2012‫العدد الثالث‬........‫مجلة كلية التربية‬
Effect of Solvent Polarity on Quantum Yield of
( 1-Naphtylamine) Molecule
Assis. prof. Dr. S. J. AL–Obaidi
Dr. Waleed S. Abdul Wahab
Yaqoob M. Jawad
AL-Mustansiriyah University, College of Sciences, Department of
Physics.
2011/9 /27 : ‫تقديــــــــم البحث‬
2011/12/19 : ‫قبول نشر البحث‬
Abstract
The absorption and fluorescence spectra for 1-Naphthylamine compound
which dissolved in some polar and non-polar solvent had been measured and
investigated. Also the quantum yield was calculated and it decreased with the
increased of solvent polarity. On the other hand, in polar solvents the
fluorescence spectra was shifted toward the long wavelength ( red shift ) and
decreased in intensity, as well as in the value of quantum yield. Diluted solution
was used to eliminate the effect of self-absorption phenomena. In addition, the
quantum yield measurement was calculated relative to standard compound of
Anthracene with ( qfm = 0.27 ) when excited wavelength
at room temperature.
53
( λex= 313 nm )
‫مجلة كلية التربية‪........‬العدد الثالث‪2012‬‬
‫تأثير قطبية المذيب على الكفاءة الكمية لجزيئة )‪ -1‬نفثايل أمين(‬
‫أ‪.‬م‪.‬د‪ .‬صبري جاسم العبيدي‬
‫د‪ .‬وليد صالح عبد الوھاب‬
‫يعقوب محمد جواد‪.‬‬
‫الجامعة المستنصرية ‪ ،‬كلية العلوم ‪ ،‬قسم الفيزياء‪.‬‬
‫الخالصة‬
‫تم قياس و دراسة أطياف االمتصاص و الفلورة لمركب )‪ -1‬نفثايل أمين ( المذاب في عدد من‬
‫المذيبات القطبية وغير القطبية‪ .‬كما احتسبت قيمة الكفاءة الكمية و وجد أنھا تقل عند زيادة قطبية المذيب‪.‬‬
‫لكن في المذيبات القطبية وجد أن ھناك إزاحة لقمة طيف الفلورة باتجاه الطول الموجي الطويل ) إزاحة‬
‫حمراء ( و االنخفاض في شدته وحينئذ النقصان في قيمة الناتج الكمي‪ .‬استخدمنا تركيزاً مخففا ً لغرض‬
‫التقليل من ظاھرة االمتصاص الذاتي‪ .‬احتسبت قيمة الكفاءة الكمية بالنسبة إلى مركب األنثراسين المذاب‬
‫باأليثانول بكفاءة مقدارھا )‪ (qfm = 0.27‬على أنه مركب قياسي عند الطول الموجي المھيج ) =‪( λex‬‬
‫‪ 313 nm‬بدرجة حرارة الغرفة ‪.‬‬
‫‪1. Introduction‬‬
‫‪In previous studies for the solvent polarity such as in 1995, Carlos M.‬‬
‫‪previtali,[1] investigated the solvent effects on the rate constant and activation‬‬
‫‪parameters of several intermolecular electron transfer reactions. In 2007,‬‬
‫‪Debabrata Seth, et.al.[2] study the solvent and rotational relaxation. In 2007,‬‬
‫‪H.K. Park, et.al.[3], as well as in 2008, M.A. Haidekker, et al [4], study the effects‬‬
‫‪of solvent polarity and solvent viscosity on the fluorescence properties of‬‬
‫‪molecular rotors and related probes.‬‬
‫‪The effects of solvent polarity are one origin of the Stokes shift, which is‬‬
‫‪from‬‬
‫‪fluorescence. Emission‬‬
‫‪in‬‬
‫‪observations‬‬
‫‪earliest‬‬
‫‪the‬‬
‫‪of‬‬
‫‪one‬‬
‫‪fluorescence generally occurs at wavelengths that are longer than those at‬‬
‫‪54‬‬
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
which absorption occurs. This loss of energy is due to a variety of dynamic
processes that occur following light absorption as shown in Fig.(1) below: [5]
Typically, the fluorescence has a larger dipole moment in the excited
state µ E than in the ground state µ G. Following excitation, the solvent dipoles
can reorient or relax around µ E, which lower the energy of the excited state. As
the solvent polarity is increased, this effect becomes larger, lead to emission
at lower energies or longer wavelengths. In general, only fluorescences that are
themselves polar display a large sensitivity to solvent polarity.
molecules,
such
as
unsubstituted
Non polar
aromatic hydrocarbons are much less
sensitive to solvent polarity.[6]
Fig (1):Jablonski diagram for fluorescence with solvent relaxation.[6]
Most polarity probes undergo intermolecular charge transfer upon excitation
so that µ E > µ G . Therefore, following excitation, the solvent cage undergoes a
relaxation, i.e. a reorganization, leading to a relaxed state of minimum free
energy as illustrated previously in figure (1). The higher polarity of the solvent
lowers the energy of the relaxed state and increases the red-shift of the emission
spectrum. [5]
55
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
The interactions responsible for general solvent effects are best understood
by derivation of the Lippert equation. This equation can be written as follows:
….(1)
where (∆ ) is the frequency shift (in cm–1) between absorption and emission,
(a) is the cavity radius, and (µE) and (µG) are the excited and ground state
dipole moments, respectively.
The (∆f ) is called orientation polarizability, one can find this parameter as in
the following equation (2). [7]
………….(2)
Where :( ) is the dielectric constant, n is the refractive index.
The quantum yield can be defined as the ratio of the number of fluorescence
photons emitted by a system of molecules in dilute solution to the number of
molecules in excited state (the number of absorbed photons), from next equation
one can observe the effect of polarity on the quantum yield. [8]
Φ FM =
K FM
K FM
+ K IM + K DM
.......... . (3)
where: KFM: the rate parameters of radiative emission (in Sec-1). KIM: the rate
parameters of non-radiative (in Sec-1).
KDM : represented any rate
(in Sec-1).
parameters effect on quantum yield
The quantum yield can be calculated from this equation:[9]
ΦFx = ΦFr (
(
)(
(
………. (4)
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2012‫العدد الثالث‬........‫مجلة كلية التربية‬
where: nr ,nx : is the refractive index for standard and unknown compound
respectively.
ΦFx, ΦFr : is the quantum yield of unknown and stander compound, respectively.
Ar, Ax : is the absorbance of standerd and unknown compound, respectively.
I(λx),I(λr): is the wavelength excitation of unknown and stander compound,
respectively.
Dx, Dr: is the area under the curve of fluorescence spectrum of unknown and
stander compound, respectively.
2. Experimental section
Materials
The 1-Naphthylamine dissolved in (hexane, diethyl ether, ethanol, methanol
and water) prepared at concentration
[1x10-5]M. (1NA) purchased from Uma
Company imported from India.
a) Absorption measurement: Absorption spectrum was measured by a (UVVis spectrophotometer SP-3000 plus) the model of this device is (January 2003
(3 edition) ) and made by OPTIMA INC.
b) Fluorescence measurement: Fluorescence spectra was recorded on a
(JASCO- model-FP-770) spectrofluorometer, samples were mounted in cubic
cell of quartz dimensions (1×1×5) cm3 at right angle (90˚) with incident beam.
This optical geometry was chosen to eliminate the effect of scattered incident
radiation and reduce the phenomenon of self-absorption. The fluorometry
dedicated computer which control instrumental operating (excitation and
emission wavelength, scan, monochromator slit width, detector parameter) and
the acquisition of spectral data.
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2012‫العدد الثالث‬........‫مجلة كلية التربية‬
In this research, exciting wavelength (λex= 313nm) is used in the
measurements and used slit width of excitation (Sex=1.5 nm) and slit width of
emission (Sem= 3 nm) were used. The measurements were made in the same
sensitivity of photomultiplier. The anthracene was used as a standard compound
dissolved in ethanol with concentration [10-4]M and quantum efficiency equal to
(qFM = 0.27) and all measurements were at room temperature.
3.Results and Discussions: In this paper, fluorescence spectra of anthracene
solution is used as a standard compound dissolved in ethanol with concentration
[1x10-4 M]. Thus, the solutions of (1NA) are studied as shown in figure (2), with
concentration [1x10-5]M (this concentration is used to reduce the self-absorption
phenomena) and the effect of polarity on the fluorescence spectrum as well as
calculation of quantum yield and other molecular parameters are observed.
Anthracene
1-Naphthylamine
C14H10
C10H9N
Figure (2): Chemical formula of compounds
Figure (3) shows the fluorescence spectrum of standard compound, the
fluorescence spectrum of anthracene which dissolved in ethanol at concentration
[1x10-4] M at exciting wavelength (λex= 313nm), where it appears in the shape
of spectrum structure, which consists of four peaks located at wavelength (378.5
nm), (398.3 nm), (422.5 nm) and
(450.1 nm).
58
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
Fig.(3): the fluorescence and absorption spectra to
Anthracene dissolved in ethanol [1x10-4 M].
Figure (4) shows the fluorescence spectrum of
1-
naphthylamine solutions in (hexane, diethyl ether, ethanol, methanol and water)
at concentrations [1x10-5]M and exciting wavelength (λex= 313 nm) structureless with peak located at wavelength (λmax=378 nm) in hexane, (λmax=400 nm) in
diethyl ether, (λmax= 426 nm) in ethanol , (λmax= 428 nm) in methanol and (λmax=
448 nm) in water.
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‫مجلة كلية التربية‪........‬العدد الثالث‪2012‬‬
‫‪60‬‬
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
Figure (4): absorption and fluorescence spectra of 1-naphthylamine
solutions in (a)hexane (b)diethyl ether (c)ethanol (d)methanol(e)water
at concentration [1x10-5] M.
From figure (4) above one can observe the solvent polarity increases, but
the fluorescence intensity decreases because molecule absorbed the light and
transitions to the excited electronic state , the molecule electronic configuration
is changed and hence the change in the dipole moment for molecule.
The quantum yield is calculated. It decreased when the solvent polarity
increased because of the charge transfer phenomena. In the excited state, the low
of the energy appears as red shift of fluorescence spectrum as shown in figure
(5) in the following page. The intermolecular charge transfer (ICT) phenomena
that occurs, when an electron is transferred from the amine group to the aromatic
ring upon light absorption, producing an (ICT) excited state.[10] Hence the
dipole moment value is increased because the relaxation process to solvent
molecules in the excited state is large in comparison with the ground state
causing the polarization force was increased for solvent molecule.[11]
61
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
Fig.(5): fluorescence spectra of 1-naphthylaminesolution in (hexane, diethyl
ether, ethanol, methanol and water) at concentration [1x10-5 M].
From this figure, one can observe that, when the polarity was increased the
fluorescence spectrum shiftted to a long wavelength. This shift value is
dependent on the dielectric constant (ε) value of solvent and on the difference
between dipole moment values of solvent.[12]
A change in the excited state location leads to the change in the life time and
hence the results are a decrease in the rate parameters of radiative emission KFM
value.
So the decrease in the rate parameters of radiative emission leads to decrease
the quantum yield value with the more increasing of solvent polarity, as shown
in table (1) in the following page. Thus any increase in dielectric constant value,
leads to the decrease in the quantum yield as shown in
62
figure (6) below.
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
Fig.(6):show the relation between quantum yield value and dielectric constant
to 1-Naphthylamine molecule dissolved in many different solutions at
concentration [1x10-5 M]
Table (1): the quantum yield Фfm , stokes shift and orientation Polarizability
(∆f ), dielectric constant(ε), refractive index(n)
Solvents Quantum stokes orientation
yield Фfm
shift
dielectric
refractive
polarizability constant(ε) index(n)
(nm)
(∆f )
hexane
0.33
44
0.00079
1.89
1.3727
Diethyl
0.30
69
0.2049
4.2666
1.3526
0.28
98
0.2897
25.3
1.3611
methanol 0.26
101
0.3091
33.62
1.3288
0.23
124
0.3243
80.10
1.33
ether
ethanol
water
63
2012‫العدد الثالث‬........‫مجلة كلية التربية‬
4. Conclusions:
Throughout the study of 1-Naphthylyamine (1NA) dissolved in ( hexane,
diethyl ether, ethanol, methanol and water ) with a concentration [1x10-5] M the
following conclusions are reached to :
1. The quantum yield was decreased with the increasing of solvent polarity.
2. The quantum yield was decreased with the increasing of dielectric constant
value (ε).
3. The red shift of fluorescence was increased with the increasing of solvent
polarity.
5. References:
1-
C. M. Previtali, " Solvent effects on intermolecular electron transfer
processes", Appl. Chem., , Vol. 67, p.p. 127-134, (1995).
2- D. Seth, Palash Setua, Anjan Chakraborty and Nilmoni Sarkar, "Solvent
relaxation of a room-temperature ionic liquid [bmim] [PF6] confined in a
ternary microemulsion", Journal of Chemical Sciences, Vol. 119, p.p. 105-111,
(2007).
3- K.H. Park, J.W. Park and A.D. Hamilton, "Solvent and pH effects on
fluorescence of 7-(Dimethylamino)-2-fluorenesulfonate", J. Fluoresc, Vol. 17,
p.p. 361-369, (2007).
4- M.A. Haidekker and T.P. Brady, "Effect of solvent polarity and solvent
viscosity on the fluorescence properties of molecular rotors and related probes",
Bioorganic Chemistry, Vol. 33, p.p. 415-425, (2005).
5- B. Valeur, "Molecular fluorescence: principles and applications", Wiley-VcH
Verlag GmbH, (2001).
6- J.R. Lakowics, "principles of fluorescence spectroscopy", Springer science
and Business media LLC, 3rd edition (2002).
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2012‫العدد الثالث‬........‫مجلة كلية التربية‬
7- A. S. R. Koti and N. Periasamy, "Solvent Exchange in Excited-State
Relaxation in Mixed Solvents", Journal of Fluorescence, Vol.10, p.p. 177-184,
(2000).
8- T.S. Peter, "Fluorescence spectro photometry", Macmillan Publishers Ltd,
Nature Publishing group,(2002).
9- J.N. Demas and G.A. Crosby, "The measurement of photoluminescence
quantum yields", J. Phys. Chem., Vol.75, PP(991-1031), (1971).
10- P. L. Muińo and P. R. Callis," Solvent Effects on the Fluorescence
Quenching of Tryptophan by Amides via Electron Transfer. Experimental and
Computational Studies", J. Phys. Chem., (2008).
11- Y. Huang, T. Cheng, Fuyou Li, Chuping Luo, and Chun-Hui Huang, "
Photophysical Studies on the Mono- and Dichromophoric Hemicyanine Dyes II.
Solvent Effects and Dynamic Fluorescence Spectra Study in Chloroform and in
LB Films ", J. Phys. Chem., Vol. 106, p.p.10031-10040, (2002).
12- J. Petit, M. Denis-Gay and Marie-Hélène Ratinaud, " Assessment of
fluorochromes for cellular structure and function studies by flow cytometry
", Biol Cell, Vol. 78, p.p.1-13, (1993) .
65