A DFT study of the hyperfine coupling constants of triplet carbenes and biradicals

Motivated by our recent investigation of spin-orbit mixing in the simplest singlet carbene, HCF, we report Density Functional Theory (DFT) calculations of the isotropic and anisotropic hyperfine coupling constants (HFCCs) of HCF (a˜A″3) and other important triplet carbenes and biradicals. We conducted extensive DFT calculations on the prototypical triplet carbene, CH2, and compare our results with experimental constants determined from Electron Spin Resonance (ESR) and microwave spectroscopy. We subsequently report DFT calculations of the HFCCs of other prototypical triplet carbenes and biradicals including HCF, HCCN, and C3H2, and the arylcarbenes diphenylmethylene (DPM; C13H10) and fluorenylidene (C13H8). The calculated HFCCs are compared in each case with experimental ESR and microwave data. This study provides an example of the utility of DFT for the calculation of HFCCs of open-shell species.