Dynamic behavior, electrochromism, and two-photon absorption of dicyanomethylenated quinacridone

Molecular structures of dicyanomethylenated quinacridone (1) as a solid and in solution were examined on the basis of single-crystal X-ray structural analysis, temperature-dependent ¹H NMR in CD₂Cl₂, and theoretical calculations. Crystal 1 had a curved, butterfly-shaped molecular structure. Thermally activated flipping between the curved, butterfly-shaped structure and an armchair structure occurred in solution. Electrochemical reduction triggered a dynamic change from the curved, butterfly-shaped conformation in the neutral state to a planar conformation in the dianion state, which represented electrochromic behavior with electrochemical bistability. A large two-photon absorption cross section of compound 1 was observed in the resonance-enhancement region of 423 GM (1 GM = 1 × 10^-50 cm⁴ s photon^-1 molecule^-1) at 710 nm. Multiple donor-acceptor charge-transfer pathways of molecule 1 enhanced two-photon absorption. (Chemical Equation Presented).