Ammonia and Humidity Sensing by Phthalocyanine–Corrole Complex Heterostructure Devices

Abstract

The versatility of metal complexes of corroles has raised interest in the use of these molecules as elements of chemical sensors. The tuning of the macrocycle properties via synthetic modification of the different components of the corrole ring, such as functional groups, the molecular skeleton, and coordinated metal, allows for the creation of a vast library of corrole-based sensors. However, the scarce conductivity of most of the aggregates of corroles limits the development of simple conductometric sensors and requires the use of optical or mass transducers that are rather more cumbersome and less prone to be integrated into microelectronics systems. To compensate for the scarce conductivity, corroles are often used to functionalize the surface of conductive materials such as graphene oxide, carbon nanotubes, or conductive polymers. Alternatively, they can be incorporated into heterojunction devices where they are interfaced with a conductive material such as a phthalocyanine. Herewith, we introduce two heterostructure sensors combining lutetium bisphthalocyanine (LuPc2) with either 5,10,15-tris(pentafluorophenyl) corrolato Cu (1) or 5,10,15-tris(4-methoxyphenyl)corrolato Cu (2). The optical spectra show that after deposition, corroles maintain their original structure. The conductivity of the devices reveals an energy barrier for interfacial charge transport for 1/LuPc2, which is a heterojunction device. On the contrary, only ohmic contacts are observed in the 2/LuPc2 device. These different electrical properties, which result from the different electron-withdrawing or -donating substituents on corrole rings, are also manifested by the opposite response with respect to ammonia (NH3), with 1/LuPc2 behaving as an n-type conductor and 2/LuPC2 behaving as a p-type conductor. Both devices are capable of detecting NH3 down to 10 ppm at room temperature. Furthermore, the sensors show high sensitivity with respect to relative humidity (RH) but with a reversible and fast response in the range of 30–60% RH.

Ambipolar Heterojunction Sensors: Another Way to Detect Polluting Gases

“…In the realm of conductometric sensors or gas sensing applications in real environmental conditions, careful consideration of humidity’s impact is crucial. Humidity poses a potential interference, which can highly influence the sensing and electrical properties of the device . Initially, both heterojunction sensors were investigated under changing relative humidity conditions.…”

π-Extended Porphyrin–Phthalocyanine Heterojunction Devices Exhibiting High Ammonia Sensitivity with a Remarkable Light Effect

“…The electrodes were cleaned properly through stepwise ultrasonication in CH 2 Cl 2 and ethanol, followed by drying in an oven for 1 h at 100 °C. The sublayers were coated on the IDE by using the quasi-dip coating method that we developed recently (Scheme S1), and bilayer heterostructures were fabricated on the Ace-PQ-Ni and AM6 resistors by thermal evaporation in a UNIVEX 250 thermal evaporator under secondary vacuum (ca. 10 –7 mbar).…”

Effects of Visible Light on Gas Sensors: From Inorganic Resistors to Molecular Material-Based Heterojunctions

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