Localized triplet diradicals as a probe for electronic substituent effects in benzyl-type radicals: The ΔD scale

Abstract

Abstract

Extremely Long Lived Localized Singlet Diradicals in a Macrocyclic Structure: A Case Study on the Stretch Effect

“…The large D value suggests that the triplet state is not derived from the 1,3‐diradical moiety but from a benzene moiety. The typical D value for triplet 1,3‐diphenylpropane‐1,3‐diyl diradical species is known to be about 0.05 cm −1 ; D values of about 0.12–0.15 cm −1 have been reported for the triplet state of benzene derivatives such as benzene itself and 1,3‐dicyanobenzene . Disappearance of the typical triplet signals under dark conditions indicated that they were derived from the 470 nm species.…”

EPR spectroscopic and computational characterization of the 2‐dehydro‐m‐xylylene and 4‐dehydro‐m‐xylylene triradicals

“…The traditional approach relies on the concept of ‘atomic spin densities’ and a simple point dipole model of spin–spin interactions. In ‘localized’ diradicals (such as cyclopentane‐1,3‐diyls), the D parameter decreases with the third power of the distance d AB between the ‘radical sites’ A and B and is proportional to the spin densities ρ at both centers (Eqn (2)): …”

“…This relationship has been firmly established by elegant EPR studies on various diradicals by Adam and coworkers and it has been used to study substituent effects on the spin density distribution within these systems . It relies on the assumption that spin‐orbit contributions to the ZFS can be completely neglected (which is usually justified for hydrocarbon systems) and that the spin–spin interactions can be treated within a simple point dipole scheme.…”

Unusually Long‐Wavelength Emissions of Cyclopropanes: New Insight into C−C Bond Homolysis

“…In the last decade, the isolation of persistent singlet and triplet 1,3‐diphenylpropane‐1,3‐diyl diradicals, DR , has been developed by using appropriate molecular designs and low‐temperature matrix‐isolation techniques in the photochemical denitrogenation of 2,3‐diazabicyclo[2.2.1]heptane derivatives, AZ (Scheme b) . Herein, the emission spectroscopic analyses of the 1,2‐diarylcyclopropane derivatives CP1 a (Ar=Ph, X=OMe), CP1 b (Ar=Ph, X=Me), CP2 a (Ar=2‐Naph, X=OMe), and CP2 b (Ar=2‐Naph, X=Me) were investigated under low‐temperature glassy matrix conditions.…”

“…As was mentioned above, the 1,2‐diphenylcyclopropanes with X=Me ( CP1 b and CP2 b ) did not show any long‐wavelength emission over 450 nm. To obtain more insight into the emission phenomena, the matrix isolation of T‐ DR1 b (Ar=Ph, X=Me) and its emission analysis were conducted at 77 K in 3MeP (Figure F). First, the triplet diradical T‐ DR1 b was generated using photochemical denitrogenation of AZ1 b ( λ max ≈365 nm, 1.0×10 −3 m ) at 77 K in a sealed 3MeP solution under degassed conditions.…”