A special focus on the photodegradation of 6'-indolino-1-isobutyl-3,3- dimethylspiro[indoline-2,3'-[3H]naphtho[2,1-b][1,4]oxazine]

Article abstract of DOI:10.1246/bcsj.20120092

The photodegradation of 6'-indolino-1-isobutyl-3,3-dimethylspiro[indoline- 2,3'-[3H]naphtho[2,1-b][1,4]oxazine] (1) following exposure to polychromatic light, was investigated in fluid solution (toluene, T) and in a solid matrix (polyurethane, PU). The ph

Full text of DOI:10.1246/bcsj.20120092

1048 Bull. Chem. Soc. Jpn. Vol. 85, No. 9, 1048-1052 (2012)
© 2012 The Chemical Society of Japan
A Special Focus on the Photodegradation of 6¤-Indolino-1-isobutyl-
3,3-dimethylspiro[indoline-2,3¤-[3H]naphtho[2,1-b][1,4]oxazine]
Angelo Alberti,1 Claude Aubert,2 Mylène Campredon,*3 and Renaud Demadrille4
1Area della Ricerca di Bologna, CNR-ISOF, Via P. Gobetti 101, I-40129 Bologna, Italy
2UPRES EA 3286, Faculté de Pharmacie de La Timone, Aix-Marseille Université, F-13385 Marseille Cedex 5, France
3UMR-CNRS 7313, Campus de St Jérôme, Aix-Marseille Université, Service 512, F-13397 Marseille Cedex 20, France
4Laboratoire d’Electronique Moléculaire Organique et Hybride, CEA-INAC, UMR5819-SPrAM (CEA/CNRS/UJF),
17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France
Received March 24, 2012; E-mail: mylene.campredon@univ-amu.fr
The photodegradation of 6¤-indolino-1-isobutyl-3,3-dimethylspiro[indoline-2,3¤-[3H]naphtho[2,1-b][1,4]oxazine]
(1) following exposure to polychromatic light, was investigated in fluid solution (toluene, T) and in a solid matrix
(polyurethane, PU). The photoproducts formed under irradiation were identified using HPLC and GC/MS. These
included, beside the expected degradation derivatives, some new photoproducts derived from a secondary degradation
pathway.
Organic photochromes are compounds that may undergo a
reversible color change under the action of polychromatic
light.1,2 In early studies dating back to the late ‘60s, it was
shown that the photodegradation of a nitrospiropyrane resulted
through oxidation reactions in the formation of oxindoles and
of salicylaldehyde derivatives originating from the indolinic
and pyranic moieties, respectively.3-5 Few studies followed in
the ‘70s,6 until in the ‘80s the behavior of a large number of
differently condensed spiropyranes was investigated either
Figure 1. Structure of the 6¤-indolino-1-isobutyl-3,3-
in solution or in the solid state.7 However, the real growth of
dimethylspiro[indoline-2,3¤-[3H]naphtho[2,1-b][1,4]-
the attention on this subject started in the ‘90s when the studies
oxazine], 1, and of 1,3-dihydro-1,3,3-trimethylspiro[2H-
were extended to spiro[indoline-naphthopyranes] and spiro-
indole-2,3¤-[3H]naphtho[2,1-b][1,4]oxazine], 2.
[indoline-naphthoxazines] both in solution8-10 and in polymer
matrices.11
More recently, the attention has been focused on some fluoro-
2H-benzopyran derivatives,12 spiro[fluorene-naphthopyrane]
derivatives13 and on degradation processes of photochromes
in the presence of additives exerting an antioxidant or radical
trapping activity.14,15
photochromic performance, we have endeavored in a study of
the photodegradation of compound 1 in fluid solution (toluene)
and in a solid matrix (polyurethane) with the aim of determin-
ing the nature of the degradation products.
Results and Discussion
The properties of photochromic dyes are taken advantage
of in a wide range of applications. While ophthalmic lenses
represent by fair and large their most important end use, other
major applications include children’s toys, gadgets of different
nature, packaging items, security markers, clothes, cosmetics as
well as protective agricultural screens. 6¤-Indolino-1-isobutyl-
3,3-dimethylspiro[indoline-2,3¤-[3H]-naphtho[2,1-b][1,4]oxa-
zine] (1) (Figure 1), also known as Palatinate Purple, is an
important member of the spiro[indoline-naphthoxazines] fam-
ily due to its industrial relevance: in particular, this compound
and Berry Red (2,2-bis(4¤-methoxyphenyl)-5,6-dimethyl-2H-
naphtho[1,2-b]pyran), are largely used in the production of
acrylic glasses having photochromic properties. In this light
and in view of the fact that after UV-vis exposure all of these
materials are subject to fatigue, that is a reduction of their
Product Studies. A preliminary step of the degradation
study consisted in determining the products derived from the
photodegradation of the media where the process was taking
place. Thus irradiation of pure toluene in the Atlas Suntest for
5 h, that is the time required for the complete degradation of
compound 1, resulted in the formation of several oxidation
products the most abundant of which being benzylic alco-
hol, benzaldehyde, benzoic acid, o-cresol, and p-cresol. As for
the polyurethane matrix (PU), its photostability was tested by
monitoring the loss of transmission of the vibrational band
at 3334 cm¹1, characteristic of the NH bond. After 36 h inside
the Atlas Suntest, the loss of transmission only amounted to ca.
4%. No decrease of transmission at all was detected by keeping
PU at 80 °C for the same time span.
Published on the web September 8, 2012; doi:10.1246/bcsj.20120092

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012) 1049
versely, cleavage of the oxazinic ring in the initial radical
cation followed by fragmentation leads to either m/z = 202 or
m/z = 286.
The photodegradation of 1 resulted in a fairly large number
of different products. The twelve most abundant species P1-
P12 were identified on the basis of their HPLC retention time
and their GC retention time in addition to their mass spectra
(Table 1).
With a few exceptions all the products had markedly
shorter HPLC elution times with respect to 1 due to their
smaller mass and/or to a greater polarity. Actually, products
P8 and P9 have longer elution times than 1 (23.97 and
24.94 min, respectively), their main structural difference with
the starting compound being the lack of the alkyl group bound
to the nitrogen atom of the indolinic moiety. Two other
products, P10 and P11, that mainly differ from 1 due the
expansion of the spiro-indolic ring, have an elution time only
slightly shorter or fairly similar (22.34 and 23.16 min,
respectively) than that of 1. Finally, P12, a photoproduct
differing from 1 only for the presence of an “external” indolic
rather than indolinic moiety, had a retention time only slightly
shorter than that of 1.
The photodegradation of 1 may be envisaged to proceed
through several different mechanistic pathways. A homolytic
opening of the oxazinic ring with formation of a biradical has
long since been proposed,16 and indeed the formation of such
biradical has been proven in a double-trapping ESR experiment
in the presence of nitric oxide, whereby a 7-membered cyclic
oxynitroxide was identified.17 P1-P12 are new photoproducts
detected in the photodegradation of 1 in solution and polymer
matrix. Scheme 2 shows a possible route to products P1-P4,
based on a reaction between the biradical and triplet oxygen.
The formation of P4 analogue has been previously observed
under various experimental conditions during the photodegra-
dation of 2.18
P1 has been detected in the degradation of previously
investigated spiro[indoline-naphthoxazine] derivatives,9 how-
ever, it is interesting to note its presence in the mixture
of the photodegradation products of 1. The formation of P5
is expected to result from a secondary degradation pathway
involving a photochemical aromatization of the indoline sub-
stituent of P4 as it is presented in Scheme 3. Such reaction has
already been evidenced to take place on nitroindoline deriv-
atives by Papageorgiou and co-workers.19
The same type of reaction could explain the formation of
P12 starting from 1. Photoproducts P1-P7 have been identified
on the basis of their HPLC retention times that were found
identical to those of authentic samples previously synthesized
in our laboratory or provided by our industrial partner.
A photodegradation mechanism involving a radical inter-
mediate can also be invoked to account for the initial stage
of the processes leading to higher molecular weight photo-
products.20
The identification of the heavier P8-P12 is based on
the rationalization of their MS fragmentation pattern. In this
respect, we wish to point out that the pair of products P8 and
P9, P10 and P11, P12 and 1 exhibit the same fragmentation
pattern with a two mass units difference, consistently with their
proposed structures.
Scheme 1. Proposed fragmentation of 1 following electron
impact.
The main peaks in the MS spectrum of 1 are m/z 487
(M•+, 45), 472 (26), 444 (33), 286 (71), 230 (28), 202 (43),
201 (30), 186 (15), 158 (100), and 144 (41). A fragmen-
tation pattern accounting for these peaks is outlined in
Scheme 1. Cleavage of the initially formed radical cation
(m/z = 487) leads to fragment m/z = 201 which, by further
loss of a methyl, propyl, or butyl residue leads to fragments
m/z = 186, m/z = 158, and m/z = 144, respectively. Con-

1050 Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012)
Photodegradation of Spiro[indoline-naphthoxazine] Derivatives
Table 1. Photoproducts Detected in the Photodegradation of Compound 1 after Two Hours of Irradiation in Toluene (T) and
Polyurethane (PU)
Mass
/g mol
Retention time
/min
Structure
Ta)
PUa)
Code
MS most important fragments
¹1
M+ = 161 (3), 117 (100), 104 (19),
O
161
6.16
+
+
P1
90 (40), 76 (15)
N
H
O
O
N
N
217
231
9.00
++++ +++
P2
P3
M+ = 217 (29), 174 (57), 146 (100), 130 (33)
M+ = 231 (14), 188 (100), 160 (29),
10.18
+++
+++
144 (19), 130 (23)
O
286
284
15.90
15.30
++
++++ P4
M+ = 286 (100), 230 (15), 115 (13)
M+ = 284 (100), 228 (37), 114 (51)
N
N
N
N
O
O
++++
++
++
P5
P6
M+ = 201 (31), 158 (100), 143 (16),
N
201
215
9.84
8.61
++
+
135 (12), 115 (10)
M+ = 215 (48), 200 (27), 172 (51),
+
P7
N
O
159 (100), 144 (76), 115 (13)
M+ = 427 (100), 412 (16), 282 (21),
427
429
23.97
24.94
+
+
+
P8
P9
N
228 (18), 205 (21), 144 (14)
N
N
N
O
M+ = 429 (100), 414 (11), 230 (15),
++
N
207 (17), 144 (10), 91 (14)
N
O
M+ = 483 (97), 468 (73), 442 (27), 338 (100),
N
483
485
22.34
23.16
+
+
+
+
P10
P11
N
N
O
228 (41), 200 (58), 184 (62), 144 (60)
M+ = 485 (89), 470 (67), 444 (21), 340 (85),
N
N
N
O
230 (30), 200 (100), 184 (48), 144 (54)
N
M+ = 485 (34), 470 (27), 442 (22), 284 (17),
228 (24), 202 (23), 201 (30), 186 (12),
158 (100), 144 (42)
N
O
485
22.73
+++
+++
P12
N
Continued on next page:

A. Alberti et al.
Continued:
Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012) 1051
Mass
/g mol
Retention time
/min
Structure
Ta)
PUa)
Code
MS most important fragments
¹1
N
M+ = 487 (45), 472 (26), 444 (33), 286 (71),
230 (28), 202 (43), 201 (30), 186 (15),
158 (100), 144 (41)
N
O
487
23.47
1
N
a) +: small amount, +++: high amount.
N
N
O
N
1
hν
N
3O2
N
O
N
N
O
N
O
O
N
+H
N
O
N
O
O
N
H
-OH
N
N
OH
O.
O
N
+H
N
N
N
O
O
N
N
N
O
P4
P2
3O2
-H
OH
N
+H
-OH
O
O
N
N
O
N
N
O
O
O
O
P9
P8
+H
N
O
N
O
O
N
H
P1
P3
Scheme 2. Possible degradation pathway from 1 to P1-P4 and P8, P9.

1052 Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012)
Photodegradation of Spiro[indoline-naphthoxazine] Derivatives
N
N
N
N
.
O
+ OH
- H2O
hν
O
O
O
.
N
N
N
N
- H
HO
P4
P5
Scheme 3. Possible secondary degradation pathway from P4 to P5.
We thank Essilor Int. and PPG Industries, Inc. for their
generous support to this research and Professor G. Giusti for
helpful discussions.
Experimental
Compound 1 was purchased from James
Chemicals.
Robinson Ltd. and recrystallized from ethanol before use.
The polyester-polyurethane copolymer (poly[4,4¤-methyl-
enebis(phenyl isocyanate)-alt-1,4-butanediol/poly(butylene
adipate)]) (Aldrich) was used to prepare polymer films. The
thermal stability of the polymer matrix was checked using
a Perkin-Elmer1605 FT-IR spectrophotometer. The Tg value
measured using differential scanning calorimetry was ¹18 °C.
Photochromic polymer films were prepared mixing the dye
and PU in THF that had been previously distilled in order
to eliminate the BHT stabilizer. The mixture was deposited on
glass plates (ORMA CR39 support) after soaking. The polymer
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¹1
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Conclusion
We have investigated the photodegradation mechanism of
6¤-indolino-1-isobutyl-3,3-dimethylspiro[indoline-2,3¤-[3H]-
naphtho[2,1-b][1,4]oxazine] (compound 1) in toluene solution
(T) and in a polyurethane matrix (PU).
Most of the photoproducts formed in the degradation of
1 following its prolonged irradiation indicate separation of
the indolic and naphthopyranic moieties due to cleavage of
both the tertiary carbon-oxygen and the tertiary-carbon-carbon
bonds of the oxazinic ring, while photoproducts retaining both
the indolic and naphthoxazinic reflected the cleavage of only
the tertiary carbon-oxygen bond.
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