Visible Light‐fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals

Abstract

In the quest for essential energy solutions towards an ecological friendly future, the transformation of visible light/solar energy into mechanical motions in metal‐free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, and all‐organic electronic devices. Such green energy‐triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid‐base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both ultraviolet (UV) and visible light associated with quantitative single‐crystal‐to‐single‐crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light‐promoted dynamic green RTP as their emission peaks promptly blue‐shift, due to instantaneous photomechanical effects. Time‐dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X‐ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light‐driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli‐responsive multi‐functional crystalline materials.

Boron‐Nitrogen Lewis Pairs in the Assembly of Supramolecular Macrocycles, Molecular Cages, Polymers, and 3D Materials

“…Multiply charged supramolecular polymers were accessed by BÀ N LP formation between diborylated imidazolium-based ionic liquids and pyrazine or 1,4-diazabicyclo-[2.2.2]octane. [31] Matsumi and co-workers reported that these polymers were soluble in highly polar solvents such as methanol, showing 11 B NMR signals in the expected region of tetracoordinate boron. Lithium ion conductivities of up to 8.8 × 10 À 6 S cm À 1 at 51 °C were measured in the presence of equimolar amounts of lithium triflimide, LiNTf 2 .…”

“…Even cooperative N 2 activation has been achieved with a diboraanthracene‐samarocene pair [9d] . B−N LP formation has also been exploited to position photoactive molecules in close proximity to one another in a way that allows for topochemical [2+2] olefin photodimerization to occur rapidly (e.g., 5 ) [10] or to trigger visible light‐fueled photomechanical processes [11] . Finally, B−N LP formation has been exploited to modulate the electronic structure and photophysical properties of π‐conjugated organic materials.…”

“…[9d] BÀ N LP formation has also been exploited to position photoactive molecules in close proximity to one another in a way that allows for topochemical [2 + 2] olefin photodimerization to occur rapidly (e.g., 5) [10] or to trigger visible light-fueled photomechanical processes. [11] Finally, BÀ N LP formation has been exploited to modulate the electronic structure and photophysical properties of π-conjugated organic materials. For instance, the band gap of π-conjugated polymers containing N-heterocyclic building blocks can be effectively altered via BÀ N LP formation.…”

Mechanical Effects of Elastic Crystals Driven by Natural Sunlight and Force

“…Organic light-emitting crystals composed of π-conjugated molecules can be applied in sensors, [1] optical waveguide devices, [2] smart materials. [3][4][5][6][7] These crystals have attracted great interest from the scientific community. Some stimuliresponsive materials can convert light, thermal, or mechanical energy into mechanical motion at the macro-, micro-, or nano-scale, making them promising materials for various applications, such as light harvesting, mechanical actuation, molecular mechanics, smart switches, and optical sensing.…”

“…Organic light‐emitting crystals composed of π‐conjugated molecules can be applied in sensors, [1] optical waveguide devices, [2] smart materials [3–7] . These crystals have attracted great interest from the scientific community.…”