This PDF file contains the front matter associated with SPIE Proceedings Volume 10740, including the Title Page, Copyright information, Table of Contents, Author listing and Conference Committee listing.

Upconverting nanoparticles (UCNPs) convert near-infrared (NIR) light to UV or visible light that can trigger photoreactions of photosensitive compounds. This process is called UCNP-assisted photochemistry. In this talk, I will present the use of UCNPs to assist photosubstitution of Ru complexes.[1-5] We demonstrate UCNPs converted 974 nm light at an intensity of 0.35 W/cm2 to blue light that triggered the cleavage of photocleavable Ru complexes. This light intensity is lower than the maximum permissible exposure of skin and it is the lowest intensity reported for UCNP-assisted photochemistry. Overheating problems of NIR light were minimized and photodamage to biomaterials was prevented at such a low light intensity. We used this UCNP-assisted photochemistry for drug delivery, patterning of biomaterials, and control pH. For drug delivery, mesoporous silica coated UCNPs were loaded with the anticancer drug doxorubicin and grafted with Ru complexes as photoactive molecular valves. NIR light passed through tissue and induced the cleavage of Ru complexes and the release of doxorubicin. The released doxorubicin inhibited the growth of cancer cells. To pattern proteins using NIR light, proteins and an upconverting-nanoparticle-decorated substrate were linked via photocleavable Ru complexes. The substrate was irradiated using NIR light with a photomask. In the exposed areas of the substrate, upconverting nanoparticles converted the NIR light into blue light, which induced cleavage of the Ru complexes and release of the proteins. References [1] Z. Chen, S. He, H.-J. Butt, S. Wu, Adv. Mater., 2015, 27, 2203. [2] S. Wu, H.-J. Butt, Adv. Mater. 2016, 28, 1208. [3] S. He, K. Krippes, S. Ritz, Z. Chen, A. Best, H.-J. Butt, V. Mailänder, S. Wu, Chem. Commun., 2015, 51, 431. [4] Z. Chen, W. Sun, H.-J. Butt, S. Wu, Chem. Eur. J., 2015, 21, 9165. [5] Z. Chen, Y. Xiong, R. Etchenique, S. Wu, Chem. Commun. 2016, 52, 13959.

Three-dimensional imaging of molecular distribution in a living cell without labeling or slicing the sample has been a dream of bio-scientists. We have made it possible with use of a gold nanoparticle which explores inside a cell for detecting intracellular molecules based on SERS mechanism [1, 2]. This can be considered as a version of plasmonic tip-enhanced Raman microscopy [3,4], but the tip (as a 50nm particle) is free in a cell. Rather than controlling the nanoparticle motion with a laser trapping technology [5,6], the motion is governed by the cell function. Simultaneous tracking of particle motion provides us a molecular map of organelle transport and lysosomal accumulation. Intracellular environment e.g. pH is also mapped by a surface-functionalized particle. Spatial resolution of this microscope is ~ 65nm (the particle size) and temporal resolution ~50ms. In the presentation, movies of particle motion and a molecular map in a cell will be shown with many other results. 1. J. Ando.et. al., Nano Lett. 11, 5344, 2011 2. K.-C. Huang, et. al., Methods, 68, 348, 2014 3. Y. Inouye and S. Kawata, Opt. Lett. 19, 159, 1994 4. S. Kawata, Y. Inouye, P. Verma, Nat. Photon. 31, 388, 2009 5. S. Kawata, Y. Inouye, T. Sugiura, Jpn. J. Appl. Phys. 33, 1725, 1994 6. T. Sugiura, et. al. Opt. Lett. 22, 1663, 1997

Reversible switching of physical and chemical properties can be achieved by light, by means of photochromic substances. A large number of applications are sought for: protection against light, hyper-resolution microscopy, memories, etc. Moreover, photochromic molecules or moieties can be associated to other molecules or moieties with high performance in a given property for the purpose of switching. For example, materials containing photochromic and fluorescent molecules or moieties, interacting at a nanometric scale, are being investigated, for fluorescence photoswitching between OFF (no emission of light) and ON (with emission of light) states. A general concern is to obtain big effects with small inputs. In this regard, our strategy is based on the exploitation of nanoscale interactions, such as energy transfer or plasmonic effect, in order to amplify photoswitching. In our presentation, we will focus on two aspects: 1. Accelerated photoswitching, in hybrid systems, containing gold nanoparticles and photochromic molecules. Due to plasmonic effect taking place in the gold nanoparticles, an increase of the photoswitching rate of the photochromic molecules is observed. 2. Enhanced photoswitching of fluorescence in nanoparticles containing photochromic and fluorescent moieties. The fluorescence of a large number (up to 400 moieties) can be turned ON or OFF by only one photon. This unconventional phenomenon was obserd in various systems: multichromophoric molecules, nanoparticles containing photochrome-fluorophore dyads, and silica nanoparticles grafted with photochromic and fluorescent moieties. This effect stems from the multiple energy transfer occurring at molecular and nanometric scale.

Materials which can be actuated by light have potential to lead to light fueled robots and machines. Such materials deform and move by the action of photo-active molecules; e.g. molecular machines. Azobenzene derivatives are such a molecules, and they undergo a high rate of light-induced cyclic molecular shape change from an elongated, trans form, to a more globular, cis form; a feature which imparts macroscopic motion into materials in the presence of intensity gradients. That is photoisomerization leads to matter motion in inhomogeneous irradiation light fields. In viscoelastic materials, matter motion, in concept, is due to competing forces, including viscous and photoisomerization forces, and possible radiation pressure and elastic forces, as well as random forces due to thermal fluctuations. In solid films of azopolymers, the photoisomerization force overcomes other forces due to softening and decrease of viscosity of the material by photoisomerization. In this paper, we give a brief overview of the theoretical concept of matter motion induced by photoisomerization; e.g. photochemical tweezing, and we show that light absorption provides the energy needed by the system for isomerization and matter motion.

Optical vortex beams, possessing various unique physical properties, such as an annular intensity profile with a dark core, a helical wavefront, and an orbital angular momentum of ℓħ (where ħ is the reduced Planck constant) per photon, provide us many new fundamental light-matter interactions. In recent years, we and our collaborators have discovered that optical vortex beams can twist melted or softened materials to complete various chiral structured materials, including chiral metal needles, chiral monocrystalline silicon microstructures, and chiral organic surface reliefs on a nano-/micro-scale, by orbital angular momentum transfer effects. We call this ‘optical vortex materials processing’. This optical vortex materials processing should open potentially the door towards the development of chiral optical devices, for instance, chiral metasurfaces, sensitive detectors of the chiral chemical composites, and chiral chemical reactors at high time, cost and energy efficiencies. In this presentation, we review the state-of-art of the chiral nano-/micro-structures fabrictaed by optical vortex materials processing. We further address wavelength-versatile optical vortex sources for the optical vortex materials processing.

The development of polymers with switchable glass transition temperatures (Tg) can address scientific challenges, including the healing of cracks in high-Tg polymers and the processing of hard polymers at room temperature without using plasticizing solvents. In this talk, I will show you that light can switch the Tg of azobenzene-containing polymers (azopolymers) and induce reversible solid-to-liquid transitions of the polymers (Nature Chemistry 2017, 9, 145). The azobenzene groups in the polymers exhibit reversible cis-trans photoisomerization. Trans azopolymers are solids with Tg above room temperature, while cis azopolymers are liquids with Tg below room temperature. Because of the photoinduced solid-to-liquid transitions of these polymers, light can reduce the surface roughness of azopolymer films, repeatedly heal cracks in azopolymers, and control the adhesion of azopolymers for transfer printing. The photoswitching of Tg provides a new strategy for designing healable polymers with high Tg and allow for control over the mechanical properties of polymers with high spatiotemporal resolution.

Over the past two decades, surface relief gratings have attracted much interest owing to their potential applications in optical data storage and optical communication and holography. Azobenzene-containing polymer films show an interesting behavior under irradiation with light interference patterns. The inhomogeneous irradiation; e.g. due to the interference pattern, of the azo-polymer film causes mass movement of the polymer from bright to dark area, and the mechanism underlying the formation of SRG finds its origin in the photoisomerization force. The latter is due to an inhomogeneous light irradiation which causes photoisomerization and increases the polymer mobility in the bright area, and owing to the intensity gradient, due to light interference, the photoisomerization force moves the polymer from the bright area into the dark. In this paper we discuss our experiments of holographic recording in films of Poly (Disperse Red 1 methacrylate); e.g. azo-polymer films, and the recorded surface relief gratings were investigated by using atomic force microscopy. The dependence of the polarization state and intensity of the writing beams was studied, and the diffraction efficiency was monitored in real time during the process of inscription. A brief description of the photoisomerization force is given.

Light-induced patterns of surface deformations in azobenzene containing polymer films have attracted much attention because of possible applications in optical data storage and in micro/nano fabrication. It is well known that such patterns reflect the state of the incident light polarization and the light intensity distribution. Trans ↔ cis photoselective isomerization and molecular reorientation play important roles in the deformation process. Among a variety of applications utilizing light-induced mass movement in azo-polymers, sub-diffraction imaging of optical near-fields is one of the most promising applications. In this application, optical near-field distribution in the vicinity of nano structures is transferred to surface deformations of azo-polymers through light-induced mass movement, where the spatial resolution can exceed the diffraction light of light. In addition to the high spatial resolution, not only intensity distribution but also polarization state of near-fields can be measured. In this presentation, we will report on photo-induced polymer movement induced by optical near-field in the vicinity of single gold nano-particles (GNPs). A linearly polarized (Ex) laser beam was irradiated into GNPs to excite local surface plasmon resonance that enhanced the near-field around the GNPs. The findings indicated that different GNP diameters (that is, 50 nm and 80 nm) resulted in different deformation patterns on the films. The results were compared with theoretical calculations of near-field distributions, and the observations revealed that the deformation patterns were dependent on the ratio between Ex and Ey wherein each possessed a different field distribution.

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host-guest interactions are an effective tool to introduce switching and functional properties into materials. This paper focuses on the photo responsive supramolecular actuators. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). To prepare a supramolecular actuator using host-guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing length of the cross-linking points. Both actuators exhibit contractive bending behavior. This paper summarizes advancements in supramolecular materials that function through the chemical mechanism of host-guest interactions and the physical mechanism of the sliding motion of ring molecules.

Manipulating objects at the micro and nano scale is still an open fascinating challenge that scientists are addressing by proposing different approaches to obtain machines with basic or complex functions. Combining shape changing polymers that differently respond to optical stimuli on the basis of the molecular alignment, together with 3D structuration at the microscale (with nanometric features), we demonstrated synthetic microrobots entirely powered by light. The arbitrary design allowed to mimic diverse animal and even humanoid tasks as walking, grabbing or manipulating objects, even overcoming natural limitations present at such small scale. Liquid crystalline networks offer the possibility to perform different movements depending on their molecular alignment and, controlling by light their elastic deformation, wireless activation of micro-machines was obtained. We report here how tuning intrinsic parameters, as the lithographic ones, and an external setting as the actuation power, it is possible to induce diverse deformations and time responses. Such results can be exploited to tailor the working mechanism and actuation speed of different micro robots. Engineering a proper structural design and combining different time responding materials would generate not reciprocal motion, basic and necessary property to achieve swimming at the microscale. This first technical demonstration paves the way to a micro swimmer fueled by light.

As a 3D micronanostructure enabler, laser processing has contributed to 3D miniaturized intelligent robots greatly. For example, laser processing has been widely used for print photopolymers through two-photon/multi-photon absorption. To make general photopolymers “smart”, doping or post-deposition of functional materials provides a way to fabricate miniaturized intelligent robots. Alternatively, laser processing based on stimuli responsive materials, for instance, hydrogel and protein, has also been reported for the development of miniaturized intelligent robots. Recently, the spatial resolution of laser processing has been significantly improved to tens of nanometers; and processible materials have been extended to a broad range, for instance, photopolymers, protein, hydrogel, carbon, metal, and even nanoparticles. The rapid progress of laser processing technology push forward the rapid advances of min-iaturized intelligent robots.

Two photon polymerization, based on two-photon absorption, is a powerful and potential technique to fabricate 3D micro/nanostructures with submicrometric resolution. We use a photopolymerizable resin based on methyl methacrylate monomers as a photosensitive medium, in which the polymerization is triggered by the nonlinear optical effect. Nonlinear effect photoreaction occurs only in a submicrometric volume, voxel, much smaller than the cube of the wavelength, λ³. By using a femtosecond laser, 780 nm wavelength, we investigate the effect of different parameters on the resolution of our custom made micro/nanofabrication set up. The fabrication accuracy and the resolution of 3D micro/nanostructures depend on the accuracy of the focal spot position in z-direction, in the glass substrate-resin interface. We control the focal spot position by using ascending scan process meaning the focus spot level. Employing the proposed process, the lateral resolution of individual voxels, is improved almost to 94 nm. The resolution of two photon absorption polymerized voxels is studied as a function of focus spot level, laser power and single-shot irradiation time. Finally, we show 3D microstructures and a micro-device, which present great potential for future applications.