Gas Sensing Mechanism in Chemiresistive Cobalt and Metal-Free Phthalocyanine Thin Films

Abstract

The gas sensing behaviors of cobalt phthalocyanine (CoPc) and metal-free phthalocyanine (H2Pc) thin films were investigated with respect to analyte basicity. Chemiresistive sensors were fabricated by deposition of 50 nm thick films on interdigitated gold electrodes via organic molecular beam epitaxy (OMBE). Time-dependent current responses of the films were measured at constant voltage during exposure to analyte vapor doses. The analytes spanned a range of electron donor and hydrogen-bonding strengths. It was found that, when the analyte exceeded a critical base strength, the device responses for CoPc correlated with Lewis basicity, and device responses for H2Pc correlated with hydrogen-bond basicity. This suggests that the analyte-phthalocyanine interaction is dominated by binding to the central cavity of the phthalocyanine with analyte coordination strength governing CoPc sensor responses and analyte hydrogen-bonding ability governing H2Pc sensor responses. The interactions between the phthalocyanine films and analytes were found to follow first-order kinetics. The influence of O2 on the film response was found to significantly affect sensor response and recovery. The increase of resistance generally observed for analyte binding can be attributed to hole destruction in the semiconductor film by oxygen displacement, as well as hole trapping by electron donor ligands.

Reversible Change of the Spin State in a Manganese Phthalocyanine by Coordination of CO Molecule

“…In metal-phthalocyanines and metal-porphyrins the metal center is usually coordinatively unsaturated and presents a local reactive site, which opens a unique possibility of controlling the magnetic moment in situ by external chemical stimuli [2][3][4][5][6][7][8]. The axial coordination of small molecules like CO, NO or O 2 to those complexes substantially alters their electronic properties, which has led to a successful implementation of phthalocyanines and porphyrins in gas sensors [9,10]. Studies specifically addressing the magnetic state are, however, scarce.…”

Toluene vapor sensing characteristics of novel copper(II), indium(III), mono-lutetium(III) and tin(IV) phthalocyanines substituted with 2,6-dimethoxyphenoxy bioactive moieties

“…Their characteristic B1 and B2 bands (3)(4)(5)(6)(7)(8)(9)(10) were observed at a range of 313-405 nm (Fig. 1).…”

“…Because of their potential contribution to the next generation of molecular electronic devices such as electrochromic and electro-luminescent displays, nonlinear optics, photovoltaics, chemical sensors nanotechnology, and photosensitizers for photodynamic cancer therapy (PDT) of tumors, studies on the synthesis and characterization of novel phthalocyanines (Pcs) compounds are of considerable interest [1][2][3][4][5][6][7][8][9][10][11]. All the properties of Pcs are influenced and enhanced both by the nature of central metals and the substituent and substituent's position (peripheral or non-peripheral) in the Pc ring.…”

Doping and photo-induced current in discotic liquid crystals thin films: Long-time and temperature effects

“…Discotic liquid crystals (DLCs) [1] are a class of liquid crystals proposed for many applications in organic electronics [2][3][4][5], including organic field effect transistors (OFETs) [6,7], in photovoltaics [8][9][10], as sensors [11,12] and in information storage [12]. DLCs are formed by a rigid aromatic core and highly flexible peripheral chains, which provide solubility and drive self-organizing properties of these materials in columns forming different mesophases [13,14].…”

“…It is known that the electrical conduction in liquid crystals and in particular in phthalocyanine-based materials is greatly affected by contaminants and environmental conditions [11,[28][29][30][31][32]. Although a controlled doping produces a strengthening of the sensing capability, it becomes a major limitation in organic electronics applications.…”