Anchoring effect on (tetra)carboxyphenyl porphyrin/TiO₂composite films for VOC optical detection

Abstract

The optical gas sensing properties of Zn-(II) -5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP) and Zn-(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP) bound to microcolumnar TiO 2 thin films have been compared and explained in terms of their different molecular structure and anchoring to the titania surface. This different binding has been confirmed by specular reflectance FTIR revealing that m-ZnTCPP is bound by its four carboxylic groups in contrast to p-ZnTCPP where two or three of these groups remain unanchored. As a consequence, the Soret band of the para derivative is blue shifted with respect to the solution, indicating H aggregation, while m-ZnTCPP remained in its monomeric form due to the planar anchoring by the four COOH groups to the titania matrix that would avoid porphyrin aggregation. The sensing performance of the two systems has been assessed by analyzing the spectral changes in their UV-visible spectra under exposure to six volatile organic compounds. Although the highly porous and non-dispersive TiO 2 matrix allow good sensing ability in both cases, the response of the m-ZnTCPP/TiO 2 composite has been found to be more intense and faster than that of p-ZnTCPP.Moreover, the use of identification patterns also indicates that the meta derivative achieves a more selective recognition of the selected analytes. This improvement in the sensing capabilities of m-ZnTCPP has been attributed to the absence of aggregation between adjacent macrocycles.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…5.14 [247]. This confirms that the selectivity and performance of these hybrid systems are determined by how the sensing molecules are bonded to the porous OAD matrix [248]. .…”

“…In the liquid phase of a photonic sensor incorporating dye molecules in transparent OAD thin films (see Section 5.4), we have observed that the pH of the medium greatly modifies the adsorption capacity of cationic or anionic organic molecules from the rhodamine and porphirine families [229,230,[242][243][244][245][246][247][248]. To account for this pH dependent behavior, we have used the classical zero point of charge concept (zpc), which is widely used in colloidal chemistry [249].…”

Fluorescent Rosamine/TiO2 Composite Films for the Optical Detection of NO2

“…An important challenge derived from the deposition of dyes onto solid substrates is their strong tendency to form aggregates, which are known to be detrimental for gas sensing purposes [14]. Aggregation of dye molecules results in important changes in their photophysical properties, such as the broadening of the absorption bands because of the coexistence of various species, resulting in less-defined peaks and poorer monitoring of the spectral changes induced by the sensed analyte and limiting their use as optical probes [15][16][17]. At the same time, high molecular aggregation hinders the access of gas analytes to the active recognition sites of the dyes, causing a delay in their spectral response [14].…”

Self assembled nanocages from DNA–protoporphyrin hybrid molecules

“…19 PpIX is a p-electron rich light sensitive molecule and thus envisioned to have multiple applications involving conductivity, FRET, ROS and sensing volatile organic compounds (VOCs). [20][21][22][23][24] Recently, cationic porphyrin-tetrapeptide conjugates were synthesized which are good candidates for peptide delivery. 25 Free base porphyrin acting as molecular glue is used to assemble noncomplementary DNA sequences at ionic strength greater than 60 mM.…”