Photoinduced Tetrazole‐Based Functionalization of Off‐Stoichiometric Clickable Microparticles

Abstract

We report the preparation of tetrazole-containing step-growth microparticles, and the subsequent use of photo-induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) reactions on the particles with spatiotemporal control. Microparticles with an average diameter of 4.1 µm and with inherent tetrazole-ene dual-functionality were prepared by a one pot offstoichiometric thiol-Michael addition dispersion polymerization. The NITEC reaction was performed efficiently in the solid phase by UV irradiation, leading to the formation of fluorescent pyrozoline adducts, with an estimated quantum yield of 0.7. Particle concentration independent reaction kinetics were observed and full conversion was reached within 10 min of UV exposure at an intensity of 8 mW cm -2 . Temporal control was demonstrated with either UV or rooftop sunlight irradiation of variable duration. By using two-photon writing with a laser centered around 700 nm wavelength, spatial control was demonstrated with micron-scale resolution via surface patterning of the microparticles. Further, microparticles with exclusive tetrazole functionality were prepared by a onepot, two-step thiol-Michael addition dispersion polymerization. The NITEC reaction between tetrazole-functional particles and acrylates in solution was examined at various tetrazole/alkene molar ratios, and a 10:1 excess of alkenes in solution was found necessary for efficient functionalization.

Intrinsically Fluorescent, Stealth Polypyrazoline Nanoparticles with Large Stokes Shift for In Vivo Imaging

“…Remarkably, the current synthesis relies on the photopolymerization of nonfluorescent precursors, which become fluorescent upon coupling based on the so‐called nitrile imine‐mediated tetrazole–ene cycloaddition (NITEC): Upon irradiation, the tetrazole turns into a very reactive nitrile imine, which can be trapped with a large variety of enes. The mild reaction conditions accessible to NITEC have been exploited for the (bio)functionalization of organic or inorganic nanomaterials, as well as protein labeling in living bacteria or mammalian cells . NITEC was also recently used to intramolecularly crosslink water‐soluble polymer chains, leading to sub‐5 nm fluorescent single‐chain nanoparticles.…”

Light-Stimulated Permanent Shape Reconfiguration in Cross-Linked Polymer Microparticles

“…This narrow polydispersity is consistent with previous step-growth thiol-Michael dispersion polymerization results. 35,36 …”

“…The diameter of the unswollen particles was measured via AFM (DI 3100, Bruker) to be 3.1 μ m ± 0.3 μ m ( n = 30); this narrow polydispersity is consistent with existing literature. 35,36 The particles were also imaged in top-down and side-view mode using an FE-SEM (Zeiss, Supra 60). Prior to SEM imaging, the deposited particles were sputter-coated with an approximately 5 nm layer of gold.…”

TEMPO Driven Mild and Modular Route to Functionalized Microparticles

“…Tyson et al reported thiol‐ene reactions initiated by visible light in presence of a transition metal polypyridyl photocatalyst and p ‐toluidine as an additive. Critically, thiol‐ene chemistry is widely used for a variety of applications such as the synthesis of crosslinked functional polymeric microspheres as well as the functionalization of microspheres . Dispersion polymerization based on thiol‐ene/thiol‐yne chemistry features some characteristics associated with the “click” principle, i.e., high reactivity with monomers, excellent yields, selectivity, and reaction orthogonality .…”

“…In addition, they reported the functionalization of these particles and degradation of polymeric microspheres in basic media. Recently, Bowman and co‐workers synthesized photoresponsive polymeric particles by photoinduced nitrile imine‐mediated tetrazole‐ene cycloaddition (NITEC) and thiol‐Michael addition dispersion polymerization in which the polymeric particles feature an inherent tetrazole‐ene functionality for postparticle formation chemistry. Alimohammadi et al synthesized polymeric particles by thiol‐ene and thiol‐yne free radical dispersion polymerization studying the effect of initiator (photo, thermal, and redox) on the particle size.…”