(Invited) A Soft-Crystal Chemiluminescence System: Luminescence Property of Adamantylideneadamantane 1,2-Dioxetanes Conjugated with a Fluorophore

Abstract

Chemiluminescence (CL) produces photon by a chemical reaction of a CL substrate to give a product in the excited state. Because emitted photons are readily detectable, CL is a powerful tool to monitor a chemical event in an analyte. In the materials science, CL will be useful to analyze an event at the molecular level in a solid material for developing functional devises. For instance, CL has been used to measure mechanical forces applied to polymers.1 In this study, we have investigated CL reactions in molecular crystals, to create the chemistry of “soft crystals”2 as reaction fields. For this purpose, we investigated CL properties of adamantylideneadamantane 1,2-dioxetanes (Adox) conjugated with a fluorophore in the crystalline state. We report here characteristic CL properties of the Adox derivatives and talk about the molecular mechanism of the crystalline-state CL.3 Adox is one of stable 1,2-dioxetanes, and its thermal decomposition partially gives the excited singlet (S1) or triplet (T1) state of 2-adamantanone (AdCO).4 The S1 state of AdCO can fluoresce weakly with the maximum at 420 nm. A designed Adox derivative 1 has a non-π-conjugatively linked phthahlimide as a crystal structure modulator and the emitting moiety by accepting energy from the excited AdCO. We first prepared syn- and anti-isomers of the Adox derivative 1 and investigated their CL properties in crystals. The isomers showed contrastive CL properties by heating their crystal samples at 160 °C. Each crystal structure of the isomers has its own distinctive packing pattern of the Adox and phthalimide moieties, and the clear differences in CL intensities, emission maxima and reaction kinetics of the isomers are well correlated to the packing patterns. Thus, CL emission properties and reaction kinetics in the crystalline-state were precisely manipulated by the crystal structures. To understand the crystalline-state CL reactions in detail, we further investigated CL of modified Adox derivatives along with thermoanalytical studies. The results provide information on the origins of the characteristic CL behaviors and the reaction mechanism in soft crystals.1) Chen, Y.; Spiering, A. J. H.; Karthikeyan, S.; Peters, G. W. M.; Meijer, E. W.; Sijbesma, R. P., Nat. Chem., 2012, 4, 559.2) Kato, M.; Ito, H.; Hasegawa, M.; Ishii, K., Chem. Eur. J., 2019, 25, 5105.3) Matsuhashi, C.; Ueno, T.; Uekusa, H.; Sato-Tomita, A.; Ichiyanagi, K.; Maki, S.; Hirano, T., Chem. Commun., 2020, 56, 3369.4) Hummelen, J. C.; Luider, T. M.; Wynberg, H., Pure Appl. Chem., 1987, 59, 639. Figure 1