Charge-transfer reactions lead compounds

Binary ion-molecule reactions are indicated by thin arrows (c.t. indicates charge transfer), the radiative association reaction of C+ with H2 is indicated by the thick arrow and the dissociative recombination reactions are indicated by dashed arrows leading to the neutral molecules inside the compound brackets (e indicates free electrons). The molecules indicated in bold are known (observed) interstellar molecules. 

Chemical oxidation of the TTF groups in compounds 34 and 35 has been achieved by reaction with an excess of iodine in dichloromethane solution, leading to new low-energy absorptions in the UV/visible spectra which are diagnostic of TTF cation radicals the broad absorption at = 830 nm for the iodide salt of 35 suggests the formation of aggregated TTF species. A charge transfer complex formed by 35 and tetracyano-p-quinodimethane (TCNQ) has been isolated as an insoluble black powder. The stoichiometry is (35), (TCNQ)3 (i.e. 8 TTF units 3... 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

Intermolecular photoreaction of an aryl halide with another aromatic compound may lead to the formation of biaryls. In this section several examples of such reactions will be discussed. In some cases, information concerning the reaction mechanism is available but the depth to which mechanisms have been investigated varies greatly. In many cases aryl radicals formed by homolysis of the carbon-halogen bond are the reactive species. Such radicals may also be produced via electron transfer, followed by departure of halide anion. In some cases aryl cations have been proposed as intermediates. Intermolecular bond formation may also be preceded by charge transfer within an exciplex or by formation of radical ion pairs. 

Excitation to the LC states may also result in population of the CT-excited states, especially the LLCT states. These phenomena are frequently encountered in complexes containing both rc-acceptor (eg 1,10-phenantroline or 2,2 -bipyridyl) and 7r-donor ligands (eg aromatic thiols). Then the LC excitation can induce charge transfer between these ligands through central atom (LLCT) that leads to a photoredox reaction. Such reactions were reported in the case of heteroleptic organometallic compound [Rh CylLXCsHs)]3 [37], heteroleptic Re1 complex fac-[Re (L)(CO)3(bpy)]n+ [46] and metal-carbon-bonded platinum complexes [47]. 

The mechanism of the [3 + 2] cycloaddition is summarized in Scheme The first intermediate results from charge transfer interaction between the eli tronically excited aromatic compound at its singlet state S1 with the alkene w] leads to the formation of the exciplexes K. A more stable intermediate is generated by the formation of two C-C bonds, leading to the intermediates These intermediates have still singlet multiplicity and therefore possess zwii ionic mesomeric structures mainly of type M. In most cases and especially intramolecular reactions, chiral induction occurs during the formation of L. final products are then obtained by cyclopropane formation in the last step. 

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