The photodissociation dynamics of CF 2 ICF 2 I in solution was investigated from 0.3 ps to 100 μs, after the excitation of CF 2 ICF 2 I with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.3 ps, producing a haloethyl radical having a classical structure: anti-CF 2 ICF 2 and gauche-CF 2 ICF 2 . All the nascent gauche-CF 2 ICF 2 radicals reacted with the dissociated I atom within the solvent cage to produce a complex, I 2 ••C 2 F 4 , in <1 ps. The quasi-stable I 2 •• C 2 F 4 complex in CCl 4 (CH 3 CN or CD 3 OH) further dissociated into I 2 and C 2 F 4 with a time constant of 180 ± 5 (46 ± 3) ps. Some of the anti-CF 2 ICF 2 radicals also formed the I 2 ••C 2 F 4 complex with a time constant of 1.5 ± 0.3 ps, while the remaining radicals underwent secondary elimination of I atom in a few nanoseconds. The time constant for the secondary dissociation of I atom from the anti-CF 2 ICF 2 radical was independent of the excitation wavelength, indicating that the excess energy in the nascent radical is relaxed and that the secondary dissociation proceeds thermally. The formation of the I 2 ••C 2 F 4 complex and the thermal dissociation of the anti-CF 2 ICF 2 radical clearly demonstrate that even a weakly interacting solvent plays a significant role in the modification and creation of reaction.
Photoexcited CF2I2in c-C6H12undergoes various secondary reactions including complex and isomer formation, after ultrafast two- or three-body dissociations.
The
corrole derivative meso-oxoisocorrole has
been theoretically predicted to be antiaromatic, despite its formally
cross conjugated electronic system. In this study, this prediction
has been experimentally proven by the facile preparation of meso-oxoisocorrole via the oxidation of a meso free corrole with MnO2 and its comprehensive characterization
using NMR, UV/vis absorption, FT-IR, and transient-absorption spectroscopy,
cyclic voltammetry, and X-ray diffraction analysis. Furthermore, the
free base meso-oxoisocorrole was metalated by treatment
with Ni(acac)2, PdCl2(PhCN)2, and
Zn(OAc)2 to give the corresponding metal complexes. These
complexes are more strongly antiaromatic, and their degree of paratropicity
depends on their planarity. Thus, fine tuning of their antiaromaticity
was achieved with concomitant modulation of their HOMO–LUMO
gaps. In the presence of tris(pentafluorophenyl)borane, their antiaromaticity
is significantly enhanced due to the elongation of the CO
bond, which promotes the polarized C+–O– resonance state. Furthermore, a distinct frequency shift of the
CO vibrational mode in the triplet state was observed in the
time-resolved IR spectra in accordance with the Baird rule, which
indicates aromaticity reversal in the excited state.
The rotational isomerization of 1,2-disubstituted ethyl radical derivatives, reaction intermediates often found in the reaction of 1,2-disubstituted ethane derivatives, has never been measured because of their short lifetime and ultrafast rotation. However, the rotational time constant is critical for understanding the detailed reaction mechanism involving these radicals, which determine the stereoisomers of compounds produced via the intermediates. Using time-resolved infrared spectroscopy, we found that the CF 2 BrCF 2 radical in a CCl 4 solution rotationally isomerizes with a time constant of 47 ± 5 ps at 280 ± 2 K. From this value and the rotational barrier heights of related compounds, CH 3 CH 2 and CH 3 CH 2 CHCH 3 radicals in CCl 4 were estimated to rotationally isomerize within 1 ps at 298 K, considerably faster than ethane and n-butane, which rotationally isomerize with time constants of 1.8 and 81 ps, respectively. The time constant for the rotational isomerization was similar to that calculated using transition state theory with a transmission coefficient of 0.75.
The dynamics of photoexcited chlorobenzene (PhCl) and 4-fluoroiodobenzne (4-FPhI) in CCl 4 were investigated using time-resolved infrared spectroscopy. When excited at 267 nm, 50% (70%) of the excited PhCl (4-FPhI) dissociates the Cl (I) atom immediately, and the remaining molecules relax into the T 1 state via intersystem crossing (ISC) with a time constant of 70-80 ps. About half of the dissociated halogen atoms geminately recombine with the nascent radical with a time constant of 100-150 ps, reducing the number of generated radicals that are available to react with other reaction partners. The remaining radicals also recombine with the dissociated halogen atom on a timescale of tens of nanoseconds. Interestingly, the ISC of the light Cl-atom-involved PhCl was as efficient as that of the heavy I-atom-involved 4-FPhI. Detailed photoexcitation dynamic studies of PhCl and 4-FPhI can be utilized to understand the reaction dynamics of Ph and its derivatives. K E Y W O R D S intersystem crossing, phenyl radical, radical of phenyl derivatives, reaction dynamics in solution, time-resolved vibrational spectroscopy
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