Solvent effects on the solvatochromism of 7-aminocoumarins in neat and binary solvent mixtures:...
1
Solvent effects on the solvatochromism of 7- aminocoumarins in neat and binary solvent mixtures: Correlation between the electronic transition energies and the solvent polarity parameters Jin-Young Choi, T. J. Kang Department of Chemistry, Daegu University Gyoung san, 712-714 Korea The change in the electronic absorption and emission energies of 7-aminocoumarin derivatives in binary solvent mixtures has been studied. The electronic transition energy along with the Stokes’ shift is correlated with the orientation polarizability of the solvent as well as the empirical solvent polarity parameters E T (30). It is observed that the emission peak shift traces polarity change very nicely in the binary solvent mixtures. The emission transition is more strongly depend on the solvent polarity than the absorption. From the dependence of the Sokes’shift of 7-aminocoumarins with the solvent polarity parameters and the ground state dipole moment obtained by the semi-empirical AM1 calculations, the excited state dipole moment was estimated. The fluorescence lifetime change of 7-aminocoumarins in binary solvent mixtures was measured and the results are explained in terms of molecular conformation and solvent polarity. The study indicates the empirical solvent polarity E T (30) is a good measure of microscopic solvent polarity and it probes in general the non-specific solvent interactions. Abstract Introduction Theorical background Results and discussion Conclusions 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 (a) E T N 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 (b ) E T N 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 (c) E T N X m o re p o lar so lven t 0.0 0.2 0.4 0.6 0.8 1.0 18 19 20 21 22 23 (d ) v f (× 10 3 cm -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 18 19 20 21 22 23 (e) v f (×1 0 3 cm -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 18 19 20 21 22 23 (f) X m o re p o lar so lven t v f (× 10 3 cm -1 ) Solvation is important for understanding the solvent effects on chemical and biochemical processes. Biological systems in which various physiological processes such as transportation, signaling, metabolism are controlled by solvation. Changes in local polarity by solute-solvent interactions in biological systems are related to malfunction or disease. A variety of solvent polarity parameters proposed. But, there is no such thing as a single polarity parameter in explaining a multitude of solvent effects. Structure of 7-aminocoumarin dyes Effect of general solvent polarity Solvent Polarity Parameters O O N CH 3 C oum arin 102 O O (C 2 H 5 ) 2 N CF 3 C oum arin 481 Solvatochromism and the estimation of the dipole moment 350 400 450 500 550 600 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 R ed sh ift (b ) (a) W a ter m ole fraction R ed sh ift N o rm a lize d a b so rp tio n a n d flu o re sce n ce sp e ctra in te n sity W avelen g th (n m ) 0.971 0.959 0.934 0.904 0.826 0.703 0.145 0.195 0.000 (a) Absorption and (b) fluorescence Spectra of coumarin 102 were measured in dioxane/ water binary solvent system. Comparison of emission peak shifts with the change of E T N Fig(a)~(c), The empirical solvent polarity parameter plotted as a function of X , the mole fraction of the more polar component of binary solvent mixtures.(d)-(f)the wavenumbers of the emission peaks for coumarin 102 dissolved in three binary solvent mixtures plotted as a function of mole fraction of more polar solvent. The microscopic solvent polarity is probed very nicely by an empirical polarity measure of E T N . (a) and (d) : benzene/acetonitrile mixture, (b) and (e) : benzene/methanol Correlation of Stokes’shift with Δf(ε,n) and E T N 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.0 1.0 2.0 3.0 4.0 5.0 6.0 (2) R =0.95347 E T N v a - v f (×10 3 cm -1 ) 0.0 0.1 0.2 0.3 0.0 1.0 2.0 3.0 4.0 5.0 6.0 (1) R =0.90113 v a - v f (× 10 3 cm -1 ) Δf(ε,n ) Fig(1) (R=0.95347)seems to give better correlation Than Fig(2) (R=0.9011). The plot of the Stokes’ shift of coumarin 102 in benzene-methanol binary solvent as a function of E T N is compare to the plot of the Stokes’shift as a function of the Δf(ε,n). Compounds m 1 (cm - 1 ) m 2 (cm - 1 ) m 0 (cm - 1 ) a * (Cavity Radius, Å) Δμ (D) μ g ** (D) μ e / μ g μ e (D) f(ε ,n) C102 165 6 480 2 6.3 8 2.0 5 13.1 0 C481 192 4 516 9 6.2 4 2.1 9 13.6 4 E T N C102 2249 3.98 2.0 6 8.44 C481 4.00 2.2 2 8.46 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.0 2.0 4.0 6.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 2.0 4.0 6.0 f 1 + 3(n 4 -1)/(n 2 +2) 2 v a + v f (× 10 4 cm -1 ) v a - v f (× 10 3 cm -1 ) f 1 0.0 0.2 0.4 0.6 0.8 0.0 2.0 4.0 6.0 v a - v f (×10 3 cm -1 ) E T N Estimation of the excited dipole moment Solvent polarity and fluorescence lifetime change C E a a N T B B f a 3 2 ) ( ) ( 11308 μ μ *Calculated from the molecular volume assuming a spherical shape **Semi- empirical AM1 Calculation The shape of the cavity in 7-amonocoumarin dyes is not spherical but is very much elliptical. Thus whenever the cavity radius is required for calculations, it should be taken very carefully. 1. The solvent effect on the solvatochromism is correlated to the empirical polarity parameter E T N better than the bulk solvent parameter function. The E T N value measures microscopic solvent polarity and it seems to probe more or less non-specific solvent interactions. 2. The dipole moment 7-aminocoumarins increases by almost twice upon excitation. The cavity shape is assumed to be very much elliptical and the cavity radius is predicted to be much larger than the generally considered value for these 7-aminocoumarins. 3. Preferential solvation is taking place in binary solvent mixture since the change of peak shift seems to reflect the change of E T N very closely. 4. The lifetime of coumarin 102 gradually increases with increasing solvent polarity, but the fluorescence lifetime of coumarin 481 rapidly decreases as the solvent polarity increases. This is attributed to the nonradiative decay ① Δf(ε,n) : Orientation polarizability 1 2 1 1 2 1 ) , ( 2 2 n n n f A T N c h E ) 30 ( TMS T Water T TMS T solvent T N T E E E E E ) 30 ( ) 30 ( ) 30 ( ) 30 ( ② E T (30) : Empirical solvent polarity ● The E T (30) measures solvent polarity with the charge transfer absorption maxima of propidium phenol betaine known as Reichardt dye . ③ Other empirical polarity parameters ● Z value : Kosower ● Y-scale and π* ② Bakhshiev, Kawski C n f m f a ) , ( 1 1 C n f n f m f a )] ( 2 ) , ( [ 2 1 2 ③ Ravi et al olvatochromic shift of 7-aminocoumarin dye 0.0 0.1 0.2 0.3 0.0 0.2 0.4 0.6 0.8 * * * * * E T N Δf(ε,n) Correlation between E T N and Δf(ε,n) E T N was measured for 14 aprotic solvents and 5 protic solvents, and plotted versus Δf(ε,n). It is noted that there is a linear correlation between E T N and Δf(ε,n) for aprotic solvents, but large deviation is observed for protic solvents. They show batochromic shift as solvent polarity increases. 0 5 10 15 20 25 30 35 100 1000 10000 In creasin g p o larity M ethanol m o le fra ctio n 0 .939 0 .917 0 .898 0 .869 0 .815 0 .688 0 .525 0 .356 0 .000 laser pulse 400nm In ten sity(C o u nts) T im e(n s) 0.0 0.2 0.4 0.6 0.8 1.0 0 1 2 3 4 5 6 F lu o rescen ce L ifetim e(n s) E T N C 102 C 481 Plotting fluorescence lifetime against solvent polarity indicates characteristic curvilinear change for different coumarin fluorophores. C n f hca g e f a ) , ( 4 ) ( 2 3 0 0 2 ① Lippert, Mataga
Solvent effects on the solvatochromism of 7-aminocoumarins in neat and binary solvent mixtures: Correlation between the electronic transition energies
Solvent effects on the solvatochromism of 7-aminocoumarins in
neat and binary solvent mixtures: Correlation between the
electronic transition energies and the solvent polarity parameters
Jin-Young Choi, T. J. Kang Department of Chemistry, Daegu
University Gyoung san, 712-714 Korea The change in the electronic
absorption and emission energies of 7-aminocoumarin derivatives in
binary solvent mixtures has been studied. The electronic transition
energy along with the Stokes shift is correlated with the
orientation polarizability of the solvent as well as the empirical
solvent polarity parameters E T (30). It is observed that the
emission peak shift traces polarity change very nicely in the
binary solvent mixtures. The emission transition is more strongly
depend on the solvent polarity than the absorption. From the
dependence of the Sokesshift of 7-aminocoumarins with the solvent
polarity parameters and the ground state dipole moment obtained by
the semi-empirical AM1 calculations, the excited state dipole
moment was estimated. The fluorescence lifetime change of
7-aminocoumarins in binary solvent mixtures was measured and the
results are explained in terms of molecular conformation and
solvent polarity. The study indicates the empirical solvent
polarity E T (30) is a good measure of microscopic solvent polarity
and it probes in general the non-specific solvent interactions.
AbstractIntroductionTheorical backgroundResults and
discussionConclusions Solvation is important for understanding the
solvent effects on chemical and biochemical processes. Biological
systems in which various physiological processes such as
transportation, signaling, metabolism are controlled by solvation.
Changes in local polarity by solute-solvent interactions in
biological systems are related to malfunction or disease. A variety
of solvent polarity parameters proposed. But, there is no such
thing as a single polarity parameter in explaining a multitude of
solvent effects. Structure of 7-aminocoumarin dyes Effect of
general solvent polarity Solvent Polarity Parameters
Solvatochromism and the estimation of the dipole moment ( a)
Absorption and (b) fluorescence Spectra of coumarin 102 were
measured in dioxane/ water binary solvent system. Comparison of
emission peak shifts with the change of E T N Fig(a)~(c), The
empirical solvent polarity parameter plotted as a function of X,
the mole fraction of the more polar component of binary solvent
mixtures.(d)-(f)the wavenumbers of the emission peaks for coumarin
102 dissolved in three binary solvent mixtures plotted as a
function of mole fraction of more polar solvent. The microscopic
solvent polarity is probed very nicely by an empirical polarity
measure of E T N. (a) and (d) : benzene/acetonitrile mixture, (b)
and (e) : benzene/methanol mixture, (c) and (f) : dioxane/water
Correlation of Stokesshift with f(,n) and E T N f(,n)
Fig(1)(R=0.95347)seems to give better correlation Than
Fig(2)(R=0.9011). The plot of the Stokes shift of coumarin 102 in
benzene-methanol binary solvent as a function of E T N is compare
to the plot of the Stokesshift as a function of the f(,n).
Compounds m 1 (cm -1 ) m 2 (cm -1 ) m 0 (cm -1 ) a * (Cavity
Radius, ) (D) g ** (D) e / g e (D) f(,n) C102165648026.382.0513.10
C481192451696.242.1913.64 ETNETN C10222493.982.068.44
C48125524.002.228.46 Estimation of the excited dipole moment
Solvent polarity and fluorescence lifetime change *Calculated from
the molecular volume assuming a spherical shape **Semi-empirical
AM1 Calculation The shape of the cavity in 7-amonocoumarin dyes is
not spherical but is very much elliptical. Thus whenever the cavity
radius is required for calculations, it should be taken very
carefully. 1.The solvent effect on the solvatochromism is
correlated to the empirical polarity parameter E T N better than
the bulk solvent parameter function. The E T N value measures
microscopic solvent polarity and it seems to probe more or less
non-specific solvent interactions. 2.The dipole moment
7-aminocoumarins increases by almost twice upon excitation. The
cavity shape is assumed to be very much elliptical and the cavity
radius is predicted to be much larger than the generally considered
value for these 7-aminocoumarins. 3.Preferential solvation is
taking place in binary solvent mixture since the change of peak
shift seems to reflect the change of E T N very closely. 4.The
lifetime of coumarin 102 gradually increases with increasing
solvent polarity, but the fluorescence lifetime of coumarin 481
rapidly decreases as the solvent polarity increases. This is
attributed to the nonradiative decay process which involves the
formation of twisted intramolecular charge transfer state. f(,n) :
Orientation polarizability E T (30) : Empirical solvent polarity
The E T (30) measures solvent polarity with the charge transfer
absorption maxima of propidium phenol betaine known as Reichardt
dye. Other empirical polarity parameters Z value : Kosower Y-scale
and * Bakhshiev, Kawski Ravi et al Solvatochromic shift of
7-aminocoumarin dye f(,n) Correlation between E T N and f(,n) E T N
was measured for 14 aprotic solvents and 5 protic solvents, and
plotted versus f(,n). It is noted that there is a linear
correlation between E T N and f(,n) for aprotic solvents, but large
deviation is observed for protic solvents. They show batochromic
shift as solvent polarity increases. Plotting fluorescence lifetime
against solvent polarity indicates characteristic curvilinear
change for different coumarin fluorophores. Lippert, Mataga
