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8/18/2019 Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solu…
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J. Photochem. Photobi oL A: Chem. 70 (1993) 157-161 157
Com parative pho todegradation study between spiro[indoline-oxazine]
and spiro[indoline-pyran] derivatives in solution
G. Baillet, G. Giusti and R. Guglielmetti
Laboratok de photochimie appI i@e, CNRS UK4 1320, Fact de Luminy, 13288 Marseil le Ct?dex 09 (F rance)
(Received July 13, 1992; accepted
September
17, 1992)
The photochrom ic compound s 1,3-dihydro-l,3,3-trimethylspiro[2H-indole-~3’-[3H]naphth[2,l-b][1,4]oxazine], 1,3-
dihydro-1,3,3-trimethylspiro[2H-indole-2,2’-[3H]naphth[l,2-b]p~an] and 1,3-dihydro-8’-methoxy-6’-nitro-1,3,3-t+
methylspiro[W-indole-2,2’[3H]benzopyran] were degraded u nder UV light irradiation in toluene solution. The
resulting main photoproducts separated by gas chromatography and high performance liquid chromatography
were identified by different couplings with UV-visible diode array detection, mass spectromeq and Fourier
transform IR spectroscopy and were compared with synthetic standards. The different nature of the photoproducts
involving the chrom ene part of the molecules could sug gest different mechanisms of degradation between the
spiropyran and Spiro-oxazine series and could explain the b etter fatigue resistance o the latter.
1 Introduction
Spiropyrans and Spiro-oxazines are thermally
reversible dyes
under UV
light irradiation which
exhibit photochromism in solution or as polymer
matrix films [l]. Recently, Spiro-oxazines have at-
tracted considerable interest because of their good
fatigue resistance under a long period of irradiation
in comparison with spiropyran derivatives [2].
Quantitative
studies of the photostability of sub-
stituted spire-oxazines and mainly substituted spi-
ropyrans have been carried out by flash photolysis
techniques in solution [3-8].
The literature concerning the qualitative deg-
radation aspects of photochromic compo unds in
terms of fragm ent identification is practically in -
consistent. Indeed, it seems evident that photo-
product identification mu st be done in order to
propose mech anisms of degradation. This formal
approach could help to prevent fatigue resistance
by improving the synthesis strategies for obtaining
more stable photochromic compo unds, T his ap-
proach could be also fruitful in order to study the
role of different protective agents (i.e. hindered
amine light stabilizers, nickel complexes, UV
quenchers, etc.) which are know n to maintain the
photochromism phenom enon. The major amo unt
of work involving photoproduct analysis has been
performed by R. Gautron on indolinospiropyrans
in solution, w ho had come to the conclusion that
lOlO-6030/93/ 6.00
the degradation process w as led mainly by photo-
oxidation g iving the salicylaldehyde derivatives and
oxindols compound s [9]. Recently, Yosh ida et al.
[lo] have described ‘H NM R a nd IR studies on
the resulting m ixture of a photodegraded indo-
linospiropyran in the solid state and they also
came to the conclusion that an oxidation process
took place. Td date nothing has been published
concerning indolinospiro-oxazine photoproduct
identification. So, it appeared interesting to com-
pare the photoproducts obtained after irradiation
from the indolinospiropyran and indolinospiro-
oxazine series in order to try to connect them
with mech anisms of degradation and to understand
the superior fatigue resistance of the Spiro-oxazine
series. In this work, the photochromic compo unds
are degraded in toluene solution w ith the aim of
obtaining relatively easy information about the
photoproducts and later to investigate the fatigue
phenom enon in polymer matrix films.
2. Experimental details
2.1. Photodegradation experiments
1,3-dihydro-8’-methoxy-6’-nitro-1,3,3-trimethyl-
spiro-[2H-indole-2,2’-[3H]benzopyran](I),1,3-di-
hydro-1,3,3-trimethylspiro-[2H-indole-2,2’-[3H]-
naphth[l,Zb]pyran](II),1,3-dihydm-1,3,3-trime-
thylspiro-[ZH-indole-2,3’-[SH]naphth[2,lb][1,4]-
Q
1993 - Elsevier Sequoia. All righta reserved
8/18/2019 Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solu…
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158 G.
Bail let et al . / Photodegmdati on of
spimpyrans
and spim w ines
I II
Fig. 1. Structural formulae of the photochromic compound s.
Fig. 2. Gas chromatograpbic separation of photoproducts of (I),
(II) and (III). C& unn SE 54 25 mx0.32 mm,
fi jm 0.25 pm. T
injector 280 “C (Ross) T detector 300 “C (FID). pHe=O.9 bar.
80 “C to 300 “C at 5 “C min-‘.
oxazine](III) (Fig. 1) were dissolved in anhydrous
toluene (SDS France) (C = lop3 M). The aerated
solutions w ere irradiated in a quartz flask with
magne tic stirring w ith a 500 W high-pressure mer-
cury lamp I BO Osram housed in a light box
(Arquantiel, Ile St Denis, France)_ The different
solutions containing the photochromic compo unds
are analysed regularly by chromatography till the
complete bleaching of the solutions (I =2 hours,
II=2 days, III = 5 days). An aliquot of each is
111
directly injected for gas chromatographic analysis
or, after evaporation under a stream of nitrogen,
is dissolved in acetonitrile for HPLC analysis.
2.2. Separation and identi fi cation o hotoproducts
The
current ga s chromatographic system (GC)
consisted of a Varian Vista 600 0 equipped with
a Ross injector and an FID detector. The column
was a Pierce 0.32 mmX 25 m capillary column
coated with a non-polar SE-54 phase (film 0.25
pm). T he pressure of helium (carrier gas) was set
to 0.9 bar. The high performance liquid chro-
matograp h consisted of a Beckm an H PLC Go ld
system coupled with a 168 diode array detector
to allow screening for peak purity and peak com-
parison. The separation system consisted of a C8
RX Zorbax reversed phase column (Rockland
technologies) 25 cmX 4.6 mm with a gradient of
acetonitrile in water from 35% to 100% during
40 minutes set at 1 ml min
‘.
Mass spectra w ere obtained with an HP 5985
spectrometer under electronic imp act mode (El)
(70 ev) and positive chemical ionisation mode
(CI+) w ith methane (150 ev).
IR spectra were obtained with a Nicolet 2 0 SXB
FTIR system coupled with a 60 m x 0.32 mm J&W
capillary column type DB-1 (film 0.25 pm) housed
in a Carlo Erba Vega 6000 gas chromatograph
equipped with an ‘on-column’ injector. The d if-
ferent photoproducts separated by GC and HPLC
were identified initially by GC /MS and G C/FTIR.
Com plete confirmation of the structures was car-
ried out by comp aring the mass spectra, IR spectra
and retention times with reference standards.
Screening with GC and HPLC allowed u s to be
certain of detecting all compo unds in the case of
non-volatile, thermolabile and non-responsive W
compounds.
2.3. Syntheses of reference compounds
The photochromic compo unds (I) and (II) are
prepared according to the ref. 11, 12. The spi-
ronaphtho-oxazine (III) was supplied by Enichem
Synthesis (Milan, Italy). 5-Nitrovanillin and 2-
hydroxy-1-naphthaldehyde are comm ercially avail-
able (Aldrich). The 1,3,3-trimethyloxindol is pre-
pared by ozonolysis of the 2-methylene-1,3,3-tri-
8/18/2019 Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solu…
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G. Bai ll et et
aL I
Phatodegraduti on spiqyrarw and +m-oxazines 159
4
Fig 3 Mass spectra of photoproducts under electronic
methylindoline (Aldrich ) in methan ol. Th e
compound purified on silica (toluene/ethyl acetate:
3,3-Dimethyloxindul is a brown solid synthesized
95/5) is a viscous plate yellow liquid: ‘H NM R
by reaction of the phenylhydrazine with isobutyric
(80 Ma) in CDC k &.s(G(c~L~)~) H), ~3.15~-~3~
acid and heat cyclization according to ref. 13: m.p.
(s,3H) and &.7-7.2(n
atom.) OH); JR gas phase
145 “C, ‘H NMR (80 MHz) in CDCl,:
3069, 2977, 2939, 2896, 1741 (CO), 1612, 1486,
&3(G (cH3h (s,6H), &.o(~-~~ (s, 1H) and &.7-7.2(namm.j
1376, 1340, 1242, 1123, 739 cm-‘; UVcmm 211,
(m,4H); IR (gas phase) 3477 (NH), 2981, 1764
252 nm; [M]‘+ = 175.
(CO), 1474, 1146, 741 cm-‘; UVtCHJC Nj 208, 248
nm; [M]‘* = 161.
8/18/2019 Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solu…
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160
G. Bai ll et et al. i Photodegradation of spim~r ans and spim-amzincs
E
.A A
1 1 m
4 air0
lS,D
a 1;s. A
Fig. 4. GC/FT-IR spectrum of the 1,2,3,4-dihydro-2 ,3-dioxo4,4-
dimethylquinoline.
Fig. 5. Kinetics of photoproduct formation under UV light
irradiation for compound s (II) and (III): (I)- 1,3,3-trimethylox-
indol, (2) = 3,3-dimethyloxindol,
(4) = Z-hydroxy-l-naphthalde-
hyde, (5) - naphth[l,2-dloxazole, (Q- 1,2,3,4-tetrahydro-2,3-
dioxo4,4-dimethylquinoline.
Napth[l,2-dloxazole, crystallized in cyclohexane,
is a white solid that consists of crystals formed in
plate-like configuration is obtained by the reaction
of 1-nitroso-Znaphthol with iodomethane in ace-
tone according to ref. 14: m.p. 64 “C H NMR
(80 MHz) in CDC b: S~.T(~ rom.)@-OH), I(~~I~
GH) O-0,
57.9(H arom.) Cd,
J=4IWH) and
SB.S(H
_,,) (d, J=4Hz,lH); IR (gas phase)
3070, 679,
1586,1511,1377,1266,1234,1080,1~1,00,743,
693, 25 m- ; cmcN j
221, 75, 85, 06, 20
nm; Ml‘+ = 169.
3. esults
The chromatographic separations (GC /FID) of
the photoproducts for compo unds (I), (II) and
(III) are shown in Fig. 2. The degradation process
leads mainly to oxidation products identified as
1,3,3-trimethyloxindol (I) and 3,3-dimethyloxindol
(3) for each of the three com pounds. The chromene
part of compou nd (I) leads to 5-nitrovanillin
(3) and to the hydroxynaphthaldehyde (4) for
compo und (II). As to compo und (III) it is inter-
esting to notice the formation of the naphthoxazole
derivative (5;) as the fragment resulting from the
right heterocyclic part of the molecule. T hese
compo unds have been identified formaIly by ma ss
spectrometry and by comparison with their syn-
thetic references (Fig. 3). The structure of the
compou nd denoted by its raw formula C,,H,,NO ,
(I;) on the chromatographic profiles has been
elucidated by quadripolar ma ss spectrometry,
IT-IR gas chromatography and by high resolution
mas s spectrometry with a magn etic m ass spec-
trometer (SCEA -CNR S-Vem aison, France) after
concentrating collections of HPLC fractions (Fig.
4). The exact mass determined as being 18 9.16426
allows us to attribute reasonably the structure of
1,2,3,4-tetrahydro-2,3-dioxo-4,4-dimethylquinoline
to this compo und, which would result from a ring
extension of the indoline cycle.
The kinetics of degradation for compo unds (II)
and (III) m easured by regular injection into the
chromatographic systems show that photoproduct
formation increases practically linearly a s a func-
tion of time, indicating good stability of the pho-
toproducts involved (Fig. 5).
4. Discussion
These results confirm Gautron’s work concern-
ing the photo-oxidation products of compou nd (I),
but very few high molecular weight products were
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G. Baillet et al. I Photodegradation of spiropymns and spin-oxazkes
161
found. In the same way, spiro[indolincF-
naphthopyran] (II) leads mainly to oxindol type
derivatives and 2-hydroxy-1-naphthaldehyde in-
volving the chromenic part of the molecule. It is
interesting to note that 1,3,3-trimethyloxindol is
more abund ant from this compou nd than from
the benzopyran derivative (I). A verification ex-
periment by irradiating synthetic 1,3,34rimethyl-
oxindol in toluene has shown that no 3,3-dime-
thyloxindol wa s formed. It is reasonable to consider
that 3,3-dimethyloxindol results from direct oxi-
dation of the N-C& bond of the photochromic
compound itself.
Concerning the spironaphtho-oxazine (III) pho-
toproducts involving the indoline part of the mol-
ecule are still oxidation derivatives like the oxindol
compo unds and the dioxo derivative. The impo rtant
result w ith this series is that no direct oxidation
takes place on the right heterocyclic part of the
molecule. This part leads to the naphth[l,2-
dloxazole compou nd which could be considered
as a rearrangement product.
No l-nitroso-2-naphthol was detected w ith com-
pound (III) whereas no naphthofuran was detected
with compou nd (II) as the corresponding hetero-
cycle to the naphthoxazole.
This analytical study show s a difference in the
photo-oxidation processes between the spiro-ox-
azine and the spiropyran series: the introduction
of a nitrogen atom into the chromene heterocycle
seems to modify the ability of the photochromic
compou nd to oxidize. It seems clear that the di-
and trimethylated oxindols result from oxidation
of the Spiro carbon atom in the two series, whe reas
the salicylaldehyde derivatives obtained with the
pyran series result from direct oxidation of the
carbon 4’.
After the verification that oxidation processes
were responsible for photochromic compo und deg-
radation in the two series (no photolysis products
seem to be generated from these compounds in
the experimental conditions) it will be interesting
to study the mechanisms of these oxidation pro-
cesses in order to assess the efficiency of antiox-
idizing agents and to improve their use.
Do these p rocesses take place via the reaction
of ambient oxygen with radical species that appear
during homolytic C-O bond dissociation under
light irradiation, or do they take place via pho-
tosensitized reactions (by the photoproducts them-
selves) involving ‘4 attack at the double bon ds
of the merocyanine forms involving dioxetan as
intermediates? Further studies are in progress in
our laboratory, in order to explain the contribution
of each mechanism in the degradation processes.
Acknowledgments
We would like to thank C. Aubert for ma ss
spectrometry analyses and ESSILOR Int. for the
financial suppo rt of this work.
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