182162-47-6Relevant academic research and scientific papers
Photochemically generated cyclopentane-1,3-diyl triplet diradicals as model systems for the assessment of spin delocalization in heteroaryl-substituted benzyl-type monoradicals through the EPR spectral D parameter
Adam, Waldemar,Emmert, Oliver,Harrer, Heinrich M.
, p. 687 - 694 (1997)
The zero-field D parameters of a comprehensive set of cyclopentane-1,3-diyl triplet diradicals 2 were determined at 77 K in a 2-MTHF glass matrix. The D values were found to be dependent on the heteroaryl substituents in the decreasing order 3-furyl ? 3-t
Wavelength-selective photodenitrogenation of azoalkanes to high-spin polyradicals with cyclopentane-1,3-diyl spin-carrying units and their photobleaching: EPR/UV spectroscopy and product studies of the matrix-isolated species
Adam,Maas,Nau
, p. 8790 - 8796 (2007/10/03)
The photolysis of the mono-, bis-, and trisazoalkanes 1, 2, and 3 in a toluene matrix at 77 K has been studied by EPR and UV spectroscopy. The purpose was to find the optimal conditions for the generation of the corresponding organic high-spin polyradicals (the triplet diradicals D-1, D-2, and D-3, the tetraradicals T-2 and T-3, and the hexaradical H-3) all with localized cyclopentane-1,3-diyl spin-carrying units, connected by m-phenylene (except D-1) as ferromagnetic coupler. Irradiation of these azoalkanes at 333, 351, or 364 nm gave different polyradical compositions. This observed wavelength dependence is due to the secondary photoreaction (photobleaching) of the polyradical intermediate. The photobleaching process has been examined in detail for the triplet diradical D-1, for which π,π* excitation affords the cyclopentenes 5 instead of the housane 4 (the usual product of the diradical D-1 on warm-up of the matrix). The π,π*-excited diradical D-1 fragments into a pair of allyl and methyl radicals (the latter was observed by EPR spectroscopy of a photobleached sample), and recombination affords the cyclopentene. Similar photochemical events are proposed for the photobleaching of the tetraradical T-2 and hexaradical H-3, derived from the respective azoalkanes 2 and 3. Thus, photobleaching of the polyradicals competes effectively with their photogeneration from the azoalkane. This unavoidable event is the consequence of spectral overlap between the cumyl-radical π,π* chromophore of the polyradical and the n,π* chromophore of the azoalkane at the wavelength (364 nm), at which the latter is photoactive for the required extrusion of molecular nitrogen.
The EPR D parameter as a measure of spin delocalization in cyclopentane-1,3-diyl triplet diradicals with extended conjugation π-type substituents
Adam, Waldemar,Van Barneveld, Claus,Emmert, Oliver
, p. 637 - 641 (2007/10/03)
π-Substituted cyclopentane-1,3-diyl triplet diradicals 2 were readily prepared from the corresponding azoalkanes 1 by photodenitrogenation in a 2-methyltetrahydrofuran matrix at 77 K. The D values of these triplet diradicals, obtained from the EPR spectra under matrix isolation, depend on the π substituent in the order butadienyl > 2-anthryl > vinyl > 2-naphthyl > phenyl. Good linear correlations of the D values have been obtained with the reported hyperfine coupling constants (α-hfc), with the ab initio (B3LYP) spin densities for the corresponding monoradicals 3, and with the radical stabilization energies (RSE). The present results for these extended π systems are compared with those for previously reported heteroaryl-substituted triplet diradicals.
