Photosalient Effect Research Articles

Solution State-Like Reactivity of a Flexible Crystalline Werner-Type Metal Complex.

Flexible crystalline solids exhibit unique properties in response to external stimuli like heat and light. However, challenges exist in developing crystalline solids that have similar degrees of flexibility as in solution. Herein, we report the preparation of the new flexible crystalline metal complex [Cd(CF3SO3)2(4-spy)4] (4-spy=4-styrylpyridine), which contains photoreactive 4-spy ligand. Unlike traditional solids, this metal complex displays solution state-like [2+2] photocycloaddition reactivity. Specifically, UV irradiation of the crystalline material leads to formation of the same diverse array of dimers and cis isomer that are generated by photoreaction in the solution state. In addition, the photoresponsive flexibility of the solid leads to a photosalient effect and photo-induced formation of pores. The origin of the solution state-like photoreactivity of the solid is related to properties of the Cd(II) cation and fluorinated CF3SO3 anion, and the multi-orientational arrangement of the 4-spy ligands.

Coordination Site Selective Occupation Strategy for Tuning the Photosalient Effects of Photoactive Cd Complexes.

The application of photo responsive crystals to useful actuation demands a rational design to elicit controllable movement. The [2+2] photocycloaddition reaction triggers mechanical motion using associated photosalient (PS) effects. We herein report a coordination site selective occupation strategy to modulate the arrangement of C=C bonds and thereby tune the PS effect. Replacing or repositioning the donor atom at one end of the linear ligand allowed for a greater level of molecular structural flexibility, facilitating [2+2] photocycloaddition. The distance between photoreactive centres and coordination sites was adjusted by ligand design to regulate PS behaviour. This work suggests new avenues for modulating PS movement to achieve useful motion.

Solution State‐Like Reactivity of a Flexible Crystalline Werner‐Type Metal Complex

AbstractFlexible crystalline solids exhibit unique properties in response to external stimuli like heat and light. However, challenges exist in developing crystalline solids that have similar degrees of flexibility as in solution. Herein, we report the preparation of the new flexible crystalline metal complex [Cd(CF3SO3)2(4‐spy)4] (4‐spy=4‐styrylpyridine), which contains photoreactive 4‐spy ligand. Unlike traditional solids, this metal complex displays solution state‐like [2+2] photocycloaddition reactivity. Specifically, UV irradiation of the crystalline material leads to formation of the same diverse array of dimers and cis isomer that are generated by photoreaction in the solution state. In addition, the photoresponsive flexibility of the solid leads to a photosalient effect and photo‐induced formation of pores. The origin of the solution state‐like photoreactivity of the solid is related to properties of the Cd(II) cation and fluorinated CF3SO3 anion, and the multi‐orientational arrangement of the 4‐spy ligands.

Strategies to Diversification of the Mechanical Properties of Organic Crystals

AbstractStructurally ordered soft materials that respond to complementary stimuli are susceptible to control over their spatial and temporal morphostructural configurations by intersectional or combined effects such as gating, feedback, shape‐memory, or programming. In the absence of general and robust design and prediction strategies for their mechanical properties, at present, combined chemical and crystal engineering approaches could provide useful guidelines to identify effectors that determine both the magnitude and time of their response. Here, we capitalize on the purported ability of soft intermolecular interactions to instigate mechanical compliance by using halogenation to elicit both mechanical and photochemical activity of organic crystals. Starting from (E)‐1,4‐diphenylbut‐2‐ene‐1,4‐dione, whose crystals are brittle and photoinert, we use double and quadruple halogenation to introduce halogen‐bonded planes that become interfaces for molecular gliding, rendering the material mechanically and photochemically plastic. Fluorination diversifies the mechanical effects further, and crystals of the tetrafluoro derivative are not only elastic but also motile, displaying the rare photosalient effect.

Strategies to Diversification of the Mechanical Properties of Organic Crystals.

Structurally ordered soft materials that respond to complementary stimuli are susceptible to control over their spatial and temporal morphostructural configurations by intersectional or combined effects such as gating, feedback, shape-memory, or programming. In the absence of general and robust design and prediction strategies for their mechanical properties, at present, combined chemical and crystal engineering approaches could provide useful guidelines to identify effectors that determine both the magnitude and time of their response. Here, we capitalize on the purported ability of soft intermolecular interactions to instigate mechanical compliance by using halogenation to elicit both mechanical and photochemical activity of organic crystals. Starting from (E)-1,4-diphenylbut-2-ene-1,4-dione, whose crystals are brittle and photoinert, we use double and quadruple halogenation to introduce halogen-bonded planes that become interfaces for molecular gliding, rendering the material mechanically and photochemically plastic. Fluorination diversifies the mechanical effects further, and crystals of the tetrafluoro derivative are not only elastic but also motile, displaying the rare photosalient effect.

Solid‐State Photochemical Cascade Process Boosting Smart Ultralong Room‐Temperature Phosphorescence in Bismuth Halides

AbstractMolecular ultralong room‐temperature phosphorescence (RTP), exhibiting multiple stimuli‐responsive characteristics, has garnered considerable attention due to its potential applications in light‐emitting devices, sensors, and information safety. This work proposes the utilization of photochemical cascade processes (PCCPs) in molecular crystals to design a stepwise smart RTP switch. By harnessing the sequential dynamics of photo‐burst movement (induced by [2+2] photocycloaddition) and photochromism (induced by photogenerated radicals) in a bismuth (Bi)‐based metal‐organic halide (MOH), a continuous and photo‐responsive ultralong RTP can be achieved. Furthermore, utilizing the same Bi‐based MOH, diverse application demonstrations, such as multi‐mode anti‐counterfeiting and information encryption, can be easily implemented. This work thus not only serves as a proof‐of‐concept for the development of solid‐state PCCPs that integrate photosalient effect and photochromism with light‐chemical‐mechanical energy conversion, but also lays the groundwork for designing new Bi‐based MOHs with dynamically responsive ultralong RTP.

Solid-State Photochemical Cascade Process Boosting Smart Ultralong Room-Temperature Phosphorescence in Bismuth Halides.

Molecular ultralong room-temperature phosphorescence (RTP), exhibiting multiple stimuli-responsive characteristics, has garnered considerable attention due to its potential applications in light-emitting devices, sensors, and information safety. This work proposes the utilization of photochemical cascade processes (PCCPs) in molecular crystals to design a stepwise smart RTP switch. By harnessing the sequential dynamics of photo-burst movement (induced by [2+2] photocycloaddition) and photochromism (induced by photogenerated radicals) in a bismuth (Bi)-based metal-organic halide (MOH), a continuous and photo-responsive ultralong RTP can be achieved. Furthermore, utilizing the same Bi-based MOH, diverse application demonstrations, such as multi-mode anti-counterfeiting and information encryption, can be easily implemented. This work thus not only serves as a proof-of-concept for the development of solid-state PCCPs that integrate photosalient effect and photochromism with light-chemical-mechanical energy conversion, but also lays the groundwork for designing new Bi-based MOHs with dynamically responsive ultralong RTP.

The Photosalient Effect and Thermochromic Luminescence Based on o‐Carborane‐Assisted π‐Stacking in the Crystalline State

AbstractHerein, we report the unique multiple‐stimuli responsiveness of anthracene‐tethered o‐carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o‐carborane units. Two compounds had characteristic crystal structures involving the columnar π‐stacking structures of the anthracene units. From the analysis of crystalline‐state structure–property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature‐dependent photophysical dual‐emission properties including excimer emission of anthracene. Those properties were considered as non‐radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π‐stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X‐ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested.

The Photosalient Effect and Thermochromic Luminescence Based on o-Carborane-Assisted π-Stacking in the Crystalline State.

Herein, we report the unique multiple-stimuli responsiveness of anthracene-tethered o-carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o-carborane units. Two compounds had characteristic crystal structures involving the columnar π-stacking structures of the anthracene units. From the analysis of crystalline-state structure-property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature-dependent photophysical dual-emission properties including excimer emission of anthracene. Those properties were considered as non-radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π-stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X-ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested.

Single-Crystal-to-Single-Crystal Photosynthesis of Supramolecular Organoboron Polymers with Dynamic Effects.

The solid-state synthesis of single-crystalline organic polymers, having functional properties, remains an attractive and developing research area in polymer chemistry and materials science. However, light-triggered topochemical synthesis of crystalline polymers comprising an organoboron backbone has not yet been reported. Here, we describe an intriguing example of single-crystal-to-single-crystal (SCSC) rapid photosynthesis (occurs on a seconds-scale) of two structurally different linear organoboron polymers, driven by environmentally sustainable visible/sun light, obtained from the same monomer molecule. A newly designed Lewis acid-base type molecular B ← N organoboron adduct (consisting of an organoboron core and naphthylvinylpyridine ligands) crystallizes in two solid-state forms featuring the same chemical structure but different 3D structural topologies, namely, monomers 1 and 2. The solvate molecule-free crystals of 1 undergo topochemical photopolymerization via an unusual olefin-naphthyl ring [2 + 2] cyclization to yield the single crystalline [3]-ladderane polymer 1P growing along the B ← N linkages, accompanied by instantaneous and violent macroscopic mechanical motions or photosalient effects (such as bending-reshaping and jumping motions). In contrast, visible light-harvesting single crystals of 2 quantitatively polymerize to a B ← N bond-stabilized polymer 2P in a SCSC fashion owing to the rapid [2 + 2] cycloaddition reaction among olefin double bonds. Such olefin bonds in the crystals of 2 are suitably preorganized for photoreaction due to the presence of solvate molecules in the crystal packing. Single crystals of 2 also show photodynamic jumping motions - in response to visible light but in a relatively slower fashion than the crystals of 1. In addition to SCSC topochemical polymerization and dynamic motions, both monomer crystals and their single-crystalline polymers feature green emissive and short-lived room-temperature phosphorescence properties upon excitation with visible-light wavelength.

Releasing a bound molecular spring with light: a visible light-triggered photosalient effect tied to polymorphism.

Here we present a study on the solid state properties of trans tetra-ortho-bromo azobenzene (4Br-Azo). Two distinct crystal polymorphs were identified: the α-phase and β-phase. Notably, only the β-phase exhibited an extraordinary photosalient effect (jumping/breaking) upon exposure to a wide range of visible light. Powder X-ray diffraction and Raman spectroscopy revealed that the β-phase is metastable and can transition to the α-phase when subjected to specific stimuli like heat and light. Furthermore, single crystal X-ray diffraction and density functional theory calculations highlighted the significance of a highly strained conformer in the β-phase, showing that the metastability of the phase potentially arises from relieving this strain. This metastability leads to a light induced phase transition, which appears to be the cause of the photosalient effect in these crystals. Interestingly the polymorphism at the core of 4Br-Azo's dynamic behavior is based on different arrangements of halogen based intermolecular interactions. It is possible that continued study on combining visible light capturing chromophores with halogen interaction-based polymorphism will lead to the discovery of even more visible light controlled dynamic crystal materials.

Solid-state excimer emission of o-carborane derivatives and applications for stimuli-responsive luminescent materials.

o-Carborane is an icosahedral cluster containing boron and has been paid attention as a versatile platform for constructing stimuli-responsive materials with solid-state luminescence properties by suppressing aggregation-caused quenching (ACQ), which is the emission annihilation process observed in condensed states, such as concentrated solutions, solids and films. Non-specific intermolecular interactions in the condensed states resulting in ACQ are disturbed by the spherical boron cluster. More recently, it has been demonstrated from several reports that o-carborane is capable of assisting solid-state excimer emission in aryl-modified o-carboranes. Moreover, some of these materials provide unique stimuli-responsiveness. In the commodity design for solid-state luminescent materials, o-carboranes are responsible for disturbing intermolecular interactions and subsequently presenting solid-state luminescence. On the other hand, excimer emission, which is inducible from the intermolecular photophysical process, has been discovered in the solid state based on o-carborane materials. In this manuscript, recent progress in stimuli-responsive luminescent materials via excimer formation will be described. Moreover, as the further potential of o-carborane materials, recent findings on the photo-salient effect which can be induced through excimer formation followed by photoreaction will also be explained.

Photosalient effect and photodimerization of mono- and dicationic organic salts incorporated in 4-styrylpyridine

The study presents the photodimerization of mono- and dicationic organic salts incorporated with 4-styrylpyridine and their photo-bending behavior.

Dynamic organic crystals as exceptionally efficient artificial natural light-harvesting actuators.

Dynamic organic crystal materials that can directly convert solar energy into mechanical work hold the potential to be efficient artificial actuators. However, developing dynamic organic crystals that can efficiently transform natural light energy into mechanical energy is still quite challenging. Herein, a novel dynamic organic crystal whose two polymorphs (Form I and Form II) are both capable of effectively converting natural light into work was successfully synthesized. Under the irradiation of ultraviolet (UV), blue and natural light, the on/off toggling of a photosalient effect could be triggered. Specifically, under UV light irradiation, Form I demonstrates output work densities of about 4.2-8.4 × 104 J m-3 and 1.6-4.9 × 102 J m-3 before and after disintegration, respectively. Form II exhibits output work densities of about 1.3 × 102 to 1.9 × 103 J m-3 by means of photoinduced bending, suggesting that controllable bending may be more favorable for energy harvesting than the photosalient effect. Utilizing the exceptionally high energy transduction efficiency of Form I, we developed a natural light-driven micro-actuator that can realize output work densities of 2.8-5.0 × 104 J m-3. The natural light-harvesting performance of this actuator significantly surpasses those of previously reported photomechanical crystals and could even be comparable to thermal actuators.

Photoresponsive metal-organic framework materials for advance applications.

The interaction between light and materials produces a range of phenomena within molecular systems, leading to advanced applications in the field of materials science. In this regard, metal-organic framework (MOF) materials have become superior candidates to others because of their easy tailor-made synthetic methods via incorporation of photoactive moieties into their structural assembly. Photoresponsive MOFs exhibit a massive variety of exciting properties, including photochromism, photomagnetism, photoluminescence, photon up or down conversion, photoconductivity, nonlinear optical properties, photosalient effects and photoinduced switching of conformations. These photoresponsive properties of MOFs regulate different potential applications, such as on-demand gas sorption and separation, optical sensing, fabrication of photoactuators and photosensing electronic devices, dye degradation, catalysis, cargo delivery, ink-free erasable printing, bio-imaging and drug delivery in biological systems. Therefore, judicious crystal engineering along with an understanding of their structure-property relationship will lead to the fabrication of desired photosensitive MOFs. Herein, we attempted to incorporate categorical descriptions based on advanced applications of photoresponsive MOFs considering a wide range of recent publications.

The photomechanical bending and photosalient effect of flexible crystals of an acylhydrazone

Elastically flexible single crystals of an acylhydrazone derivative displayed photosalient effect preceded by photomechanical bending, demonstrating their utilisation for the design of multi-performance materials.

Polymorph driven diversification of photosalient responses in a zinc(II) coordination complex.

A novel crystallographic form of a Zn(II) coordination complex [Zn(4-ohbz)2(4-nvp)2] (1-Form-III) (H4-ohbz = 4-hydroxybenzoic acid and 4-nvp = (E)-4-(1-naphthylvinyl)pyridine), undergoes a solid-state photochemical [2+2] cycloaddition reaction accompanied by a moderate photosalient effect, whereby single-crystals show cracking and splitting. This UV-induced cycloaddition accompanies a single-crystal to single-crystal transformation, allowing for continuous monitoring of the unit cell parameters. The new polymorph represents an intermediate form of the two previously reported crystallographic forms of [Zn(4-ohbz)2(4-nvp)2], and provides novel insight into moderating the magnitude of photosalient responses across polymorphic materials.

Integrating dual photoresponsive molecules via a cocrystal strategy: photosalient effects, negative photochromism, and fluorescence enhancement

Integrating dual photoresponsive molecules via a cocrystal strategy: photosalient effects, negative photochromism, and fluorescence enhancement

Solid-State Photodimerization Reaction with Photosalient Effect and Photophysical and Electrochemical Properties of N-Methylated 1-Naphthylvinyl-4-Quinoline

Solid-State Photodimerization Reaction with Photosalient Effect and Photophysical and Electrochemical Properties of <i>N</i>-Methylated 1-Naphthylvinyl-4-Quinoline

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

AbstractIn 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.