Morphological effects on the third-order nonlinear optical response of polydiacetylene nanofibers
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Research Letter
Morphological effects on the third-order nonlinear optical response of polydiacetylene nanofibers Haruki Maki, Rie Chiba, Tsunenobu Onodera , and Hitoshi Kasai , Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8755, Japan Rodrigo Sato and Yoshihiko Takeda , Hydrogen Materials Engineering Group, Center for Green Research on Energy and Environmental Materials, National Institute for Materials Science (NIMS), Sakura 3-13, Tsukuba 305-0003, Japan Hidetoshi Oikawa , Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8755, Japan Address all correspondence to Hidetoshi Oikawa at [email protected] (Received 16 May 2019; accepted 8 July 2019)
Abstract The third-order nonlinear optical (NLO) susceptibility for morphologically controlled polydiacetylene (PDA) nanocrystals (NCs) and PDA nanofibers (NFs) have been determined for the first time by the experimental combination of transient pump-probe spectroscopy and spectroscopic ellipsometry. The figure of the merit of PDA NFs was much superior to PDA NCs and/or PDA bulk crystals, and the excitonic relaxation time was of order of sub-pico second. Namely, this is the first case to reveal the morphological effect on NLO response. PDA NFs having the long effective π-conjugation length are one of the most promising organic third-order NLO nanomaterials toward the photonic device application.
Introduction A nonlinear optical (NLO) response is one of the most important optical process and key technology toward next-generation optoelectronic and/or photonic device applications,[1] e.g., optical wiring,[2] optical transistor,[3] random lasing,[4] optical memory,[5] and all optical computing system.[6] NLO materials should be needed to provide much large third-order NLO susceptibility, χ (3)(ω), and femto-second order of highly optical response so as to fulfill these optical and/or photonic devices. In common, organic NLO materials exhibit rapid optical response, whereas inorganic NLO materials take large χ (3)(ω).[7,8] Polydiacetylene (PDA) is synthesized by topochemical solidstate polymerization of diacetylene (DA) monomer in a crystal state and a unique one-dimensional π-conjugated polymer.[9] Some PDA derivatives are well known as one of the most promising organic NLO materials.[10,11] Instead of material designs and synthetic developments, morphologically controlled nanostructures such as nanocrystallization and/or hybridization on a nano-scale level would be expected to further enhance NLO properties,[12] but this is still much challenging and interesting topics in current organic NLO material science, although the enhancement of χ (3)(ω) has been already reported in semiconductor quantum dots, owing to the quantum confinement effect.[12] On the other hand, π-conjugated organic and polymer nanocrystals (NCs) (hereinafter, organic NCs),[13,14] for example, PDA NCs and fluorescent perylene NCs, exhibited t
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