Sensors and Actuators B 142 (2009) 159–165 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Interaction of Langmuir–Blodgett and spin-coated films of -carbido-bridged ironphthalocyanine with NO 2 : Optical and conductimetric behaviour Aldo Capobianchi a , Anna Maria Paoletti a , Gentilina Rossi a , Gloria Zanotti b , Giovanna Pennesi a,∗ a CNR, Istituto Struttura della Materia, Sede di Montelibretti, C.P. 10, 00016 Monterotondo Stazione, Italy b Università di Tor Vergata, Dipartimento di Ingegneria Elettronica, Roma, Italy article info Article history: Received 16 April 2009 Received in revised form 11 August 2009 Accepted 12 August 2009 Available online 19 August 2009 Keywords: Bridged phthalocyanine Langmuir–Blodgett films Spin-coated films Sensors Nitric oxide abstract The present study investigates the interaction of NO 2 gas and -carbido-bridged iron phthalocyanine (PcFe C FePc) films obtained by Langmuir–Blodgett (LB) and spin-coating (SC) techniques. The phthalo- cyanine bridged dimer under study belongs to the polynuclear unsubstituted phthalocyanines class and presents poor solubility: in contrast the corresponding N-base bis-adducts are soluble enough in organic solvents to be deposited by Langmuir–Blodgett and spin-coating techniques. The reaction with NO 2 is monitored by visible spectra variation that shows identical behaviour for both kinds of films, indicating that the chemical reaction between the gas and the films is independent of the deposition method. The electrical conductivity change as a function of time with NO 2 is instead dissimilar: for spin-coated films it shows a behaviour already observed for sandwich-type phthalocyanine whereas for LB films it resem- bles that of monomeric phthalocyanine. Such a response implies that the charges (holes) generated in the oxidation/reduction process are carried differently through the material, and we attempt to explain this behaviour taking into account the two different structural and morphological features induced by the two techniques. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Thin films, with reproducible characteristic (thickness, uni- formity, and morphology), are needed for the exploration and exploitation of the fascinating optical and electronic proper- ties of phthalocyanine (Pc) macrocycle derivatives [1,2]. Beside the vacuum evaporation technique [3], largely used for ther- mally stable and insoluble molecules, Langmuir–Blodgett (LB) and spin-coating (SC) film technologies [4,5], suitable for solu- ble derivatives, have been thoroughly investigated, although the control and the ordering of the molecular architecture at the nanoscale level are followed in a different way. It is worth point- ing out that the first method allows the construction of highly organised structures, and the second one has the great advan- tage of fast and easy fabrication, which makes it attractive for the manufacture of devices on an industrial scale. Among the numerous technological applications (xerography, optical data storage, molecular electronics, photodynamic cancer therapy, solar energy conversion, catalysis), the incorporation of phthalocya- nine molecules as an active component in gas-sensor devices is one of the most attractive research activities [6,7], ranging from the fundamental chemistry of phthalocyanine–gas interaction to ∗ Corresponding author. E-mail address: gianna.pennesi@ism.cnr.it (G. Pennesi). the emulation of human senses by electronic nose or tongue [8]. The importance of monitoring NO 2 traces in different envi- ronments (it is considered one of the major pollutants which have relevant public health impact) and the good performances of phthalocyanines as sensing materials have been the reason why this topic has received considerable attention up to now [9]. Nevertheless, the majority of the current literature deals with monophthalocyanine compounds, which are commercially available, while the sensing behaviour of synthesised phthalocya- nine derivatives containing, for instance, two macrocycle rings (sandwich-type), has not been so extensively studied [10] owing to the difficulty of the synthesis and purification processes. It is highly likely that the same obstacles, added to processing problems, have affected the class of single-atom bridged dimers (PcM–X–MPc; X = O, N, C) [11–13]; in fact, in spite of their remarkable electronic properties, the literature is still lacking in any insight into the sens- ing properties shown by these materials. The iron phthalocyanine -carbide dimer (PcFe) 2 C [13] under investigation is a rare phthalo- cyanine derivative (Fig. 1), carrying a linear PcFe C FePc-bond system with  electrons flowing through carbon atoms between the two iron centres. The two cofacially joined Pc units closely approach one another (ca. 3.4 Å), minimising inter-ring steric and electronic repulsion by relative rotation to a quasi-staggered posi- tion. Each iron centre is bound to the bridging carbon atom and to the four Pc nitrogen atoms. Previous Mössbauer studies allowed 0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2009.08.021