Spectroscopic Properties of Langmuir−Blodgett Films of Lanthanide Bis(phthalocyanine)s Exposed to Volatile Organic Compounds. Sensing Applications

Abstract

The possibility of using Langmuir−Blodgett (LB) films of bis(phthalocyaninate) rare earth compounds (LnPc2) (including praseodymium, gadolinium, and lutetium bis(phthalocyanine)s and their octa-tert-butyl derivatives) as optical sensors has been explored. Special attention has been paid to the previously unexplored near-infrared (NIR) region. First of all, the NIR spectra of the unexposed LB films have been recorded. The NIR spectra of the bis(phthalocyanine) LB films are reported here for the first time. The changes in the UV−vis−near-infrared spectra caused by the interaction with several gases including NOx and vapors of volatile organic compounds (VOCs) such as alcohols, aldehydes, and esters (which are mainly responsible for odors in foods and beverages) have been studied. The influences of the response of the central metal atom of the phthalocyanine molecules and of the presence of tert-butyl groups in the peripheral benzene rings have been evaluated. It has been evidenced that the changes that take place in the NIR region occur at telecommunications wavelengths and open the possibility of using the bis(phthalocyanine) LB films as the sensitive part in industrial fiber optic sensors.