Azacalix[3]arene-Carbazole Conjugated Polymer Network Ultrathin Films for Specific Cation Sensing Chatthai Kaewtong, †,‡ Guoqian Jiang, † Yushin Park, † Tim Fulghum, † Akira Baba, † Buncha Pulpoka,* ,‡ and Rigoberto Advincula* ,† Department of Chemistry and Department of Chemical Engineering, UniVersity of Houston, 136 Fleming Building, Houston, Texas 77204-5003, and Department of Chemistry, Faculty of Science, Chulalongkorn UniVersity, Bangkok 10330, Thailand ReceiVed January 28, 2008. ReVised Manuscript ReceiVed May 8, 2008 Developing highly selective and sensitive chemical sensors is a challenge with respect to new materials for chemical recognition. In this study, a new conjugated polymer network precursor, hexahomotri- azacalix[3]arene-carbazole has been synthesized and electrochemically cross-linked to form ultrathin films using cyclic voltammetry. The incorporation of hexahomotriazacalix[3]arene moiety as a neutral cation-binding receptor into a conjugated polycarbazole network facilitates high selectivity and sensitivity for Zn 2+ . The ultrathin films were characterized spectroscopically using UV-vis absorption and fluorescence spectroscopy. Surface morphology properties were examined by atomic force microscopy. Electrochemical deposition parameters and sensor transduction was studied by an electrochemical quartz crystal microbalance, surface plasmon resonance spectroscopy, and open-circuit potentiometry techniques. The results indicate that the high selectivity and sensitivity for Zn 2+ compared to those of other cations is due to the combined size and dipole specificity of the azacalixarene unit and nonspecific ionic interaction with the redox couple of the conjugated polycarbazole units. Introduction The basic recognition element of a chemical sensor is essentially a molecular or macromolecular structure designed to recognize a specific analyte. The binding or complexation constant, K asso , of the analyte is dependent on the strength of noncovalent interaction and accessibility to this structure. A high surface area is also a factor as it affects the diffusion kinetics of the analyte to the binding site. In the presence of a conducting (π-conjugated) polymer, a polymeric chemosen- sor system can be made electrochemically active, electrically conducting, and fluorescent, depending on the structure of the polymer, mode of electric field application, and wave- length excitation. Thus, it is not necessary for the receptor- analyte unit of the polymeric chemosensor to have an inherently high K asso . Only partial occupancy of the recogni- tion site may be required for signal transduction since the conjugated polymer also contributes to signal amplification and improved sensitivity. 1 A number of well-investigated π-conjugated polymers such as polythiophenes, polypyrroles, polyanilines, etc. have been used successfully for sensor and device applications. 2 As a class of semiconducting polymers, polycarbazoles possess good electroactivity and useful thermal, electrical, and photophysical properties which have led to there use in redox catalysis, electrochromic displays, electroluminescent devices, and sensors. 3 For example, polycarbazole has been used to develop copper(II) ion-selective microelectrochemical transistors 4a and L-dopa-selective sensors 4b due to its neg- ligible sensor response hysteresis and greater chemical and thermal stability compared to other conducting polymers. 4 Calixarenes have received significant attention for the construction of molecular receptors due to their unique molecular recognition properties and ease of functionaliza- tion. 5 The size of the macrocyclic cavity and the presence of ion-dipole interactions with the heteroatoms can be made specific for a particular ion. 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