged with 5,5'-bimethyl-2,2'-biindanylidene-1,1',3,3'-
tetraone (3.18 g, 0.01 mol) suspended in dry benzene (50 ml).
The suspension was added portion-wise over a period of 20 min.
The dark green reaction mixture was stirred at room temperature
under nitrogen atmosphere for 12 h, and then exposed to air
for another 3 h. Finally, quenching the reaction with saturated
NH4Cl aqueous solution gave immiscible liquid phases. The crude
In order to examine the magnetic properties of the photochromic
compounds 1, 2, 3 and 4, their magnetic susceptibilities were
measured by a SQUID susceptometer within the temperature
range of 2–300K. The data are summarised in Table 1. The
magnetic interaction of photo product 1, 2, 3 could not be
identified, due to the too weak signal on the magnetometer.
While after introducing nitroxide to the biindenylidene system,
the significant changes of magnetic properties were observed
along with the photochromism in solid state. Antiferromagnetic
interactions have been observed for 4. According to Curie–
Weiss law, Curie constants as well as Weiss temperatures
favour an antiferromagnetic interaction for 4.14-16
In conclusion, biindenylidene derivative having nitronyl
nitroxide radicals at both ends of the molecule was synthesised,
Table 1 Magnetic data of photochromic compound 1, 2, 3 and 4
Compound
Magnetic interactiona
Cb (emu K mol-1)
qc (K)c
1
2
3
4
—
—
—
—
—
—
—
–9.26
Antiferromagnetic
0.63(78)
aFitting for Curie–Weiss law. bCurie constant. Values in parentheses denote the estimated spin concentration. cWeiss temperature.

600 JOURNAL OF CHEMICAL RESEARCH 2008
desired compound I precipitated as insoluble power between the
organic and aqueous phases. Filtration afforded crude product,
which was purified by column chromatography on silica gel.
Yield: 29.6%. Yellow crystals: m.p. 163–164°C. 1H NMR
(300 MHz, CDCl3): δ(ppm) 7.77–7.27 (m, 6H, 6 × –ArH), 6.79–
6.68 (m, 2H, 2 × –OH), 2.55(s, 6H, 2 × ArCH3), 2.27–2.09(m, 4H,
2 × –CH2–), 1.13–0.879(m, 14H, 2 × –CH2CH2CH3). Anal. Calcd
for C28H32O4: C, 77.75; H, 7.46; Found: C, 77.89; H, 7.48%.
IR(KBr):3334(–OH),1675(–C=O)cm-1.CrystaldataforI.C28H32O4,
M = 432.54, Triclinic, a = 9.704(2), b = 10.822(3), c = 12.743(3) Å,
a = 75.290(4)°, g = 78.439(4)°, b = 73.240(4)°, V = 1769.1(4) Å3,
T = 294(2) K, space group C2/c, Z = 2, d = 1.170 Mg/m3, m(Mo-
at ambient temperature. Concentration in vacuum gave radical 4
as brown powdery solid that was recrystallised from methanol and
dichloromethane in 53% yield. Brown powder, m.p. 266–267°C. Ms
(ESI) Calcd for: m/z 834.44. Found: 834.42. IR (KBr) νmax(cm-1):
3362(–OH), 1673 (–C=O) cm-1. Anal. Calcd for C52H58 N4O6: C
74.79, H 7.00, N 6.71. Found: C 74.82, H 6.74, N 6.63%.
The author would like to thank Education Department of
Hebei Province (grant no. Z2007202) for financial support.
Received 18 July 2008; accepted 15 August 2008
Paper 08/0059 doi: 10.3184/030823408X360300
Published online: 10 October 2008
Ka) = 0.077 mm-1, 6288 reflections measured, 4310 unique (Rint
=
0.0293), which were used in calculations. CCDC-695295.
Synthesis of 3,3'-di-(4-diethyl acetal benzaldehyde)-3,3'-dihydroxyl-
7,7'-dimethyl-[2,2'-bi-1Hindene]-1,1'-dione (2): Following the
procedure previously described for 1, the crude desired compound
2 precipitated as insoluble yellow power between the organic and
aqueous phases. Filtration afforded crude product, which was purified
bycolumnchromatographyonsilicagelin43.1%yield.Yellowpowder,
m.p. 258–260°C. 1H NMR (300 MHz, CDCl3) δ(ppm): 7.59–7.09 (m,
14H, –ArH), 7.04–7.04 (m, 2H, 2¥–OH), 5.40 (s, 2H, –CH), 3.58–3.47
(q, –CH2, J = 7.5 Hz), 2.38 (s,–ArCH3),1.21–1.18 (t,–CH3, J = 7.5 Hz).
IR (KBr) νmax(cm-1): 3375(–OH), 1675 (–C=O) cm-1. Ms (ESI)
Calcd for: m/z 676.30. Found: 676.48(M+). Anal. Calcd for C42H44O8:
C 74.54, H 6.55. Found: C 74.61, H 6.57%.
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3
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1
powder, m.p.>300°C. H NMR (300 MHz, CDCl3) δ(ppm): 9.95 (s,
2H, –CHO), 7.83–7.26 (m, 14H, –ArH), 6.99–6.94 (d, 2H, –OH), 2.40
(s, –ArCH3). IR (KBr) νmax(cm–1): 3344(–OH), 1698 (–CHO), 1675
(–C=O) cm–1.Ms (ESI) Calcd for: m/z 528.16. Found: 528.37. Anal.
Calcd for C34H24O6: C 77.26, H 4.54. Found: C 77.39, H 4.48%.
Synthesis of radical (4): A mixture of 3 (0.106 g, 0.2 mmol) and
4-amino-2,2,6,6-tetramethylpiperidinooxy (0.068 g, 0.4 mmol) with
a small amount of acetic acid was stirred for 4 h in dichloromethane