Interaction of Copper Phthalocyanine with Nitrogen Dioxide and Ammonia Investigation Using X-ray Absorption Spectroscopy and Chemiresistive Gas Measurements

Abstract

The interaction site of phthalocyanine (Pc) with nitrogen dioxide (NO 2 ) has been characterized using different methods and found to be conflicting. By knowing the interaction site, the Pc molecule can be better customized to improve the gas sensitivity. In this article, the interaction sites of copper phthalocyanine (CuPc) with oxidizing NO 2 or with reducing gas (ammonia, NH 3 ) were identified using in situ X-ray absorption spectroscopy (XAS). The sensitivity of CuPc to sub-ppm levels of the tested gases was established in the CuPc chemoresistive gas sensors. The analyte–sensor interaction sites were identified and validated by monitoring the Cu K-edge XAS before and during gas exposure. From the X-ray absorption near-edge structure and its first derivative, a low or lack of axial coordination on the Cu metal center of CuPc is evident. Using the extended X-ray absorption fine structure with molecular orbital information of the involved molecules, the macrocycle interaction between CuPc and NO 2 or NH 3 was proposed to be the dominant sensing mechanism on CuPc sensors.

Ferrous to Ferric Transition in Fe‐Phthalocyanine Driven by NO2 Exposure

“…To restore the magnetic moment of the ion, which is quenched due to the molecule‐surface interaction, two different approaches were previously proposed: electron doping [16, 46] or functionalization with an external ligand, e.g., a small gaseous molecule [21–25] . Inspired by the latter, we exposed the FePc/Cu(100) interface to gaseous NO 2 to restore the magnetic moment of the iron ion.…”

Photon assisted-inversion of majority charge carriers in molecular semiconductor-based organic heterojunctions

“…13,14 For example, chemiresistors based on p-type transition metal MPc displayed unipolar carrier transport in redox gases sensing, depicting current increase under electron acceptor gases and current decrease under donor gases. 15,16 On the other hand, chemiresistors based on substituted lanthanide complexes of double or triple decker phthalocyanine exhibited current increase under NO 2 as well as for NH 3 exposure, clearly demonstrating ambipolar chemosensing regime. 17, 18 The carrier transport modulation in MPc by changing the peripheral ligands, among fluoro, alkoxy and ester, and its implication on NH 3 sensing were exemplified in our recent works based on an organic heterojunction device.…”

Resonant Plasmon‐Enhanced Absorption of Charge Transfer Complexes in a Metal–Organic Monolayer

“…[ 49–51 ] This CT complex is presumably formed during the coordination of the NO 2 molecule at the zinc atom in ZnPc. [ 52–55 ] The transition of ZnPc to [ZnPc] +• in the complex with nitrogen dioxide leads to the quenching of the initial Q‐band absorption and the appearance of the so‐called “fingerprint” band in the region of ≈520 nm (see Figure S5, Supporting Information), associated with the single‐electron excitations from low‐lying doubly occupied orbitals 5 e g , 6 e g (HOMO– n ) toward the half‐empty 2 a 1u orbital (SOMO). [ 49 ] We also managed to observe the appearance of this band under the action of NO 2 on a bare monolayer of the ZnPc studied herein ( Figure a).…”