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The influence of temperature on C153 steady-state absorption and fluorescence kinetics in hydrogen bonding solvents.

Dobek K, Karolczak J - J Fluoresc (2012)

Bottom Line: It leads to a modulation of the fluorescence transition dipole moment and it is the primary source of the experimental effects observed.Additionally, we have found that proticity of the solvent induces a rise in the fluorescence transition dipole moment, which leads to a shortening of the fluorescence lifetime.We show that while such bonds do not affect the transition probability, they do change the S(0) an S(1) energy gap which in turn implies a change in non-radiative transition rate in a similar way as in protic solvents, as well as in the fluorescence spectrum position.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Physics, Adam Mickiewicz University, Poznań, Poland. dobas@amu.edu.pl

ABSTRACT
In a recent paper (J Fluoresc (2011) 21:1547-1557) a temperature induced modulation of Coumarin 153 (C153) fluorescence lifetime and quantum yield for the probe dissolved in the polar, nonspecifically interacting 1-chloropropane was reported. This modulation was also observed in temperature dependencies of the radiative and nonradiative rates. Here, we show that the modulation is also observed in another 1-chloroalkane-1-chlorohexane, as well as in hydrogen bonding propionitrile, ethanol and trifluoroethanol. Change in the equilibrium distance between S (0) an S (1) potential energies surfaces was identified as the source of this modulation. This change is driven by temperature changes. It leads to a modulation of the fluorescence transition dipole moment and it is the primary source of the experimental effects observed. Additionally, we have found that proticity of the solvent induces a rise in the fluorescence transition dipole moment, which leads to a shortening of the fluorescence lifetime. Hydrogen bonds are formed by C153 also with hydrogen accepting solvents like propionitrile. We show that while such bonds do not affect the transition probability, they do change the S(0) an S(1) energy gap which in turn implies a change in non-radiative transition rate in a similar way as in protic solvents, as well as in the fluorescence spectrum position. Finally, the influence of temperature on the energies of hydrogen bonds formed by C153 when acting as hydrogen donor or acceptor is reported.

No MeSH data available.


Modulus squared of fluorescence (Me→g) transition dipole moments in ClH (filled circles), PPN (empty circles), EtOH (filled triangles) and TFEtOH (empty triangles)
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Fig9: Modulus squared of fluorescence (Me→g) transition dipole moments in ClH (filled circles), PPN (empty circles), EtOH (filled triangles) and TFEtOH (empty triangles)

Mentions: Non-radiative deactivation in C153 is known to be governed by internal conversion. According to our knowledge no ISC for this molecule has ever been observed. Relative knr values at the same temperatures in all solvents indicate that the energy-gap law partly controls non-radiative deactivation. The order in which knr values increase at a selected temperature corresponds well to the energy of emission in the solvents, thus to the emission position. However, the energy-gap law predicts an exponential decay of knr with temperature rising [19,20]. The temperature range in which measurements were made does not correspond to the tail of decaying knr(T) dependence, see Fig. 8 in [7]. In EtOH the non-exponentiality is evident in the low temperature range. However, in this solvent the retardation of the solvent relaxation is the source of the low-temperature knr(T) dependence, as the emission spectrum is not shifted totally to the red, which in turn leads to a drop in knr at the lowest T. In ClH and PPN knr(T) slope sign changes at higher temperatures. Similarly to what was observed for C153 in ClP [7], this effect is in conflict with the energy-gap law. Radiative rate kF(T) dependencies have also similar features in all solvents. Using them, the modulus squared emission transition dipole moments at subsequent temperatures were determined, as shown in Fig. 9. These values were found using the Birks equation [21]:2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left/ M \right/_{e \to g}^2 = \frac{{3h}}{{64{\pi^4}}}\frac{1}{{{n^3}}}{k_F}\widetilde{v}_F^{ - 3}, $$\end{document}3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \widetilde{v}_F^{ - 3} = \frac{{\int {I(v){v^{ - 3}}dv} }}{{\int {I(v)dv} }}. $$\end{document}Fig. 9


The influence of temperature on C153 steady-state absorption and fluorescence kinetics in hydrogen bonding solvents.

Dobek K, Karolczak J - J Fluoresc (2012)

Modulus squared of fluorescence (Me→g) transition dipole moments in ClH (filled circles), PPN (empty circles), EtOH (filled triangles) and TFEtOH (empty triangles)
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3473193&req=5

Fig9: Modulus squared of fluorescence (Me→g) transition dipole moments in ClH (filled circles), PPN (empty circles), EtOH (filled triangles) and TFEtOH (empty triangles)
Mentions: Non-radiative deactivation in C153 is known to be governed by internal conversion. According to our knowledge no ISC for this molecule has ever been observed. Relative knr values at the same temperatures in all solvents indicate that the energy-gap law partly controls non-radiative deactivation. The order in which knr values increase at a selected temperature corresponds well to the energy of emission in the solvents, thus to the emission position. However, the energy-gap law predicts an exponential decay of knr with temperature rising [19,20]. The temperature range in which measurements were made does not correspond to the tail of decaying knr(T) dependence, see Fig. 8 in [7]. In EtOH the non-exponentiality is evident in the low temperature range. However, in this solvent the retardation of the solvent relaxation is the source of the low-temperature knr(T) dependence, as the emission spectrum is not shifted totally to the red, which in turn leads to a drop in knr at the lowest T. In ClH and PPN knr(T) slope sign changes at higher temperatures. Similarly to what was observed for C153 in ClP [7], this effect is in conflict with the energy-gap law. Radiative rate kF(T) dependencies have also similar features in all solvents. Using them, the modulus squared emission transition dipole moments at subsequent temperatures were determined, as shown in Fig. 9. These values were found using the Birks equation [21]:2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left/ M \right/_{e \to g}^2 = \frac{{3h}}{{64{\pi^4}}}\frac{1}{{{n^3}}}{k_F}\widetilde{v}_F^{ - 3}, $$\end{document}3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \widetilde{v}_F^{ - 3} = \frac{{\int {I(v){v^{ - 3}}dv} }}{{\int {I(v)dv} }}. $$\end{document}Fig. 9

Bottom Line: It leads to a modulation of the fluorescence transition dipole moment and it is the primary source of the experimental effects observed.Additionally, we have found that proticity of the solvent induces a rise in the fluorescence transition dipole moment, which leads to a shortening of the fluorescence lifetime.We show that while such bonds do not affect the transition probability, they do change the S(0) an S(1) energy gap which in turn implies a change in non-radiative transition rate in a similar way as in protic solvents, as well as in the fluorescence spectrum position.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Physics, Adam Mickiewicz University, Poznań, Poland. dobas@amu.edu.pl

ABSTRACT
In a recent paper (J Fluoresc (2011) 21:1547-1557) a temperature induced modulation of Coumarin 153 (C153) fluorescence lifetime and quantum yield for the probe dissolved in the polar, nonspecifically interacting 1-chloropropane was reported. This modulation was also observed in temperature dependencies of the radiative and nonradiative rates. Here, we show that the modulation is also observed in another 1-chloroalkane-1-chlorohexane, as well as in hydrogen bonding propionitrile, ethanol and trifluoroethanol. Change in the equilibrium distance between S (0) an S (1) potential energies surfaces was identified as the source of this modulation. This change is driven by temperature changes. It leads to a modulation of the fluorescence transition dipole moment and it is the primary source of the experimental effects observed. Additionally, we have found that proticity of the solvent induces a rise in the fluorescence transition dipole moment, which leads to a shortening of the fluorescence lifetime. Hydrogen bonds are formed by C153 also with hydrogen accepting solvents like propionitrile. We show that while such bonds do not affect the transition probability, they do change the S(0) an S(1) energy gap which in turn implies a change in non-radiative transition rate in a similar way as in protic solvents, as well as in the fluorescence spectrum position. Finally, the influence of temperature on the energies of hydrogen bonds formed by C153 when acting as hydrogen donor or acceptor is reported.

No MeSH data available.