Photomechanical Research Articles

Tropisms of Underground Shoots—Stolons and Rhizomes

In the review, the problem of plant movements (photo- and gravitropism) is discussed. The contemporary data on physiological and molecular mechanisms of tropisms in underground shoots and roots are presented. Special attention is paid to diagravitropism phenomenon in underground shoots (stolons and rhizomes) that grow in perpendicular direction to the Earth's gravitational axis. The role of phytochrome control in maintaining the horizontal growth of stolons and rhizomes is demonstrated, and physiological mechanisms of photo- and diagravitropism are discussed. It is shown that switching of an underground shoot tip from diatropic to ortotropic (vertical) growth is dependent on the carbohydrate and phytohor-mone balance. The perspectives are outlined for further exploratory studies on mechanisms of growth orientation and morphogenesis of underground diagravitropic shoots.

Features of Laser-Induced Modification of Sclera and Cornea

Results are presented from studying collagen degradation in scleral and corneal tissues upon CW IR laser irradiation at a wavelength of 1.56 μm and powers of 1.4 and 7 W. The exposure time is such that the radiometrically determined maximum tissue temperature ranges from 55 to 70°C. It is shown that at a power of 1.4 W, laser-induced collagen denaturation in sclera and cornea starts at 55 and 60°C, respectively. When the power is increased to 7 W, the temperature of denaturation onset rises by 2°C. These findings are discussed from the viewpoint of the joint photothermal and photomechanical effects of laser irradiation.

Stomata-Inspired Photomechanical Ion Nanochannels Modified by Azobenzene Composites.

A low-powered and highly selective photomechanical sensor system mimicking stomata in the epidermis of leaves harvested from nature is demonstrated. This device uses a light-responsive composite consisting of 4-amino-1,1'-azobenzene-3,4'-disulfonic acid monosodium salt (AZO) and poly(diallyldimethylammonium chloride) (PDDA) coated on a membrane with tens of nanometer-size pores. The ionic current change through the pore channels as a function of pore size variation is then measured. The tran-cis isomerism of AZO-PDDA during light irradiation and the operation mechanism of photomechanical ion channel sensor are discussed and analyzed using UV-vis spectroscopy and atomic force microscopy analysis. It presents the discriminative current levels to the different light wavelengths. The response time of the photoreceptor is about 0.2 s and it consumes very low operating power (≈15 nW) at 0.1 V bias. In addition, it is found that the change of the pore diameter during the light irradiation is due to the photomechanical effect, which is capable of distinguishing light intensity and wavelength.

Laser Initiation of Photo- and Thermal Processes on a Pentaammine (5-Nytrotetrazolato-N2) Cobalt(III) Perchlorate Example

Microscopic mechanisms of photo- and thermal structural transformations initiated by laser radiation are considered. The results obtained are illustrated on an energy-saturated metal complex of pentaamine (5-nytrotetrazolato-N2) cobalt(III) perchlorate and its fullerene modifications.

Liquid-Crystalline Dynamic Networks Doped with Gold Nanorods Showing Enhanced Photocontrol of Actuation.

A near-infrared-light (NIR)- and UV-light-responsive polymer nanocomposite is synthesized by doping polymer-grafted gold nanorods into azobenzene liquid-crystalline dynamic networks (AuNR-ALCNs). The effects of the two different photoresponsive mechanisms, i.e., the photochemical reaction of azobenzene and the photothermal effect from the surface plasmon resonance of the AuNRs, are investigated by monitoring both the NIR- and UV-light-induced contraction forces of the oriented AuNR-ALCNs. By taking advantage of the material's easy processability, bilayer-structured actuators can be fabricated to display photocontrollable bending/unbending directions, as well as localized actuations through programmed alignment of azobenzene mesogens in selected regions. Versatile and complex motions enabled by the enhanced photocontrol of actuation are demonstrated, including plastic "athletes" that can execute light-controlled push-ups or sit-ups, and a light-driven caterpillar-inspired walker that can crawl forward on a ratcheted substrate at a speed of about 13 mm min-1 . Moreover, the photomechanical effects arising from the two types of light-triggered molecular motion, i.e., the trans-cis photoisomerization and a liquid-crystalline-isotropic phase transition of the azobenzene mesogens, are added up to design a polymer "crane" that is capable of performing light-controlled, robot-like, concerted macroscopic motions including grasping, lifting up, lowering down, and releasing an object.

Photomechanical effects in liquid crystalline polymer networks and elastomers

ABSTRACTLiquid crystals are widely employed as stimuli‐responsive materials. Liquid crystallinity can be retained in polymeric form. Photoinduced mechanical effects in liquid crystalline polymer networks and elastomers have been a topic of considerable recent research. This review details the historical underpinnings and recent advances in the synthesis and the corresponding photomechanical response of these materials. In nearly all cases, the conversion of light into mechanical work has employed azobenzene as either a guest additive or covalently attached to the network. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 695–705

The contribution of hydrogen bonding to the photomechanical response of azobenzene-functionalized polyamides

Photomechanical effects in materials can directly convert light stimulus into mechanical work.

Photomechanical Deformation of Azobenzene-Functionalized Polyimides Synthesized with Bulky Substituents.

Photomechanical effects realized in azobenzene-functionalized polyimides have shown large deformation and an exceptional increase in photogenerated force output. Here, we synthesize and characterize the photomechanical output of a series of linear polyimide materials prepared with a bulky substituent, incorporated via the development of a new bis(azobenzene-diamine) monomer containing a 9,9-diphenylfluorene cardo structure (azoCBODA). All six azoCBODA-containing polyimides are amorphous and exhibit high glass transition temperatures (Tg) ranging from 298 to 358 °C, storage moduli ranging from 2.27 to 3.81 GPa (at 30 °C), and good thermal stability. The magnitude of the photoinduced mechanical response of the azobenzene-functionalized polyimide is correlated to the rotational freedom of the polyimide chains (resulting in extensive segmental mobility) and fractional free volume (FFV > 0.1).

Light-induced Conductance Switching in Photomechanically Active Carbon Nanotube-Polymer Composites

Novel, optically responsive devices with a host of potential applications have been demonstrated by coupling carbon nanomaterials with photochromic molecules. For light-induced conductance switching in particular, we have recently shown that carbon nanotube-polymer nanocomposites containing azobenzene are very attractive and provide stable and non-degradable changes in conductivity over time at standard laboratory conditions. In these composites, the photoswitching mechanisms are based on light-induced changes in electronic properties and related to the Pool-Frenkel conduction mechanism. However, no link between conductivity switching and the molecular motion of azobenzene chromophores could be found due to application of high elastic modulus polymer matrices. Here we report on single wall carbon nanotube-polymer nanocomposites with a soft polycaprolactone polymer host. Such a system clearly shows the transfer of light-induced, nano-sized molecular motion to macroscopic thickness changes of the composite matrix. We demonstrate that these photomechanical effects can indeed overshadow the electronic effects in conductivity switching behavior and lead to a reversion of the conductivity switching direction near the percolation threshold.

Spectroelectrochemical analysis of the mechanism of (photo)electrochemical hydrogen evolution at a catalytic interface

Multi-electron heterogeneous catalysis is a pivotal element in the (photo)electrochemical generation of solar fuels. However, mechanistic studies of these systems are difficult to elucidate by means of electrochemical methods alone. Here we report a spectroelectrochemical analysis of hydrogen evolution on ruthenium oxide employed as an electrocatalyst and as part of a cuprous oxide-based photocathode. We use optical absorbance spectroscopy to quantify the densities of reduced ruthenium oxide species, and correlate these with current densities resulting from proton reduction. This enables us to compare directly the catalytic function of dark and light electrodes. We find that hydrogen evolution is second order in the density of active, doubly reduced species independent of whether these are generated by applied potential or light irradiation. Our observation of a second order rate law allows us to distinguish between the most common reaction paths and propose a mechanism involving the homolytic reductive elimination of hydrogen.

A study on micro hydroforming using shock wave of 355 nm UV-pulsed laser

In this paper, we proposed a new manufacturing technology of micro hydroforming using 355nm ultraviolet(UV)-pulsed laser. Hydroforming is known as a well-established technology to manufacture metallic parts, in particular for mass production of sheet metal, for several industrial applications such as automobiles, battery and military products. In addition laser shock processing(LSP) has been developed as the expanded applications of electrical and mechatronic devices. When the material was exposed to laser beam, multiple phenomena like the photochemical, the photothermal and the photomechanical effect are simultaneously occurred at the spot area. Especially, the photothermal effect due to laser heat transfer makes it hard to improve the accuracy of laser processing. To reduce the thermal effect and to enhance the photomechanical effect, the laser was irradiated under water in this paper. Strong forming pressure of LSP was provided by the higher density of water than air, which could help directly manufacture the thin sheet metal materials like as laser direct writing. We also conducted computer simulation using finite element method(FEM) to demonstrate its deformation behaviour with and without the strain rate effect of 104–105 (sec−1). Compared with conventional processing technology, this new method can provide high selectivity, excellent hydroforming efficiency and lower cost to achieve micro grooving pattern on the surface of thin metal sheet.

Theranostics for Drug Delivery Based on Short Pulsed Light-Induced Photoacoustic and Photomechanical Effects

Theranostics for Drug Delivery Based on Short Pulsed Light-Induced Photoacoustic and Photomechanical Effects

ピコ秒レーザーによる刺青および良性色素性病変に対する治療

Since 2013, novel picosecond duration lasers (ps-lasers) have become commercially available and the subsequent clinical trials have reported the safety and efficacy in treating multicolored and recalcitrant tattoos. It is considered that irradiation of targets with the ultra-short picosecond pulses can induce almost instantaneous heating of chromophores in the skin and greater fragmentation of the targets in an almost nonlinear fashion, with even less damage to adjacent structures than was achieved with the ns-domain lasers. These laser-tissue interaction caused by picosecond duration laser irradiation is named photoacoustic or photomechanical effect, not photothermal effect.Application of the ps-laser for the treatment of unwanted tattoos was started in authors’ clinic from December 2013. From our experience of the great success of tattoo removal with the ps-laser, we have also started the treatment of epidermal or dermal benign pigmented lesions with ps-lasers, and have obtained good clinical results without persistent adverse effects such as post-inflammatory hyper-pigmentation, hypo-pigmentation and scarring.These novel laser devices, which have been developed based on the theory of ps-laser tissue interaction, might set the fashion for the new approach to treat the cutaneous pigmented lesions.

Photoactive/Passive Molecular Glass Blends: An Efficient Strategy to Optimize Azomaterials for Surface Relief Grating Inscription.

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Disperse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol % of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE, and initial inscription rate reach a maximum when Tg is 25-40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol % azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE 6-fold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo-orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo-orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Shaping photomechanical effects in tissue ablation using 355 nm laser pulses.

We investigate the influence of the cladding diameter of an optical delivery fiber on the ablation dynamics of porcine aorta immersed in tetracycline antibiotic solution using 355 nm nanosecond pulses. We manipulate the pressure transients by enforcing a rear rigid interface (applied by an enlargement of the cladding diameter) to the ablated area, which leads to enhanced ablation efficiency along with a reduction in tissue disruption effects. Numerical simulations, based on the finite elements method, are used to study the propagation of the pressure transients within the suggested scheme. Ultrasonic transducers are used for measuring the increased pressure in front of the fiber's facet and the reduced pressure at the fiber's circumference in the presence of large diameter cladding. The increase and decrease are both found to be by a factor of ˜1.8. The width of the cavitation bubble is measured by high-speed photography. An enlargement of 13.8% is demonstrated, at the expense of backward expansion along the fiber's axis. A histopathological in vitro study demonstrates an average enhancement of 12.27% in the diameter of the ablated crater, as well as significant reduction in the disruption effects. Our study sheds light on the potential to improve the ablation efficiency without additional energy cost, along with attaining improved safety for interventional medical procedures.

Photo-induced refractive index and topographical surface gratings in functionalized nanocarbon solid film

We demonstrate that a single-walled carbon nanotube network noncovalently coupled with a pyrene-modified azo-benzene chromophore functions as a host matrix for a broad range of photo-orientation and photomechanical effects. The chromophore could be efficiently reoriented through repeated trans-cis-trans isomerization under linearly polarized 480 nm light, with Δn of 0.012 at 650 nm and fast characteristic rise-times of 0.12 s. Erasable phase diffraction gratings could also be written, with permanent surface relief gratings forming at sufficiently long irradiation times. In addition to demonstrating a mechanism for photo-manipulation of single-walled carbon nanotubes, these results show photo-orientation of chromophores in azo-functionalized single-walled carbon nanotube networks as a path towards the photosensitive tuning of the electrostatic environment of the nanotube.

Surface and Bulk Effects in Photochemical Reactions and Photomechanical Effects in Dynamic Molecular Crystals.

The increasing number of reports on photomechanical effects in molecular crystals necessitates systematic studies to understand the intrinsic and external effectors that determine and have predictive power of their type and magnitude. Differential light absorption and product gradient between the surface and the bulk of the crystal are often invoked to qualitatively explain the mechanical response of crystals to light; however, the details on how this difference in photochemical response accounts for macroscopic effects such as surface modification, deformation, or disintegration of crystals are yet to be established. Using both bulk- and surface-sensitive analytical techniques, a rare instance of benzylidenefuranone crystals is studied here, and it is capable of several distinct types of photomechanical response including surface striation and delamination, photosalient effect (ballistic disintegration and motion), and photoinduced bending by dimerization. The results provide a holistic view on these effects and set the stage for the development of overarching theoretical models to describe the photomechanics in the ordered solid state.

Theranostic system for drug delivery and pharmacokinetic imaging based on nanosecond pulsed light-induced photomechanical and photoacoustic effects

For efficient and side effects-free pharmacological treatment, we here propose a theranostic system that enables transvascular drug delivery by photomechanical waves (PMWs) and photoacoustic (PA) imaging of the drug distribution; both functions are based on nanosecond laser pulses and can therefore be integrated in one system. Through optical fibers arranged around an ultrasound sensor, low-energy and high-energy nanosecond light pulses were transmitted respectively for PA imaging and PMW-based drug delivery by temporal switching. With the system, we delivered a test drug (Evans blue) to tumors in mice and visualized distributions of both the blood vessels and drug in the tissue in vivo, showing the validity of the system.

Photomechanical effects in crystals: the role of temperature. A case study of linkage isomerization in [Co(NH3)5NO2]Cl(NO3)

Photomechanical effects in crystals: the role of temperature. A case study of linkage isomerization in [Co(NH₃)₅NO₂]Cl(NO₃)

Porous Au-Ag Alloy Particles Inlaid AgCl Membranes As Versatile Plasmonic Catalytic Interfaces with Simultaneous, in Situ SERS Monitoring.

We present a novel porous Au-Ag alloy particles inlaid AgCl membrane as plasmonic catalytic interfaces with real-time, in situ surface-enhanced Raman spectroscopy (SERS) monitoring. The Au-Ag alloy particles inlaid AgCl membranes were obtained via a facile two-step, air-exposed, and room-temperature immersion reaction with appropriate annealing process. Owing to the designed integration of semiconductor component AgCl and noble metal Au-Ag particles, both the catalytic reduction and visible-light-driven photocatalytic activities toward organic contaminants were attained. Specifically, the efficiencies of about 94% of 4-nitrophenol (4-NP, 5 × 10(-5) M) reduction after 8 min of reaction, and degradation of rhodamine 6G (R6G, 10(-5) M) after 12 min of visible light irradiation were demonstrated. Moreover, efficiencies of above 85% of conversion of 4-NP to 4-aminophenol (4-AP) and 90% of R6G degradation were achieved as well after 6 cycles of reactions, by which robust recyclability was confirmed. Further, with distinct SERS signals generated simultaneously from the surfaces of Au-Ag particles under laser excitation, in situ SERS monitoring of the process of catalytic reactions with superior sensitivity and linearity has been realized. Overall, the capability of the Au-Ag particles inlaid AgCl membranes to provide SERS monitored catalytic and visible-light-driven photocatalytic conversion of organic pollutants, along with their mild and cost-effective fabrication method, would make sense for in-depth understanding of the mechanisms of (photo)catalytic reactions, and also future development of potable, multifunctional and integrated catalytic and sensing devices.