The fluorescence quenching of pyrene (Py) by a series of
N-methyl and N-H substituted indoles was studiedin isooctane at 298 K. The fluorescence quenching rate constants were evaluated by mean of steady-state andtime-resolved measurements. In all cases, the quenching process involves a charge-transfer (CT) mechanism.The
Io/
I and
o/
![](/images/gifchars/tau.gif)
Stern-Volmer plots obtained for the N-H indoles show a very unusual upward deviationwith increasing concentration of the quenchers. This behavior is attributed to the self-quenching of the CTintermediates by the free indoles in solution. The efficiency of quenching of the polyaromatic by the N-Hindoles increases abruptly in the presence of small amount of added pyridine (or propanol). A detailed analysisof the experimental data obtained in the presence of pyridine provides unambiguous evidence that the self-quenching process involves proton transfer from the CT states to indoles.