The introduction of mechanophores into polymers makes it possible to transduce mechanical forces into chemical reactions that can be used to impart functions such as self-healing, catalytic activity, and mechanochromic response. Here, an example of mechanically induced metal ion release from a polymer is reported. Ferrocene (Fc) was incorporated as an iron ion releasing mechanophore into poly(methyl acrylate)s (PMAs) and polyurethanes (PUs). Sonication triggered the preferential cleavage of the polymers at the Fc units over other bonds, as shown by a kinetic study of the molar mass distribution of the cleaved Fc-containing and Fc-free reference polymers. The released and oxidized iron ions can be detected with KSCN to generate the red-colored [Fe(SCN) (H O) )] complex or reacted with K [Fe(CN) ] to afford Prussian blue.

Low-power light upconversion by triplet-triplet annihilation (TTA-UC) was only recently achieved in glassy materials. Here, a new strategy based on covalent tethering of diphenylanthracene (DPA) emitters to a polymeric backbone is reported. The design aims to optimize the efficiency of this photophysical process in glassy polymeric materials by increasing the emitter content. To that end, DPA molecules were covalently attached to a methacrylate-type monomer and further copolymerized with methylmethacrylate (MMA). Green-to-blue (543 to 440 nm) upconversion was observed at power densities as low as 32 mW/cm 2 in films prepared by solution casting and compression molding (co)polymers containing 8-72 wt% of DPA and palladium octaethyl porphyrin (PdOEP) as a sensitizer (0.03-0.7 wt%). The upconversion intensity was studied as a function of DPA and PdOEP contents and the results suggest that upconversion is optimal for DPA and PdOEP weight fractions of 34 and 0.05 wt% respectively.Several optical upconverting schemes are known to cause an anti-Stokes shift, i.e., the emanating photons have a higher energy than the incident electromagnetic radiation (Fig. 1). [1][2][3] While most upconverting processes require coherent, highpower light produced by lasers (e.g. second-or third-harmonic generation, two-photon absorption emission), upconversion by triplet-triplet annihilation (TTA-UC) is feasible at much lower power densities and with non-coherent, polychromatic excitation. 4,5 The framework is therefore attractive for a range of applications, for example biological imaging and display techniques. [6][7][8][9][10][11][12] Perhaps the biggest promise of TTA-UC is that it can overcome the Shockley-Queisser solar power conversion limit, 13-15 as it permits harnessing photons from the portion of the solar spectrum beyond a solar cell's bandgap. 16,17 The TTA-UC process relies on a series of energy transfer steps between a pair of chromophores, a sensitizer and an emitter ( Fig. 1). 3,[18][19][20][21][22] The sensitizer absorbs incident photons and undergoes intersystem crossing, before a triplet excited state is transferred to the emitter. Two excited emitter molecules then form an encounter complex, and via a triplettriplet annihilation step an emitter singlet excited state is populated. Delayed fluorescence from that singlet manifold ultimately leads to emission of an upconverted photon.Since its discovery in the 1960s, TTA-UC has long been limited to liquid solutions, in which the intermolecular energy transfer steps are facilitated by high degrees of translational and rotational mobility. 5,23 Since solvent-based TTA-UC systems exhibit several drawbacks for practical applications, including limited lifetime 1 and complex implementation, 6,8,[24][25][26][27] the discovery that TTA-UC could be achieved in properly chosen polymers 28 has triggered new interest solid upconverting materials. 7 The first examples of TTA-UC in polymers were based on physical mixtures of sensitizers in conjugated polymers. 3,29 One further improve...

ABSTRACT. Molecules comprising aliphatic azo moieties are widely used as radical polymerization initiators, but only few studies have explored their usefulness as stimuliresponsive motifs in macromolecular constructs. The controlled degradation of azo-containing polymers has indeed remained largely unexplored. Here we present the syntheses of linear azocontaining polyamides and polyurethanes and report on their thermally and optically induced responses in solution and the solid state. We show that the stimuli-induced degradation behavior depends strongly on the nature of the polymer backbone, the state of matter, and in solution, on the nature of the solvent. The stimuli-responsive solid-state properties of the azo-containing materials may be particularly useful. In the case of the polyurethanes studied here, temperatureor light-induced cleavage of the azo motifs led to a controllable decrease of the molecular weight, which in turn caused a reduction of the elongation at break, modulus and strength. The controlled degradation of the polymer in well-defined areas can be readily achieved via photopatterning, and this approach was shown to be useful to produce solid structures with graded mechanical properties.2