6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Mixed-valence (MV) compounds are excellent model systems for the investigation of basic electron-transfer (ET) or charge-transfer (CT) phenomena. These issues are important in complex biophysical processes such as photosynthesis as well as in artificial electronic devices that are based on organic conjugated materials. Organic MV compounds are effective hole-transporting materials in organic light emitting diodes (OLEDs), solar cells, and photochromic windows. However, the importance of organic mixed-valence chemistry should not be seen in terms of the direct applicability of these species but the wealth of knowledge about ET phenomena that has been gained through their study. The great variety of organic redox centers and spacer moieties that may be combined in MV systems as well as the ongoing refinement of ET theories and methods of investigation prompted enormous interest in organic MV compounds in the last decades and show the huge potential of this class of compounds. The goal of this Review is to give an overview of the last decade in organic mixed valence chemistry and to elucidate its impact on modern functional materials chemistry.

Organic mixed-valence compounds: a playground for electrons and holes.

L'etude demontre que les radicaux cationiques CH 3 OH +• , CH 3 NH 2 +• et CH 3 Cl +• ont des isomeres stables: • CH 2 OH 2 + , • CH 2 NH 3 + et • CH 2 ClH +

Distonic radical cations in gaseous and condensed phase

Cation radical cycloadditions and related sigmatropic reactions

Optical pulse shaping approaches to coherent control

The hexamethylethane radical cation (Me/sub 3/C.CMe/sub 3/)/sup +/ has been generated through positive charge transfer by ..gamma.. irradiation of both glassy and polycrystalline Freon solutions, its EPR spectrum consisting of seven lines with binomial intensities and having the parameters /sup 1/A(6) = 29.0 +- 0.2 G and g = 2.0031 +- 0.0003. In contrast, only neutral alkyl radicals are produced from the hydrocarbon by ..gamma.. irradiation of the hexamethylethane matrix, even when powerful electron scavengers are present. It is suggested that the formation of the radical cation by positive charge transfer in a Freon matrix is a more relaxed process than that of vertical ionization by electron impact in a hexamethylethane matrix.

EPR evidence for the formation of the hexamethylethane radical cation by charge transfer in a freon matrix

The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.

Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate

ESR spectra and structure of the n-butane and n-hexane radical cations

The ESR spectra of the radical cation of dimethyl ether, (CH/sub 3/)/sub 2/O/sup +/, which is isoelectronic with the dimethyl aminyl radical, (CH/sub 3/)/sub 2/N, are reported. The first- and second-derivative spectra were obtained from a ..gamma..-irradiated solid solution of dimethyl ether in trichlorofluoromethane at 97/sup 0/K. Analysis of the spectrum is discussed, and assignment of the spectrum to the oxygen-centered radical cation of dimethyl ether is felt to be unambiguous. (BLM)

Jih Tzong Wang

Papers

EPR evidence for the formation of the hexamethylethane radical cation by charge transfer in a freon matrix

Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate

ESR spectra and structure of the n-butane and n-hexane radical cations

ESR detection of the dimethyl ether radical cation

ESR evidence for the formation of the ring-opened cation CH2OCH2± from ethylene oxide