Understanding the VOC sorption processes on fluoro alkyl substituted phthalocyanines using ATR FT-IR spectroscopy and QCM measurements

In this work the sorption of volatile organic compounds (VOCs) by phthalocyanines is studied and modelled using in situ attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy and gas sensor data. A series of fluoropropoxyphthalocyanines (Pcs) either in the metal free form or as nickel and cobalt complexes were synthesised and coated on quartz crystal microbalance and ZnSe ATR substrates as thin films with the jet spray technique. The VOCs for the gas exposure experiments were selected according to their physico-chemical properties such as acidity, basicity, polarity etc. The influence of the humidity on the interaction mechanism and the sensor signal was also investigated. The in detail analysis of the ATR FT-IR measurements revealed that the analytes interact mainly with the centre of the Pcs (a metal ion or NH group), the aromatic CH group of the Pc core, and the substituent group. The aromatic CH groups of the Pc core were identified as active centres for the first time and were found to play an active role in the sensing mechanism and determine the sensitivity of the sensors. They may interact with a π system of an analyte via Hπ bonding or with OH groups via hydrogen bonds.