^{1}

^{*}

^{1}

A study is made on the previously ignored problem of the dependence of a static fluorescence quenching Stern-Volmer constant <i>K</i><sub>sv</sub> on the initial concentration of [F]<sub>0</sub> fluorophore F. This correlation is shown to exist. It is concluded that the Stern-Volmer quenching constant may be used as association constant <i>K</i> only with .

Determination of the association constants K is one of the most common tasks of physical chemistry, biochemistry, chemistry, etc. The constant K in equation (1) is taken as the association constant

In (1) and (2), F and Q are the complexing reagents; FQ is the complex of reagents;

initial concentrations of F and Q according to preparation.

From equation (2) it easily follows [

where

One of the numerous methods to determine the value of K is the fluorescence one [

The essence of this approach is that the fluorescence quenching constant

In (3), I_{0} and I are the fluorescence intensities of the fluorophore F in the absence and in the presence of quencher Q. The resulting constant

However, in the case of static quenching, the constant

The present work is devoted to the extent of correction to the experimental Stern-Volmer constant

Consider now luminescence quenching in the presence of complex formation under stationary excitation. The following scheme holds for this case:

In (7)-(9), _{ex} is the intensity of exciting illumination, k_{1} and k_{2} are the radiative and non-radiative constants of the excited electronic states of fluorophore F^{*}, respectively, and the K value is the same as that in (1). From (7)-(9), we get

Thus, in general, from (10) the fluorescence intensity I is of the form

However, for a particular case of

In fluorescence quenching the

Taking into account that

we get either

or

For the small values of р, we have

To determine the Stern-Volmer constants,

on

Comparing (18) with (6) indicates that in the case of complex formation, the Stern-Volmer quenching constant

Thus,

constant. This correction to unity in the denominator of Equation (19), equal to

accepted equating of the experimental quenching constant

valid only if

The value of K can be estimated from the dependence of

The

It is concluded then that introducing the above correction may be a key moment in obtaining the true values of

the association constants. The relation

quantum yield. In this case, the high concentrations of

necessitates the introduction of a corrective factor which is also obligatory for the case of large complexing constants.