Synthesis, characterization and photochromic properties of novel spirooxazines

Article abstract of DOI:10.14233/ajchem.2013.13846

A series of spirooxazine compounds were synthesized via condensation reaction of 1,3,3-trimethyl-2-methyleneindoline with orthohydroxynitroso aromatic derivatives, then esterification with acyl chlorides. Their structures were confirmed by FTIR, ¹H NMR, ¹³C NMR and elemental analyses. Absorption bands in the visible region were observed in UV-VIS absorption spectra (λ_max: 530-665 nm), which were red-shifted as the polarity of solvent increased. Furthermore, these absorption bands also red-shifted with the increase of the electron-donating ability of the 6′-heterocycle substituent, but were nearly unaffected by 9′-acyloxy. The experimental results of thermal decoloration showed that the thermal relaxation progress of the photomerocyanine followed first order kinetics and the relaxation time was tuned in a broad range from 125-1886 s (at 20 °C) by changing electron-donating power on 6′-heterocycle and 9′-acyloxy, these provided a new design strategy to synthesize photochromic molecules which features different and acceptable relaxation time.

Full text of DOI:10.14233/ajchem.2013.13846

Asian Journal of Chemistry; Vol. 25, No. 5 (2013), 2758-2762
http://dx.doi.org/10.14233/ajchem.2013.13846
Synthesis, Characterization and Photochromic Properties of Novel Spirooxazines
1,2
1
1
1,*
XIAO-LI YANG , BAO-JIE YANG , YUAN-YUAN LIU and HONG-JUN ZHU
1College of Science, Nanjing University of Technology, Nanjing, P.R. China
2School of Material Engineering, Jinling Institute of Technology, Nanjing, P.R. China
*Corresponding author: Fax: +86 25 83587428; Tel: +86 25 83172358; E-mail: zhuhjnjut@hotmail.com
(Received: 4 April 2012;
Accepted: 21 November 2012)
AJC-12448
A series of spirooxazine compounds were synthesized via condensation reaction of 1,3,3-trimethyl-2-methyleneindoline with ortho-
1
hydroxynitroso aromatic derivatives, then esterification with acyl chlorides. Their structures were confirmed by FTIR, H NMR, 13C
NMR and elemental analyses. Absorption bands in the visible region were observed in UV-VIS absorption spectra (λmax: 530-665 nm),
which were red-shifted as the polarity of solvent increased. Furthermore, these absorption bands also red-shifted with the increase of the
electron-donating ability of the 6'-heterocycle substituent, but were nearly unaffected by 9'-acyloxy. The experimental results of thermal
decoloration showed that the thermal relaxation progress of the photomerocyanine followed first order kinetics and the relaxation time
was tuned in a broad range from 125-1886 s (at 20 ºC) by changing electron-donating power on 6'-heterocycle and 9'-acyloxy, these
provided a new design strategy to synthesize photochromic molecules which features different and acceptable relaxation time.
Key Words: Spirooxazine, Merocyanine, Photochromism, Heterocycle, Esterification.
OR2
INTRODUCTION
Spirooxanzines are a well-known class of photochromic
compounds due to their superior photochromic prosperties,
OR2
N
such as photo-fatigue resistance and photocolouration1-3, which
facilitate their application in memory devices, optical switches,
displays, chemical sensors and ophthalmic plastic lenses4-7.
The photochromism of spirooxazines is attributable to a hetero-
lytic spiro-C-O bond cleavage via UV irradiation that generates
the coloured merocyanine form (MC). The merocyanine form
form reverts to the closed colourless form (SO) either thermally
or photochemically (Scheme-I)8-10. The reported work are quite
interesting, however, the commercial application of most
spirooxazines has been severely restricted in the past decades
by the unacceptable thermal decoloration process of the
coloured photomerocyanine species. In this context, the
development of novel photochromic molecule which features
acceptable relaxation time and the further study of the
photophysical properties, photochromic behaviours and struc-
ture-property relationships present an interesting challenge.
1,3,3-Trimethyl spiro[2H]-indol-2,3'-[3H]-naphtho[2,1-
b][1,4]oxazine is a very typical spirooxazine compound
which has attracted a great interest by virtue of their excellent
photochromic properties10. In this work, a series of novel
spirooxazine compounds (1b-1c, 2b-2f) based on 1,3,3-
trimethyl spiro-[2H]-indol-2,3'-[3H]-naphtho[2,1-b][1,4]-
oxazine were designed and synthesized. Compound 1a and 2a
hv
kT
N
R1
O
N
O
N
R1
(SO)
(MC)
Scheme-I: Photochromic interconversion (hv) and thermal relexation (kT)
of the spirooxazine SO and merocyanine merocyanine form
states of compounds
have been reported in the literature11 and were synthesized as
reference compounds. Their photochromic behaviours and
thermal stability have been investigated with the aim of
understanding the structure-physical property relationships and
developing potential photochromic materials.
EXPERIMENTAL
All reagents were purchased from commercial sources
and used without further purification unless otherwise noted.
1-Nitroso-2,7-dihydroxynaphthalene was synthesized according
to the literature methods3. Melting points were measured on
an X-4 microscope electrothermal apparatus and remained
uncorrected. 1H and 13C NMR spectra were obtained in DMSO-
d6 or CDCl3 using a Bruker AV-500 spectrometer at 500 MHz
or a BrukerAV-300 spectrometer at 300 MHz. Chemical shifts

Vol. 25, No. 5 (2013)
Synthesis, Characterization and Photochromic Properties of Novel Spirooxazines 2759
were reported in δ (ppm) relative to tetramethylsilane, which
was used as the internal standard. Fourier transformation
infrared (FTIR) spectra were recorded in KBr pellets using an
FTIR spectrometer (NICOLET IS10). Elemental analyses were
carried out on a Vario EL III elemental analyzer. Optical
absorption spectra were recorded using a CARY 1101 UV-
VIS spectrophotometer.
removed in vacuo. The residue obtained was recrystallised
from hot methyl alcohol to obtain 2a-2f as pure products.
1,3,3-Trimethyl-9'-methacryloyloxy-spiro[indoline-
2,3'(3H) naphtho[2,1-b][1,4]oxazine] (2a): Gray solid, yield:
97.6 %, m.p. 151-153 ºC. IR (KBr, νmax, cm-1): 3047, 2971,
1730, 1630, 1480,1440, 1360, 1256, 1080, 1170, 1120, 978,
903, 823, 748. 1H NMR (CDCl3, 500 MHz): δ 8.27 (1H, d, J =
2.3 Hz, ArH), 7.76 (1H, d, J = 8.9 Hz, ArH), 7.71 ( 1H, s, 2'-
H), 7.65 (1H, d, J = 8.9 Hz, ArH), 7.23-7.17 (2H, m, ArH),
7.08 (1H, d, J = 7.1 Hz, ArH), 6.99 (1H, d, J = 8.9 Hz, ArH),
6.90 (1H, t, J = 7.4Hz, ArH), 6.58 (1H, d, J = 7.7Hz, ArH),
6.41 (1H, s, CH), 5.78 (1H, s, CH), 2.76 (3H, s, CH3), 2.11
(3H, s, CH3), 1.35 (6H, s, CH3). 13C NMR (DMSO, 300 MHz):
δ 18.0, 20.4, 25.1, 29.2, 51.5, 98.4, 107.1, 1123, 116.5, 119.5,
119.6, 121.5, 122.2, 126.8, 127.8, 127.8, 129.7, 130.2, 130.9,
135.3, 135.4, 144.4, 147.2, 149.6, 151.6, 165.4. Anal. calcd.
(%) for C26H24N2O3: C, 75.71; H, 5.86; N, 6.79. Found (%) C,
75.57; H, 5.84; N, 6.81.
General procedure for synthesis of compounds 1a-1c:
1-Nitroso-2,7-dihydroxynaphthalene (3.78 g, 20 mmol) was
dissolved in methanol (200 mL) and heated to reflux under
nitrogen, then treated with a solution of R1H (40 mmol) in
methanol (10 mL). The resulting mixture was heated to reflux
for 5 h and then treated, over a 5 min period, with a solution
of 1,3,3-trimethyl-2-methyleneindoline (3.46 g, 20 mmol) in
methanol (10 mL). The progress of this reaction was moni-
tored by TLC, which indicated completion of the reaction
after 36 h. Then the solution was cooled and the brown solid
was separated by filtering. The residue was purified via
column chromatography (silica, petroleum ether/ethyl acetate,
1/3, v/v).
1,3,3-Trimethyl-9'-benzoyloxy-spiro[indoline-2,3'(3H)
naphtho[2,1-b][1,4]oxazine](2b): Gray solid, yield: 96.6 %,
m.p. 214-216 ºC. IR (KBr, νmax, cm-1): 3047, 2960, 1630, 1480,
1370, 1250, 1060, 1114, 971, 829, 741. 1H NMR (CDCl3, 500
MHz): δ 8.38 (1H, d, J = 1.9 Hz, ArH), 8.27 (2H, d, J = 7.2
Hz, ArH), 7.81 (1H, d, J = 8.8 Hz, ArH), 7.71 (1H, s , 2'-H),
7.64 (2H, t, J = 7.4 Hz, ArH ), 7.54 (2H, t, J = 7.7 Hz, ArH),
7.28 (1H, d, J = 2.2 Hz, ArH), 7.22 (1H, t, J = 7.7 Hz, ArH),
7.08 (1H, d, J = 7.2 Hz, ArH), 7.01 (1H, d, J = 8.8 Hz, ArH),
6.90 (1H, t, J = 7.4 Hz, ArH), 6.58 (1H, d, J = 7.7 Hz, ArH),
2.77 (3H, s, CH3), 1.36 (3H, s, CH3), 1.35 (3H, s, CH3). Anal.
calcd. (%) for C29H24N2O3: C, 77.66; H, 5.39; N, 6.25. Found
(%) C, 77.53; H, 5.38; N, 6.27.
1,3,3-Trimethyl-9'-hydroxy-spiro[indoline-2,3'(3H)-
naphtho[2,1-b][1,4]oxazine] (1a): Gray solid, yield: 51.2 %,
m.p. 167-170 ºC (lit.: m.p. 167-168 ºC)12. IR (KBr, νmax, cm-1):
3330, 2970, 1625, 1480, 1450, 1360, 1235, 1090, 1190, 980,
897, 835, 844, 744.Anal. calcd. (%) for C22H20N2O2: C, 76.72;
H, 5.85; N 8.13. Found (%): C,77.02; H, 5.82; N, 8.16.
1,3,3-Trimethyl-6'-morpholino-9'-hydroxy-spiro-
[indoline-2,3'(3H)naphtho[2,1-b][1,4] oxazine] (1b): Blue
solid, yield: 3.6 %, m.p. 246-248 ºC. IR (KBr, νmax, cm-1): 3400,
2960, 1620, 1460, 1360, 1230, 1110, 1150, 982, 825, 742. 1H
NMR (DMSO, 500 MHz): δ 9.79 (1H, s, OH), 7.86 (1H, d,
J = 8.9 Hz, ArH), 7.73 (1H, s, 2'-H), 7.66 (1H, s, ArH), 7.16-
7.12 (2H, m, ArH), 6.93 (1H, d, J = 8.2 Hz, ArH), 6.82 (1H, t,
J = 7.3 Hz, ArH), 6.63 (1H, d, J = 7.6 Hz, ArH), 6.41 (1H, s,
ArH), 3.80 (4H, t, J = 4.3 Hz, 2CH2), 2.95 (4H, t, J = 4.3 Hz,
2CH2), 2.67 (3H, s, CH3), 1.26 (6H, s, CH3). Anal. calcd. (%)
for C26H27N3O3: C, 72.71; H, 6.34; N 9.78. Found (%): C,72.59;
H, 6.32; N, 9.81.
1,3,3-Trimethyl-9'-(p-chlorobenzoyloxy)-spiro-
[indoline-2,3'(3H)naphtho[2,1-b][1,4]oxazine] (2c): Gray
solid, yield: 98.5 %, m.p. 234-235 ºC. IR (KBr, νmax, cm-1):
3048, 2961, 1624, 1465, 1362, 1263, 1067, 1116, 975, 848,
753, 680. 1H NMR (CDCl3, 500 MHz): δ 8.37 (1H, d, J = 1.7
Hz, ArH), 8.20 (2H, d, J = 8.4 Hz, ArH), 7.78 (1H, d, J = 8.8
Hz, ArH), 7.71 (1H, s , 2'-H), 7.68 (1H, d, J = 8.9 Hz, ArH),
7.51 (2H, d, J = 8.4 Hz, ArH), 7.26 (1H, d, J = 2.1 Hz, ArH),
7.22 (1H, t, J = 7.6 Hz, ArH), 7.09 (1H, d, J = 7.2 Hz, ArH),
7.01 (1H, d, J = 8.9 Hz, ArH), 6.90 (1H, t, J = 7.4 Hz, ArH),
6.58 (1H, d, J = 7.7 Hz, ArH), 2.76 (3H, s, CH3), 1.35 (6H, s,
CH3). 13C NMR (DMSO, 300 MHz): δ 20.4, 25.1, 29.2, 51.5,
98.5, 107.1, 112.4, 116.6, 119.4, 119.6, 121.4, 122.3, 126.9,
127.8, 127.8, 129.1, 129.7, 130.2, 130.9, 131.7, 135.4, 138.99,
144.4, 147.2, 149.5, 151.7, 163.9. Anal. calcd. (%) for
C29H23ClN2O3: C, 72.12; H, 4.80; N, 5.80. Found (%) C, 71.98;
H, 4.78; N, 5.82.
1,3,3-Trimethyl-6'-indolino-9'-hydroxy-spiro[indoline-
2,3'(3H)naphtho[2,1-b][1,4]oxazine] (1c): Grey-green solid,
yield: 3.5 %, m.p. 124-126 ºC. IR (KBr, νmax, cm-1): 3420,
2960, 1620, 1480, 1460, 1260, 1030, 1160, 982, 748. 1H NMR
(DMSO, 500 MHz): δ 9.89 (1H, s, OH), 7.79 (1H, d, J = 2.5
Hz, ArH), 7.72 (1H, s, 2'-H), 7.65 (1H, d, J = 9.0 Hz, ArH),
7.13-7.10 (4H, m, ArH), 6.90 (1H, t, J = 2.6 Hz, ArH), 6.81-
6.64 (3H, m, ArH), 6.61 (1H, d, J = 7.7Hz, ArH), 6.08 (1H, d,
J = 7.8 Hz, ArH), 3.86 (2H, t, J = 8.5 Hz, CH2), 3.08 (2H, t,
J = 8.5 Hz, CH2), 2.67 (3H, s, CH3), 1.27 (3H, s, CH3), 1.26
(3H, s, CH3). Anal. calcd. (%) for C30H27N3O2: C, 78.07; H,
5.90; N, 9.10. Found (%) C, 77.94; H, 5.88; N, 9.13.
General procedure for synthesis of compounds 2a-2f:
In a 250 mL three-necked flask equipped with a temperature
probe, dropping funnel and magnetic stirrer, 1a-1c (2 mmol)
was dissolved in a mixture of benzene (140 mL) and 1,4-
dioxane (20 mL). At 5 ºC, R2COCl (20 mmol in benzene,
10 mL) was added dropwise over a period of 0.5 h.After conti-
nuous stirring for 10 h at room temperature, a small amount
of insoluble matter was filtered off and the solution was
1,3,3-Trimethyl-9'-methacryloyloxy-6'-morpholino-
spiro[indoline-2,3'(3H) naphtho[2,1-b][1,4]oxazine] (2d):
Gray solid, yield: 78.4 %, m.p. 193-195 ºC. IR (KBr, νmax, cm-1):
3050, 2960, 1730, 1620, 1490, 1260, 1030, 1135, 978, 742.
1H NMR (CDCl3, 500 MHz): δ 8.16 (1H, d, J = 2.4 Hz, ArH),
8.08 (1H, d, J = 9.1 Hz, ArH), 7.73 (1H, s, 2'-H), 7.24 (1H, d,
J = 2.4 Hz, ArH), 7.17-7.10 (2H, m, ArH), 6.84 (1H, t, J = 7.5
Hz, ArH), 6.69 (1H, s, ArH), 6.65 (1H, d, J = 7.6 Hz, ArH),
6.35 (1H, s, CH), 5.94 (1H, s, CH), 3.82 (4H, t, J = 4.4 Hz,
2CH2), 3.01 (4H, t, J = 4.4 Hz, 2CH2), 2.70 (3H, s, CH3), 2.06

2760 Yang et al.
Asian J. Chem.
(3H, s, CH3), 1.28 (6H, s, 2CH3). 13C NMR (DMSO, 300 MHz):
δ 18.0, 20.3, 25.2, 29.2, 51.3, 52.9, 66.3, 98.6, 105.2, 107.1,
112.8, 118.6, 118.7, 119.5, 121.5, 125.5, 127.8, 132.2, 135.3,
135.50, 144.9, 147.2, 149.1, 149.6, 151.5, 165.3. Anal. calcd.
(%) for C30H31N3O4: C, 72.41; H, 6.28; N, 8.44. Found (%) C,
72.29; H, 6.26; N, 8.46.
TABLE-1
MAXIMUM ABSORPTION WAVELENGTHa OF 1a-1c AND 2a-2f
Solvent
Compound
Cyclohexane
530.0
Dichloromethane
545.1
Chloroform
565.0
1a
1b
1c
2a
2b
2c
2d
2e
2f
540.0
550.0
584.9
545.0
620.0
635.0
1,3,3-Trimethyl-9'-(p-chlorobenzoyloxy)-6'-morpho-
lino-spiro[indoline-2,3'(3H)naphtho[2,1-b][1,4]oxazine]
(2e): Gray solid, yield: 50.7 %, m.p. 177-178 ºC. IR (KBr,
νmax, cm-1): 3049, 2961, 1624, 1467, 1360, 1251, 1117, 1162,
977, 847, 754, 745. 1H NMR (CDCl3, 500 MHz): δ 8.36 (1H,
d, J = 2.1 Hz, ArH), 8.21 (2H, d, J = 8.5 Hz, ArH), 8.12 (1H,
d, J = 9.0Hz, ArH), 7.61 (1H, s, 2'-H), 7.52 (2H, d, J = 8.5Hz,
ArH), 7.25-7.21 ( 2H, m, ArH), 7.09 (1H, d, J = 7.1 Hz, ArH),
6.89 (1H, t, J = 7.4 Hz, ArH), 6.61 (1H, s, ArH), 6.58 (1H, d,
J = 7.7 Hz, ArH), 3.95 (4H, t, J = 4.4Hz, CH2), 3.07 (4H, t,
J = 4.4 Hz, CH2), 2.76 (3H, s, CH3), 1.36 (3H, s, CH3), 1.34
(3H, s, CH3). 13C NMR (DMSO, 300 MHz): δ 20.3, 25.2, 29.2,
51.3, 52.9, 66.3, 98.7, 105.4, 107.1, 112.9, 118.6, 119.5, 121.5,
121.6, 125.6, 127.8, 127.8, 129.1, 131.7, 132.2, 135.5, 138.9,
145.0, 147.2, 149.2, 149.5, 151.6, 163.9. Anal. calcd. (%) for
C33H30ClN3O4: C, 69.77; H, 5.32; N, 7.40. Found (%) C, 69.64;
H, 5.31; N, 7.42 %.
540.0
565.1
575.1
540.0
565.0
575.0
539.9
564.9
575.0
550.0
565.0
625.0
549.1
560.0
619.9
560.0
649.9
665.0
aMeasured in various solvents (c = 1 × 10-5 mol L-1) after irradiation at
365 nm with a 12 W ultraviolet lamp.
Absorption spectra of spiro compounds in various
solvents after UV irradiation: The photoisomerization
behaviour of the spirooxazine dyes were investigated by UV-
visible analysis. UV irradiation of the compounds 1a-1c and
2a-2f at 365 nm led to an increase in absorption intensity in
the visible region of the band at 530-665 nm, corresponding
to the formation of the photomerocyanine form (Scheme-I).
The absorption maxima (λmax) of these open coloured forms
measured in three different solvents (Table-1). We observed
that spirooxazines 1a-1c and 2a-2f had different absorption
νmax in different solvents (cyclohexane, dichloromethane,
chloroform). With the increase in polarity of the solvent, the
maximum absorbance of 1a-1c and 2a-2f underwent an
obvious red shift. In the strongly polar solvents, the higher
proportion of the merocyanine, the longer conjugate system
in the ring-opened form which results in the red effects13.
Compared to unsubstituted 1a, heterocycle substituted 1b and
1c showed obviously red-shift and the absorption λmax were
found in the order of 1c > 1b > 1a, with reference to earlier
work14, this was assigned to the electron-donating ability of
6'-substitutent on the naphthoxazine ring moiety. Thus, it
presumably indicated that the electron-donating power of
indolino > morpholino which resulted in red effects. Compared
to unesterificated 1a, 1b and 1c, esterificated 2a, 2d and 2f
showed varying degrees of red-shift, respectively as a result
of π-electron delocalization arised from acyloxy moiety. 2a,
2b, 2c showed nearly identical absorption in dichloromethane
at the 565.1, 565.0 and 564.9 nm implying that 9'-acyloxy as
a pendant had little effect on the absorption λmax. Preliminary
results show that solvent and group linked as a pendant effects
are responsible for these spectroscopic shifts and are intimately
correlated.
1,3,3-Trimethyl-6'-indolino-9'-methacryloyloxy-
spiro[indoline-2,3'(3H)naphtho[2,1-b][1,4]oxazine] (2f):
Green crystal, yield: 51.3 %, m.p. 206-209 ºC. IR (KBr, νmax
,
cm-1): 3050, 2957, 2920, 1730, 1630, 1480, 1460, 1385, 1256,
1099, 1180, 1125, 977, 830, 744. 1H NMR (CDCl3, 500 MHz):
δ 8.32 (1H, d, J = 2.3Hz, ArH), 7.97 (1H, d, J = 9.0Hz, ArH),
7.64 (1H, s, 2'-H), 7.21-7.18 (2H, m, ArH), 7.10 (1H, t, J =
2.3 Hz, ArH), 7.06 (1H, d, J = 3.6 Hz, ArH), 6.92 (1H, d, J =
7.7 Hz, ArH), 6.89-6.86 (2H, m, ArH), 6.75 (1H, t, J = 7.3 Hz,
ArH), 6.56 (1H, d, J = 7.7 Hz, ArH), 6.41 (1H, s, ArH), 6.31
(1H, d, J = 7.9 Hz, ArH), 5.78 (1H, s, ArH), 3.90 (2H, t, J =
8.5 Hz, CH2), 3.17 (2H, t, J = 8.5 Hz, CH2), 2.76 (3H, s, CH3),
2.11 (3H, s, CH3), 1.34 (6H, s, CH3). Anal. calcd. (%) for
C34H31N3O3: C, 77.10; H, 5.90; N, 7.93. Found (%) C, 76.98;
H, 5.88; N, 7.95.
UV-VIS spectrophotometric measurements method:
The solutions of 1a-1c and 2a-2f in different solvents (cyclo-
hexane, dichloromethane and chloroform) with the concen-
tration of 1 × 10-5 mol L-1 were prepared. The UV-VIS absor-
ption spectra was measured at 20 ºC in different solutions using
a CARY 1101 UV-VIS spectrophotometer. The samples were
irradiated with a 12 W ultraviolet lamp at 365 nm and the λmax
of the compounds were listed in Table-1. The fatigue resistance
was examined after 150-cycle irradiation of UV and visible
lights.
Decoloration process of the coloured merocyanine
form of spirooxazines in dichloromethane: The kinetics of
the thermal decoloration were recorded on a spectrophotom-
eter following the colour bleaching of the irradiated sample at
λmax, immediately after switching off the ultraviolet lamp.
Thermal decoloration of the compounds followed first order
kinetics as the plots of [ln(At – A∞)/(Ai – A∞)] were linear and
the slopes of the [ln(At –A∞)/ln(Ai –A∞)] lines gave first order
rate constants k. Kinetic runs were depicted in Figs. 1 and 2.
The relaxation time of the photomerocyanines (τMC-SO) was
obtained from the first order rate constant using the expression9
τ = 1/k. The corresponding values of k and τMC-SO are given in
RESULTS AND DISCUSSION
Spirooxazine derivatives (1a-1c) were first prepared by
the condensation reaction of 1,3,3-trimethyl-2-methylene-
indoline with the ortho-hydroxynitroso aromatic derivatives
in methanol, which further proceeded esterification with acyl
chloride to give 2a-2f (Scheme-II). All the compounds were
soluble in cyclohexane, dichloromethane, chloroform,
methanol in varying degrees. FI-IR, 1H NMR, 13C NMR and
elemental analyses on 1a-1c and 2a-2f confirmed the proposed
structures.

Vol. 25, No. 5 (2013)
Synthesis, Characterization and Photochromic Properties of Novel Spirooxazines 2761
OR2H
NO
NO
N
HO
OH
HO
OH
R1H
N
CH3OH,reflux
N
O
CH3OH,reflux
R1
R1
1a-1c
OH
OOCR2
N
N
R2COCl
N
N
O
benzene/furanidine
O
R1
R1
1a-1c
2a-2f
R1
R1
R2
R1
R2
R2
N
H-
1b
OH
N
OH
1a
2a
OH
1c
O
H-
2b
2c
2f
H-
H-
Cl
CH3
N
N
O
N
O
2d
Cl
CH3
2e
CH3
Scheme-II: Synthesis of spirooxanzines (1a-1c and 2a-2f)
0
-1
-2
-3
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
2a
2b
2c
2d
2e
2f
1a
-4
1b
1c
-5
-6
0
200 400 600 800 1000 1200 1400 1600
Time (s)
0
200 400 600 800 1000 1200 1400 1600 1800
Time (s)
Fig. 1. Thermal relaxation of compounds 1a-1c in dichloromethane
solutions (1 × 10-5 mol L-1) after irradiation at 365 nm with a 12 W
ultraviolet lamp
Fig. 2. Thermal relaxation of compounds 2a-2f in dichloromethane
solutions (1 × 10-5 mol L-1) after irradiation at 365 nm with a 12 W
ultraviolet lamp
Table-2. According to these values, the rate of decoloration is
influenced significantly by introducing morpholino and
indolino substituent at 6' position of the spirooxazine. The
τMC-SO values of the photomerocyanines derived from 1b and
1c are 13 and 15 times larger than that of the unsubstituted
compound 1a. Meanwhile, the decoloration process can also
be influenced by replacing hydroxyl group by acyloxy group
at the 9' position. For example, the τMC-SO value of photomero-
cyanines derived from esterificated compounds 2a-2c varied
in a range of 190-204 s, suggesting a 2-fold increase than that
of unesterificated 1a. Furthermore, compared to the compound
containing 6'-heterocycle, the relaxation time of the compounds
containing both 6'-heterocycle and 9'-acyloxy decreases
obviously in vary degrees. For example, the τMC-SO value of 2e
decreases about 2 times than that of 1b. The obtained results
definitively show that τMC-SO values vary gradually for 1a-1c
and 2a-2f depending on electron-donating group and their
position on the ring. Adjustable relaxation times (125-1886 s)
were obtained by tuning heterocycle on 6' position and acyloxy
on 9' position. Thus, we supposed that compounds with

2762 Yang et al.
Asian J. Chem.
Fatigue resistance of spirooxazines in dichloromethane:
The fatigue resistance was examined after 150-cycle irradiation
of UV and visible lights. Compounds 1a-1c and 2a-2f were
found to exhibit excellent fatigue resistance after repeated
photocoloration. After 170-cycle irradiation, the absorbance
was kept in 99.5 %. As it was analogized, the absorbance of
the 1200-cycle would be kept in 96.6 % (A =A0(1-X)n, A0: the
initial absorbance; X: the variational absorbance; n: cycle
times). It was shown that spirooxazines containing heterocycle
on 6' position and acyloxy on 9' position exhibited excellent
stability.
TABLE-2
RATE CONSTANTS k (s-1) OF THERMAL RING CLOSURE
OF PHOTOMEROCYANINES DERIVED FROM COMPOUNDS
1a-1c AND 2a-2f AND THEIR LIFETIMES MC-SO (s)a
SO compound
Rate constants k (s-1)
Lifetimes (s)
125
0.0080
1a
1b
1c
2a
2b
2c
2d
2e
2f
0.00060
0.00053
0.0053
1667
1886
190
0.0049
204
0.0051
196
0.0014
714
0.0011
909
Conclusion
0.0046
217
aMeasuredin dichloromethane (c = 1 × 10-5 mol L-1) after irradiation at
365 nm with a 12 W ultraviolet lamp. All measurements at 20 ºC.
A series of novel 1,3,3-trimethyl spiro [2H]-indol-2,3'-
[3H]- naphtho[2,1-b][1,4]oxazine derivatives were synthesized
and characterized. All the compounds exhibited excellent
photochromism upon UV irradiation in solutions. Furthermore,
an efficient method to adjust relaxation time was demonstrated
by the structural modification on 6'-heterocycle and 9'-acyloxy.
It is hoped that a series of spirooxazines with different and
acceptable relaxation time can be synthesized by further
investigating structure-property relationships.
different τMC-SO could be designed and synthesized by this
method, which would lead to their successful use in various
applications, such as eyewear, structural panel and recording
films.
Photodegradation of of spirooxazines in the coloured
merocyanine form in dichloromethane: the photodegra-
dation was represented by a parameter tA0/2 which defined as
the time in minute required to decrease the initial absorbance
(A0) at the λmax of the merocyanine form to the half value (A0/2).
Solutions of the compound 1a-1c and 2a-2f (1.0 × 10-5 mol L-1)
in dichloromethane were prepared. The solution was divided
into 20 parts and all the parts were irradiated at the same time
with a 12 W ultraviolet lamp. The absorbances (A) at λmax in
different irradiation time were recorded on a spectrophotometer
after irradiation for photoequilibration. A typical example of
the plot made for compound 2f is illustrated in Fig. 3. The tA0
of 2f was calculated to be 420 min.
ACKNOWLEDGEMENTS
The authors acknowledged Industrialization of Scientific
Research Promotion Projects of Colleges and Universities in
Jiangsu Province for financial support.
REFERENCES
1. V.A. Lokshin, A. Samat and A.V. Metelitsa, Russ. Chem. Rev., 71, 893
(2002).
2. N. Alhashimy, R. Byrne, S. Minkovska and D. Diamond, Tetrahedron
Lett., 50, 2573 (2009).
3. Y.A. Son,Y.M. Park, M.S. Choi and S.H. Kim, Dyes Pigments, 75, 279
(2007).
1.0
0.8
0.6
0.4
0.2
0.0
4. D. Gust, T.A. Moore and A.L. Moore, Chem. Commun., 1169 (2006).
5. H. Tian and S.J. Yang, Chem. Soc. Rev., 33, 85 (2004).
6. S. Kawata and Y. Kawata, Chem. Rev., 100, 1777 (2000).
7. T. Deligeorgiev, S. Minkovska, B. Jeliazkova and S. Rakovsky, Dyes
Pigments, 53, 101 (2002).
8. G. Berkovic, V. Krongauz and V. Weiss, Chem. Rev., 100, 1741 (2000).
9. S. Minkovska, B. Jeliazkova, E. Borisova, L.Avramov and T. Deligeorgiev,
J. Photochem. Photobiol. A, 163, 121 (2004).
10. P. Rys, R. Weber and Q.L. Wu, Can. J. Chem., 71, 1828 (1993).
11. E.U. Kulawardana, T. Kuruwita-Mudiyanselage and D.C. Neckers, J.
Polym. Sci. A: Polym. Chem., 47, 3318 (2009).
12. H. Dürr, Y. Ma and G. Corterllaro, Synthesis, 294 (1995).
13. T.F. Tan, P.L. Chen, H.M. Huang and J.B. Meng, Tetrahedron, 61, 8192
(2005).
14. M. Rickwood, S.D. Marsden, M.E. Ormsby, A.L. Staunton and D.W.
Wood, Mol. Cryst. Liq. Cryst., 246, 17 (1994).
0
100
200
300
400
500
Times(min)
Fig. 3. Absorbance change at the λmax of compound 2f (λmax = 649.9 nm,
c = 1.0 × 10-5 mol L-1)