Global tricompartmental analysis of the fluorescence decay surface of the charged fluorescent probe N,N,N-trimethyl-3-(1-pyrenyl)-1-propanaminium prchlorate

Abstract

The kinetics of the excited-state processes of the charged fluorescent probe N,N,N-trimethyl-3-( l-pyreny1)-1 -propanaminium perchlorate (PROBE) in tetrahydrofuran are reported. At very low concentrations PROBE decays monoexponentially with a lifetime z of 236 f 1 ns, from which b 1 = l/z = 4.2 x lo6 s-l is obtained. Upon addition of the quaternary ammonium salt N,N,N-trimethyl-l -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: bl = b 2 , kzl = (42 f 7) x lo9 M-' s-l; k12 = (5.7 f 0.1) x lo7 s-l. When the concentration of PROBE itself is varied, a triple-exponential decay function adequately describes the decay surface. The third excited-state 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 tricompartmental analysis is developed.Even after including the information available from experiments where NJV,N-trimethyl-1 -dodecanaminium perchlorate is added (bl = b2), and the information available from the global triple-exponential analysis (k13 = 0 and k23 = 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 lo9 < k21 < 60 x lo9 M-' s-l, k31 < 7 x lo9 M-' s-l, 1.5 x lo8 < k12 < 1.7 x lo8 s-l, and k32 < 2 x lo7 s-'. Unique values are obtained for b l , b2, and b 3 : bl = b 2 = (4.25 f 0.01) x lo7 s-l; b3 = (1.92 f 0.03) x lo7 s-l.

Intramolecular Excited-State Processes of a Halato-Telechelic Polymer, Evaluated by Global Compartmental Analysis of the Fluorescence Decay Surface with the Use of Model Compounds

“…At this concentration, all processes are intramolecular and described by Scheme 2 with all rate constants being first-order. The goal is to estimate the values of the rate constants of Scheme 2, based on the results from the two model compounds PROBE 61 and POLYPROBE 62 and through global compartmental analysis.…”

“…63,64 The decays were collected at several wavelengths between 375 and 500 nm, all observed at the magic angle (54.7°), and contained 10 000 (longer time/channel) or 5000 (shorter time/channel) peak counts. The details about the measurements on PROBE 61 and POLYPROBE 62 are given elsewhere. For POLYDIPROBE, the decays were collected in 512 channels of the multichannel analyzer at four different emission wavelengths, 375, 395, 480, and 500 nm, and with two different time increments, 408 ps/ channel and 1.185 ns/channel.…”

“…The theory of global compartmental analysis of fluorescence decay surfaces is thoroughly described, [43][44][45][46][47][48][49][50][51][52]61,62 and only the fundamental aspects of tricompartmental systems will briefly be summarized. The special case of an intramolecular tricompartmental system will be discussed in detail.…”

“…Plots of the measured decay times as a function of [M] will give the rate constant k 03 , as this rate constant equals the inverse of the concentrationindependent decay time. The variation of the two remaining decay rates can, for an intermolecular system, be used for the determination of the remaining rate constants if the decays are collected at different concentrations of M. 49,61 3.3. Special Case: Intramolecular Tricompartmental System without Added Quencher.…”

“…For the case of intermolecular tricompartmental systems, an identifiability study has been performed, 61 which we will use as the starting point for the identifiability study of an intramolecular system. For an intramolecular system as depicted in Scheme 3, the basic equations, similar to an intermolecular system, are with S 1 , S 2 , and P given by eqs 10.…”