Triplet State EPR of 1,5-Naphthyridine

Paramagnetic resonance experiments of the triplet state of 1,5‐naphthyridine in mixed crystals of durene and perdeuterated durene at 80°K are reported. The fine structure observed at 35 GHZ is described by the spin Hamiltonian, $\mathfrak{H}\mathrm{\hspace{0.17em}=\hspace{0.17em}\beta }\mathbf{H}·\mathbf{g}·\mathbf{S}{\mathrm{\hspace{0.17em}+\hspace{0.17em}D(S}}_z^2{\text{\hspace{0.17em}−\hspace{0.17em}2\hspace{0.17em}/\hspace{0.17em}3)\hspace{0.17em}+\hspace{0.17em}E(S}}_x^2{\mathrm{\hspace{0.17em}-\hspace{0.17em}S}}_y^2)$ , in which $\text{S\hspace{0.17em}=\hspace{0.17em}1, D\hspace{0.17em}/\hspace{0.17em}hc\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}0.1030\hspace{0.17em}±\hspace{0.17em}0.0008}{\mathrm{cm}}^{\text{−1}}\text{, E\hspace{0.17em}/\hspace{0.17em}hc\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}0.0167\hspace{0.17em}±\hspace{0.17em}0.0007}{\mathrm{cm}}^{\text{−1}}$ , and $g_{\mathrm{xx}}{\text{\hspace{0.17em}=\hspace{0.17em}2.0043\hspace{0.17em}±\hspace{0.17em}0.0005, g}}_{\mathrm{yy}}{\text{\hspace{0.17em}=\hspace{0.17em}2.0032\hspace{0.17em}±\hspace{0.17em}0.0008, g}}_{\mathrm{zz}}\text{\hspace{0.17em}=\hspace{0.17em}2.0018\hspace{0.17em}±\hspace{0.17em}0.0006}$ . The sign of $D$ is determined by the analysis of weak satellites in the hyperfine structure with the magnetic field along the $X$ axis. The spin densities determined from the anisotropic hyperfine interaction along the three molecular axes are ${\rho }_n{\text{\hspace{0.17em}≈\hspace{0.17em}0.113, ρ}}_2{\text{\hspace{0.17em}≈\hspace{0.17em}0.101, ρ}}_3{\text{\hspace{0.17em}≈\hspace{0.17em}0.051, ρ}}_4{\text{\hspace{0.17em}≈\hspace{0.17em}0.227, ρ}}_9\text{\hspace{0.17em}≈\hspace{0.17em}0.009}$ .