Synthesis and photoinduced behavior of DPP-anchored nitronyl nitroxides: a multifaceted approach.

Understanding and controlling spin dynamics in organic dyes is of significant scientific and technological interest. The investigation of 2,5-dihydropyrrolo[4,3-]pyrrolo-1,4-dione derivatives (DPPs), one of the most widely used dyes in many fields, has so far been limited to closed-shell molecules. We present a comprehensive joint experimental and computational study of DPP derivatives covalently linked to two nitronyl nitroxide radicals (DPP-NN). Synthesis, single crystal X-ray diffraction study, photophysical properties, magnetic properties established using steady-state and pulse EPR, fast spin dynamics, and computational modelling using density functional theory and methods of electronic structure and spectroscopic properties of DPP-NN are presented. The single-crystal X-ray diffraction analysis of DPP-NN and computational modeling of its electronic structure suggest that effective conjugation along the backbone leads to noticeable spin-polarization transfer. Calculations using methods predict a weak exchange interaction of radical centers through a singlet ground state of DPP with a small singlet-triplet splitting (Δ) of about 25 cm (∼0.07 kcal mol). In turn, a strong ferromagnetic exchange interaction between the triplet state of DPP chromophore and nitronyl nitroxides (with ∼ 250 cm) was predicted.