Solid‐State Oxygen and Hydrogen Sensing Devices Based on Copper Dicyanoanthraquinone Diimines

Substituted dicyanoanthraqumone diimines (DCNAQI) and their related copper complexes, Cu(DCNAQI), have been synthesized and characterized. Most Cu(DCNAQI) complexes possess an activation energy 80–400 meV and strongly absorb in the IR range. Electrochemical investigations with polycrystailine electrodes as thin films reveal that Cu(DCNAQI) behaves as an n‐type semiconductor. Under bandgap excitation (4000 cm⁻¹), the photoconductance measured with these Cu(DCNAQI) electrodes was greatly promoted under nitrogen, but very sensitive to O₂ or H₂. When the conductance difference, Δσ/σ_dark = (σ_light ‐ σ _dark)σ _dark, was plotted vs the partial pressure of the target molecule, a nearly linear relationship was observed. Among Cu(DCNAQI), Cu(β‐methyl‐DCNAQI) gave the greatest senstivity for detection of hydrogen, but Cu(α,α′‐dichloro‐DCNAQI) appeared most sensitive toward oxygen. This remarkable relationship is likely due to retardation of the mobility of electron or hole by interaction with oxygen or hydrogen at the Cu(DCNAQI) electrode surface; a solid‐state oxygen/hydrogen sensing device based on these organic semiconductors is proposed.