Synthesis, Spin Delocalization, and Charge Transport Properties of Phenol-Substituted Aza-Dipyrromethene Complexes of Co, Ni, Cu, and Zn and Their Oxidized Forms

We report the synthesis and characterization of homoleptic Co(II), Ni(II), Cu(II), and Zn(II) complexes of a phenol-substituted aza-dipyrromethene ligand. The complexes adopt distorted tetrahedral geometries, display ligand-centered redox activity, and exhibit panchromatic absorption. Chemical and electrochemical oxidation of the ML 2 complexes generate quinone/bis(diradicaloid) species that exhibit strong near-infrared absorption and antiferromagnetically coupled ligand-centered spins in the Zn(II) complex. Charge-transport measurements reveal modest electron mobilities and unusually high hole mobilities (≈10 –3 cm 2 V –1 s –1 ) for the quinone/bis(diradicaloid) complexes, making them potential hole transport materials. DFT and TD-DFT calculations confirm ligand-dominated frontier orbitals with metal-dependent electronic modulation. These results highlight aza-dipyrromethene metal complexes as promising platforms for redox-active and charge-transport materials.