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

Autor:	Jin Wang, Matthew S. Platz, Edwin F. Hilinski, Sandra L. Mecklenburg, Terry L. Gustafson, Jacek Kubicki
Rok vydání:	2007
Předmět:	Hexafluorobenzene General Chemistry Photochemistry Biochemistry Fluorenylidene Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Intersystem crossing chemistry Excited state Singlet fission Singlet state Physics::Chemical Physics Ground state Carbene
Zdroj:	Journal of the American Chemical Society. 129:13683-13690
ISSN:	1520-5126 0002-7863
Popis:	Ultrafast photolysis of 9-diazofluorene (DAF) produces a broadly absorbing transient within the instrument time resolution (300 fs), which is assigned to an excited state of the diazo compound. The diazo 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 singlet carbene has a lifetime of 20.9 ps in acetonitrile and decays to the lower energy singlet state (1Fl), which relaxes to the triplet ground state (3Fl) in acetonitrile, cyclohexane, benzene, and hexafluorobenzene. The equilibrium mixture of singlet and triplet fluorenylidene reacts with these solvents. Singlet fluorenylidene reacts with methanol and cyclohexene in competition with relaxation to 3Fl. One of the reaction products in methanol is the 9-fluorenyl cation. The rate of intersystem crossing (ISC) in hexafluorobenzene and other halogenated solvents is remarkably slow given that carbene ISC rates are generally fastest in nonpolar solvents. An explanation of this effect is advanced.
Databáze:	OpenAIRE
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