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On the chemiluminescent reaction of ozone with rhodamine B
Analytica
Cltimica Acta.
225
67 ( 1973) ‘225-228 Company,
Q Elsevier Scientific Publishing
SHORT
F. CELARDIN (Received
- Printed
in The Netherlands
COMMUNICATION
On the chemiluminescent
Department
Amsterdam
reaction
of ozone with rhodamine
B
and M. MARCANTONATOS
01 Itlorganic 26th March
urtcl Analytical
Chemistry,
University
OJ Geneva,
Getwva (Switzerlam~)
1973)
The chemiluminescent reaction between ozone and rhodamine B was first applied to the determination of ozone by Bersis and Vassiliou’. More recently, this reaction has been applied with improved results by I-Iodgeson et cd2 and by Guicherit3. As pointed out by Hodgeson et al., the mechanisms related to the chemiluminescent emission are not well understood. The data they obtained with rhodamine B and eosin Y suggested that a resonance energy transfer, from excited intermediate to unreacted dye, occurs as an integral part of the mechanism. Our observations of the reaction between rhodamine B and ozone in glacial acetic acid, indicate that it is a product of this reaction which yields, on further reaction with ozone, an electronically excited species. Energy transfer from this excited moiety to the excess of rhodamine B in solution, is found to be responsible of the chemiluminescent emission of the dye at 590 nm.
Experimen ml Ozone was generated by passing dry oxygen over a high-voltage discharge lamp. Solutions of rhodamine B were prepared by dissolving the analytical grade dye (Merck), in 100% acetic acid (Merck G.R.). Chemiluminescent and spectral measurements were made with a modified Aminco-Bowman spectrofluorimeter equipped with an RCA IP 28 photomultiplier tube. The reaction cell with a fritted glass bottom for ozone entry was designed to fit the cell holder of the instrument. Absorption, excitation and fluorescence spectra were recorded with Beckman DB-G and Hitachi Perkin Elmer MPF-2 spectrophotometers.
Results
and discussiort
Investigations were made under ozone steady-state conditions at room temperature. Chemiluminescent emission DeI’sus time showed an induction period (Fig. 1) followed by a rapid increase in intensity to a maximum value which remained constant over a period proportional to the initial concentration of rhodamine B and to the sate of ozone flow. When the variation of rhodamine B concentration was followed during the reaction by absorption spectrophotometry, it was found that a continuous decrease of the rhodamine B absorption at 556 nm occurred
226
SHORT
Fig. 1. (a) Total chemilumincscencc emission followed by cm&ion at 540 nm (1).
500
L 600
Dcrst4.s time. (b) Chemilumincscencc
COMMUNICATION
emission
at 600 nm
0 (nm)
Fig. 2. (a) Absorption spectra of reaction mixture (S-4 al’iquots diluted at different times (1. start). (b) Absorption spectra of reaction mixture
to 1 ml with glacial acetic acid) at the end of reaction (2, end).
even during the time interval corresponding to the chemiluminescence induction period (Fig. 2a). Towards the end of the reaction, the solution exhibited a weak absorption at 510 nm which disappeared on further introduction of ozone (Fig. 2b). Monitoring of the reaction by fluorescence spectroscopy at an excitation wavelength of 490 nm, showed a decrease of rhodamine B emission at 586 nm and an increase of the resultant compound emission at 535-540 nm (Fig. 3). Both the presence of an induction period and the initial consumption of rhodamine B without chemiluminescent emission suggest that the excited species (X*) is not formed directly by the reaction of ozone with the dye, but is rather a product of the consecutive reaction of the intermediate compound (A) with ozone (see reaction scheme below). The immediate intensity drop to zero after the ozone supply has been cut off, supported this reaction sequence (Fig. 4). There was
SHORT
COMMUNICATION
227
i 2
4
6
8
(mln)
*
3
IMC I
Fig. 3. Fluorescence start; 2, end).
spectra
Fig. 4. Chemiluminesccncc
w
(nm)
600
of reaction
emission
mixture
at di!crcnt
UWSI~Stime with ozone
times (excitation
wavelength.
(mid
490 nm) (1.
flow on (1, 3. 5. 7) and off (2. 4. 6).
virtually no induction period when the ozone supply was restarted immediately after its cut-off. The longer the time elapsed after ozone cut-off, the longer the induction period preceding the chemiluminescent emission. This supports the view that the accumulated intermediate compound (A) is of limited stability at room temperature. Chemiluminescent spectra corroborate the intermediate compound-ozone reaction giving the excited state (reaction 2) and suggest that there is in fact energy transfer from the excited molecule (X*) to rhodamine B (reaction 3). Throughout the reaction, chemiluminescent emission occurs at 590 nm, which corresponds to the fluorescence emission of the dye. But as soon as the rhodamine B concentration falls to zero, the chemiluminescence emission occurs at 540 nm and decreases exponentially towards zero intensity (Fig. lb). It is very likely that this emission is due to the excited state of the final compound (X*). The strong overlap of the emission band of the excited moiety at 540 nm with the absorption band of rhodamine B at 556 nm favours the idea of an energy-transfer step (Fig. 5). On the basis of these preliminary observations, is proposed : Rh-B+03 A+Oa
the following reaction
sequence
ki
--*A
(1)
2
(2)
X*
228
SHORT
c
(“ml
600
500
Fig. 5. Chcmilumincscence no rhodaminc B remains
X* +Rh-B (Rh-B)*
COMMUNICATION
(+
spectrum of reaction mixture ( -). Chcmilumincscencc + +). Absorption spectrum of rhodamine B (----).
spectrum
when
-% X + (Rh-B)*
(3)
2
(4
Rh-B
+ hv,
ks
x*--,x
(5)
Thus, rhodamine B reacts with ozone to give an intermediate A which reacts with B after ozone to form an excited molecule X *. There is emission from rhodamine of rhodamine B, there is emission energy transfer from X *. After total consumption according to ks
X*
(6)
+X+hv,
In this scheme, radiationless deactivation processes of rhodamine B have been neglected since the dye has a high fluorescence efficiency; moreover, all radiationless deactivations of X* besides reaction (3) are summed up by reaction (5). Further investigations on these topics are in progress. REFERENCES 1 D. Bcrsis and E. Vassiliou. Atdyst. 91 (1966) 499. 2 J. A. Hodgeson. K. J. Krost. A. E. O’Kccfe and R. K. Stevens. 3 R. Guichcrit. Z. Ahal. Cknt.. 256 ( 197 1) 177.
AWL Chettr., 42 ( 1970) 1795.
Cltimica Acta.
225
67 ( 1973) ‘225-228 Company,
Q Elsevier Scientific Publishing
SHORT
F. CELARDIN (Received
- Printed
in The Netherlands
COMMUNICATION
On the chemiluminescent
Department
Amsterdam
reaction
of ozone with rhodamine
B
and M. MARCANTONATOS
01 Itlorganic 26th March
urtcl Analytical
Chemistry,
University
OJ Geneva,
Getwva (Switzerlam~)
1973)
The chemiluminescent reaction between ozone and rhodamine B was first applied to the determination of ozone by Bersis and Vassiliou’. More recently, this reaction has been applied with improved results by I-Iodgeson et cd2 and by Guicherit3. As pointed out by Hodgeson et al., the mechanisms related to the chemiluminescent emission are not well understood. The data they obtained with rhodamine B and eosin Y suggested that a resonance energy transfer, from excited intermediate to unreacted dye, occurs as an integral part of the mechanism. Our observations of the reaction between rhodamine B and ozone in glacial acetic acid, indicate that it is a product of this reaction which yields, on further reaction with ozone, an electronically excited species. Energy transfer from this excited moiety to the excess of rhodamine B in solution, is found to be responsible of the chemiluminescent emission of the dye at 590 nm.
Experimen ml Ozone was generated by passing dry oxygen over a high-voltage discharge lamp. Solutions of rhodamine B were prepared by dissolving the analytical grade dye (Merck), in 100% acetic acid (Merck G.R.). Chemiluminescent and spectral measurements were made with a modified Aminco-Bowman spectrofluorimeter equipped with an RCA IP 28 photomultiplier tube. The reaction cell with a fritted glass bottom for ozone entry was designed to fit the cell holder of the instrument. Absorption, excitation and fluorescence spectra were recorded with Beckman DB-G and Hitachi Perkin Elmer MPF-2 spectrophotometers.
Results
and discussiort
Investigations were made under ozone steady-state conditions at room temperature. Chemiluminescent emission DeI’sus time showed an induction period (Fig. 1) followed by a rapid increase in intensity to a maximum value which remained constant over a period proportional to the initial concentration of rhodamine B and to the sate of ozone flow. When the variation of rhodamine B concentration was followed during the reaction by absorption spectrophotometry, it was found that a continuous decrease of the rhodamine B absorption at 556 nm occurred
226
SHORT
Fig. 1. (a) Total chemilumincscencc emission followed by cm&ion at 540 nm (1).
500
L 600
Dcrst4.s time. (b) Chemilumincscencc
COMMUNICATION
emission
at 600 nm
0 (nm)
Fig. 2. (a) Absorption spectra of reaction mixture (S-4 al’iquots diluted at different times (1. start). (b) Absorption spectra of reaction mixture
to 1 ml with glacial acetic acid) at the end of reaction (2, end).
even during the time interval corresponding to the chemiluminescence induction period (Fig. 2a). Towards the end of the reaction, the solution exhibited a weak absorption at 510 nm which disappeared on further introduction of ozone (Fig. 2b). Monitoring of the reaction by fluorescence spectroscopy at an excitation wavelength of 490 nm, showed a decrease of rhodamine B emission at 586 nm and an increase of the resultant compound emission at 535-540 nm (Fig. 3). Both the presence of an induction period and the initial consumption of rhodamine B without chemiluminescent emission suggest that the excited species (X*) is not formed directly by the reaction of ozone with the dye, but is rather a product of the consecutive reaction of the intermediate compound (A) with ozone (see reaction scheme below). The immediate intensity drop to zero after the ozone supply has been cut off, supported this reaction sequence (Fig. 4). There was
SHORT
COMMUNICATION
227
i 2
4
6
8
(mln)
*
3
IMC I
Fig. 3. Fluorescence start; 2, end).
spectra
Fig. 4. Chemiluminesccncc
w
(nm)
600
of reaction
emission
mixture
at di!crcnt
UWSI~Stime with ozone
times (excitation
wavelength.
(mid
490 nm) (1.
flow on (1, 3. 5. 7) and off (2. 4. 6).
virtually no induction period when the ozone supply was restarted immediately after its cut-off. The longer the time elapsed after ozone cut-off, the longer the induction period preceding the chemiluminescent emission. This supports the view that the accumulated intermediate compound (A) is of limited stability at room temperature. Chemiluminescent spectra corroborate the intermediate compound-ozone reaction giving the excited state (reaction 2) and suggest that there is in fact energy transfer from the excited molecule (X*) to rhodamine B (reaction 3). Throughout the reaction, chemiluminescent emission occurs at 590 nm, which corresponds to the fluorescence emission of the dye. But as soon as the rhodamine B concentration falls to zero, the chemiluminescence emission occurs at 540 nm and decreases exponentially towards zero intensity (Fig. lb). It is very likely that this emission is due to the excited state of the final compound (X*). The strong overlap of the emission band of the excited moiety at 540 nm with the absorption band of rhodamine B at 556 nm favours the idea of an energy-transfer step (Fig. 5). On the basis of these preliminary observations, is proposed : Rh-B+03 A+Oa
the following reaction
sequence
ki
--*A
(1)
2
(2)
X*
228
SHORT
c
(“ml
600
500
Fig. 5. Chcmilumincscence no rhodaminc B remains
X* +Rh-B (Rh-B)*
COMMUNICATION
(+
spectrum of reaction mixture ( -). Chcmilumincscencc + +). Absorption spectrum of rhodamine B (----).
spectrum
when
-% X + (Rh-B)*
(3)
2
(4
Rh-B
+ hv,
ks
x*--,x
(5)
Thus, rhodamine B reacts with ozone to give an intermediate A which reacts with B after ozone to form an excited molecule X *. There is emission from rhodamine of rhodamine B, there is emission energy transfer from X *. After total consumption according to ks
X*
(6)
+X+hv,
In this scheme, radiationless deactivation processes of rhodamine B have been neglected since the dye has a high fluorescence efficiency; moreover, all radiationless deactivations of X* besides reaction (3) are summed up by reaction (5). Further investigations on these topics are in progress. REFERENCES 1 D. Bcrsis and E. Vassiliou. Atdyst. 91 (1966) 499. 2 J. A. Hodgeson. K. J. Krost. A. E. O’Kccfe and R. K. Stevens. 3 R. Guichcrit. Z. Ahal. Cknt.. 256 ( 197 1) 177.
AWL Chettr., 42 ( 1970) 1795.