End-to-end cyclization of polymer chains

New fluorescent reagents, 2,2‘-[oxybis(3-oxapentamethyleneoxy)]-bis[N-(1-pyrenylmethyl)benzamide)] (4) and its analogues (2, 3, and 5) which have two pyrenes at the both terminals of polyoxyethylene compounds, were synthesized, and their complexation behavior with alkaline earth cations was investigated by fluorescence spectrometry, fluorescence lifetimes, and 1H NMR spectrometry. These reagents (3−5) showed strong intramolecular excimer emissions around at 480 nm in the fluorescence spectra. On the complexation with alkaline earth metal cations, the increase of monomer emission around at 400 nm accompanied by the disappearance of intramolecular excimer emission of free reagents was observed. These reagents formed a 1:1 complex, and the order of complex formation constants was Ca2+ ≅ Sr2+ > Ba2+ > Mg2+ > Li+ for all reagents. 1H NMR spectra of these complexes with alkaline earth cations suggested the helical structures of the complexes. Fluorescence spectral changes at the formation of complexes depended ...

New Fluorimetric Alkali and Alkaline Earth Metal Cation Sensors Based on Noncyclic Crown Ethers by Means of Intramolecular Excimer Formation of Pyrene

Pyrene-labeled poly(ethylenimine) (PEI) containing different amounts of pyrene per polymer were prepared by reductive amination of PEI with 1-pyrenecarboxaldehyde. Aqueous solutions of the pyrene-labeled PEI (PEI−Py) exhibit typical pyrene monomer and excimer emission, and the excimer-to-monomer ratio IE/IM decreases with decreasing Py content of the macromolecule. The excimer emission arises from preassociated pyrene aggregates. Both the monomer and excimer emission intensities increase with decreasing pH of the solution. A decrease in pH of the solution from pH = 10 to pH ≈ 1.5 led to approximately a 100-fold increase in IM, whereas IE increased just 2- to 3-fold. A major feature of this system is the quenching of the Py fluorescence by amino groups of the PEI. This quenching depends on the degree of protonation of these groups. Model experiments with pyrenemethanol show that triethylamine is 20 times more effective as a quencher than diethylamine in water, implying that most of the quenching in PEI is ...

Synthesis and characterization of pyrene-labeled poly(ethylenimine)

This review exposes the current poor understanding of the internal segmental chain dynamics of dendrimers in solution probed by monitoring the process of excimer formation between pyrene labels covalently attached to the chain ends of dendrimers. The review begins by covering the bases of fluorescence and the kinetics of pyrene excimer formation before describing a procedure based on the Model Free (MF) analysis that is used to analyze quantitatively the fluorescence decays acquired for dendrimers, the ends of which have been fully and covalently labeled with pyrene. Comparison of the various trends obtained by different research groups describing the efficiency of pyrene excimer formation with the generation number of dendrimers illustrates the lack of consensus between the few studies devoted to the topic. One possible reason for this disagreement might reside in the presence of minute amounts of unattached pyrene labels which act as potent fluorescent impurities and affect the analysis of the fluorescence spectra and decays in an uncontrolled manner. The review points out that the MF analysis of the fluorescence decays acquired with pyrene-labeled dendrimers enables one to account for the presence of unattached pyrene and to retrieve information about the internal segmental dynamics of the dendrimer. It provides guidelines that should enable future studies on pyrene-labeled dendrimers to yield results that are more straightforward to interpret.

https://www.mdpi.com/2073-4360/4/1/211/pdf

Jarda Danhelka

Papers

Cyclization dynamics of polymers: 10 Synthesis, fractionation, and fluorescent spectroscopy of pyrene end-capped polystyrenes

Cyclization dynamics of polymers: 7. Applications of the pyrene excimer technique to the internal dynamics of poly(dimethylsiloxane) chains

Fractionation of end-labelled polystyrenes by silica gel column chromatography