Mussel glue: Bioinspired underwater chemical bonding with the possibility of phototriggered debonding is reported. A four-arm star-poly(ethyleneglycol) endfunctionalized by nitrodopamine was synthesized. The nitrodopamine offered the reactivity of catechol and the chemistry of the photocleavable o-nitrophenyl ethyl group (see picture).
The intrinsic photoluminescence properties of hyperbranched polyethylenimines (PEIs) and their linear counterpart (LPEIs) have been studied in absence of any classical fluorescent probes. The comparison of the inherent fluorescence emission between hyperbranched polyethylenimines and their linear analogues demonstrates that linear polyamines are capable of producing strong intrinsic photoluminescence species having long excited lifetimes without need of having a tridimensional‐branched structure. The creation of inherently fluorescent polymeric centers from hyperbranched and linear polyethyleimines can be modulated by specific chemical modification and oxidation of amine groups as well as by adjusting the acidity of the polymer.magnified image
Der Klebstoff von Muscheln: Eine bioinspirierte chemische Verklebung wird vorgestellt, die unter Wasser geknüpft und durch Bestrahlung mit Licht wieder gelöst werden kann. Zu diesem Zweck wurde ein vierarmiges Polyethylenglycol‐Sternpolymer mit Nitrodopamin‐Endgruppen bestückt, die zum einen als 1,2‐Dihydroxybenzol reagieren und zum anderen als photospaltbare o‐Nitrophenylethyl‐Gruppe wirken (siehe Bild).
A photosensitizer core has been covalently incorporated into a hyperbranched polyether polyol structure, using a one-step protocol. Partially deprotonated 2,2′,4,4′-tetrahydroxybenzophenone was used as initiator in the anionic polymerization of glycidol, yielding hyperbranched polyglycerols with benzophenone core in every macromolecule 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 polymers of lowered polarity. The photochemical and photophysical behavior of the obtained benzophenone core-containing hyperbranched polyglycerols has been investigated in a variety of solvents and compared with that of the model compound 2,2′,4,4′-tetramethoxybenzophenone. The hyperbranched polymer periphery induced molecular weightdependent properties in the photoactive core. Although absorption spectra of the polymers show the typical bands of a tetra(alkoxy)benzophenone unit, a dramatic hyperchromic effect of the band assigned to the 2,4-dialkoxybenzoyl chromophore was observed with increasing molecular weight. Steady-state and time-resolved fluorescence measurements evidenced an increase of both the fluorescence quantum yield and the singlet lifetime with the increase of molecular weight. On the other hand, laser flash photolysis (LFP) experiments showed that, as in the case of the reference compound, the lowest-lying triplet of the hyperbranched derivatives in methanol is mainly of the π,π* nature, while both triplets n,π* and π,π* are populated in acetonitrile, which is indicative of easy access of the solvent to the core. However, the quenching rate constant of the aromatic ketone triplet excitedstate by naphthalene decreased with the polymer molecular weight, which agrees with the role of the branched shell as a barrier for external quenching. The polymers showed good photostability, i.e., degradation was insignificant upon 1 h of irradiation in methanol.
The aromatic ketone 2,2',4,4'-tetramethoxybenzophenone has a strong absorption band between 300 and 375 nm, and its pi,pi* triplet excited-state is selectively populated in methanol. Both facts make this aromatic ketone a versatile and efficient triplet photocatalyst for the transformation of alpha-diazo carbonyl compounds into mainly the cyclopropanation product.
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