Photoisomerization of charge-transfer complexes of hexamethyl(Dewar benzene). Contrasting paths for rearrangement involving adiabatic reaction and ionic photodissocation

Journal Article · Wed Mar 09 04:00:00 EST 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00343a033· OSTI ID:5682529

Jones, G II; Becker, W G

The charge-transfer (CT) complexes of hexamethyl(Dewar benzene) (HMDB) with electron acceptors, fumaronitrile, diethyl 1,2-dicyanofumarate, and 1,2,4,5-tetracyanobenzene, have been characterized and compared to similar complexes of hexamethylbenzene (HMB). Irradiation of HMDB CT bands in the 313-435-nm region under a variety of conditions leads to HMDB ..-->.. HMB isomerization. The quantum yield of rearrangement in a nonpolar solvent is low (e.g. 0.06), although the relative yield of adiabatic isomerization, monitored by emission for excited complexes of HMB, is high (0.72). Quantum efficiencies for isomerization of complexes in polar media generally exceed unity, consistent with a radical-ion chain mechanism for ring opening. The quatum chain reaction depends on the polarity of the solvent, the reduction potential of the acceptor, the extent of conversion, and the wavelength of irradiation. The wavelength effect is associated with excitation to upper vibrational levels of a CT band with enchancement of ionic photodissociation. Comparison of the quantum yield results for excited CT complexes with the findings for rearrangement of HMDB via exciplexes reveals generally different patterns of reactivity.

• Research Organization: Boston Univ., MA
• OSTI ID: 5682529
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:5; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AROMATICS
BENZENE
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CONVERSION
CYANIDES
DICARBOXYLIC ACIDS
EFFICIENCY
ELECTRON TRANSFER
EMISSION SPECTROSCOPY
ENERGY LEVELS
EXCITED STATES
FUMARIC ACID
HYDROCARBONS
IRRADIATION
ISOMERIZATION
NITRILES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
QUANTUM EFFICIENCY
REACTIVITY
REDUCTION
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS