Controlling Chain Coupling and Single-Chain Ligation by Two Colours of Visible Light.

While photochemical synthesis offers access to spatiotemporal reaction control, its potential to selectively address specific reactions by the colour of light is usually limited by ubiquitous spectral absorption overlaps of the reactive groups. Herein, a new concept is introduced that actively suppresses one ligation reaction by triggering the cycloreversion of the [2+2] cycloaddition of styrylpyrene. Combination of the photoreversible styrylpyrene chemistry with the [4+4] cycloaddition of 9-triazolylanthracene makes it possible to initially induce chain coupling using UV light and to subsequently ligate the formed single-chain nanoparticle (SCNP) with a second polymer chain using blue light. Seizing upon the first sequence-independent λ-orthogonal reactivity established here, the same macromolecular architecture was obtained in reverse irradiation sequence, by blue and subsequent violet light irradiation-completely foregoing high-energy UV light.