A Case for Using Randomly Labeled Polymers to Study Long-Range Polymer Chain Dynamics by Fluorescence

Abstract

The process of excimer formation was studied for a series of pyrene end-labeled polystyrenes (PS(X)-Py 2 where X is the polymer molecular weight equal to 3, 4.5, 8, 12.7, and 14.6 K) and two series of polystyrenes randomly labeled with pyrene (CoE-PS and CoA-PS) in seven different solvents. The solvent viscosities ranged from 0.41 to 1.92 mPa x s, while the solvent quality ranged from good to poor solvents for polystyrene, as determined by intrinsic viscosity measurements. Steady-state fluorescence spectra of the pyrene-labeled polymers were acquired, and the excimer to monomer ratios showed that excimer formation increased strongly with a decrease in solvent viscosity. The monomer and excimer time-resolved fluorescence decays were also acquired and fitted globally to either the Birks' scheme or the fluorescence blob model (FBM) for the end- or randomly labeled polymers, respectively. All parameters reporting on the long-range polymer chain dynamics (LRPCD) obtained from the analysis of the fluorescence data acquired with the PS(X)-Py 2, CoE-PS, and CoA-PS series yielded virtually identical trends, demonstrating that these fluorescence experiments yield results that are internally consistent with one another. Considering the substantial advantages associated with the preparation and study of randomly labeled polymers, this report presents an appealing case for the use of randomly labeled polymers in the study of LRPCD.

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

“…In a log-log plot of η × (I E /I M ) SS Figure 4. contradict a tenet of pyrene excimer formation that states that (I E /I M ) SS and <k> are two equivalent quantities that should scale in a similar manner and which has been found experimentally in a number of examples [73,74,98]. (×) Reference [134] assuming that each chain end of the dendrimer is labeled with a pyrenyl pendant; (∆) Reference [130], dendrimer in acetonitrile; (♦) Reference [128] assuming τ M = 72.6 ns; (□) Reference [126].…”

Long Range Polymer Chain Dynamics Studied by Fluorescence Quenching

“…Second, it will reiterate the statement already made by this laboratory 34 that long chains randomly labeled with dyes and quenchers are much better suited to study LRPCD than monodisperse oligomers labeled with a dye at one end and a quencher at the other end. This goes against the entrenched belief that short monodisperse polymers labeled at one end with a fluorophore and a quencher at the other end represent the sole experimental means to obtain <k1> quantitatively.…”

“…As illustrated in Figure 5, a polystyrene sample randomly labeled with pyrene (PyBA-PS, chemical structure in Table 2) showed greatly enhanced pyrene excimer formation at 480 nm for a same pyrene content when compared to the pyrene end-labeled polystyrene equivalent (Py2-PS(8K), see Table 2 for chemical structure). 67,34 This massive enhancement in pyrene excimer formation can be explained as follows.…”

Ab initio study on the excited states of pyrene and its derivatives using multi-reference perturbation theory methods

“…27 The excimer uorescence emission band is signicantly red-shied, broad, and structureless, so that it is clearly distinguishable from that of the monomer. Given the substantial distinction between monomer and excimer emissions, as well as their sensitivity to the surrounding environments, pyrene is used to study the molecular structural properties of polymers [30][31][32][33][34] and macromolecules, such as proteins 35,36 and DNA. [37][38][39][40][41][42] It is also used as a probe in chemosensors that detect particular metal ions [43][44][45][46][47][48][49][50][51] and molecules.…”