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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.


Stokes shift vs temperature for C153 in: ClP (filled circles), ClH (empty circles), PPN (filled triangles), EtOH (empty triangles) and TFEtOH (filled squares)
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Fig7: Stokes shift vs temperature for C153 in: ClP (filled circles), ClH (empty circles), PPN (filled triangles), EtOH (empty triangles) and TFEtOH (filled squares)

Mentions: Above, μg and μe are C153 dipole moments in the ground and excited states, a is the Onsager radius of the probe molecule, αg and αe are the ground and excited state probe polarizabilities, J and JS are the probe and solvent ionization potentials and h and c have the usual meanings. These calculations were made assuming the same parameter values for C153 in the Franck-Condon and in the relaxed states, thus assuming the same dipole moment μg = 6.6 D [17] in and , μe = 9.7 D in and , and the same αg in both S0 states and αe in both S1 states [2]. EtOH ionization potential JS = 11.05 eV was determined using AM1 hamiltonian with the MOPAC suite, EtOH n(T) and ε(T) were determined from the data given in [9]. For the other C153 and solvents parameters see [1,2]. The shifts in absorption of C153 in all solvents were predicted at subsequent temperatures. The values of ∆vAbs were compared with experimental νp(T) in the following way: for a selected solvent the absorption spectrum peak value νp(293 K) was added to the absolute value of the shift ∆vAbs (293 K). In this way a pseudo “gas-phase” position of the spectrum was obtained. Next, from the absolute values of ∆vAbs(T) were subtracted at subsequent temperatures different from 293 K. The results of such a procedure are shown in Fig. 3 as solid lines. It led to the following values: 26,060 cm−1 (ClH), 26170 (ClP), 26120 (PPN), 25840 (EtOH) and 24920 (TFEtOH). As expected, values are not the same as they were determined assuming that all solvents interacted exclusively nonspecifically which is obviously incorrect. But, they indicate which solvents most probably interact specifically with C153 in the ground state and these solvents are EtOH and TFEtOH. It is especially important that in PPN fall into the same range as found for 1-chloroalkanes, and that the vp (T) dependence slope in PPN corresponds exactly to the ∆vAbs (T) dependence slope, see Fig. 3. Both these observations indicate that PPN interacts only nonspecifically with C153 in , or that the H-bond formed by PPN with C153 do not change in energy after C153 excitation to , contrary to what was deduced from the emissive results for C153 in the same solvent [2]. On the other hand, a comparison of values obtained in 1-chloroalkanes and PPN with those found in alcohols indicates that in EtOH a slight additional specific stabilisation take place already in , while in TFEtOH the specific interaction with C153 in is significantly higher in energy than in . No temperature dependence of this additional specific stabilisation is observed in EtOH, while in TFEtOH its energy increases with decreasing temperature. This last result is in contrast to that found for [2]. It means that the Stokes shift in this solvent should decrease with decreasing temperature and indeed it is observed. Figure 7 shows the temperature dependence of the experimental Stokes shifts, ∆vS, for C153 in all solvents.Fig. 7


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

Dobek K, Karolczak J - J Fluoresc (2012)

Stokes shift vs temperature for C153 in: ClP (filled circles), ClH (empty circles), PPN (filled triangles), EtOH (empty triangles) and TFEtOH (filled squares)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3473193&req=5

Fig7: Stokes shift vs temperature for C153 in: ClP (filled circles), ClH (empty circles), PPN (filled triangles), EtOH (empty triangles) and TFEtOH (filled squares)
Mentions: Above, μg and μe are C153 dipole moments in the ground and excited states, a is the Onsager radius of the probe molecule, αg and αe are the ground and excited state probe polarizabilities, J and JS are the probe and solvent ionization potentials and h and c have the usual meanings. These calculations were made assuming the same parameter values for C153 in the Franck-Condon and in the relaxed states, thus assuming the same dipole moment μg = 6.6 D [17] in and , μe = 9.7 D in and , and the same αg in both S0 states and αe in both S1 states [2]. EtOH ionization potential JS = 11.05 eV was determined using AM1 hamiltonian with the MOPAC suite, EtOH n(T) and ε(T) were determined from the data given in [9]. For the other C153 and solvents parameters see [1,2]. The shifts in absorption of C153 in all solvents were predicted at subsequent temperatures. The values of ∆vAbs were compared with experimental νp(T) in the following way: for a selected solvent the absorption spectrum peak value νp(293 K) was added to the absolute value of the shift ∆vAbs (293 K). In this way a pseudo “gas-phase” position of the spectrum was obtained. Next, from the absolute values of ∆vAbs(T) were subtracted at subsequent temperatures different from 293 K. The results of such a procedure are shown in Fig. 3 as solid lines. It led to the following values: 26,060 cm−1 (ClH), 26170 (ClP), 26120 (PPN), 25840 (EtOH) and 24920 (TFEtOH). As expected, values are not the same as they were determined assuming that all solvents interacted exclusively nonspecifically which is obviously incorrect. But, they indicate which solvents most probably interact specifically with C153 in the ground state and these solvents are EtOH and TFEtOH. It is especially important that in PPN fall into the same range as found for 1-chloroalkanes, and that the vp (T) dependence slope in PPN corresponds exactly to the ∆vAbs (T) dependence slope, see Fig. 3. Both these observations indicate that PPN interacts only nonspecifically with C153 in , or that the H-bond formed by PPN with C153 do not change in energy after C153 excitation to , contrary to what was deduced from the emissive results for C153 in the same solvent [2]. On the other hand, a comparison of values obtained in 1-chloroalkanes and PPN with those found in alcohols indicates that in EtOH a slight additional specific stabilisation take place already in , while in TFEtOH the specific interaction with C153 in is significantly higher in energy than in . No temperature dependence of this additional specific stabilisation is observed in EtOH, while in TFEtOH its energy increases with decreasing temperature. This last result is in contrast to that found for [2]. It means that the Stokes shift in this solvent should decrease with decreasing temperature and indeed it is observed. Figure 7 shows the temperature dependence of the experimental Stokes shifts, ∆vS, for C153 in all solvents.Fig. 7

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.