Radical and Diradical Formation in Naphthalene Diimides through Simple Chemical Oxidation.

We successfully synthesized, for the first time, a naphthalene diimide (NDI) radical and diradical by simple chemical oxidation using lead(IV) dioxide. The formation of the (di)radical is confirmed by UV/Vis/NIR absorption, 1 H NMR, and electron paramagnetic resonance (EPR) measurements. In particular, temperature-dependent EPR, SQUID (superconducting quantum interference device) measurements, and quantum calculations demonstrated that the generated NDI diradical has a singlet diradical character of y=0.69 in the ground state. Subsequent characterization of this (di)radical revealed its stabilities, large two-photon absorption cross-section, and short excited-state lifetime.