(Invited) Study on Soft-Crystal Chemiluminescence, a Solid-State Chemistry to Support Devise Development
Authors: Hirano Takashi , Matsuhashi Chihiro , Koura Fumiya , Maki Shojiro , Uekusa Hidehiro , Sato-Tomita Ayana , Ichiyanagi Kouhei , Ryu Meguya , Morikawa Junko 
Published: July 2021

Photofunctional devises such as solar cells consist of layered solid materials including molecular crystal. In the devises, their functions are achieved based on several fundamental processes such as electron transfer and a chemical reaction. To support developments of photofunctional devises, it is essential to understand chemical events in solid materials. Molecular crystal is one of the attractive materials with “soft” character for functions.1 In “soft crystals,” restricted spaces and relatively weak intermolecular interactions allow to proceed a particular chemical reaction. To confirm the theoretical background of the chemical reactions in soft crystals, we have investigated chemiluminescence (CL) reactions in crystals systematically. CL is a phenomenon showing light emission from the excited product generated by a chemical reaction and is useful to analyze chemical events happening inside a solid material by photon detection. In fact, CL has been used to monitor mechanical forces applied to polymers.2 While several studies on CL in the crystalline state have already been reported,3,4 it is needed to investigate various crystalline-state CL reactions to establish the chemistry of CL in soft crystals. For the purpose, we investigated CL properties of 1,2-dioxetane derivatives in the crystalline state and found their unique reaction characteristics. In this presentation, we talk about examples of crystalline-state CL to show the changes in the molecular environments in crystals associated with the progresses of CL reactions.5

We investigated CL properties of the 1,2-dioxetane derivatives 1 and 2 with the known structures6,7 in the crystalline state. Compounds 1 have a fluorophore part for modulating energy transfer property and crystal structure. Compounds 2 have an aryl (Ar) ester part for increasing the stability and for modulating the crystal structure. CL in crystals was initiated by heating a crystalline sample and the reactions were traced by monitoring emitted light. Crystalline-state CL of 1 and 2 showed spectral and kinetic changes during progresses of the reactions, indicating that molecular environments of the reaction sites were changed by generations of the CL reaction products. Thus, the reactivities and the properties of the excited products of the CL reactions reflected changing character of the soft crystal lattices. We will talk about these dynamic properties of the CL reactions in soft crystals from the viewpoint of the reaction mechanism.
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5) Matsuhashi, C.; Ueno, T.; Uekusa, H.; Sato-Tomita, A.; Ichiyanagi, K.; Maki, S.; Hirano, T., Chem. Commun., 2020, 56, 3369.
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7) Imanishi, T.; Ueda, Y.; Tainaka, R.; Miyashita, K.; Hoshino, N., Tetrahedron Lett., 1997, 38, 841.

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