Time-resolved monomer and excimer fluorescence of 1,3-di(1-pyrenyl)propane at different temperatures: no evidence for distributions from picosecond laser experiments with nanosecond time resolution

Abstract

Monomer and excimer fluorescence decays of 1,3-di( 1 -pyrenyl)propane (!Py(3)lPy) in «-heptane are measured at different temperatures by using time-correlated single-photon counting (SPC). The decays at 61 °C are triple-exponential with decay times and amplitudes independent of the number of total counts, excitation wavelength, and width of the excitation pulse. At -43 °C and lower temperatures, single-exponential monomer decays are obtained, next to triple-exponential excimer records. Aggregates of lPy(3)lPy are not detected. These results can be described by the three-state model, DMD, comprising one group of rapidly interconverting excited-state monomers (M*) and two excimers (D*). No evidence for distributed decay times is found down to a time resolution of 0.1 ns/channel and 2000 channels. In support of the DMD model, molecular mechanics calculations backed by *H NMR measurements are presented, showing that only two monomer conformen of lPy(3)lPy are populated in the ground state. The interconversion between these two monomers in the excited state is too fast to be resolved by the present SPC measurements.

Intramolecular Excimer Formation Dynamics of 1,3-Bis-(1-pyrenyl)propane within 1-Butyl-3-methylimidazolium Hexafluorophosphate and Its Polyethylene Glycol Mixtures

“…It has been argued in the literature that in organic solvents close to ambient and higher temperatures 1Py(3)1Py excited-state intensity decays do not comply to a double-exponential decay model. 45 The Thistlethwaite group reported that in common organic solvents, 1Py(3)1Py time profiles of emission intensities did not fit to a double-exponential model (the Birk's scheme, Scheme 2) under ambient conditions. 50 While the monomer decay could be analyzed as a sum of two exponentials, the excimer decay did not take the form of a difference between two exponentials.…”

“…While it is observed for 1,5-bis(1-pyrenylcarboxy)pentane in alkane solvents and toluene under ambient conditions, 53 for 1Py(3)1Py it is only reported at and below −43°C in heptane. 45 It is clear that a solubilizing medium constituted of PEG hinders the dissociation of intramolecular excimer formed by 1Py (3) 6 ] in the temperature range 10−90°C and PEG200, PEG400, PEG600, and in PEG1000 in the range 60−90°C were fitted to two-and three-exponential functions (extracted parameters and the corresponding best fit exponential function are reported in Tables 1 and S1). Careful examination of the data reveals that for all PEG systems in the range 60−90°C, the [I M (t)] decay better fits to a double-exponential decay model, and the fits to the triple-exponential model do not result in any meaningful improvement in reduced χ 2 values and/or other parameters.…”

Monitoring pH-dependent conformational changes in aqueous solutions of poly(methacrylic acid)-b-polydimethylsiloxane copolymer based on fluorescence spectra of pyrene and 1,3-bis(1-pyrenyl)propane

“…Another useful probe is 1,3-bis(1-pyrenyl)propane (P3P) containing two pyrenyl moieties, which can form an intramolecular excimer as a result of conformational changes that bring the excited and non-excited chromophores together. This process is expected to be more efficient in a more fluid environment; for this reason the intensity ratio of the excimer to monomer emission maxima, I E =I M ; in the P3P fluorescence spectra can be used to estimate the local viscosity in the host [3,4]. This approach was used in recent work from our laboratories, where both P3P and P were used to examine self-assembling of ionomers in aqueous solutions [5,6].…”

Host/Guest Simulation of Fluorescent Probes Adsorbed into Low-Density Polyethylene, 1. Excimer Formation of 1,3-Di(1-pyrenyl)propane

“…[3] A correlation between excimer-forming probability and polymer relaxation processes was qualitatively explained on the basis of some simple excimer-formation kinetic scheme under the low-and high-temperature limit approximations. [25,27] Using this kinetic scheme, we considered in that paper: 1. The formation of sandwich complexes of Py3MPy inside the LDPE matrix was a diffusion-controlled process described at the lower temperature limit, ca.…”

“…[4,5] Several of these studies concerned the excimer formation mechanism for these molecules in fluid media. Nevertheless, the mechanism of excimer formation is still controversial.…”