Probing the Conformations for Polymeric Bottle Brushes in Solution by Pyrene Excimer Formation Janine Thoma, Jean Duhamel Acknowledgements Introduction A strong interest in polymeric bottle brushes (PBBs) has led to a growing number of their applications. The characterization of these novel polymers in solution, where they are in their native conformation, has not yet been accomplished. Depending on the length of a PBBs’ side chains, either a globular or cylindrical conformation is obtained in solution. By covalently bonding a chromophore to the end of the PBBs’ side chains, the conformation of the labeled PBB can be probed. By using a fluorescent chromophore such as pyrene, the distribution of PBB end-groups can be characterized from the pyrene excimer fluorescence. The authors thank Shiva Farhangi, Remi Casier and NSERC for generous support. Synthesis Results and Discussion Figure 1: Probing pyrene location in a globular (left) and cylindrical (right) chain conformation. Scheme 1: Monotosylation of OEGs and covalent addition of pyrene. Scheme 2: Methacrylation and free radical polymerization of pyrene labelled monomer. Figure 2: 1 H-NMR of Py-EG 5 -OH (left) and Py-EG 5 -MA (right) Py-EG 5 -OH monomer and Py-EG 5 -MA were both synthesized and characterized using 1 H-NMR and time-resolved and steady-state fluorescence. Figure 3: Time-resolved (left) and steady-state fluorescence (right) data from Py- EG 5 -MA. A series of poly(ethylene glycol) (PEG) methacrylates terminated with a pyrene group are being prepared using a range of PEG molecular weights. These constructs can be viewed as polymeric bottle brushes (PBBS). Free radical polymerization will be used to synthesize these PBBs and they will be studied using both fluorescence and non-fluorescence based techniques. The Model Free Analysis (MFA) will be applied to fit the fluorescence decays and calculate the average rate constant of excimer formation. Abstract The time-resolved fluorescence decays for both Py-EG 5 -OH and Py- EG 5 -MA were monoexponential with a lifetime of 280 ns in THF. The average rate constant of excimer formation,, is expected to be directly related to the concentration of local pyrene. Therefore, as the side chain length increases the concentration of local pyrene is expected to decrease as the cylindrical volume of the PBB increases. The fluorescence decays of the EG 3 and EG 5 PBBs were acquired and their pyrene monomer and excimer decays were analyzed according to the Model Free Analysis (MFA). The average rate constant of excimer formation,, was then calculated. EG 3 and EG 5 PBBs were found to have values of 0.55 ns -1 and 0.42 ns -1 in DMF, respectively. Figure 4: Time resolved fluorescence decays from the EG 5 -PBB. After studying the EG 3 and EG 5 PBBs it was found that as the side chain length increased, the rate constant of excimer formation decreased. Based on the steady-state fluorescence spectra, excimer formation was found to increase with increasing linker length. This contradicts the values obtained by time-resolved fluorescence. Possible reasons for the contradicting values could be due to solvent type or aggregation of pyrene. Further experiments are required to understand what is happening. Future work involves synthesizing higher molecular weigh ethylene glycol monomers and then plotting side chain length versus. A discontinuity in the plot is expected to correspond to a PBBs’ transition from globular to cylindrical conformational in solution. Figure 5: Steady state fluorescence spectrum of EG 3 () and EG 5 ( ・・・ ) PBBs.