Synthesis and [2+2]-photodimerisation of monothiomaleimide functionalised linear and brush-like polymers

Abstract

[2 + 2]-Photodimerisation of monothiomaleimides has been demonstrated on functionalised linear and brush-like polymers. In water/acetonitrile (95 : 5) mixtures the rate of reaction is accelerated significantly by irradiation of...

Intramolecular thiomaleimide [2 + 2] photocycloadditions: stereoselective control for disulfide stapling and observation of excited state intermediates by transient absorption spectroscopy

“…In contrast, the exo product with the protons trans to Scheme 1 Previous work on [2 + 2] photocycloadditions of thiomaleimides. [25][26][27] Scheme 2 Synthesis and endo selective [2 + 2] photocycloaddition of N-tethered bis-thiomaleimides 4a-c. one another will have a dihedral angle of $100 , giving a much smaller 3 J value of 3 Hz; 31 and this was indeed seen for the intermolecular exo photoproduct 2 (see ESI Fig. 1 †).…”

“…The reaction is rapid, reaching completion in just 5 min; which is notably much faster than maleimide itself under the same conditions, which requires a 1 h irradiation time. We envisaged that this highly efficient reaction could have broad utility, and have carried out initial exemplications in photo-crosslinking polymers 26 and in the photocyclisation and photorebridging of bioconjugates with spatiotemporal control. 27 Encouraged by the broad potential of this 'photoclick' reaction of thiomaleimides, we were motivated to investigate the underlying photophysical processes.…”

Reversible Transformations of Polymer Topologies through Visible Light and Darkness

“…In other words, the dynamic formation of covalent bonds possesses limitations when different molecular units are involved. Broadly speaking, in the context of (macro)­molecular architecture transformations, dynamic covalent bond (re)­formation between structures can be traditionally achieved through [2 + 2] and [4 + 4] photodimerizations. − In these cases, photocycloaddition occurs under one wavelength (λ up to 550 nm), while cycloreversion requires a different one, typically of a higher energy (λ < 250 nm), which can be invasive for the material involved. − All the above-mentioned examples represent notable approaches toward smart polymer systems that can alter their shape, and hence properties, in response to external stimuli on-demand. However, the stimuli used so far (e.g., elevated temperatures or high energy light irradiation), as well as the prolonged reaction times (e.g., up to 48 h) and disruptive multi-step processes with intermediate purification, necessitate the design of intelligent polymer systems that can adapt to the desired transformation in the least invasive manner, whilst maintaining practicality, absolute control, and high uniformity.…”

Photocrosslinking of Polyacrylamides Using [2 + 2] Photodimerisation of Monothiomaleimides

“…24 The substitution on the maleimide ring by a thiol group was shown to red-shift the This led to MTMs being excellent candidates for photochemically rebridging the disulfide bond in biomolecules (Figure 1b). 25 Only recently, the potential of [2 + 2] photodimerization of MTMs was explored in polymer conjugation reactions, as illustrated by the quantitative coupling of linear and brush-like MTM end-capped hydrophilic polymers in only 10 min 26 Herein, we further extend the scope of the thiolmaleimide [2 + 2] photodimerization reaction into polymer chemistry by reporting, for the first time, the synthesis of MTM side chainfunctionalized polymers and their subsequent photocrosslinking under irradiation (Figure 1c).…”

“…This led to MTMs being excellent candidates for photochemically rebridging the disulfide bond in biomolecules ( Figure 1 b). 25 Only recently, the potential of [2 + 2] photodimerization of MTMs was explored in polymer conjugation reactions, as illustrated by the quantitative coupling of linear and brush-like MTM end-capped hydrophilic polymers in only 10 min 26 …”