Characterization of the Local Volume Probed by the Side-Chain Ends of Poly(oligo(ethylene glycol) 1-Pyrenemethyl ether methacrylate) Bottle Brushes in Solution Using Pyrene Excimer Fluorescence

Abstract

Four poly(oligo(ethylene glycol) 1-pyrenemethyl ether methacrylate) [P(PyEG y MA), with y = 3, 5, 8, and 12] samples were synthesized, where each side chain was terminated with a 1-pyrenemethoxy derivative. The efficiency of excimer formation between an excited-state pyrene and a ground-state pyrene was used to assess the conformation of the PyEG y side chains in these polymeric bottle brushes by conducting timeresolved fluorescence measurements in tetrahydrofuran (THF), N,Ndimethylformamide (DMF), dioxane, and dimethylsulfoxide (DMSO). These experiments took advantage of the dependency of the average rate constant ⟨k⟩ of pyrene excimer formation (PEF) on the local pyrene concentration [Py] loc experienced by an excited pyrene bound to the P(PyEG y MA) samples. [Py] loc could be estimated theoretically by assuming that the EG y side chains adopted a Gaussian conformation. Linear plots of ⟨k⟩/f diff as a function of [Py] loc , where f diff is the molar fraction of pyrenyl labels forming excimers by diffusion and was introduced to account for residual pyrene aggregation, were obtained in all four solvents, with slopes that depended on solvent viscosity and the probability of PEF upon the diffusive encounter between two pyrenyl labels. Solvent-induced differences in PEF efficiency could be accounted for by determining the bimolecular rate constant k diff [inter] for intermolecular PEF with the model compound 1-pyrenemethyl diethylene glycol methyl ether in the four solvents. Except for DMSO, which was too polar and led to the segregation of the pyrenyl labels close to the polymethacrylate backbone, the data obtained for all P(PyEG y MA) samples in THF, DMF, and dioxane collapsed on a master line, similar to the one obtained earlier with a series of pyrene-labeled dendrons, when plotting ⟨k⟩/( f diff × k diff [inter])-vs-[Py] loc . The ⟨k⟩/(f diff × k diff [inter])-vs-[Py] loc master line confirmed the direct relationship that exists between the PEF efficiency and [Py] loc , a relationship that could be used to probe the conformation of highly branched macromolecules in solution.

Macromolecular Conformation of Low-Generation PAMAM Dendrimers Probed by Pyrene Excimer Formation

“…An excellent correlation was observed between ⟨ k ⟩ and n Py /( L Py / l ) 3 in N , N -dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), the two solvents where the PyCX-PAMAM-GY samples were fully soluble. The effect of solvent viscosity and PEF efficiency could be accounted for by normalizing ⟨ k ⟩ by k diff , the bimolecular rate constant for diffusive PEF for the model compound hexyl-1-pyrenebutyramide, as was done earlier. , Furthermore, all ⟨ k ⟩/ k diff ratios obtained for the PyCX-PAMAM-GY and PyC4-HMPA-GY samples in DMF and DMSO clustered around a master line when plotted as a function of n Py /( L Py / l ) 3 , , suggesting that these trends are general and could also apply to a wider range of pyrene-labeled constructs. Consequently, two conclusions can be drawn from this study.…”

Persistence Length and Encounter Frequency Determination from Fluorescence Studies of Pyrene-Labeled Poly(oligo(ethylene glycol) methyl ether methacrylate)s

“…Molecular mechanics optimization (MMOs) were conducted with HyperChem to determine the theoretical N blob value ( N blob MMO ) representing the maximum reach of a 1-pyrenebutyl label along an extended poly­(methyl methacrylate) chain made of 80 methyl methacrylate monomers, which had been generated in an earlier publication . An SU was randomly selected along the backbone with the random number generator in MS Excel at a position between the 10th and 70th SU of the PMMA construct.…”

“…Molecular mechanics optimization (MMOs) were conducted with HyperChem to determine the theoretical N blob value (N blob MMO ) representing the maximum reach of a 1-pyrenebutyl label along an extended poly(methyl methacrylate) chain made of 80 methyl methacrylate monomers, which had been generated in an earlier publication. 32 An SU was randomly selected along the backbone with the random number generator in MS Excel at a position between the 10th and 70th SU of the PMMA construct. Although the PMMA chain was prepared with 80 methyl methacrylate units, 30 the boundaries at the 10th and 70th SU of the PMMA construct were chosen during the random selection of an SU to ensure that the selected SU was sufficiently distant from the chain ends.…”

Facile Obtainment of Fluorescent PEG Hydrogels Bearing Pyrene Groups by Frontal Polymerization

“…The excimer emission band of the pyrene excimer appears at a longer wavelength, around 480 nm. Pyrene excimer emission has been used as a fluorescent probe to investigate the local volume and internal dynamics (ID) of polymer chains and dendrimers in solution [ 20 , 21 , 22 ]. The coexistence of monomer and excimer emission bands has allowed investigations into numerous applications in organic electronic devices [ 23 , 24 ], protein conformation [ 25 ], and chemosensing [ 26 ].…”