Energy consumption in chemical fuel-driven self-assembly

Nature extensively exploits high-energy transient self-assembly structures that are able to perform work through a dissipative process. Often, self-assembly relies on the use of molecules as fuel that is consumed to drive thermodynamically unfavourable reactions away from equilibrium. Implementing this kind of non-equilibrium self-assembly process in synthetic systems is bound to profoundly impact the fields of chemistry, materials science and synthetic biology, leading to innovative dissipative structures able to convert and store chemical energy. Yet, despite increasing efforts, the basic principles underlying chemical fuel-driven dissipative self-assembly are often overlooked, generating confusion around the meaning and definition of scientific terms, which does not favour progress in the field. The scope of this Perspective is to bring closer together current experimental approaches and conceptual frameworks. From our analysis it also emerges that chemically fuelled dissipative processes may have played a crucial role in evolutionary processes

Pi-extended anthracenes as sensitive probes for mechanical stress

Smart molecular systems having the ability to report on mechanical strain or failure in polymers via alteration of their optical properties are of great interest in materials science. However, only limited attention has been devoted to targeted chromophore engineering to fine-tune their physicochemical properties. Here, we describe the synthesis of π-extended anthracenes that can be released from their respective maleimide Diels–Alder adducts through the application of mechanical stress in solution and in the solid state. We demonstrate the improvement of fluorescence quantum yield as well as the tuning of excitation and emission wavelengths while retaining their excellent mechanochemical properties laying the foundation for a new series of mechanophores whose spectral characteristics can be modularly adjusted

Optical sensing of stress in polymers

This chapter discusses recent approaches towards the optical detection of stress and deformation in polymeric materials, an important tool in monitoring material integrity and in the study of failure mechanisms of polymeric materials. Optical sensing has specific advantages based on the ease of detection, high sensitivity and spectral resolution of light. In this chapter, a classification of sensing mechanisms is used that distinguishes between the molecular phenomena of isomerization, bond scission, change in conjugation and collective phenomena such as changes in chromophore aggregation and photonic band gap tuning. Molecular mechanisms are discussed that have been used to obtain stress-induced changes in absorption and fluorescence properties and recent work is presented in which the chain scission of dioxetanes is used to produce a luminescent signal with high detectability. Pi-conjugated systems play an important role in optical detection of stress and damage in polymers because their optical properties are very sensitive to changes in conformation and aggregation state. Finally, photonic band gap polymers and cholesteric liquid crystals are discussed, in which the periodic organization of structural features at the scale of the wavelength of light leads to strain-dependent reflection and absorption bands

Pi-extended anthracenes as sensitive probes for mechanical stress

Smart molecular systems having the ability to report on mechanical strain or failure in polymers via alteration of their optical properties are of great interest in materials science. However, only limited attention has been devoted to targeted chromophore engineering to fine-tune their physicochemical properties. Here, we describe the synthesis of π-extended anthracenes that can be released from their respective maleimide Diels–Alder adducts through the application of mechanical stress in solution and in the solid state. We demonstrate the improvement of fluorescence quantum yield as well as the tuning of excitation and emission wavelengths while retaining their excellent mechanochemical properties laying the foundation for a new series of mechanophores whose spectral characteristics can be modularly adjusted

Stress-induced colouration and crosslinking of polymeric materials by mechanochemical formation of triphenylimidazolyl radicals

\u3cp\u3eUnder mechanical stress, the hexaarylbiimidazole (HABI) motif can cleave to triphenylimidazolyl radicals when incorporated into a polymer matrix. The mechanically produced coloured radicals can initiate secondary radical reactions yielding polymer networks. Thus, the HABI mechanophore combines optical reporting of bond scission and reinforcement of polymers in a single molecular moiety.\u3c/p\u3

Optical sensing of stress in polymers

\u3cp\u3eThis chapter discusses recent approaches towards the optical detection of stress and deformation in polymeric materials, an important tool in monitoring material integrity and in the study of failure mechanisms of polymeric materials. Optical sensing has specific advantages based on the ease of detection, high sensitivity and spectral resolution of light. In this chapter, a classification of sensing mechanisms is used that distinguishes between the molecular phenomena of isomerization, bond scission, change in conjugation and collective phenomena such as changes in chromophore aggregation and photonic band gap tuning. Molecular mechanisms are discussed that have been used to obtain stress-induced changes in absorption and fluorescence properties and recent work is presented in which the chain scission of dioxetanes is used to produce a luminescent signal with high detectability. Pi-conjugated systems play an important role in optical detection of stress and damage in polymers because their optical properties are very sensitive to changes in conformation and aggregation state. Finally, photonic band gap polymers and cholesteric liquid crystals are discussed, in which the periodic organization of structural features at the scale of the wavelength of light leads to strain-dependent reflection and absorption bands.\u3c/p\u3

Autonomous repair of polymer networks by stress-induced catalyst activation

development of future ‘smart’ materials and devices. Here we present the development of a novel second generation Grubb's catalyst that can be activated through the application of mechanical force in solution as well as in the solid state. We show thorough kinetic analyses as well as extensive optimization for the improvement of the catalyst's activity and lifetime and have eventually translated the concept to the solid state. It could be successfully proven that mechanical activation initiates the ROMP to linear as well as cross-linked polymers in the solid state and by this we present for the first time the autonomous repair of a material that relies on the mechanochemical activation of catalysts on the molecular level. We are certain that this tailor-made prototypical catalyst-system establishes an important step for the implementation of self-healing materials in an everyday environment and are confident that this novel motif will stimulate future research on this field

Going with the Flow: Tunable Flow-Induced Polymer Mechanochemistry

Mechanical forces can drive chemical transformations in polymers, directing reactions along otherwise inaccessible pathways, providing exciting possibilities for developing smart, responsive materials. The state-of-the-art test for solution-based polymer mechanochemistry development is ultrasonication. However, this does not accurately model the forces that will be applied during device fabrication using processes such as 3D printing or spray coating. Here, we take a step towards predictably translating mechanochemistry from molecular design to manufacturing by demonstrating a highly controlled nozzle flow setup in which the shear forces being delivered are precisely tuned. Our results show we can individually study solvent viscosity, fluid strain rate and the nature of the breaking bond. Importantly, we show the influence of each is different to that suggested by ultrasonication (altered quantity of chain breakage and critical polymer chain length). We present significant development in the understanding of polymer bond breakage during manufacturing flows to help guide design of active components that trigger on demand. Using an anthracene-based mechanophore we demonstrate the triggering of a fluorescence switch-on through careful selection of the flow parameters. This work opens the avenue for programmed chemical transformations during inline manufacturing processes leading to tunable, heterogeneous final products from a single source material