Fig. 2: Characterizations of :PDI²⁻/PDI²⁻ precursor.

a UV-vis absorption spectra of PDI and :PDI²⁻/PDI²⁻ precursor in aqueous solutions. Inset shows the color comparison of different solutions. b ESR spectra of PDI and :PDI²⁻/PDI²⁻ precursor. c Photographs of PDI and self-assembled :PDI²⁻/PDI²⁻ nanobelt (120 h). Inset shows the magnified optical microscope image of the self-assembled :PDI²⁻/PDI²⁻ nanobelt (120 h). d The PL spectrum (λ_ex = 450 nm) of :PDI²⁻/PDI²⁻ solid precursor sample. e In-situ PL spectra (λ_ex = 450 nm) tracking the emission of PDI after the 2e⁻ reduction by hydrazine hydrate in DMF solution in 30 min. With the addition of 0.25 μL hydrazine hydrate (85%), PDI was first converted to non-fluorescent :PDI²⁻ diradicals. A tautomeric equilibrium from the non-fluorescent diradicals to fluorescent quinoids was then achieved in 30 min. f Comparing PL spectra (λ_ex = 450 nm) between pristine PDI and :PDI²⁻/PDI²⁻ samples from in-situ 2e⁻ reduction of PDI for 30 min before and after removing residue hydrazine hydrate in DMF solutions. The hydrazine hydrate component was removed by evaporating the solvent by N₂ flow and then redissolving the sample in an identical concentration. Without hydrazine hydrate, :PDI²⁻/PDI²⁻ sample in DMF shows identical PL emissions to the :PDI²⁻/PDI²⁻ solid sample as in d. g Schemes show the two-electron reduction pathway of PDI molecules generating :PDI²⁻ diradical anions (T₁) and the tautomeric PDI²⁻ quinoid isomer (S₀).