Fuat Bayrakçeken

Optical properties and chemical behavior of Laser-dye Coumarin-500 and the influence of atmospheric corona discharges.

Structure elucidation of Coumarin-500 Laser-dye in cyclohexane at room temperature has been studied by UV-Vis, Raman, and FTIR spectroscopic techniques. Optical properties and chemical behavior under the influence of atmospheric positive electric pulsed corona discharges were also examined. The effects of UV-Vis irradiation changed some optical parameters, such as decrease in optical density on the absorption spectrum and formation of photoproducts, due to the chromaticity removal. No significant optical changes were observed in the light absorption upon UV-irradiation but large changes in absorption spectrum were observed after positive electric corona discharge treatments, FTIR and Raman spectra in non-polar solvent are recorded and interpreted.

A new type of delayed fluorescence of rubrene in solution

Abstract A new type of delayed fluorescence was observed for the first time for rubrene. Rubrene molecules were excited in a two step process. In the first step an excited singlet S 1 is created, which undergoes intersystem crossing to T 1 ; then T−T absorption creates an excited triplet rubrene molecule, which returns to the first excited singlet level by intersystem crossing. The recreated first excited singlet of rubrene decays back to the ground state by emitting this new type of delayed fluorescence, hereafter called the B-type of delayed fluorescence.

High resolution electronic absorption spectra of anisole and phenoxyl radical

High resolution absorption spectra of anisole and phenoxyl radical has been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the radicals decay which occurred predominantly by bimolecular recombination. The concentration of the phenoxyl radical calculated from the concentration of diphenoxyl molecules formed in the reaction cell during the optical pumping. The absolute extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95 x 10(+4) mol(-1) 1 cm(-1).

Flash photolysis of 2-methylbut-1-ene

The radicals formed in the flash photolysis of 2-methylbut-1-ene and then subsequent reactions have been investigated by kinetic spectroscopy and gas–liquid chromatography. Less than 10% of products are formed by a molecular mode of fission of the excited olefin, and of the radical modes the relative probabilities of bond fission, β(C—H): β(C—H): α(C—C) are 13:1.37:1. The extinction coefficient of the β methallyl radical measured for the strongest band (238 nm) was Iµ= 1.32 ± 0.11 × 104 1. mol–1 cm–1. The decay of the methyl and β methallyl radicals was second order. The rate constant for methyl combination was in agreement with the literature value and that for β methallyl combination measured for the first time was 2.6 ± 0.3 × 1010 mol–1 1. s–1 at 295 ± 2 K.

B-type delayed fluorescence of rubreneperoxide in solution.

Abstract B-type of delayed fluorescence was observed for the first time for rubreneperoxide. Rubreneperoxide molecules were excited in a two step process. In the first step an excited singlet S1 is created, which undergoes intersystem crossing to T1; then T-T absorption creates an excited triplet rubreneperoxide molecule, which returns to the first excited singlet level by intersystem crossing. The recreated first excited singlet of rubreneperoxide decays back to the ground state by emitting B-type of delayed fluorescence.

Extinction coefficients for the β-methallyl radical

Abstract The radicals formed in the flash photolysis of 2-methylbut-1-ene and iso-butene and subsequent reactions have been investigated by kinetic spectroscopy and gas liquid chromatography. The extinction coefficients of the β-methallyl radical were measured from the absorption bands. The decay of the radical was second order. The measured rate constant for β-methallyl combination was (2.6±0.3) × 10 10 mol −1 & s −1 at 295 ± 2K.

High resolution electronic absorption spectra of aniline, anilino and silicon dioxide.

High resolution electronic absorption spectra of aniline and anilino free radical have been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the anilino radicals decay which occurred predominantly by bimolecular recombination. Decay parameters of anilino free radical were measured from the absorption bands.

Fluorescence, Decay Time, and Structural Change of Laser Dye Cresyl Violet in Solution due to Microwave Irradiation at GSM 900/1800 Mobile Phone Frequencies

Microwave irradiation at GSM 900/1800 MHz mobile phone frequencies affects the electronic structure of cresyl violet in solution. These changes are important because laser-dye cresyl violet strongly bonds to DNA- and RNA-rich cell compounds in nerve tissues. The irradiation effects on the electronic structure of cresyl violet and its fluorescence data were all obtained experimentally at room temperature. For most laser dyes, this is not a trivial task because laser dye molecules possess a relatively complex structure. They usually consist of an extended system of conjugated double or aromatic π-bonds with attached auxochromic (electron donating) groups shifting the absorption band further towards longer wavelength. Because of the intrinsically high degree of conjugation, the vibrational modes of the molecular units couple strongly with each other. We found that the fluorescence quantum yield was increased from to due to intramolecular energy hopping of cresyl violet in solution which is exposed to microwave irradiation at mobile phone frequencies, and the photonic product cannot be used as a laser dye anymore.

Triplet–triplet optical energy transfer from benzophenone to naphthalene in the vapor phase

In principle the optical energy absorbed by a complex molecule raises that molecule to one of its excited states, and afterwards this excitation energy decays through the different relaxation channels. Initially, electronically excited benzophenone emits photons in the phosphorescence band of benzophenone and these emitted photons, as a stream of particles, are absorbed by the acceptor molecule naphthalene, then excited naphthalene phosphoresces. In this investigation, sensitized phosphorescence decay times in different conditions were measured for benzophenone-naphthalene system in the vapor phase. The ultraviolet-visible spectra of the system in the vapor phase at room temperature conditions were broad and structureless.

High resolution electronic absorption and extinction coefficients of the allyl radical

Electronic absorption spectra in the 210-250 nm region, were reported for the allyl radical in the vapor phase and subsequent reactions have been investigated by kinetic spectroscopy and gas-liquid chromatography. Extinction coefficients are calculated for the strong absorption bands of the allyl free radical by measured rate constants at room temperature.