More about the inner filter effect: corrections of Stern-Volmer fluorescence quenching constants are necessary at very low optical absorption of the quencher

The steady-state fluorescence quenching of 2,6-bis(diethanolamino)-4,8-dipi peridin-pyrimido [5,4-d]pyrimidine (dipyridamole) by a stable nitroxyl radi cal 2,2,6,6-tetramethyl-piperidine-N-oxyl (TEMPO) was used to clear up the influence of the quencher light absorption on the values of the Stern-Volme r quenching constants (K-SV). We demonstrate the necessity of the K-SV corr ection by the quencher absorbance (A(q)) already at very low A(q) and rathe r high K-SV. Thus, for A(q) < 0.02 and K(SV)congruent to 50 M-1 the noncorr ected K-SV value appears about 50% higher than the real (corrected) one. Mo reover, the noncorrected K-SV values do depend on the excitation and emissi on wavelengths, while the corrected ones are independent of them. (C) 1999 Elsevier Science B.V. All rights reserved.