In the field of light-responsive polymers, coumarin is one of the most commonly used structural motifs. By applying different wavelengths, materials' properties can be changed. Hereby, limited reversibility of the reaction is reported in many cases. By introducing a novel intramolecular coumarin dimer (ICD) based polymer architecture, the reversibility of the reaction is increased significantly. The photoreaction of the reversion and addition reaction is performed over several illumination cycles with alternating UV-wavelength light (λ = 265 nm for cycloreversion, λ = 345 nm for cycloaddition). A high degree of reversibility is reached by keeping the mobility low. Performing the illumination cycles at low temperatures and using a highly crosslinked material for structural confinement, the clean photochemical reaction path is maintained. Loss of the preferred molecular orientation, e.g. by heating, resembles the coumarin moieties, which results in non-defined photoreaction and decreased reversibility. By incorporating the ICD structure in different polymers, a bunch of applications are presented. Besides light-induced refractive index modulation, also fluorescence changes in polymer thin films were achieved. In addition, the cycloreversion reaction was performed under two-photon absorption (TPA) conditions using intense visible light laser pulses. For the TPA-induced reaction, a different reaction mechanism compared to the UV-light-induced reaction was found. The TPA-induced reaction offers great potential in further applications in the field of light-responsive polymers, e.g. for optical data storage or waveguide technologies.
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