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Spectrochimica Acta Part A 66 (2007) 111–113

Fluorescence quenching of 3-methyl 7-hydroxylCoumarin in presence of acetone

Vijay Kumar Sharma a,∗, D. Mohan b, P.D. Sahare c

a Department of Physics, Skyline Institute of Engineering and Technology, Gr. Noida, UP, Indiab Department of Applied Physics, Guru Jambeshwar University, Hisar Haryana, India

c Department of Physics and Astrophysics, University of Delhi, Delhi, India

Received 5 September 2005; received in revised form 8 February 2006; accepted 9 February 2006

bstract

Fluorescence quenching of 3-methyl 7-hydroxyl Coumarin in prescence of the acetone is reported here. It was found that the quenching observedas of dynamic nature. It is also observed that quenching of the fluorescence of the indicator had a full reversiblity. As it has a full reversibilty, aovel optical sensor for acetone can be constructed on this quenching.

2006 Elsevier B.V. All rights reserved.

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eywords: Quenching; Fluorescence; Sensor; Coumarin

. Introduction

The devlopment of sensors based on immobilized fluores-ent reagents is a matter of growing interset [1,2]. Optical andOCSs (fiber optical chemical sensors) can have advantagesver conventional sensors such as electrodes etc. because theyre simple, reliable, cost effective and relatively easy to main-ain [3,4]. Chemiluminscence seems to be attractive becauseight is generated through chemical or biochemical reactions. Noigth sourece is needed and experimental set-up can be put veryimple. In the present work; the sensor presented is a optical sen-or based on fluorescence quenching. Fluorescence quenchingefers to any process which decreases the fluorescence inten-ity of a certain fluorophore. A variety of processess can resultn such a decrease in intensity such as collisional or dynamicaluenching, static quenching etc. Dynamic quenching (Fig. 1)esults with collision between fluorophore in its excited statend quenching molecule. The fluorophore returns to ground stateithout emission of light. On other hand in static quenching, a

on-fluorescent complex is formed between the fluorophore andhe quencher. Usually only a fluorophore which is not complexedan exhibit fluorescence. As in both cases, the fluorescene inten-

∗ Corresponding author.E-mail addresses: vasuvijay2001@yahoo.com, nonuvijay@rediffmail.com

V.K. Sharma).

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386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2006.02.032

ity is related to the concentration of the quencher. Therfore, theuenched fluorophore can serve as an indicator for quenchinggent. The dynamic fluorescence quenching can be described byhe Stern–Volmer equation as follows

I0

I= τ0

τ= 1+Kd{Q} = 1+Kqτ0{Q} (1)

here, I0 and I are the fluorescence intensities in the absecncend prescence of a quencher, relatively. Kd = quenching constantr Stern–Volmer constant, {Q}= concentration of the quenchernd Kq = biomolecular quenching constant. τ0 and τ are the life-imes of the excited state of the fluorophore in the absence andresece of the quencher, respectively.

Since collision of the quencher with fluorophore occurs ints excited state, the life time of the excited state is reducedoo. Dynamic fluorescence quenching is a diffusion process andherefore, is also influenced by the solvent viscosity and tem-ertature. Static quenching can be represented as the eqvationimilar to eqvation discribed earlier as

I0

I= 1+Ks{Q} (2)

he quenching constant Ks, is now identical with associa-

ion constant of the complex formed between fluorophore anduencher. In case of static quenching a fraction of fluorophores removed by complexation where as the fluorescence of thencomplexed portion remains unpertubated. Therefore, lifetime

112 V.K. Sharma et al. / Spectrochimica Acta Part A 66 (2007) 111–113

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ripststTacetone and C 4 dye.

A significant decrement of the intensity of the fluorophore (C4) is observed as the concentration of the acetone is increased.Stern–Volmer plot (Fig. 3) shows a good linear relationship

Fig. 1. Scematic diagram of collisional quenching.

f the excited state of fluorophore is unchanged. Hence, in casef complex formation there is a frequently change in absorptionpectrum of the fluorophore, whereas collisional quenching onlyffects the excited state.

Coumarin class of dyes are most effective and usefull mate-ial in blue green regions. These dyes are of great intrest forany of researchers [5–8]. Coumarin dyes are as efficient asantene dyes. Through Coumarins even for flash pump a long

ise time, efficient lasing can be expected as well as for shortulse pumping. In the presented study the 3-methyl 7-hydroxyloumarin (C 4) was selcted as fluorophore. It is selected here

o study because of its stabilty against the structural changesith a change in envoirnment i.e. temperature, solvent, con-

entration etc. Acetone is a commercially used solvent of greatmportance as it has got a wide application in biomedical andhemical reactions. Exposure to moderate to high amounts ofcetone can irritate to one’s eyes, respiratory system and makene dizzy. Very high exposure may cause loss of conciousness.his chemical has been found in atleast 572 of 1416 National Pri-rities List sites identified by Enviormetnal Protection Agency.nimals exposed to acetone in air also had long irritation andecame unconscious and some died. Hence, detection of thecetone has a immense importance.

. Experimental set-up used

The Coumarin dye under study was procured from Sigmahemicals (USA) and was used without further purification.or significant quenching one require solution of relatively lowiscosity to permit rapid diffusion of quencher. The quenchingrocedure is particularly useful for biological macromolecules.his is because it permits the relaxation rates to be measuredithout verification of the temperature. Methanol was used for

he same purpose because of the same reason. Methanol andcetone used were of AR grade. The methanol found to beransparent and non-fluorescent in the range of excitation and flu-rescence emission and was also confirmed by their absorptionpectra. Absorption spectra were recorded using Shimadzu (260)V–vis spectrophotometer. Aminco–Bowman spectrophotoflu-

rometer, fitted with photo-multiplier tube RJ-758 and 150 Wenon lamp, was used to record the fluorescence spectra of

he dyes under investigation. No correction factor for the photo-ultiplier tube was needed due to its good flat response over this

Fig. 2. Emission spectra of C 4 in presence of acetone quencher.

ange. Only correction factor of Xenon lamp according to Mel-uish [9] was applied. Excitation curves were found to be similarith the absorption curves of the dyes. Therefore, the excitation

urves were taken as the absorption curves to select the peakavelength. Dye concentration was kept as low as 2× 10−5 M

o avoid self-quenching or inner filter effects. Recorded fluores-ent emission wavelengths were accurately estimated to within2 nm and absorption wavelength ±1 nm. Acetone used wasixed in microlitres as a quencher.

. Results and discussion

The observed fluorescence of the indicator has a fulleversibility. It may be considered that the process of quench-ng is dynamic in nature and a diffusion controlled bimolecularrocess is responsible for observed quenching. This inference isupported by the fact that no change in absorption spectrum ofhe dye is observed in presence of the acetone. The peak emis-ion wavelength (at 402 nm) (Fig. 2) remains unaltered duringhe quenching experiments performed in methanolic solution.his ruled out the possibility of a chemical reaction between

Fig. 3. Stern–Volmer plot.

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V.K. Sharma et al. / Spectrochim

regression coefficient = 0.95). Further the Stern–Volmer con-tant was found to be 46.3 M−1. The lifetime of this C 4 dyes reported as 3.5 ns (calculated by theoretical method [10]).ence the value of Kq is found to be 13.23× 10−9 M−1 S−1.ince the collision of the fluorophore with the quencher occurs

n its excited state, the lifetime of the excited state is reducedoo. Hence fluorescence intensity is also decreased. It is also con-luded this quenching is of S0← S2 (or other higher transitions)ature.

. Conclusion

This may be concluded from above that the quenching is ofynamic nature and reversible. A novel sensor-based upon abovean be constructed very easily for its application for detection [

cta Part A 66 (2007) 111–113 113

f acetone in vapor or solution form. The quenching is due to0← S2 (or other higher transitions).

eferences

[1] S.A. Borman, Anal. Chem. 53 (1991) 1616.[2] C. Nylander, J. Phys. E 18 (1985) 736.[3] O.S. Wolfbesis, Z. Anal. Chem 325 (1985) 387.[4] J.F. Alder, Z. Anal. Chem. 324 (1986) 372.[5] V.K. Sharma, P.D. Sahare, A. Pandey, D. Mohan, Spectrochim. Acta A 59

(2003) 1035.[6] V.K. Sharma, P.D. Sahare, N. Sharma, R.C. Rastogi, S.K. Ghoshal, D.

Mohan, Spectrochim. Acta A 59 (2003) 1161.[7] S. Sanghi, et al., Asian J. Phys. 4 (1995) 283.[8] L. Taneja, et al., Opt. Commun. 111 (1994) 463.[9] N.G. Melhuish, J. Opt. Soc. Am. 52 (1962) 1250.10] D. Mohan, Thesis submitted to M.D. University, Rohtak, India, 1991.