Near Infrared Emission from Radical Ions

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Fluorescence properties of radical cations 1,3,5-trioxylbenzenes, which belong to pseudo-D_<3h> symmetry point group, has been studied as functions of molecular structures and solvents to elucidate photophysical dynamics of excited radical ions. Introduction of alkyl or acetyl groups on the of the oxygen atoms reduced fluorescence quantum yield through an enhancement of nonradiative decay or electron transfer quenching of the excited radical cations, respectively. Fluorescence was also observed from excited radical cations whose one oxygen atom was substituted with amino or dimethylamino group, indicating that radiative process in the D_2 state of the isoelectronic structures of pseudo-D_<3h> symmetry point group could compete with the nonradiative transition to the D_1 state. A detailed study on the absorption and fluorescence spectra of radical cations of 1,3,5-trimethoxybenzene, hexamethoxybenzene, and 1-methy-2,4,6-trimethoxybenzene in 1,2-dichloro-ethane revealed the incorporation … More of the Jahn-Teller distortion of the radical cations in the ground state. Solvent effect on the Stokes shift of 1,3,5-trimethoxybenzene radical cation indicated that solvation of the radical cation in polar solvent reduced the Stokes shift through breaking the molecular symmetry.The fluorescent nature of 1,3,5-trimethoxybenzene radical cation was utilized to monitor the ion pair formation or dissociation which occurred in radiation chemistry in chlorinated solvent or in photoindeced electron transfer reactions in polar solvent.Transient absorption measurement system for the infrared region was developed and used in the observation of an intramolecular dimmer radical anions in room temperature solution. For the observation of infrared emission from excited radical ions, an upconversion detection system using femtosecond laser is currently of our subject. We also now study dynamics of radical ions in the excited state using a tandem laser photolysis sysmtem consisted of a nanosecond and femtosecond lasers. Less