Dual-Mode Emission and Solvent-Desorption Dependent Kinetic Properties of Crystalline-State Chemiluminescence Reaction of 9-Phenyl-10-(2-phenylethynyl)anthracene Endoperoxide

• Published in: Journal of the American Chemical Society 2024-12
• Main Authors: Yamasaki, Norihisa, Matsuhashi, Chihiro, Uekusa, Hidehiro, Nakayama, Naofumi, Obata, Shigeaki, Goto, Hitoshi, Maki, Shojiro, Hirano, Takashi
• Format: Article
• Language: English
• ISSN: 1520-5126; 1520-5126
• DOI: 10.1021/jacs.4c12958

The chemiluminescence (CL) feature and reactivity of the aromatic endoperoxide 9-phenyl-10-(2-phenylethynyl)anthracene endoperoxide (PPEA-O ) were investigated in the crystalline state. For this, PPEA-O crystals were prepared using dichloromethane and -hexane. These crystals exhibited an α-phase structure containing -hexane as a crystal solvent. The crystal structure of nonperoxidic anthracene (i.e., PPEA) was also confirmed. After optimizing heating conditions to 120 °C for the thermolytic reaction of PPEA-O in crystals while maintaining the solid state, its CL characteristic and reactivity were investigated. Two key findings were derived: (1) dual-mode emission with maxima at 510 and 1275 nm and (2) distinct observation of CL emission at the first 2-3 min after the start of heating owing to the rapid thermolytic reaction coupled with -hexane desorption. The 510 and 1275 nm emissions were attributed to the PPEA excimer and O ( Δ ), respectively. We proposed a mechanism involving the triplet-triplet annihilation of the excited triplet states of PPEA to explain excimer production with postulated pathways for generating these triplet states from PPEA-O . The rapid thermolytic reaction of PPEA-O in α-phase crystals with simultaneous -hexane desorption was attributed to the formation of transient vacant spaces, which increased the molecular freedom necessary for the reaction ("transient vacant space effect"). Thus, the CL of PPEA-O proved useful for identifying characteristic reactivity and analyzing the luminescence mechanism of aromatic endoperoxides in the crystalline state.