Wavelength-Orthogonal Approaches Enabling Reprogrammable Gradient Materials

The reversible and visible light induced cycloaddition of styrylpyrene has been investigated with regard to its formed isomeric photoproducts as well as its most efficient photochemical reaction conditions – i.e. trigger wavelength and number of photons required for maximum conversion – via a newly developed technique called Wavelength-dependent Photon Efficiency Analysis (WPEA). With wavelengths at 435 nm for the dimerisation and 330 nm for the dissociation, the investigated cycloaddition is among the mildest of its kind. The chromophore was further exploited in polymer studies, on the one hand towards wavelength-orthogonal reaction systems to alter material properties simply by using disparate colours of light, and on the other hand for reprogrammable gradient materials. In particular, styrylpyrene has been successfully employed in reversible block-copolymer formations over several dimerisation / dissociation cycles demonstrating the capability of styrylpyrene for reprogrammability. A further reversible visible light moiety based on a pyrenyl cinnamic acid derivate was combined with o-methyl benzaldehyde – which reacts in an irreversible cycloaddition under irradiation with UV light – in one molecule. ... mehrThe dichromophore was employed in wavelength-orthogonal studies with subsequent irradiation of distinct wavelengths to pathway-independently obtain the same product. Such a dichromophore can be further utilised as a cross-linking molecule for the generation of light responsive materials. Moreover, polymer strands with styrylpyrene or o-methyl benzaldehyde side groups were investigated in-depth for wavelength-orthogonal systems in small molecule, polymer and material studies including analysis via XPS and AFM. It is demonstrated that curing the latter with disparate colours of light induced different cross-linking reactions resulting in distinct material properties such as softness and adhesiveness. As a result, reversible visible light moieties such as styrylpyrene are suitable for reprogrammable gradient materials that can be combined with additional wavelength-orthogonal reactions to introduce further functionalisation.