Photoactivation of fluorescence of rhodamine dyes in the presence of haloalkanes

Article abstract of DOI:10.1007/s11172-013-0163-5

Organic halogen derivatives, viz., hexachloroethane, 2,2,2- trichloroethanol, 2,2,2-tribromoethanol, butyl trichloroacetate, 2,2,2-trichloroethyl methacrylate, can efficiently activate fluorescence of lactone forms of rhodamine dyes by UV irradiation through the UFS-1 light filter in both solutions and polymer poly(methyl methacrylate) films. This ability is also typical of the copolymer of methyl methacrylate and 2,2,2-trichloroethyl methacrylate, which is promising for the development of detecting media for archive optical data storage with fluorescent readout.

Full text of DOI:10.1007/s11172-013-0163-5

Russian Chemical Bulletin, International Edition, Vol. 62, No. 5, pp. 1195—1200, May, 2013
1195
Photoactivation of fluorescence of rhodamine dyes
in the presence of haloalkanes
a
a
b
b
b
a
I. V. Ivanov, S. M. Dolotov, O. I. Kobeleva, T. M. Valova, V. A. Barachevsky, and V. F. Traven
аD. I. Mendeleev Russian University of Chemical Technology,
9
Miusskaya pl., 125047 Moscow, Russian Federation.
Fax: +7 (495) 609 2964. Eꢀmail: traven@muctr.ru
b
Photochemistry Center, Russian Academy of Sciences,
Building 1, 7a ul. Novatorov, 119942 Moscow, Russian Federation.
Fax: +7 (495) 936 1255. Eꢀmail: barva@photonics.ru
Organic halogen derivatives, viz., hexachloroethane, 2,2,2ꢀtrichloroethanol, 2,2,2ꢀtribromoꢀ
ethanol, butyl trichloroacetate, 2,2,2ꢀtrichloroethyl methacrylate, can efficiently activate fluoꢀ
rescence of lactone forms of rhodamine dyes by UV irradiation through the UFSꢀ1 light filter in
both solutions and polymer poly(methyl methacrylate) films. This ability is also typical of the
copolymer of methyl methacrylate and 2,2,2ꢀtrichloroethyl methacrylate, which is promising
for the development of detecting media for archive optical data storage with fluorescent readout.
Key words: rhodamines, halogen derivatives, fluorescence, photochemical activation,
date storage.
Fast development of computer and information techꢀ
nologies form demands in more highly productive systems
capable of recording, storage, and reproduction of huge
information volumes.1 One of the most promising apꢀ
proaches to an increase in the volume of detected inforꢀ
mation on optical carriers is its recording on multilayer
optical disks using the twoꢀphoton transformation of
organic substances by laser irradiation with fluorescent
acid, or acid photogenerator (APG), whose role is the
conversion of the precursor molecule to the fluorescing
2
0,21
product due to the elimination of the protecting group
or opening of the lactone/lactam ring of the leucoꢀ
—7
1
7,22,23
base.
When working with fluorescent precursors, the
deactivation of their fluorescence or shift of the emission
maximum to a longerꢀwavelength region is attained by the
1
4,20
protonation at their amino groups.
8
readout. This method provides basically new possibilities
The typical acid photogenerators proposed for use in
detecting media for archive information recording are triꢀ
arylsulfonium and triaryliodonium salts of some organic
of information detection compared to the modern optical
accumulators based on recording on one or two surfaces of
an optical disk.
2
0,24,25
26,27
and inorganic acids,
sulfonic acid derivatives,
2
2,23
Single information recording and possibility of its mulꢀ
tiple readout are performed on optical disks for archive
information storage. Information is recorded due to irreꢀ
versible photochemical transformations of nonꢀfluoresꢀ
cent precursors (initial organic substrates) into compounds
with intense fluorescence (the reversible process of fluoꢀ
rescence decay is possible in the course of the photochemꢀ
ical reaction). These phototransformations should be charꢀ
acterized by a high quantum yield, the photoproduct has a
high fluorescence quantum yield. In addition, both the
precursor and photoproduct should have a high thermal
nitrobenzaldehydes and nitronaphthaldehydes.
halogen derivatives, in particular, carbon tetrabromide
and 2,2,2ꢀtribromoethanol,
Some
8—32
2
30—32
which was applied, for
example, to fix the open form of spiropyrans, were proꢀ
posed as fluorescence activators. Chlorineꢀsubstituted
derivatives of alkanes have certain prospects as APGs. For
instance, it has previously been shown that a CCl moleꢀ
4
cule can act as an electron acceptor. Accepting an electron,
this molecule gives an unstable radical anion, which
very rapidly decomposes to eject the chloride ion and
to form the trichloromethyl radical capable of further
abstracting the hydrogen atom from the corresponding
substrate; in turn, the chloride ion can act as a proton
9
,10
stability.
Photosensitive derivatives of coumarins, lactones, and
3
2,33
lactams of xanthene dyes of the rhodamine series are used,
acceptor.
Examples for the photodehydrogenation
in particular, as fluorescent precursors1
1—15
for archive
of dihydropyridine and pyrazoline derivatives upon the
1
1,16—19
information recording with fluorescent readout.
As
irradiation of their solutions in CCl should be menꢀ
4
34,35
a rule, the precursor is irradiated in the presence of a photoꢀ
tioned.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1195—1200, May, 2013.
066ꢀ5285/13/6205ꢀ1195 © 2013 Springer Science+Business Media, Inc.
1

1
196
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
Ivanov et al.
In this work, a series of organic halogen derivatives,
namely, hexachloroethane (C Cl ), 2,2,2ꢀtrichloroethanol
Scheme 1
2
6
(
CCl CH OH), 2,2,2ꢀtribromoethanol (CBr CH OH),
3 2 3 2
butyl trichloroacetate (CCl COOBu), 2ꢀchloroethanol
3
(
CH ClCH OH), 2ꢀbromoethanol (CH BrCH OH), and
2 2 2 2
2
,2,2ꢀtrichloroethyl methacrylate (CH =C(Me)ꢀ
2
COOCH CCl ), was studied as fluorescence activators of
2
3
one of the most promising groups of precursors.
In addition, copolymer of 2,2,2ꢀtrichloroethyl methꢀ
acrylate with methyl methacrylate (1 : 20) was synthesized,
and the photoactivation of the fluorescent forms of two
rhodamine dyes in the obtained copolymer was studied.
Lactone forms of Rhodamine B and Rhodamine 19 were
examined as precursors. In all measurements, the polymer
films were irradiated through the UFSꢀ1 light filter.
cent form, and this process is not accompanied by the
photodecomposition of the dye formed. The spectra of the
colored fluorescent forms of rhodamine dyes formed during
photoactivation are identical to the spectra of these dyes
in solutions. The absorption and fluorescence spectra of
the PMMA films containing Rhodamine B in the presꢀ
ence of trichloroethanol are shown as an example in Fig. 2.
It is seen that the photogeneration of the colored form
of the precursor is not accompanied, under these condiꢀ
tions, by noticeable dye decomposition. The results of
spectral measurements for the irradiation of the PMMA
films containing lactones of Rhodamine B or Rhodꢀ
amine 19 in the presence of various halogen derivatives are
given in Table 1.
We also studied butyl trichloroacetate as a photoꢀ
activator of fluorescence of rhodamine dyes, which can
simultaneously act as a plasticizer of the polymer film.
The irradiation of the PMMA film containing butyl
Poly(methyl methacrylate) (PMMA) was used as
a polymer binding.
Results and Discussion
A
I (arb. units)
Lactone forms of rhodamine dyes can transform into
the colored fluorescing state under UVꢀirradiation in the
absence of any photoactivators as well (Scheme 1). As
follows from Fig. 1, under UVꢀirradiation in the PMMA
film, the lactone cycle of Rhodamine 19 is opened to form
the colored fluorescent form. However, when lactone of
the rhodamine dye in the polymer film is directly irradiatꢀ
ed, the colored fluorescent form of the dye is formed and
also the dye partially decomposes, which is indicated by
a significant increase in the absorbance in the 400—450 nm
range of the absorption spectra.
0
0
0
0
.4
.3
.2
.1
3
2
500
800
4
2100
1
7
400
00
2
1
3
The introduction of compounds with trihalomethyl
fragments into the composition of the polymer films conꢀ
taining lactones of Rhodamine B and Rhodamine 19 faꢀ
vors an efficient photoactivation of the colored fluoresꢀ
300
400
500
600
/nm
Fig. 1. Absorption (1, 2) and fluorescence (3, 4) spectra of the
PMMA film containing lactone of Rhodamine 19 before (1, 3)
and after (2, 4) irradiation through the UFSꢀ1 light filter.

Photoactivated fluorescence of rhodamine dyes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
1197
A
I (arb. units)
A
I (arb. units)
1
8
6
4
2
0000
000
000
000
000
8
7
6
000
000
000
1
1
0
.5
.0
.5
1.4
4
2
4
1
1
.2
.0
2
5000
000
0.8
4
0
0
.6
.4
3000
2000
1000
3
1
3
3
00
400
500
600
/nm
0.2
1
Fig. 2. Absorption (1, 2) and emission (3, 4) spectra of the PMMA
film containing Rhodamine B and trichloroethanol before (1, 3)
and after (2, 4) irradiation through the UFSꢀ1 light filter.
300 350 400 450 500 550 600 700 /nm
Fig. 3. Absorption (1, 2) and emission (3, 4) spectra of the PMMA
film containing Rhodamine B and butyl trichloroacetate before
(
1, 3) and after (2, 4) irradiation through the UFSꢀ1 light filter.
trichloroacetate and Rhodamine B lactone results in the
formation of the colored fluorescent form of Rhodamine B
(
Fig. 3) without noticeable properties (according to the
The PMMA films containing lactones of rhodamine
electronic absorption spectra) of dye photodestruction.
Similar results were obtained for the PMMA films conꢀ
taining Rhodamine 19 and butyl trichloroacetate.
dyes were also irradiated in the presence of ethylene chloroꢀ
hydrin and ethylene bromohydrin. However, the irradiation
of the corresponding samples resulted only in a weak coloraꢀ
Table 1. Compositions of the studied PMMA films and the spectral results of their irradiation
Sample
Composition
C
maxabs
/nm
Dph
maxfl
/nm
I0
Iact
mmol L–
1
/
arb. units
1
2
3
Rhodamime 19
Rhodamine B
Rhodamine B +
5.0
6.0
5.8
130
1.1
180
8.5
52
2.4
620
8.5
52
532
560
560
0.2
0.3
1.0
560
587
587
100
80
90
2220
2500
5840
+
hexachloroethane
Rhodamime 19 +
hexachloroethane
Rhodamine B +
ethylene bromohydrin
Rhodamime 19 +
ethylene bromohydrin
Rhodamine B +
2,2,2ꢀtrichloroethanol
Rhodamime 19 +
2,2,2ꢀtrichloroethanol
Rhodamine B +
2,2,2ꢀtribromoethanol
Rhodamime 19 +
2,2,2ꢀtribromoethanol
Rhodamine B +
butyl trichloroacetate
Rhodamime 19 +
butyl trichloroacetate
4
5
6
7
8
9
532
560
532
560
532
560
532
560
532
0.7
0.3
0,2
1.1
0.4
2.5
1.4
1.9
1.2
563
585
560
584
562
585
563
586
560
150
530
500
570
550
530
510
110
120
6880
1203
1018
5910
4910
7723
9280
7500
5520
+
+
+
+
2.1
52
+
1.1
130
1.8
180
8.4
50
+
1
1
1
0
1
2
+
+
8.4
52
+
Note. C is concentration; maxabs and maxfl are the wavelengths of maximum of photoinduced absorption and
ph
fluorescence bands, respectively; D is the maximum photoinduced change in the absorbance at the absorption
band maximum of the dye; I and I are the fluorescence intensity at the fluorescence band maximum before
0
act
and after activating irradiation in the state of photoequilibrium, respectively.

1
198
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
Ivanov et al.
tion of the film with a low fluorescence intensity (see
Table 1), which can be related to the lactone ring opening
in the rhodamine dye directly under the action of UV
radiation involving no halogenꢀcontaining alcohol. This is
indicated, in particular, by the increase in the absorption
at 400—450 nm of the electronic absorption spectrum, as
in the case of sample 1 containing no halogen derivative.
Several schemes were proposed in literature to explain
the activating influence of organic halogen derivatives on
the photoinduced fluorescence of the precursors. In parꢀ
ticular, the following routes of photoactivation of fluoresꢀ
cence of triarylmethane dyes in the presence of carbon
protonated form, indicating that the acid is accumulated
in the film.
Thus, the introduction of compounds bearing trihaloꢀ
methyl fragments into the composition of the polymer
films containing Rhodamine B or Rhodamine 19 lactone
favors the efficient photoactivation of their colored fluoꢀ
rescent forms, most probably, due to opening of their lacꢀ
tone fragments by the photogenerated acid.
The data presented in Table 1 indicate the high effiꢀ
ciency of trichloroethanol and tribromoethanol as acid
photogenerators in the systems containing lactones of
rhodamine dyes. However, free hydroxy groups in these
alcohols can impede their practical use because of potenꢀ
tially possible lactone ring opening in the dye already in
the course of film preparation. This process can increase
the background color of the initial film and decrease conꢀ
trast of the fluorescent centers formed.
30,31
tetrabromide are discussed
:
—
reaction of the tribromomethyl radical formed upon
irradiation with aromatic amine followed by the condenꢀ
sation of the intermediate under the action of irradiation
to the triarylmethane dye;
—
generation of atomic bromine followed by the forꢀ
This disadvantage of trihaloethanols can evidently be
overcome by the esterification of the free hydroxy group of
alcohols. In addition, the introduction of the group capꢀ
able of polymerization during esterification provides the
possibility to obtain a polymer containing trihalomethyl
groups in its structure. The migration of the acid photoꢀ
generator in the polymer material bulk is excluded in this
polymer, which should unambiguously enhance its quality
when applied in devices of information recording. The
transesterification of methyl methacrylate (MMA) with
2,2,2ꢀtrichloroethanol gave 2,2,2ꢀtrichloroethyl methꢀ
acrylate (TCEMA), which exhibited the properties of
photoacid. The combined radical polymerization of MMA
and TCEMA produces their copolymer with the ratio of
monomer units 20 : 1. As assumed, in films of the obꢀ
tained copolymer, the photogeneration of the fluorescent
form of the rhodamine dye requires no additional monoꢀ
mation of hydrogen bromide that converts the leucobase
to the colored form;
—
generation of atomic bromine acting as an oxidant
of the leucobase to the colored form.
To confirm the ability of the studied halogen derivaꢀ
tives to act as acid photogenerators in polymer films, we
prepared and irradiated through the UFSꢀ1 light filter the
PMMA films containing hexachloroethane, tribromoꢀ
ethanol, or trichloroethanol in the presence of the acid—base
indicator Methyl Red. The change in the electronic abꢀ
sorption spectrum of this indicator in the film under UV
irradiation in the presence of tribromoethanol is shown in
Fig. 4. The initial spectrum of the indicator in the films
indicates the presence of two forms: neutral (absorption
band with a maximum at 410 nm) and protonated (shoulꢀ
der at 490 nm). The films containing hexachloroethane,
tribromoethanol, or trichloroethanol in the presence of
the indicator during irradiation exhibit a decrease in
the intensity of the shortꢀwavelength absorption band
of the indicator with a simultaneous increase in the
longꢀwavelength band at 490 nm corresponding to its
3
6
meric halogen derivative (Fig. 5, Table 2).
Comparing the data presented in Tables 1 and 2, we
may assert that the use of copolymers acting simultaneousꢀ
A
I (arb. units)
A
4
4
500
000
1
1
.4
.2
0
0
0
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
8
3500
3000
2
1
4
1
8
1.0
2
2
1
1
5
500
000
500
000
00
0
0
0
0
.8
.6
.4
.2
1
3
3
50
400
450
500
550
/nm
350 400 450 500 550 600 650 700 /nm
Fig. 4. Absorption spectra of the PMMA film containing triꢀ
bromoethanol and acid—base indicator Methyl Red before (1)
and after (2—8) irradiation through the UFSꢀ1 light filter.
Fig. 5. Absorption spectra of the film of the copolymer of TCEMA
(1, 2) and MMA (3, 4) containing Rhodamine B before (1, 3)
and after (2, 4) irradiation through the UFSꢀ1 light filter.

Photoactivated fluorescence of rhodamine dyes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 5, May, 2013
1199
Table 2. Composition of the studied polymer films based on TCEMA and the spectral results of their irradiation
Sample
Film composition
C
maxabs
/nm
Dph
maxfl
/nm
I0
Iact
arb. units
mmol L–
1
/
1
1
3
4
Rhodamine B + copolymer
TCEMA with MMA (1 : 20)
Rhodamine 19 + copolymer
TCEMA with MMA (1 : 20)
1.1
475
2.0
560
532
0.7
0.5
585
562
100
110
4100
3020
475
ly as polymer bindings and acid photogenerators provides
high spectral characteristics required for their successful
work as media for archive information recording.36
rectification column. The solution was heated to boiling in an oil
bath until the temperature of the upper part of the column
reached 63—64 C corresponding to the boiling point of a methꢀ
anol—MMA azeotropic mixture. As the azeotrope was formed,
it was distilled off. After methanol stopped to form (~8 h), unreꢀ
acted MMA was removed. 2,2,2ꢀTrichloroethyl methacrylate
Thus, it was shown that a series of halogen derivatives,
viz., hexachloroethane, 2,2,2ꢀtrichloroethanol, 2,2,2ꢀtriꢀ
bromoethanol, butyl trichloroacetate, and 2,2,2ꢀtrichloroꢀ
ethyl methacrylate, are capable of efficient activating the
fluorescence of lactone forms of rhodamine dyes upon UV
irradiation through the UFSꢀ1 light filter in both solutions
and polymer PMMA films. The copolymer of MMA and
TCEMA also manifests this ability, which is promising for
the development of detecting media in archive recording
of optical information with fluorescent readout.
was purified by distillation, b.p. 85 C (10 Torr) (cf. Ref. 38: b.p.
1
4
8 C (1.5 Torr)). Н NMR (CDCl ), : 1.95 (s, 3 Н, Me); 4.74
3
(s, 2 Н, СОСН ); 5.67, 7.23 (both m, 1 Н each, =СН ).
2
2
Copolymer of MMA and 2,2,2ꢀtrichloroethyl methacrylate.
A mixture containing MMA (5 mL), 2,2,2ꢀtrichloroethyl methꢀ
acrylate (0.3 mL) nꢀdodecylmercaptane (60 L), and azobisisoꢀ
butyric acid dinitrile (5 mg) was placed in a glass ampule. Oxyꢀ
gen was removed by freezing—defreezing, and the ampule was
sealed off. Polymerization was conducted in the temperature
range 50—70 C for 24 h and then at 110—115 C for 2 h. After
cooling, the ampule was broken and solid copolymer was taken
out. The copolymer was dried by triple reprecipitation from ethyl
acetate to ethanol. The copolymer was dried to a constant weight
in vacuo (5•10–2 Torr) at 80 C. The molecular weight was
Experimental
Spectrophotometric measurements (photostationary spectra)
and investigation of the kinetics of photocoloration of the photoꢀ
induced form of the studied compounds in the polymer were
carried out using a Cary 50 bio spectrophotometer (Varian). The
spectra and kinetics of changes in fluorescence were measured
using a Cary Eclipse spectrofluorimeter (Varian).
Irradiation was conducted with the filtered light from an
LCꢀ4 lamp (Hamamatsu). The UFSꢀ1 light filter was used for
photocoloration. The fluorescence intensity was measured upon
excitation with the visible light through the ZhSꢀ10 light filter,
i.e., at the absorption band of the photoproduct (the formed dye).
Ethylene chlorohydrin, ethylene bromohydrin, hexachloroꢀ
ethane, 2,2,2ꢀtrichloroethanol (TCE), and 2,2,2ꢀtribromoꢀ
ethanol (TBE) (all Aldrich) and butyl trichloroacetate were used
as organic halogen derivatives.
9
3 kDa. The purity of the obtained copolymer was confirmed by
1
1
Н NMR. Н NMR (CDCl ), : 0.70—1.15 (m, 3 Н, Me);
3
1
.70—2.20 (m, 2 Н, СН ); 3.51 (s, 3 Н, OMe); 4.53 (s, 0.09 Н,
2
СН CCl ).
2
3
Film preparation. The films were prepared by the method of
pouring the solution containing PMMA, lactone of rhodamine
dye, and halogen derivative in a toluene—ethyl acetate mixture
of solvents on a horizontally mounted glass Petri dish followed
by solvent removal by drying. Prior to irradiation, the films were
taken from the support. The films of the MMA copolymer with
2
,2,2ꢀtrichloroethyl methacrylate and lactone of Rhodamine B
or Rhodamine 19 but containing no monomeric halogen derivaꢀ
tives were prepared similarly. The film thickness was 90—100 m.
Butyl trichloroacetate. A mixture of trichloroacetic acid (13.5 g),
concentrated sulfuric acid (2 mL), and butyl alcohol (55 mL)
was refluxed for 4—4.5 h. Then the flask was cooled to ~20 C,
water (40 mL) was added to the content of the flask, and butyl
trichloroacetate was extracted with diethyl ether. The ethereal
extracts were washed with a 10% solution of sodium carbonate
and dried with anhydrous magnesium sulfate, and diethyl ether
was distilled off. This final product was purified by distillation.
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