Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solution

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


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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-


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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.


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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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Documents

Comparative photodegradation study between spiro[indoline-oxazine] and spiro[indoline-pyran] derivatives in solution