Photo-force controlled molecular systems and materials

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We have explored new phenomena by applying photon pressure of a focused 1064 nm laser beam to molecular and nanoparticle systems in solution and analyzed their trapping and assembling dynamics from molecular viewpoints. New laser deposition phenomena were found and elucidated, while new spectroscopic and patterning methods for individual nanoparticles were proposed. The results are novel and form a new research area on "photon pressure chemistry", whose main results are listed below.1. Fiber-like structure of polymers in solution at room temperature are prepared by the focused beam and deposited on a substrate. The preparation is made possible under the super-saturated condition realized by trapping polymers in the flowing solvent.2. When the beam is intense, simultaneous trapping of the polymer and deformation of the solution surface is made possible. As a result polymer assembly is left at the focal point, whose volume is largest at the medium laser power, for which a model was presented.3. Optical trapping dynamics of fluorescent polymer nanospheres were measured by single particle fluorescence measurement and fluorescence correlation spectroscopy, and how trapping of individual nanoshperes evolves to a large aggregate was analyzed.4. Laser trapping and spectroscopy of single nanoparticles and nanocrystals in solution was successfully demonstrated for gold nanoparticles, J-aggregates, and silver nanopaticles with dyes.5. A 3-dimensional trapping and patterning method of single nanoparticles in solution was presented by combining trapping, heating, and polymerization. This method will be useful to pattern soft materials such as polymers, dendrimers, proteins, living cells, and others in solution.