Gesteuerte Reaktionsorthogonalität in der Polymer‐ und Materialwissenschaft

Photo Click Reaction of Acylsilanes with Indoles

Light-mediated coupling of acylsilanes with indoles is reported. This photo click reaction occurs under mild conditions (415 nm) mostly in quantitative yield and provides stable silylated N,O-acetals via light mediated siloxycarbene generation with subsequent indole-N-H insertion. We show that this very efficient and fully atom economic coupling process can be applied to conjugate complex systems, as documented by the clicking of carbohydrates with indole alkaloids. The method is also applicable to the conjugation of polymer chains. The linking acetal moiety can be readily cleaved and it is also shown that wavelength-selective coupling and cleavage with acyl silanes bearing a second photoactive moiety is possible. This is documented by a successful polymerization/depolymerization sequence and by a polymer folding/unfolding process.

Wavelength-Selective Photopolymerization of Hybrid Acrylate-Oxetane Liquid Crystals

We report on the wavelength-selective photopolymerization of a hybrid acrylate-oxetane cholesteric liquid crystal monomer mixture. By controlling the sequence and rate of the orthogonal free-radical and cationic photopolymerization reactions, it is possible to control the degree of phase separation in the resulting liquid crystal interpenetrating networks. We show that this can be used to tune the reflective color of the structurally colored coatings produced. Conversely, the structural color can be used to monitor the degree of phase separation. Our new photopolymerization procedure allows for structuring liquid crystal networks in three dimensions, which has great potential for fabricating liquid crystal polymer materials with programmable functional properties.

Wavelength-Gated Photochemical Synthesis of Phenalene Diimides

Herein, we pioneer a wavelength‐gated synthesis route to phenalene diimides. Consecutive Diels–Alder reactions of methylisophthalaldehydes and maleimides afford hexahydro‐phenalene‐1,6‐diol diimides via 5‐formyl‐hexahydro‐benzo[f]isoindoles as the intermediate. Both photoreactions are efficient (82–99 % yield) and exhibit excellent diastereoselectivity (62–98 % d.r.). The wavelength‐gated nature of the stepwise reaction enables the modular construction of phenalene diimide scaffolds by choice of substrate and wavelength. Importantly, this synthetic methodology opens a facile avenue to a new class of persistent phenalenyl diimide neutral radicals, constituting a versatile route to spin‐active molecules.