Folding polymer chains with visible light.

We introduce a mild and efficient avenue to induce the folding of single chain polymer nanoparticles (SCNPs) using visible light. The versatility of the method is based on three folding mechanisms exploiting tetrazole chemistry, i.e., nitrile imine-mediated tetrazole-ene cycloaddition (NITEC), nitrile imine carboxylic acid ligation (NICAL) as well as nitrile imine self-dimerization. To our knowledge, this visible light driven approach is the to-date mildest avenue to fold single polymer chains into compact particles using light.

Exploiting λ-Orthogonal Photoligation for Layered Surface Patterning.

We exploit λ-orthogonal photoligation of nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) chemistry to generate complex, interconnected surface modifications via a simple layered surface patterning approach. By judicious choice of activating chromophores, we introduce a one pot reaction where nitrile imine formation can be triggered independently of other tetrazoles present. When irradiated with visible light, a tetrazole bearing a pyrene chromophore undergoes quantitative elimination of nitrogen to release nitrile imine (which subsequently undergoes trapping with a dipolarophile in a 1,3 dipolar cycloaddition) whereas a tetrazole bearing a phenyl moiety remains unreacted. Subsequent irradiation of the solution with UV light yields the N-phenyl containing nitrile imine quantitatively, while the pyrene pyrazoline adduct remains unchanged. This λ-orthogonal photoligation was subsequently exploited for the generation of layered patterned surfaces. Specifically, the visible light active tetrazole was grafted to a silicon wafer and subsequently photolithographically patterned with a dipolarophile modified with a UV-active tetrazole. Various electron deficient olefins were then patterned in a spatially resolved manner relying on different light activation. The desired functionality was successfully imaged on the silicon wafers using time-of-flight-secondary ion mass spectrometry (ToF-SIMS), demonstrating that a powerful mask-less lithographic platform technology has been established.

Near-Infrared Photoinduced Coupling Reactions Assisted by Upconversion Nanoparticles.

We introduce nitrile imine-mediated tetrazole-ene cycloadditions (NITEC) in the presence of upconversion nanoparticles (UCNPs) as a powerful covalent coupling tool. When a pyrene aryl tetrazole derivative (λabs, max =346 nm) and UCNPs are irradiated with near-infrared light at 974 nm, rapid conversion of the tetrazole into a reactive nitrile imine occurs. In the presence of an electron-deficient double bond, quantitative conversion into a pyrazoline cycloadduct is observed under ambient conditions. The combination of NITEC and UCNP technology is used for small-molecule cycloadditions, polymer end-group modification, and the formation of block copolymers from functional macromolecular precursors, constituting the first example of a NIR-induced cycloaddition. To show the potential for in vivo applications, through-tissue experiments with a biologically relevant biotin species were carried out. Quantitative cycloadditions and retention of the biological activity of the biotin units are possible at 974 nm irradiation.

Catalyst free visible light induced cycloaddition as an avenue for polymer ligation.

The current study introduces a tetrazole species able to perform a rapid, visible light induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC). Full conversion of the tetrazole species under mild, catalyst free conditions is reported. Importantly, the visible light ligation technology is applied as a method for the modification and ligation of polymers featuring the rapid, clean and exclusive formation of the desired cycloadduct.

Design of Redox/Radical Sensing Molecules via Nitrile Imine-Mediated Tetrazole-ene Cycloaddition (NITEC).

The current study introduces a novel synthetic avenue for the preparation of profluorescent nitroxides via nitrile imine-mediated tetrazole-ene cycloaddition (NITEC). The photoinduced cycloaddition was performed under metal-free, mild conditions allowing the preparation of a library of the nitroxide functionalized pyrazolines and corresponding methoxyamines. High reaction rates and full conversion were observed, with the presence of the nitroxide having no significant impact on the cycloaddition performance. The formed products were investigated with respect to their photophysical properties in order to quantify their "switch on/off" behavior. The fluorescence quenching performance is strongly dependent on the distance between the chromophore and the free radical spin as demonstrated theoretically and experimentally. Highest levels of fluorescence quenching were achieved for pyrazolines with the nitroxide directly fused to the chromophore. Importantly, the pyrazoline profluorescent nitroxides were shown to efficiently act as sensors for redox/radical processes.