The influence of structure and conformation on electronic interactions of 4′-nitro-10-phenylphenothiazine

The crystal structure of 4′-nitro-10-phenylphenothiazine, 1 , has been determined by the single crystal x-ray diffraction studies and consists of two independent molecules in the asymmetric cell unit with a pseudo-center of symmetry. The crystal belongs to the monoclinic System with the space group P2₁/c. The central ring of the phenothiazine ring system is in a boat conformation and the 4′-nitro substituent is in a boat-axial conformation with respect to the central ring of phenothiazine. Compound 1 is the first reported 10-aryl phenothiazine in which the 10-phenyl ring is perpendicular to the plane bisecting the dihedral angle of the phenothiazine nucleus. This geometry allows for resonance interaction between the lone pair of electrons on N₁₀ and the 4′-nitro-10-phenyl ring which influences both the spectral properties and structure of the phenothiazine tricyclic ring. The correlation between the x-ray structure and ¹³C nmr spectral properties of 1 is discussed. The uv/vis and esr studies of the radical cation of 1 indicate that the 10-aryl ring is twisted with respect to the phenothiazine ring.