GLOBAL TRICOMPARTMENTAL ANALYSIS OF THE FLUORESCENCE DECAY SURFACE OF THE CHARGED FLUORESCENT-PROBE N,N,N-TRIMETHYL-3-(1-PYRENYL)-1-PROPANAMINIUM PERCHLORATE

Abstract

The kinetics of the excited-state processes of the charged fluorescent probe N,N,N-trimethyl-3-(1-pyrenyl)-1-propanaminium perchlorate (PROBE) in tetrahydrofuran are reported. At very low concentrations PROBE decays monoexponentially with a lifetime tau of 236 +/- 1 ns, from which k(01) = 1/tau = 4.2 x 10(6) s(-1) is obtained. Upon addition of the quaternary ammonium salt N,N,N-trimethyl-1-dodecanaminium perchlorate a biexponential decay function is needed to describe the decay traces. The second excited state is the aggregated PROBE. This aggregation is due to dipole-dipole or ion-dipole interactions. The rate constant values of the kinetic Scheme (Scheme 4) are obtained by global bicompartmental analysis: k(01) = k(02), k(21) = (42 +/- 7) x 10(9) M(-1) s(-1); k(12) = (5.7 +/- 0.1) x 10(7) s(-1). When the concentration of PROBE itself is varied, a triple-exponential decay function adequately describes the decay surface. The third excited-stale species is a PROBE excimer, which can be formed through two different pathways: either intermolecularly when a locally excited PROBE molecule encounters a ground-state PROBE molecule or intramolecularly when an aggregate of two PROBE molecules rearranges. To resolve the kinetics of this system, global tricompamnental analysis is developed. Even after including the information available from experiments where N,N,N-trimethyl-1-dodecanaminium perchlorate is added (k(01) = k(02)), and the information available from the global triple-exponential analysis (k(13) = 0 and k(23) = 0) (Scheme 5), the experimental time-resolved data do not allow one to obtain a unique solution for the rate constant values, By scanning the rate constant k31, bounds can be specified for the rate constants: 53 x 10(9) < k(21) < 60 x 10(9) M(-1) s(-1), k(31) < 7 x 10(9) M(-1) s(-1), 1.5 x 10(8) < k(12) < 1.7 x 10(8) s(-1) and k(32) < 2 X 10(7) s(-1). Unique values are obtained for k(01), k(02), and k(O3): k(01) = k(02) = (4.25 +/- 0.01) x 10(7) s(-1); k(03) = (1.92 +/- 0.03) x 10(7) s(-1).