Responsive materials prepared using shape‐memory photonic crystals have potential applications in rewritable photonic devices, security features, and optical coatings. By embedding chiral nematic cellulose nanocrystals (CNCs) in a polyacrylate matrix, a shape‐memory photonic crystal thermoplastic (CNC‐SMP) allows reversible capture of different colored states is reported. In this system, the temperature is used to program the shape‐memory response, while pressure is used to compress the helical pitch of the CNC chiral nematic organization. By increasing the force applied (≈140–230 N), the structural color can be tuned from red to blue. Then, on‐demand, the CNC‐SMP can recover to its original state by heating it above the glass transition temperature. This cycle can be performed over 15 times without any loss of the shape‐memory behavior or mechanical degradation of the sample. In addition, multicolor readouts can be programmed into the chiral nematic CNC‐SMP by using a patterned substrate to press the sample, while the glass transition temperature of the CNC‐SMP can be tuned over a 90 °C range by altering the monomer composition used to prepare the polyacrylate matrix.

We report the synthesis, characterization, and spectroscopic investigations of a new responsive‐at‐metal cyclometalated platinum(II) complex. With mild chemical oxidants and reductants, it was possible to obtain the same complex in three different oxidation states and each of these complexes was structurally characterized by single‐crystal X‐ray diffraction. We discovered that the platinum(II) complex displays strong solvatochromism in the solid state, which can be attributed to modulation of Pt⋅⋅⋅Pt interactions that results in switching between optical and photoluminescent states. Incorporating responsive‐at‐metal species as dynamic components in nanostructured materials might facilitate response amplification, sensing, actuation, or self‐healing processes.

Platinum(II) complexes display versatile chromic behavior as a consequence of their square planar geometry, which enables intra‐ and intermolecular Pt⋅⋅⋅Pt interactions via open axial coordination sites. These metallophilic interactions are known to generate metal‐metal‐to‐ligand‐charge transfer (MMLCT) transitions, in addition to the ligand‐to‐ligand charge transfer (LLCT) and metal‐to‐ligand‐charge‐transfer (MLCT) transitions that are already present. The electronic properties of such complexes, and consequently the magnitude and intensity of these transitions, can be modulated by various functional groups as well as environmental factors, affording control over the color and luminescence. The responsive behavior of these complexes makes them attractive candidates for chromic devices with applications in memory, encryption, sensors, and optoelectronics. This Minireview summarizes the mechanisms and reversibility of optical chromism in platinum(II) complexes, with a focus on the recent developments in the literature.

Multiresponsive materials can adapt to numerous changes in their local environment, which makes them highly valuable for various applications. Although nanostructured and polymeric multiresponsive materials are plentiful, small-molecule analogues are scarce. This work presents a compact cyclometalated platinum­(II) complex that bears a crown ether cavity (18C6-PtII); the intimate ring/emitter connectivity is key to unlocking multiresponsiveness. Complex 18C6-PtII responds to (i) cationic guests, producing changes in luminescence in both solution and the solid state, (ii) solvent molecules, which perturb the packing of the complex in the solid state and cause reversible color changes, and (iii) solvent polarity, which leads to controlled aggregation. These responses may enable 18C6-PtII to function as a sensor for ions and solvents, or as a functional unit for the fabrication of hybrid supramolecular polymers and metallogels.

Cellulose nanocrystals (CNCs) spontaneously assemble into gels when mixed with a polyionic organic or inorganic salt. Here, we have used this ion‐induced gelation strategy to create functional CNC gels with a rigid tetracationic macrocycle, cyclobis(paraquat‐p‐phenylene) (CBPQT4+). Addition of [CBPQT]Cl4 to CNCs causes gelation and embeds an active host inside the material. The fabricated CNC gels can reversibly absorb guest molecules from solution then undergo molecular recognition processes that create colorful host–guest complexes. These materials have been implemented in gel chromatography (for guest exchange and separation), and as elements to encode 2‐ and 3‐dimensional patterns. We anticipate that this concept might be extended to design a set of responsive and selective gel‐like materials functioning as, for instance, water‐pollutant scavengers, substrates for chiral separations, or molecular flasks.