Incorporation of a Photosensitizer Core within Hyperbranched Polyether Polyols: Effect of the Branched Shell on the Core Properties

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• 作者：Lourdes Pastor-Pé ; rez ; Emilie Barriau ; Elena Berger-Nicoletti ; Andreas F. M. Kilbinger ; Julia Pé ; rez-Prieto ; Holger Frey ; Salah-Eddine Stiriba
• 刊名：Macromolecules
• 出版年：2008
• 出版时间：February 26, 2008
• 年：2008
• 卷：41
• 期：4
• 页码：1189 - 1195
• 全文大小：176K
• 年卷期：v.41,no.4(February 26, 2008)
• ISSN：1520-5835

文摘

A photosensitizer core has been covalently incorporated into a hyperbranched polyether polyolstructure, using a one-step protocol. Partially deprotonated 2,2',4,4'-tetrahydroxybenzophenone was used as initiatorin the anionic polymerization of glycidol, yielding hyperbranched polyglycerols with benzophenone core in everymacromolecule formed. Molecular weights in the range of 1500 to 5800 g/mol and moderate polydispersity (1.3< M_w/M_n < 2) were obtained. Incorporation of the functional core was unequivocally evidenced by MALDI-TOF mass spectroscopy. Further modification via acetylation of the polyglycerol hydroxyl groups afforded polymersof lowered polarity. The photochemical and photophysical behavior of the obtained benzophenone core-containinghyperbranched polyglycerols has been investigated in a variety of solvents and compared with that of the modelcompound 2,2',4,4'-tetramethoxybenzophenone. The hyperbranched polymer periphery induced molecular weight-dependent properties in the photoactive core. Although absorption spectra of the polymers show the typical bandsof a tetra(alkoxy)benzophenone unit, a dramatic hyperchromic effect of the band assigned to the 2,4-dialkoxybenzoylchromophore was observed with increasing molecular weight. Steady-state and time-resolved fluorescencemeasurements evidenced an increase of both the fluorescence quantum yield and the singlet lifetime with theincrease of molecular weight. On the other hand, laser flash photolysis (LFP) experiments showed that, as in thecase of the reference compound, the lowest-lying triplet of the hyperbranched derivatives in methanol is mainlyof the ,* nature, while both triplets n,* and ,* are populated in acetonitrile, which is indicative of easyaccess of the solvent to the core. However, the quenching rate constant of the aromatic ketone triplet excited-state by naphthalene decreased with the polymer molecular weight, which agrees with the role of the branchedshell as a barrier for external quenching. The polymers showed good photostability, i.e., degradation wasinsignificant upon 1 h of irradiation in methanol.