Matvey K. Shurikov, Yuliana A. Kolesnikova, Darya E. Votkina, Pavel A. Abramov, Taisiya S. Sukhikh, Galina V. Romanenko, Sergey L. Veber, Dmitry E. Gorbunov, Nina P. Gritsan, Giuseppe Resnati, Evgeny V. Tretyakov, Vadim Yu. Kukushkin, Pavel S. Postnikov*, Pavel V. Petunin*

Cite this article: https://doi.org/10.1016/j.cjsc.2025.100653

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ABSTRACT

Six aryl- and pyridine-substituted nitronyl-nitroxide radicals were synthesized and characterized to investigate their optical anisotropic properties. Single-crystal X-ray diffraction analysis revealed molecular packing organized either by halogen and hydrogen bonding or by hydrogen bonding alone. Single-crystal electronic absorption spectra in the visible region of three studied radicals exhibited pronounced linear dichroism, while single crystals of other radicals did not demonstrate this property. Time-dependent DFT and ab initio calculations were employed to determine the transition dipole moment (TDM) vectors corresponding to the long-wavelength absorption bands. For all radicals, these vectors were found to be practically parallel to the O···O direction of the nitronyl-nitroxide chromophore. Correlation between the dichroic properties and crystal structure was established through comprehensive analysis of TDM vector orientations relative to the crystal surface. The strongest dichroic effect was observed in crystals where all projections of the TDM vectors onto the illuminated face were parallel to each other, while weaker or absent effects corresponded to non-parallel arrangements. This study constitutes the first systematic investigation of linear dichroism in paramagnetic organic crystals, thereby establishing new avenues for developing multifunctional materials that respond to both optical and magnetic stimuli.