Electronic, Optical, and Computational Studies of a Redox-Active Napthalenediimide-Based Coordination Polymer

The new one-dimensional coordination
framework (Zn­(DMF)­NO3)2(NDC)­(DPMNI), where NDC
= 2,6-naphthalenedicarboxylate
and DPMNI = N,N′-bis­(4-pyridylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide,
which has been crystallographically characterized, exhibits two redox-accessible
states due to the successive reduction of the naphthalenediimide (NDI)
ligand core. Solid-state electrochemical and vis–near-IR spectroelectrochemical
measurements coupled with density functional theory (DFT) calculations
enabled the origins of the optical transitions in the spectra of the
monoradical anion and dianion states of the material to be assigned.
Electron paramagnetic resonance (EPR) spectroscopy revealed that the
paramagnetic radical anion state of the DPMNI core could be accessed
upon broad-spectrum white light irradiation of the material, revealing
a long-lived excited state, possibly stabilized by charge delocalization
which arises from extensive π–π*
stacking interactions between alternating NDC and NDI aromatic cores
which are separated by a distance of 3.580(2) Å.