Photocycloaddition of 9,10-dichloroanthracene to 2,5-dimethyl-2,4-hexadiene. The singlet pathway for [4 + 2]-adduct formation in benzene
- Florida State Univ., Tallahassee, FL (United States)
- Oak Ridge National Lab., TN (United States)
Irradiation of 9,10-dichloroanthracene (DCA) in the presence of 2,5-dimethyl-2,4-hexadiene (DMHD) in benzene at 25{degree}C gives a single adduct (Ad) corresponding to [4 + 2] addition of DMHD to the 9,10 positions of DCA. Quantum yields for Ad formation are reported as a function of [DMHD], [DCA], and methyl iodide concentration. [MeI]. Fluorescence quantum yields and lifetimes of DCA and (DCA/DMHD) singlet exciplex as a function of [MeI] are also reported. Transient absorption measurements reveal the time evolution of excited DCA singlet, {sup 1}DCA, and triplet, {sup 3}DCA, states and of the (DCA/DMHD) singlet exciplex, {sup 1}(DCA-DMHD). They show that the dominant decay path from {sup 1}(DCA-DMHD) gives {sup 3}DCA. Quenching of {sup 1}DCA and exciplex fluorescence and transient absorption by MeI are observed. The dependence of Ad quantum yields on [DMHD] and the strict proportionally between product quantum yields and exciplex fluorescence quantum yields at different [MeI] establish singlet mechanism for adduct formation. Assuming that Ad is a primary photoproduct, the results are consistent with Yang`s proposal of stepwise collapse of polar exciplexes to seemingly forbidden cycloadducts. A singlet biradical could be the intermediate, but intersystem crossing of the singlet exciplex to a triplet biradical as the initial step cannot be ruled out. 41 refs., 8 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 106779
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 36 Vol. 117; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
Similar Records
Biradical reversion in the intramolecular photochemistry of carbonyl-substituted 1,5-hexadienes
Magnetic isotope effect on the thermolysis of 9,10-diphenylanthracene endoperoxide as a means of separation of /sup 17/O from /sup 16/O and /sup 18/O