Nobuko Watanabe

Electron-transfer-induced decomposition of 1,2-dioxetanes in negative-mode matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

1,2-Dioxetanes bearing an aromatic electron donor undergo intramolecular charge-transfer-induced chemiluminescence (CTICL). Although there has been some controversy regarding the mechanisms involved, there is little experimental evidence to strongly support any of the proposed mechanisms. In the course of our investigations, to clarify these mechanisms, we tried to effectively ionize dioxetanes bearing a phenolic group and found that poly(3-octylthiophene-2,5-diyl) was a promising matrix for negative-mode matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS). Electron-transfer ionization was found to take place for dioxetanes bearing a hydroxyphenyl moiety that had been further substituted with an aromatic group, which acted as an antenna to catch an electron from the matrix. Furthermore, the characteristic fragmentation of dioxetanes 3c–3d was thought to occur by the elimination of 2-methyl-1-propene (56 u) and pivalaldehyde (86 u) from deprotonated ion [M – H]− of dioxetanes, based on the results of muliple mass spectrometry measurements of dioxetanes using MALDI quadrupole ion trap ToF-MS. Based on a comparison of fragmentation in dioxetanes and the corresponding keto esters, dioxetanes were presumed to initially generate excited keto esters from which fragmentation took place.

Synthesis of 5-(adamantan-1-yl)-4,4-dimethyl-1-(3-oxyphenyl)-2,6,7-trioxabicyclo[3.2.0]heptanes and their base-induced chemiluminescent decomposition in liquid/solid phase

Singlet oxygenation of 4-(adamantan-1-yl)-5-(3-hydroxy)phenyl-1,2-dihydrofuran 4a effectively gave bicyclic dioxetane 3a as crystals with a high melting point. Dioxetane 3a decomposed rapidly accompanied by the emission of blue light, when treated with tetrabutylammonium fluoride (TBAF) in DMSO or acetonitrile. The chemiluminescence efficiency for 3a was as high as those for tert-butyl-analog 2. In addition to chemiluminescent decomposition in a liquid phase, a finely powdered mixture of crystalline 3a and crystalline dimethylaminopyridine (DMAP) emitted blue light upon heating at 80-110 °C while maintaining a solid state.