Wavelength-gated photoreversible polymerization and topology control

Hendrik Frisch, Kai Mundsinger, Berwyck L. J. Poad, Stephen J. Blanksby, Christopher Barner-Kowollik
2020
We exploit the wavelength dependence of [2 + 2] photocycloadditions and -reversions of styrylpyrene to exert unprecedented control over the photoreversible polymerization and topology of telechelic building blocks. Blue light (l max ¼ 460 nm) initiates a catalyst-free polymerization yielding high molar mass polymers (M n ¼ 60 000 g mol À1 ), which are stable at wavelengths exceeding 430 nm, yet highly responsive to shorter wavelengths. UVB irradiation (l max ¼ 330 nm) induces a rapid
more » ... ation affording linear oligomers, whereas violet light (l max ¼ 410 nm) generates cyclic entities. Thus, different colors of light allow switching between a depolymerization that either proceeds through cyclic or linear topologies. The light-controlled topology formation was evidenced by correlation of mass spectrometry (MS) with size exclusion chromatography (SEC) and ion mobility data. Critically, the color-guided topology control was also possible with ambient laboratory light affording cyclic oligomers, while sunlight activated the linear depolymerization pathway. These findings suggest that light not only induces polymerization and depolymerization but that its color can control the topological outcomes. Scheme 1 (A) Chemical structure of the reversible [2 + 2] photocycloaddition of styrylpyrene used as a wavelength gated binding site of telechelic polymers. (B) Action plot for the conversion of the photocycloaddition (black cubes) and the photocycloreversion of the cycloadduct (red cubes) after irradiation with the same number of photons at different wavelengths, as previously reported for the styrylpyrene derivative hydroxyl-styrylpyrene. 42 The normalized emission spectra of the herein utilized UVB lamp (grey) and LEDs (violet, l max ¼ 410 nm and blue, l max ¼ 460 nm) indicate which reaction is triggered in the respective photonic field. (C) Schematic representation of the polymerization and depolymerization of L1 comprising two terminal styrylpyrene units. Irradiation of L1 with blue light induces its photopolymerization yielding P1, which can be either cyclodepolymerized under violet light or linearly depolymerized under UVB light. This journal is
doi:10.5445/ir/1000118061 fatcat:ess2togusng2hglb3kf6lgoox4