On the photodegradation of some 2H-chromene derivatives in fluid solution or in polyurethane matrix

Article abstract of DOI:10.1246/bcsj.20100338

The time profile of the optical density was monitored during the photodegradation of three derivatives of 2,2-diphenyl-2H-naphtho[1,2-b]pyran (1), namely 2,2-bis(4-methoxyphenyl)-5,6-dimethyl-2H-naphtho[1,2-b]pyran (2), 2,2-diphenyl-5-[(ethoxycarbonyl)methoxycarbonyl]-8-methyl-2H-naphtho[1,2-b] pyran (3), and 3,3-bis(4-methoxyphenyl)-6,11-dimethyl-13-hydroxy-13-isopropyl- 3H-indeno[2,1-f ]naphtho[1,2-b]pyran (4) either in toluene solution or in a polyurethane matrix. The photoproducts were identified using HPLC, GC/MS, and direct insertion MS techniques. High molecular weight oxygenated derivatives and new photoproducts deriving from a secondary oxidative pathway were characterized along with expected degradation derivatives. Some of the photoproducts considered responsible for the yellowing of the examined materials were identified. The effect exerted by two additives generally considered to have an inhibiting action toward radical processes was also evaluated.

Full text of DOI:10.1246/bcsj.20100338

552
Bull. Chem. Soc. Jpn. Vol. 84, No. 5, 552–561 (2011)
© 2011 The Chemical Society of Japan
On the Photodegradation of Some 2H-Chromene Derivatives
in Fluid Solution or in Polyurethane Matrix
Angelo Alberti,1 Mylène Campredon,*2 and Renaud Demadrille3
1CNR-ISOF, Area della Ricerca di Bologna, Via P. Gobetti 101, I-40129 Bologna, Italy
2UMR-CNRS 6263, Aix-Marseille Université, Campus de St Jérôme, Service 512, F-13397 Marseille Cedex 20, France
3LEMOH, UMR-CNRS 589, CEA, Université de Grenoble, 17 Rue des Martyrs, F-38054 Grenoble Cedex 9, France
Received December 3, 2010; E-mail: mylene.campredon@univmed.fr
The time profile of the optical density was monitored during the photodegradation of three derivatives of 2,2-
diphenyl-2H-naphtho[1,2-b]pyran (1), namely 2,2-bis(4-methoxyphenyl)-5,6-dimethyl-2H-naphtho[1,2-b]pyran (2), 2,2-
diphenyl-5-[(ethoxycarbonyl)methoxycarbonyl]-8-methyl-2H-naphtho[1,2-b]pyran (3), and 3,3-bis(4-methoxyphenyl)-
6,11-dimethyl-13-hydroxy-13-isopropyl-3H-indeno[2,1-f]naphtho[1,2-b]pyran (4) either in toluene solution or in a poly-
urethane matrix. The photoproducts were identified using HPLC, GC/MS, and direct insertion MS techniques. High
molecular weight oxygenated derivatives and new photoproducts deriving from a secondary oxidative pathway were
characterized along with expected degradation derivatives. Some of the photoproducts considered responsible for the
yellowing of the examined materials were identified. The effect exerted by two additives generally considered to have an
inhibiting action toward radical processes was also evaluated.
The reversible phototransformation of a chemical species
compounds have been obtained that have found applications in
the production of ophthalmic lenses and sunglasses, security
inks and cosmetics packaging, optical switches, mobile phone
covers, skis and sportswear. As well as these compounds may
perform, they are all bound to experience fatigue in their
working life and to a greater or lesser extent, to undergo
degradation with time. Thus their applicability is strongly
linked to the time span within which their photochromic
performance can be considered satisfactory. While on one side
it is then clear the importance of determining the resistance to
fatigue of a given photochrome prior to its practical applica-
tion, the identification of the products resulting from its
photodegradation, and especially those responsible of yellow-
ing, is also a central issue. We report on a study of the
photodegradation of 2,2-bis(4-methoxyphenyl)-5,6-dimethyl-
2H-naphtho[1,2-b]pyran (2), of 2,2-diphenyl-5-[(ethoxycarbon-
between two forms having different absorption spectra is
normally referred to as photochromism.1,2 Several different
organic systems display this property either in solution or in a
solid phase (e.g., a polymer matrix),3 and among these an
important role is played by 2H-chromenes and spiro[benzo-
pyrans]. In both these species the photochromism reflects the
light-induced reversible opening of the pyranic ring via
cleavage of the O-C2 bond.4 The cleavage, basically consid-
ered to have an electrocyclic nature, produces an extension of
the conjugation, thus converting the virtually colorless starting
compounds to deeply colored “merocyanines,” normally
yellow or red depending on substitution.5,6 The latter may
exist in isomeric forms characterized by different abilities to
revert to the initial structures either thermally or upon ceasing
the optical excitation (Scheme 1).7,8 While the existence of
a minor homolytic component to ring opening involving a
biradical has also been proved,9 it has been associated with
irreversible degradation of the photochromic compounds.
The first chromene derivatives having practically acceptable
photochromic behavior date back to the late ‘80s;10 since then
yl)methoxycarbonyl]-8-methyl-2H-naphtho[1,2-b]pyran
(3),
and of 3,3-bis(4-methoxyphenyl)-6,11-dimethyl-13-hydroxy-
13-isopropyl-3H-indeno[2,1-f]naphtho[1,2-b]pyran (4), which
are shown in Figure 1 along with 2,2-diphenyl-2H-naph-
tho[1,2-b]pyran (1), the archetype of the family. In a previous
R
R
O
hν
O
O
O
R
Δ
R
O
R
Merocyanines
Scheme 1. Reversible photoconversion of chromenes to merocyanines.
Published on the web May 7, 2011; doi:10.1246/bcsj.20100338

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
553
MeO
O
MeO
O
O Et
O
HO
O
O
O
O
MeO
MeO
2
3
4
1
Figure 1. Structure of the investigated chromenes.
MeO
O
MeO
2
MeO
MeO
MeO
MeO
O
O
3O2
3O2
O
O
O
O
O
O
+ H
+ H
O
MeO
MeO
MeO
MeO
MeO
MeO
- OH
- OH
O
O
O
MeO
MeO
MeO
MeO
O
O
O
O
MeO
MeO
P11
P10
Scheme 2. Speculative mechanisms concerning the formation of epoxides P10 and P11.
study on the photodegradation of 2 itself,11 some high
molecular weight photoproducts have been detected, including
monoepoxide P10 and P11, the formation of which is
accounted for as indicated in Scheme 2. A diepoxide P12
was also observed, and it may be hypothesized that the [4 + 2]
addition of singlet oxygen to the cisoid form of the merocya-
nine from 2 leads to an endoperoxide which can then undergo
thermal decomposition to P12 as outlined in Scheme 3.
Our interest in these compounds stems from the fact that
the presence of different substituents induces variations of the
absorption spectra of both their closed and open forms with
respect to that of the unsubstituted parent compound 1.12 As a
matter of fact, the open forms of 2-4 have absorption -max in
the range 457 to 564 nm, values that can make them suitable for
interesting practical applications.
Results and Discussion
General Considerations. The UV-vis absorption spectra
of the merocyanines from compounds 1-4 are shown in
Figure 2 while their -max values are collected in Table 1. When
examining these data it may be convenient to use the
merocyanine from 1 as reference, having the same basic
backbone common to compounds 2-4 but without substituents.
Thus, the larger -max value exhibited by 2 with respect to 1
suggests that the presence of the methoxy groups in the para-
position of the two phenyl rings induces a bathochromic shift
of 20-25 nm, the effect of the presence of the methyl
substituent being possibly less important. On the other hand,
the much larger value of -max exhibited by the merocyanine
from 4 can be accounted for by the extension of the conjugated

554
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
Degradation of Chromenes in Different Media
MeO
O
MeO
2
Δ
hν
MeO
O
MeO
MeO
λ/nm
1O2
Figure 2. Absorption spectra for the merocyanines from 1
(blue), 2 (green), 3 (red), and 4 (pink) in toluene solution.
Table 1. Absorption -max for the Merocyanines from 1-4 in
Toluene (T) Solution and in Polyurethane (PU) Matrix
O O
Compound
-
max(T)/nm
-
max(PU)/nm
O
O
1
2
3
4
471
493
457
564
479
503
466
577
MeO
MeO
100
O
80
60
40
20
0
O
MeO
P12
Scheme 3. Speculative mechanisms concerning the forma-
tion of P12.
system in this last derivative.13 It should however be borne in
mind that like 2, 4 also features the two methoxy groups that
induce a bathochromic shift. Although an exact quantification
of the two contributions to the overall observed shift is
impossible, it seems sensible to assume a contribution of the
methoxy groups similar to that observed for compound 2.
In this light, the bathochromic shift due to the extended
conjugation in 4 would then amount to ca. 65-70 nm. Although
we do not have a clear-cut explanation for it, we note that the
merocyanine from 3 exhibits a 14 nm hypsochromic shift with
respect to that from 1.
An additional feature emerging from the data in Table 1, is
that in all cases the -max values measured in the polyurethane
matrix are ca. 10 nm larger than those measured in toluene
solution. Previous studies on structurally related compounds
have shown that the -max values are fairly independent of
solvent polarity. On the other hand, it cannot be excluded that
the polyurethane matrix exerts a sort of flattening action onto
the merocyanines which might result in a slightly better
efficiency of conjugation and hence in a slight bathochromic
shift of -max values.
0
1
2
3
4
5
6
7
Time/h
Figure 3. Time profile of the optical density exhibited by
compound 2 ( ), 3 ( ), and 4 ( ) in toluene solution
(pink) and in a polyurethane matrix (blue) under stationary
irradiation with the light from a 1.5 kW Xenon lamp.
Figure 3 shows the time profile of the decrease of optical
density observed for compounds 2-4 under photostationary
conditions of irradiation at 25 °C. As it can be seen, the
degradation is fairly slow in toluene for compounds 2 and 3
and definitely faster in the polymer matrix, while the reverse
is true for compound 4 which degrades faster in the former
medium.
It is also important to ascertain that the decrease in optical
density does indeed parallel the degradation of the photo-
chromes, as the formation of colored by-products might alter
the O.D. time profile. HPLC studies, carried out in order to
correlate the O.D. decrease with the actual degradation of the
photochrome under examination, have shown that some photo-

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
555
Table 2. Photoproducts Detected in the Photodegradation of Compound 2 after Two Hours of Irradiation
In PU
10% Tinuvin
144
MS
/g mol
Retention
time/min
In
toluene
In
PU
In PU
10% TPMPDTF
Structure
Code
¹1
P1
172
196
200
8.51
9.61
++
+++
++
++
+++
++
+++
++
+++
OH
P2
P3
+++
++
O
10.14
++
O
OH
CH2
P4
P5
P6
240
242
244
11.96
13.63
12.53
+
++++
Ta)
+
++++
Ta)
++
++++
Ta)
+
MeO
MeO
MeO
OMe
OMe
OMe
O
++++
++
OH
O
P7
P8
P9
256
266
268
12.79
14.90
14.90
+
+
+
+
MeO
MeO
OMe
CH2
n.d.b)
+++
n.d.b)
+++
++
n.d.b)
OMe
OMe
O
+++
++++
MeO
MeO
O
O
P10
P11
P12
438
438
454
47.16
47.37
47.51
++
++
+
++
++
+
+++
+++
++
+++
+++
+++
OMe
O
MeO
O
OMe
O
O
MeO
O
OMe
a) T: trace amount. b) n.d.: not detected.

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Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
Degradation of Chromenes in Different Media
Table 3. Photoproducts Detected in the Photodegradation of
Compound 3 after Two Hours of Irradiation
O
P
N
O
O
O
MS
Retention
In
In
S
Structure
Code
O
¹1
/g mol time/min toluene PU
OH
S
O
CH2
O
P13
180
182
8.28
+
+
N
O
P14
P15
9.08 ++++ ++++
Tinuvin 144
Figure 4. Structures of additives.
TPMPDTF
O
208
312
10.93
15.19
+++ +++
products do absorb in the region of activation of the photo-
chromes, thus affecting their “colorability.” Although in
solution the O.D. correlates well with the residual amount of
the photochromes, in the polymer matrix the accumulation of
colored photoproducts may originate a screen-effect that, as
time goes by, renders impossible the correlation of the O.D.
decrease with the photochrome degradation. This effect is
especially evident during the irradiation of compound 4, the
degradation of which in polyurethane is initially similar to that
in toluene but slows down significantly after the first three
hours of treatment.
It also seemed to us sensible that radical processes of some
sort might contribute to the fast degradation of 4 in toluene.
Thus additional experiments were carried out in the presence
of substances amenable to inhibiting radical processes. As a
matter of fact, the photodegradation of 4 in toluene solution
containing a substantial (10%) amount of either Tinuvin 144, a
light stabilizer of the HALS family,14 or of triphenylmethyl
diethoxyphosphoryldithioformate (TPMPDTF), an efficient
trapping agent for carbon- or oxygen-centered radicals,15
represented in Figure 4, was found to proceed exactly as
found for toluene solution not containing any additive.
O
OEt
O
P16
P17
++
+
++
+
O
O
O
O
OEt
O
O
316
478
15.27
21.69
OH
O
O
O
OEt
P18
++
++
O
resistance to light of compounds 2-4 and also to check if and
how their presence affected the photoproduct composition. We
chose Tinuvin 144 because it exerts a dual radical-based action,
due to the simultaneous presence in its molecule of hindered
pyrimidines and of a hindered phenol. As for the dithioformate
TPMPDTF, it has been shown to be a versatile spin trapping
agent toward both nucleophilic (e.g., carbon centered) and
electrophilic (e.g., oxygen centered) radicals and has been
found to be a very efficient process stabilizer in the extrusion of
polypropylene. However, preliminary trials having indicated
that both additives had little or no effect in toluene solutions
whereas they did in cases affect the relative amounts of the
photoproducts in the PU matrices, experiments with additives
were only carried out in the latter medium. A summary of the
detected products and their retention times can be found in
Tables 2-4. The retention time of the products in Tables 2-4
were compared with those of commercially available samples
P4-P9 and P13-P15 or of samples provided by an industrial
partner of ours P19-P24, while authentic P1-P317-19 were
synthesized for this purpose.
The well-expected formation of “classic” primary and
secondary photoproducts, i.e., P2, P5, P9, P14, and P15 as
main products, along with minor amounts of P1, P3, P4, P7,
P16, and P17, is in line with the results of similar studies
carried out by some of us on a number of spiro[fluorene-
naphthopyrans],20 and, as outlined in Scheme 4 for com-
pound 2, is thought to reflect an initial homolytic cleavage of
the C-O bond to form a biradical intermediate followed by its
reaction with either triplet or singlet oxygen.
The addition of the same amount of either of the two
additives to a polyurethane matrix containing 4 had instead
a noticeable stabilizing effect during the first half hour of
irradiation, and although the stabilizing effect seemed to
decrease with time, after 4 h the residual O.D. was still 10%
greater than observed in the absence of additives.
Photoproducts. Early studies on the photodegradation of
naphthopyrans carried out in the late ‘90s16 have led to the
identification of some of the photoproducts. It was then
evidenced the major role played by oxygen in the process. In
order to get a better understanding of the photodegradation
process we have endeavored in a GC/MS study aimed at the
characterization of the products originating in the photodegra-
dation of compounds 2-4. To this purpose, toluene solutions of
compounds 2-4 or polyurethane films containing these com-
pounds were subjected to irradiation in a Sun Test set for two
hours. After this time, the toluene was removed under a flow of
nitrogen and the photoinduced fragments were dissolved in
acetonitrile and then directly injected in a GC/MS apparatus.
When dealing with the polyurethane films, the photoproducts
were extracted by refluxing the films for 45 min in acetonitrile
at 60 °C. The extracts were then evaporated and redissolved
in very small amounts of acetonitrile for analyses. Similar
experiments were also carried out in the presence of the
additives Tinuvin 144 and TPMPDTF, to try and improve the

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
557
Table 4. Photoproducts Detected in the Photodegradation of Compound 4 after Two Hours of Irradiation
MS
/g mol
Retention
time/min
In
toluene
In
PU
In PU
10% Tinuvin 144
Structure
Code
¹1
CH2
P4
240
242
244
11.96
13.63
12.53
++
++++
+
++
++++
+
+++
++++
n.d.a)
MeO
MeO
MeO
OMe
OMe
OMe
O
P5
P6
OH
O
P7
P8
P9
256
266
268
14.90
14.90
14.90
+
+
+
Tb)
MeO
MeO
OMe
CH2
n.d.a)
+++
n.d.a)
+++
OMe
OMe
O
+++
MeO
n.d.a)
+++
+++
HO
P19
P20
P21
300
318
324
19.26
17.70
19.49
+
+
OH
HO
++
++
++
++
O
O
HO
P22
P23
P24
328
342
346
19.22
17.76
18.00
+
+
n.d.a)
OH
O
+++
++
+++
++
++
OH
O
HO
+++
Continued on next page:

558
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
Continued:
Degradation of Chromenes in Different Media
MS
/g mol
Retention
time/min
In
toluene
In
PU
In PU
10% Tinuvin 144
Structure
Code
¹1
MeO
Direct
insertion
P25
552
584
n.d.a)
n.d.a)
++
O
MeO
MeO
HO
O
Direct
insertion
P26
P27
Tb)
Tb)
n.d.a)
O
MeO
MeO
HO
Direct
insertion
584
Tb)
Tb)
n.d.a)
O
O
MeO
a) n.d.: not detected. b) T: trace amount.
MeO
O
MeO
MeO
2
Δ
hν
MeO
MeO
3O2
+ H
- OH
MeO
O
O
O
O
P2 + P5
O
O
1O2 UV-Vis
MeO
MeO
MeO
P3
MeO
MeO
1O2
O
O
O
O
O
1O2
O
O
MeO
MeO
MeO
P5
+
P9
P3
+
P5
Scheme 4. Possible degradation pathway from compound 2.
Although the formation of epoxides P10 and P11 and
diepoxide P12 as minor products in the photodegradation of 2
in solution has been reported,11 the identification of these
compounds upon irradiation of 2 in the PU matrix is
unprecedented. Indeed in the present investigation we found
that the amount of P10, P11, and P12 is actually greater in the
polymer matrix than in toluene solution. Furthermore, we also
found that the presence of Tinuvin 144 in the system
significantly enhances the formation of these derivatives.
While analogous epoxidic compounds were not detected in
the photodegradation of compound 3, monoepoxides P26 and
P27 were detected for the first time, albeit in trace amount, after
irradiation of 4 in toluene solution. On the other hand, we
failed to detect these compounds among the photoproducts of

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
559
H3CO
m/z: 423
H
-CH3
CH2
O
- C6H4-OCH3
m/z: 331
.
+
M
: 438
O
P10
H3CO
H3CO
H
H2C
O
O
H3CO
H
H3CO
H
H
O
O
H3CO
H3CO
H
H
H3CO
H
O
H
CH
O
m/z: 252
H3CO
H3CO
Scheme 5. Proposed fragmentation of P10 following electron impact.
the irradiation of 4 in PU matrix, even when Tinuvin 144 had
been added to the system. We wish however to stress that
this failure might be associated with a low efficiency of the
acetonitrile extraction of the matrix, taken into account that
these derivatives are probably formed in very small amount.
The two isomeric epoxides had similar but distinguishable
GC retention times (e.g., 47.16 min for P10 and 47.37 min for
P11) and the very different fragmentation pattern found in their
MS spectra allowed the discrimination between the two
isomers.
As is outlined in Scheme 2 for compound 2, to account for
the formation of epoxides P10, P11, P26, and P27 we suggest
that the fraction of biradical formed upon irradiation of the
photochromes combine with triplet oxygen. After fragmenta-
tion (loss of a hydroxy radical) biradicals are again formed, the
rearrangement of which to give the epoxides can be easily
envisaged.
structure rather than the closed form. Scheme 5 outlines
possible fragmentations routes leading to fragment 252 that
can only result from the fragmentation of P10. The fragment
ion observed at m/z 438 corresponds to the base peak and the
loss of (-CH3) and (-C6H4-OCH3) lead to stable ions m/z: 423
and m/z: 331, respectively. Other fragmentation pathways for
P11 leading to fragment m/z: 251 are presented in Scheme 6.
We are aware that epoxidic photoproducts have only been
observed from compounds 2 and 4 which share the presence of
the methoxy groups as common feature. On the other hand, the
monoepoxide derivatives 26 and 27 were only detected in
toluene solution and not in the PU matrix, and the diepoxide
from 4 could not be identified in both media. On this basis, and
in view of the fact that compounds P10, P11, P12, P26, and
P27 are minor photoproducts we do not feel to presently have
in our hands enough results neither to state that the presence
of the methoxy groups is critical to the formation of these
epoxidic derivatives, nor to suggest the possible role played by
these substituents.
Actually, in the case of 2 the MS spectral fragmentation
patterns were P10: M+ = 438 (100), 423 (40), 331 (47), 252
(50), 145 (32), 121 (41) and P11: M+ = 438 (13), 422 (71),
315 (48), 281 (21), 251 (46), 207 (100), 77 (24). The main
fragmentations occurred by cleavage of the charged open form
Finally, parallel to the GC/MS studies, the extracts obtained
from the irradiated samples of compounds 2-4 either in toluene
solutions or in PU films, were chromatographed through a

560
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
Degradation of Chromenes in Different Media
P11
H3CO
H
.
CH2
O
H
H3CO
O
M+.:438
H3CO
H
O
H3C
.
O
H3CO
H3CO
H2
C
H
O
H3CO
H3CO
O
H
O
CH2
H
H3CO
O
H2C
O
+
H3CO
H3CO
H
O
H
O
CH
H3CO
O
H3CO
m/z:281
H3CO
+
C
CH
O
H3CO
m/z:251
Scheme 6. Proposed fragmentation of P11 following electron impact.
HPLC equipped with a UV-vis diode-array detector in order to
identify the photoproducts responsible for the appearance of a
yellow color as the irradiation proceeds. It was then ascertained
that the photoproducts responsible for the observed yellowing
were essentially P3, P18, P19, P21, P22, and P23 which
exhibit absorptions in the visible region.
The photochromic polymer films were prepared mixing 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 samples were 14 mm thick and contained
¹1
2 © 10¹5 mol g (dye/polymer). Some polymer films were
formulated without dye in order to obtain blank extractions.
UV-vis Experiments. The UV-vis spectra were recorded
on a Beckman DU 7500 diode array spectrophotometer using a
quartz cell with path length of 1.0 cm, enclosed in a thermo-
regulated copper block (20 °C). The photochromic compounds
were dissolved in anhydrous toluene (10¹4 M) (Aldrich,
spectroscopic grade). The loss of optical density O.D. detected
at the absorption -max of the merocyanine, was followed with the
UV-vis spectrophotometer at the photostationary state, reached
after 10 min of irradiation with a 150-W Xenon lamp at 20 °C.
Experimental
Samples. Compound 1 was synthetised according to the
literature.5,10 Chromenes 2-4 (PPG Industries, Inc.) were
recrystallized from ethanol.
The copolymer polyester-polyurethane available from
Aldrich
poly(4,4¤-methylenebis(phenylisocyanate)-alt-1,4-
butanediolpoly(butylene adipate)) was used to prepare polymer
samples. The Tg value of the polymer matrix, measured using
differential scanning calorimetry, is ¹18 °C.

A. Alberti et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 5 (2011)
Pulishers, New York, 1998, Vols. 1 and 2.
561
Degradation Experiments. All the degradation experi-
ments were performed in a Sun Test (Atlas) equipped with a
1500 W Xenon lamp and a 290 nm filter at 25 °C. Light
2
3
4
M. Irie, Chem. Rev. 2000, 100, 1683.
K. Ichimura, Denshi Zairyo 1989, 71.
G. Favaro, F. Masetti, U. Mazzucato, G. Ottavi, P.
¹2
intensity was 80 W m measured between 300 and 400 nm.
Allegrini, V. Malatesta, J. Chem. Soc., Faraday Trans. 1994, 90,
333.
The mass spectra were obtained under electronic impact (EI
70 eV). The GC/MS (6890 HP GC system and 5973 MS
detector) apparatus was equipped with a short column (0.2 ¯m,
12 m © 0.2 mm). The injector was heated to 255 °C. The GC
system was also run using direct insertion probe interface. For
analysis, direct probe temperature was programmed from 50 to
5
6
R. S. Becker, J. Michl, J. Am. Chem. Soc. 1966, 88, 5931.
B. V. Gemert, M. Bergomi, D. Knowles, Mol. Cryst. Liq.
Cryst. 1994, 246, 67.
7
G. Ottavi, G. Favaro, V. Malatesta, J. Photochem. Photo-
biol., A 1998, 115, 123.
¹1
200 °C at 30 °C min and the ion source was held at 200 °C.
8
G. Favaro, F. Ortica, A. Romani, P. Smimmo, J. Photo-
The HPLC analyses were run on a Beckman Gold system
coupled with a UV-vis diode array detector. Separations were
carried out using a 4.6 mm © 25 cm, C18-5 ¯m reversed-phase
column with a linear gradient of acetonitrile in water from 30%
to 100% during a 45 min set at 1 mL min
chem. Photobiol., A 2008, 196, 190.
9
M. Campredon, A. Samat, R. Guglielmetti, A. Alberti,
Gazz. Chim. Ital. 1993, 123, 261.
10 H. G. Heller, S. N. Oliver, J. Whittall, I. Tomlison, U.S.
Patent 4,826,977, 1989.
¹1
.
11 R. Demadrille, M. Campredon, R. Guglielmetti, G. Giusti,
Mol. Cryst. Liq. Cryst. 2000, 345, 1.
Conclusion
The presence of epoxides among the photodegradation
products of chromenic photochromes in PU matrix is unpre-
cedented, and parallels a previous finding in toluene solution.
The present results seem however to suggest that the presence
of the methoxy sustituents in the phenyl rings is crucial. Some
of the photoproducts responsible for the yellowing of the
starting material have been identified.
Finally, it would appear that the HALS Tinuvin 144 exerts a
more efficient protective action than the spin trap TPMPDTF,
which led us to envisage the utility of carrying out further
degradation studies in an inert environment.
12 S. Jockusch, N. J. Turro, F. R. Blackburn, J. Phys. Chem. A
2002, 106, 9236.
13 P. J. Coelho, M. A. Salvador, M. M. Oliveira, L. M.
Carvalho, J. Photochem. Photobiol., A 2005, 172, 300, and
references therein.
14 E. T. Denisov, Polym. Degrad. Stab. 1991, 34, 325.
15 A. Alberti, M. Benaglia, M. Bonora, V. Borzatta, A.
Hudson, D. Macciantelli, S. Masson, Polym. Degrad. Stab. 1998,
62, 559.
16 G. Ballet, Mol. Cryst. Liq. Cryst. 1997, 298, 75.
17 R. Demadrille, Ph.D. Thesis, Université d’Aix-Marseille II,
France, 2000, p. 135.
18 M. S. Newman, R. Kannan, J. Org. Chem. 1976, 41, 3356.
19 S. L. Graham, K. L. Shepard, P. S. Anderson, J. J. Baldwin,
D. B. Best, M. E. Christy, M. B. Freedman, P. Gautheron, C. N.
Habecker, J. Med. Chem. 1989, 32, 2548.
20 R. Demadrille, A. Rabourdin, M. Campredon, G. Giusti,
J. Photochem. Photobiol., A 2004, 168, 143.
We thank PPG Industries, Inc. and Essilor Int. for their
generous support to this research.
References
1
Organic Photochromic and Thermochromic Compounds,
ed. by J. C. Crano, R. J. Gugliemetti, Kluwer Academic/Plenum