Oligotriarylamines with a Pyrene Core: A Multicenter Strategy for Enhancing Radical Cation and Dication Stability and Tuning Spin Distribution

Monoamine 1, diamines 2-4, triamine 5, and tetra-amine 6 have been synthesized by substituting dianisylami-no groups at the 1-, 3-, 6-, and/or 8-positions of pyrene. Diamines 2-4 differ in the positions of the amine substituents. No pyrene-pyrene interactions are evident in the single-crystal packing of 3, 4, and 6. With increasing numbers of amine substituents, the first oxidation potential decreases progressively from the monoto the tetraamine. These compounds show intense charge-transfer (CT) emission in CH₂Cl₂ at around 530 nm with quantum yields of 48-68%. Upon stepwise oxidation by electrolysis or chemical oxidation, these compounds were transformed into radical cations 1,⁺-6.⁺ and dications 2²⁺-6²⁺, which feature strong visible and v near-infrared absorptions. Time-dependent density functional theory studies suggested the presence of localized transitions from the pyrene radical cation and aminium radical cation, intervalence CT, and CT between the pyrene and amine moieties. Spectroscopic studies indicated that these radical cations and dications have good stability. Triamine 5 and tetraamine 6 formed efficient CT complexes with tetra-cyanoquinodimethane in solution. The results of EPR spectroscopy and density functional theory calculations suggested that the dications 2²⁺-4²⁺ have a triplet ground state, whereas 5²⁺ and 6²⁺ have a singlet ground state. The dicat-ion of 1,3-disubstituted diamine 4 exhibits a strong EPR signal.