Spectrofluorometric studies. IX. Fluorescent and triplet yields of the tetrafluorobenzenes excited in the 2600 Å region

Abstract

The gas phase fluorescent and triplet yields of 1,2,4,5-, 1,2,3,4-, and 1,2,3,5-tetrafluorobenzene (TFB) excited in the 2600 A region have been determined. For 1,2,4,5-TFB, the maximum fluorescent yield (Q, = 0.338) occurs at h,, = 2670 A and the triplet yield at this wavelength = 0.515. For 1,2,3,4-TFB, the maximum fluorescent yield is 0.186 and is obtained at h,, = 2645 A; the triplet yield at this wavelength = 0.220. For 1,2,3,5-TFB the maximum fluorescent yield = 0.029 and themaximum triplet yield is 0.141, at an exciting wavelength of 2680 A. The fluorescent and triplet yields of the three molecules, at any exciting wavelength studied, are not quenched by the addition of cis-butene-2 (c-B-2).

Excited‐State Distortions Promote the Photochemical 4π‐Electrocyclizations of Fluorobenzenes via Machine Learning Accelerated Photodynamics Simulations

“…We note that the predicted τ nr of 1 (60 ps) and 3 (12 ps) are more comparable to the measured τ nr of 1 at 250 nm (70 ps) [24] and 3 at 245 nm (29 ps) [25] As such, we could correlate the ML‐NAMD simulations to the S 1 →S 0 decay of fluorobenzenes at 265 nm with higher temperatures or at room temperature with shorter wavelengths. In contrast to 1 and 3 , Scholz and Unger report that the triplet quantum yield of 6 rises from 0.1 at 252 nm to 0.5 at 267 nm [38] . It suggests the increasing importance of the intersystem crossing in the nonradiative decay of 6 at longer wavelengths.…”

“…In contrast to 1 and 3, Scholz and Unger report that the triplet quantum yield of 6 rises from 0.1 at 252 nm to 0.5 at 267 nm. [38] It suggests the increasing importance of the intersystem crossing in the nonradiative decay of 6 at longer wavelengths. However, our simulation conditions impose higher energy than room temperature or 265 nm light.…”

Emission spectra and chemical reactions of fluorinated benzene derivatives in a high-frequency discharge

“…Many papers have already been published on the photochemistry of fluorinated benzene derivatives in the gas phase. [1][2][3][4][5][6][7][8] The quantum yield and lifetime of the first singlet (Si) and triplet states (Ti) of these compounds have been measured as functions of the exciting wavelength and the pressure. Analysis of the energy relaxation processes emphasizes the following interesting point: the value of the quantum deficit 1 -(0si + ), where 0Si and 0Ti represent the luminescence quantum yield of the first singlet and triplet states, respectively, tends to increase with both the energy of the photons and the number of fluorine atoms on the benzene ring (Table I).…”