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

Abstract

The chemiluminescence (CL) feature and reactivity of the aromatic endoperoxide 9-phenyl-10-(2-phenylethynyl)anthracene endoperoxide (PPEA-O 2 ) were investigated in the crystalline state. For this, PPEA-O 2 crystals were prepared using dichloromethane and n-hexane. These crystals exhibited an α-phase structure containing n-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 2 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 nhexane desorption. The 510 and 1275 nm emissions were attributed to the PPEA excimer and 1 O 2 ( 1 Δ g ), 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 2 . The rapid thermolytic reaction of PPEA-O 2 in α-phase crystals with simultaneous n-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 2 proved useful for identifying characteristic reactivity and analyzing the luminescence mechanism of aromatic endoperoxides in the crystalline state.