Lian C. T. Shoute

Dual fluorescence of 4,4′-bis(dimethylamino)benzophenone. Effects of specific and nonspecific interaction on the formation of twisted intramolecular charge transfer

Abstract 4,4′-bis(dimethylamino)benzophenone (BDMABP) emits dual fluorescence. The dipole-moment change determined from the solvatochromic shift is 4.0 D in alcohols and 10.4 D in polar aprotic solvents. Both short and long wavelength fluorescence is observed in 1-PrOH:DMSO mixed solvents. The Stokes shifts, the radiative rate constants, and the dipole-moment change indicate that BDMABP emits planar intramolecular charge transfer (ICT) fluorescence in alcohol and twisted intramolecular charge transfer (TICT) fluorescence in polar aprotic solvents. The study demonstrates that nonspecific dielectric interaction facilitates the formation of the TICT state and specific interaction, such as hydrogen bonding between solute and solvent, interferes with its formation.

Matrix isolation studies of transients produced in the γ -radiolysis of decafluorobenzophenone : spectral relaxation of anion and ketyl radical formation

Absorption spectra of the anion radical of decafluorobenzophenone (DFB) obtained on γ-radiolysis in various matrices were found to be blue shifted on warming. Spectra of the anion is blue shifted by as much as 0.32eV in MTHF matrix containing 0.7M ethanol (EtOH). In nonpolar 3 MP matrix containing 0.5 M isopropylalcohol (iPrOH) the extent of blue shift was found to be much lower, viz. 0.12 eV. Ketyl radical absorption obtained on warming results from protonation of the anion radical. The fact that warming of the matrix is a prerequisite for the ketyl radical formation seems to indicate that proton involved must be arising out of an ion-molecule reaction rather than the matrix itself. The formation of anion radical of DFB in 3 MP was found to be possible only in the presence of solute such as isopropylalcohol and triethylamine (TEA) where the positive hole is concomitantly trapped by the solute.

A new versatile system for matrix isolation and spectroscopic studies of cations at 77 K: Perfluoro-2-butyltetrahydrofuran

Perfluoro-2-butyltetrahydrofuran forms a clear glass at 77 K which is transparent from 220 to 2600 nm. The absorption spectrum obtained on gamma radiolysis of a pure FTHF matrix at 77 K has a band at 248 nm. Using this matrix, the absorption spectra of a number of radiolytically generated perfluoroaromatic cations were obtained. This indicates that the matrix is suitable for the radiolytic generation and spectroscopic studies of cations of perfluoroaromatic compounds which have high ionization potentials.

Absorption and conductivity studies on the transients generated in the gamma-radiolysis of perfluorobenzene in rigid matrices

Abstract Absorption spectrum of the transient produced on gamma-radiolysis of C 6 F 6 in 3-methylpentane (3MP) matrix at 77 K has bands at 370 and 460 nm. Studies using electron and hole scavengers in 3MP matrix have shown that the species responsible for the above absorption is indeed due to electron attachment to C 6 F 6 . However, electron attachment to C 6 F 6 could be dissociative or nondissociative. Conductivity measurement of a gamma-irradiated C 6 F 6 in 3MP show a peak thermostimulated current of 500 × 10 -12 A as the temperature was raised above 77K. The thermostimulated current measured for irradiated C 6 F 6 in 3MP was reduced to 50 × 10 -12 A when the absorption bands were photobleached. The decrease in the thermostimulated current correlates with the depletion of species having absorption bands at 370 and 460 nm on photobleaching, indicating that the spectrum is due to the molecular anionic species and hence electron attachment to C 6 F 6 is nondissociative.

Ionic species produced on gamma radiolysis: Studies by matrix isolation technique—I. Electronic absorption spectra of perfluorosubstituted aromatic radical anions

Abstract The absorption spectra of several perfluorosubstituted aromatic radical anions are compared with the corresponding perhydro compounds in which the various transitions involved have been assigned to those predicted theoretically. The electronic absorption spectra were obtained for pentafluorostyrene, pentafluorobenzaldehyde, pentafluorobenzoic acid, pentafluorobenzonitride, tetrafluorophthalic acid and pentafluoroaniline, by gamma radiolysis in 2-methyltetrahydrofuran at 77 K. A general similarity in the absorption spectra between the perfluorinated and the corresponding perhydro radical anion is observed except for a shift in the absorption band.

Fate of the radical anion of perfluoroaromatic compounds in aqueous solution. A pulse radiolysis study

Hydrated electrons react with substituted perfluorinated aromatic compounds with diffusion controlled rate constants. For substituents with Hammett constant σ p < 0.06, the radical anions formed very rapidly loses F - . The phenyl radical formed undergoes, in the presence of an electron donating substituent, rapid intramolecular electron transfer and protonation on a ring carbon to yield radical cation or its conjugate base. Radical anions were observed on reduction of pentafluoroacetophenone (PFA) and pentafluoronitrobenzene (PFN). Evidence for the formation of the radical anion was obtained from observation of intermolecular electron transfer from PFA. - or PFN. - to p-benzoquinone (Q), methyl viologen (MV 2+ ) and anthraquinone-2-sulfonate (AQS -) to form Q .- , MV .+ and AQS .- - . The rate constants for fluoride elimination are (7 ± 3) x 10 3 and (1 ± 0.5) x 10 3 s -1 for PFA .- and PFN .- , respectively.

Matrix isolation studies of the transients produced in the gamma radiolysis of decafluorobenzophenone and triethylamine: Radiolytically generated contact ammonium ion-pair of decafluorobenzophenone

The radiolytically generated radical anion of decafluorobenzophenone normally leads to the formation of ketyl radical by protonation. However, in the presence of triethylamine, the ketyl radical formation can be prevented by a contact ion-pair formation. The absorption spectra for such an ion-pair is located at a shorter wavelength than the corresponding solvated radical anion and exhibits solvent-dependent spectral shift characteristic of the radical anion of decafluorobenzophenone.

Studies on the transients generated in the γ radiolysis of benzoyl-1,1,1-trifluoroacetone in glassy matrices: The radiolytically induced ketonization

Abstract The transients generated in the γ radiolysis of deaerated solutions of benzoyl-1,1,1-trifluoroacetone (BTA) are stabilized at 77 K and studied by their absorption spectra in the glassy matrices of isopropyl alcohol and methanol-11 mol % H2O. The transients identified are BTA∸enol, BTA∸keto, BTAH ketyl, [BTA2∸enolate]unrelax, and [BTA2∸enolate]rela x. BTA∸enol isomerizes to BTA∸keto, apparently suggesting that anion radical formation stabilizes the keto form. BTA2∸enolate undergoes configurational relaxation from an initially unstable to a final stable relaxed configuration. Both BTA∸enol and BTA∸keto react with protons produced on γ radiolysis to give BTAH ketyl.