Substituent effects on the chemiluminescence of aromatic dioxetanes

• Main Authors: Chung-Wen Sun, 孫崇文
• Other Authors: Tai-Shan Fang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/81186358591364118747

博士 === 國立臺灣師範大學 === 化學系 === 101 === Four tricyclic 1,2-dioxetane derivatives, 1a-4a, were synthesized from their corresponding 1,4-dioxin acenaphthylene compounds, 1-4, by reaction with singlet-oxygen (1O2) in dichloromethane. The first part which involves the thermal decomposition of the compounds 1a-3a illustrates the substituent effect on the ability of the electron donating at 5-position of “acenaphtho” moiety. Evidence for formation of the dioxetanes ,1a-3a, is the chemiluminescence that corresponds to the emission from the electronically excited diesters 1b*-3b*, which are decomposed thermally from the dioxetanes 1a-3a, respectively. The highly strained 1,2-dioxetane ring decomposes from a twisted geometry by simultaneous cleavages of the O-O and C-C bonds producing the electronically excited diester that emits chemiluminescence (CL). It was observed that the CL from compound 2a is dramatically red-shifted relative to that of compounds 1a and 3a suggesting a higher degree of stabilization of the excited state by the electron donating methoxy group. Also, a study of the solvent effect on the fluorescence shows a significant red-shift in compound 2b, indicating a more polar excited state. The kinetics of the thermal decomposition of the 1,2-dioxetanes clearly demonstrate that the chemiluminescence characteristics of the compound 2a is quite different from that of compounds, 1a and 3a. These results are consistent with the proposed intramolecular chemically initiated electron exchange luminescence (CIEEL) mechanism which is enhanced by the electron-donating group of compound 2a. The second part involves the compounds 1a, and 5-halo substituted of 1,2-dioxetane tricyclic compounds (3a, 4a) to study the heavy atom effect on their chemiluminescent efficiency both in fluorescence and phosphorescence. While upon heating to temperatures between 313~353K in dichloromethane, the chemiluminescent phosphorescence (CP) of the compounds 3a, 4a can be detected along with the chemiluminescent fluorescence (CF). The activation enthalpies from Eyring plots show that the decomposition of the 1,2-dioxetane favors the pathway of the triplet chemiexcitation processes due to the internal heavy atom effect.