The optical gas-sensing properties of an asymmetrically substituted porphyrin

Abstract

In this paper we have investigated the NO 2 gas-sensing properties of LB film assemblies of 5,15-bis(4aminophenyl)-10,20-bis [3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (CAH4). The optical absorbance spectrum of these films is dramatically affected when exposed to low concentrations of NO 2 gas. LB films of CAH4 were prepared by using ultra-fast deposition and characterized by imaging ellipsometry. The high deposition rates employed (500 mm min 21 ) led to an inhomogeneous structure with high porosity. The LB film exposed to 4.6 ppm NO 2 showed a sensitivity of 60% relative absorbance change at 439 nm. The response was found to be faster than that measured in similar systems. The fast response can be explained in terms of the molecular structure of the porphyrin as well as the enhanced surface area of the porous film. The optical response of the CAH4 film gradually decreases as its temperature is increased, a result of a shift in the adsorption-desorption equilibrium towards desorption. An activation energy of 0.48 eV is obtained. Full recovery of the original spectrum after exposure to NO 2 is obtained and can be dramatically accelerated with gentle heating (353 K). The concentration dependence of the optical response over the range 0.46-4.6 ppm NO 2 obeyed a Langmuir adsorption model. Ageing experiments have shown that the basic response of the CAH4 assemblies is not affected over a time period of at least 1 year.

Pyrrolo‐Tetrathiafulvalenes and Their Applications in Molecular and Supramolecular Chemistry

“…[31] In addition, porphyrins find expanding applications in materials science, [32] reaction catalysis, [33] molecular recognition, [34] and as diagnostic/therapeutic agents [35] and sensors. [36] Scheme …”

Langmuir–Schaefer films of five different free base tetraphenylporphyrins for optical-based gas sensing of NO2

“…Previous research has shown that free base porphyrin NO 2 sensors can be recovered to their unexposed state by gentle heating (∼90 • C) and are therefore re-useable [2]. The concentration dependence of porphyrin thin films has been found to follow a Langmuir adsorption model at low concentrations (0.46-4.6 ppm) [4]. Porphyrin sensors are also being incorporated into single use colorimetric sensor arrays to detect volatile organic compounds [9].…”

“…Considerable research has been done to investigate the NO 2 -sensing properties of free base porphyrins [1][2][3][4][5][6]. This research has been driven by the need to develop more sensitive, reliable and cost-effective sensors for toxic gases.…”

Substrate Influence for the Zn‐tetraphenyl‐porphyrin Adsorption Geometry and the Interface‐Induced Electron Transfer

“…Porphyrins therefore have the potential to be used in many technological applications such as molecular optoelectronic gates, molecular wires, photo-inducible energy or electron transfer systems, light-harvesting arrays for solar cells, one-dimensional conductors and semiconductors, enzyme models, oxidation catalysts, sensors, and nonlinear optics. [3][4][5][6][7][8] Contrary to other organic molecules, such as pentacene, perylene, sexphenyl, and so forth, [1,9,10] porphyrins have several degrees of freedom and numerous possibilities of chemical modifications, thanks to the attached meso-substituents and the metal atoms added to the free base macrocycle. [3] This allows for several molecular orientations and conformations when deposited on substrates, giving origin to organic/inorganic interfaces that are morphologically slightly different, but cover a wide variety of electronic properties.…”