Ultrafast Study of 9-Diazofluorene: Direct Observation of the First Two Singlet States of Fluorenylidene

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• 作者：Jin Wang ; Jacek Kubicki ; Edwin F. Hilinski ; Sandra L. Mecklenburg ; Terry L. Gustafson ; Matthew S. Platz
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：November 7, 2007
• 年：2007
• 卷：129
• 期：44
• 页码：13683 - 13690
• 全文大小：179K
• 年卷期：v.129,no.44(November 7, 2007)
• ISSN：1520-5126

文摘

Ultrafast photolysis of 9-diazofluorene (DAF) produces a broadly absorbing transient within theinstrument time resolution (300 fs), which is assigned to an excited state of the diazo compound. Thediazo excited state fragments to form fluorenylidene (Fl) in both its lowest energy singlet state (¹Fl, 405-430 nm, depending on the solvent) and a higher energy singlet state (370 nm, ¹Fl*). The excited singletcarbene has a lifetime of 20.9 ps in acetonitrile and decays to the lower energy singlet state (¹Fl), whichrelaxes to the triplet ground state (³Fl) in acetonitrile, cyclohexane, benzene, and hexafluorobenzene. Theequilibrium mixture of singlet and triplet fluorenylidene reacts with these solvents. Singlet fluorenylidenereacts with methanol and cyclohexene in competition with relaxation to ³Fl. One of the reaction productsin methanol is the 9-fluorenyl cation. The rate of intersystem crossing (ISC) in hexafluorobenzene andother halogenated solvents is remarkably slow given that carbene ISC rates are generally fastest in nonpolarsolvents. An explanation of this effect is advanced.