3D printing techniques are often based on light‐induced chemical reactions, driven by the fascinating and powerful possibilities to control light in space and time. To date, these approaches are usually restricted to a single color of light, which does not do justice to light as an entire spectrum of distinct wavelengths. It is possible to further tap into the vast potential of light‐induced 3D printing by introducing a second color of light. While the complexity of photochemical interactions in two‐color systems is greatly increased, it concomitantly allows for enhanced control over manufacturing speed and resolution. In general, three types of two‐color interactions can be distinguished, i.e., synergistic, orthogonal, and antagonistic. In recent years, intriguing printing techniques with superior potential for the fabrication of 3D structures are emerging that require two colors of light. Their future development potential is vast yet needs to be critically underpinned by an advance in complex tunable photochemical reaction systems. The current perspective will thus explore the potential for using synergistic, orthogonal, and antagonistic photochemistries in 3D printing.
of polymers with functional groups containing heteroatoms within the main chain. This reaches from carbon-oxygen bonds (e.g., ethers, esters, and carbonates) to carbon-nitrogen (e.g., imines, [3] hydrazones, [4] and oximes [5] ). Interestingly, their sulfur-containing analogues, [6] have been underestimated for long time, although the intrinsic characteristics of these polymers are offering a myriad of superior properties (e.g., degradation, flame retardancy, film-forming ability, good solubility in polar solvents, and high refractivity with small chromatic dispersions amongst other) compared to the carbon-derivatives. This is particularly the case for sulfurnitrogen based polymers. The distinctive characteristics of the sulfur-nitrogen based polymers result from the unique chemical properties of the sulfur-nitrogen bond (e.g., its polar character and the multiple valence states of sulfur). As one of the most intriguing dynamic covalent bonds featuring a simple redox chemistry, the disulfide bond has a crucial importance in organic and polymer chemistry. [7] On the contrary, the amino-and diaminodisulfide functional groups (-S-S-N-and -N-S-S-N-, respectively) are rarely studied in organic chemistry, and the respective polymers are very much in their infancy. At the same time, diaminodisulfide and its derivatives represented with the formula -N-S-S-N-, are known for their low S-S bond dissociation energies (e.g., BDE of 180 kJ mol −1 for the simplest diaminodisulfide H 2 N-S-S-NH 2 ) in reference to diaryl and dialkyl disulfide bonds (190-230 and 250-290 kJ mol −1 , respectively). In spite of this, diaminodisulfides are stable and readily handled at ambient temperature as a result of the high stability of the respective thiyl radicals that are formed via catalyst freethermally induced reversible dissociation. Literature survey also clearly depicts that polymers with sulfur-nitrogen bond (particularly, poly(sulfenamide)s, poly(diaminosulfide)s, and poly(diaminodisulfide)s [8,9] ) could be considered as sleeping beauties and (re)appear to be promising for new materials that combine the advantages of sulfur and nitrogen solely. While, the first synthesis of organic molecules decorated with disulfidediamine dates back to 1895, [10] it took almost a century until a pioneering study on polymeric diaminodisulfide derivatives was reported in 1991. [11] Whilst the study failed to provide any complementary characterization of the reported poly(diaminodisulfide) derivatives, the first report dealing with the in-depth characterization of this polymer class dates back to 2012. [12] In a recent study, Otsuka and co-workers, [13] The preparation of polymers containing sulfur-nitrogen bond derivatives, particularly 2,2,6,6-tetramethylpiperidine-1-sulfanyl (TEMPS) dimers (i.e., BiTEMPS), has been limited to free-radical or conventional step-growth polymerization as result of the inherent thermal lability of the BiTEMPS unit. Accordingly, a novel poly(diaminodisulfide) possessing the BiTEMPS functional group is synthesized via acyc...
Inside Cover: Marrying acyclic diene metathesis polymerization and BiTEMPS chemistry offers a simple method to prepare a tailor‐made polymer with precise control over the primary structure. Pivotally, the macromolecule, decorated with sulfur‐nitrogen bonds in each repeating unit, exhibits light‐responsive reversible homolytic dissociation of disulfide linkage, where the specific treatment (e.g., anaerobic condition) is not required. The latter allows reorganization of the polymeric architecture on exposure to the stimulus, and this molecular‐based response is foreseen to be translated to the macroscopic scale. This work is found in article number 2100118 by Hatice Mutlu and co‐workers.
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