Study for Two-Photon Photoresponsive Materials Based on π conjugated molecules and polymers

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Two-photon excitation induces various photochemical reactions which can be potentially used for photo-resistive and photo-pattern formation processes. Since possibility of two photon induced reaction depends on square of light intensity, the 3D-selective photo-induced reactions and photo-pattern formations are possible, when focused laser beam is used as a light source.Novel photo-responsive polymers and photochromic molecules are developed and their two photon-induced photo-responsibility was studied.First issue is to develop novel photo-responsive conducting polymer whose electrical conductivity can be modulated with the photochromic reactions. Since pai-conjugation pathway of photochromic diarylethenes connects over the molecules when it is in the closed ring-isomer, but not in the open ring isomer. Therefore, electrical conductivity of a conducting polymer, which possesses photochromic diarylethene units on the main chain, is expected reversibly by the photochromic reactions. Indeed, our photochromic conducting polymer showed reversible changes in the electrical conductivity with the photochromic reactions. The polymer showed two-photon induced photochromic reactions reversibly when focused femto-sec ultra-short pulse laser beam was irradiated.Since possibility of the two photon induced photochemical reactions depends on the two photon cross-section of the molecules, two-photon active molecules with larger TPA cross-section is indeed required for practical use of the photo-responsive molecules and polymers. Novel photochromic molecules having enhanced TPA cross-section an prepared and their TPA cross-section are measured by the Z-scan method for the first time. Their TPA cross-section varies between 6GM and 90GM depending on the molecular structure and wavelength of the irradiated light.