Altering the Properties of Spiropyran Switches Using Coordination Cages with Different Symmetries

Abstract

Molecular confinement effects can profoundly alter the physicochemical properties of the confined species. A plethora of organic molecules were encapsulated within the cavities of supramolecular hosts, and the impact of the cavity size and polarity was widely investigated. However, the extent to which the properties of the confined guests can be affected by the symmetry of the cage�which dictates the shape of the cavity�remains to be understood. Here we show that cage symmetry has a dramatic effect on the equilibrium between two isomers of the encapsulated spiropyran guests. Working with two Pd-based coordination cages featuring similarly sized but differently shaped hydrophobic cavities, we found a highly selective stabilization of the isomer whose shape matches that of the cavity of the cage. A T d -symmetric cage stabilized the spiropyrans' colorless form and rendered them photochemically inert. In contrast, a D 2hsymmetric cage favored the colored isomer, while maintaining reversible photoswitching between the two states of the encapsulated spiropyrans. We also show that the switching kinetics strongly depend on the substitution pattern on the spiropyran scaffold. This finding was used to fabricate a time-sensitive information storage medium with tunable lifetimes of the encoded messages.

Isomerization of DASA Molecules in the Nanopores of Metal–Organic Frameworks: What Determines Its Reversibility?**

“…Among these external stimuli, light is often considered as an environmentally benign trigger to effectively switch the properties of materials owing to its noninvasive, and precise spatial and temporal control nature. [18,19] To date, photoresponsive MOFs mainly include those functionalized with azobenzenes (E/Z isomerizations), [20][21][22][23] diarylethenes, [24][25][26] spiropyrans (ring-opening/closing reactions), [27][28][29][30] and their mixture. [31] In this case, high-energy UV light irradiation is usually applied to trigger the isomerization of these organic switches, but the irradiation often leads to photodamage and high degradation, which inevitably reduce the fatigue resistance of materials.…”

Photoacidity of Indolinospirobenzopyrans in Water

“…In this regard, apart from substituent effects [122] it may be beneficial to focus on the establishment of selective non-covalent interactions through either supramolecular encapsulation and confined spaces. [127][128][129][130] Second, although we have shown the pH jumps of MCHs can be amplified by partial neutralization, it is not yet clear what the energy transduction efficiency [126] of the proton release is. We predict that systematic pH jump studies as a function of i) concentration, ii) degree of neutralization, and iii) irradiation power will be beneficial in this regard.…”

“…One for all deals with developing long‐lasting systems. In this regard, apart from substituent effects [122] it may be beneficial to focus on the establishment of selective non‐covalent interactions through either supramolecular encapsulation and confined spaces [127–130] . Second, although we have shown the pH jumps of MCHs can be amplified by partial neutralization, it is not yet clear what the energy transduction efficiency [126] of the proton release is.…”

Light-Driven Aqueous Dissipative Pseudorotaxanes with Tunable Fluorescence Enabling Deformable Nano-Assemblies

“…Developing functionalized artificial molecular machines that are stimuli-responsive, high adaptive, and self-regulating to their surroundings is highly challenging. Many research groups − have exploited diverse stimuli-responsive switches to build efficient responsive materials and dynamic molecular system, including molecular, − supramolecular, and mechanically interlocked switches . To amplify switching behavior, translational and/or rotary movements at the molecular and macro levels require rationally designed molecular building blocks and proper supramolecular arrangements to endow macroscopic smart materials with stimuli-responsiveness, adaptiveness, and intelligent behavior …”