Hexaphenylbenzene-Based Fluorescent Aggregates for Ratiometric Detection of Cyanide Ions at Nanomolar Level: Set-Reset Memorized Sequential Logic Device Subhamay Pramanik, Vandana Bhalla,* and Manoj Kumar* Department of Chemistry, UGC Sponsored Centre for Advanced Studies-1, Guru Nanak Dev University, Amritsar-143005, Punjab, India * S Supporting Information ABSTRACT: A hexaphenylbenzene-based receptor 3 has been synthesized that forms a fluorescent spherical aggregate in mixed aqueous media due to its aggregation-induced emission enhancement attributes. These fluorescent spherical aggregates show ratiometric response toward cyanide ions via nucleophilic addition and undergo deaggregation to form smaller nanoaggregates. In addition, the solution-coated paper strips of 3 can detect cyanide ions in the range of ∼2.6 ng/cm 2 , thus, providing a simple, portable, and low-cost method for detection of cyanide ions in aqueous media. Receptor 3 also behaves as a set-reset memorized sequential logic circuit with chemical inputs of CN - ions and trifluoroacetic acid or H + (pH ≤ 3). KEYWORDS: hexaphenylbenzene, AIEE, cyanide, ratiometric, fluorescent nanoaggregates, sequential device ■ INTRODUCTION Among various anions, cyanide is one of the most toxic inorganic anions to living organisms, and consequently, its release into the environment is harmful. 1 Absorption of cyanide through the lungs, gastrointestinal tract, and skin can lead to convulsions, loss of consciousness, and eventually death. 2 Further, the binding of cyanide to the iron species in cytochrome-c oxidase reduces the activity of this enzyme and inhibits oxygen utilization by cells. 3 It is known that 0.5-3.5 mg per kg of body weight is lethal for humans. 4 According to the World Health Organization (WHO), water having cyanide concentrations lower than 1.9 μM are acceptable for drinking. 5 Recent studies have shown that the poisonous cyanide concentration in the blood of fire victims is ca. 20 μM. 6 Unfortunately, the use of cyanide ions cannot be avoided due to its widespread applications in various industrial processes, such as gold mining, 7 electroplating, metallurgy, and production of organic chemicals and polymers, e.g., nitriles, nylon, and acrylic plastics. 8 Keeping in view the utility of cyanide ions in day-to-day life, there is a great need for receptors that can selectively detect cyanide ions by simple spectral analysis. In this context, various types of fluorometric 9 and colorimetric 10 CN - selective receptors have been reported 11-18 based on the mechanism of coordination, 19 hydrogen-bonding interac- tions, 20,21 nucleophilic addition reactions, 22-26 and metal- cyanide affinity 27-29 (displacement approach). Among various types of chemosensors reported so far, the reaction based chemosensors showing ratiometric response toward cyanide are advantageous due to their high selectivity and sensitivity. Ratiometric responses are attractive because the ratio between the two emission intensities can be used to measure analyte concentration and provide built-in correction for environmental effects and stability under illumination. Thus, reaction based chemosensors showing ratiometric responses toward cyanide ions are highly desirable. However, there are many more reports in the literature about reaction based chemosensors showing ratiometric response toward cyanide ions, 30-32 but most of the reported reaction based chemosensors suffer from several limitations, such as poor selectivity, require high temperature or basic medium, slow response toward cyanide ions, 33,34 high detection limits, risk of releasing HCN, 35 irreversibility (based on reaction), and require an organic environment to function. 36,37 Thus, development of a quick, 38,39 facile, reversible and ratiometric reaction based fluorogenic sensor, which works in aqueous media with low detection limit, is still a challenge. 40,41 Our research work involves the development of fluorogenic chemosensors for selective detection of different types of analytes. 42-45 Recently, we reported a hexaphenylbenzene (HPB) derivative 1 (Chart 1) appended with β-naphthol moieties that showed aggregation-induced emission enhance- ment (AIEE) phenomena in mixed aqueous medium to form spherical nanoaggregates. 20 These nanoaggregates undergo further self-assembly to form the modulated nanorods in the Received: February 12, 2014 Accepted: March 31, 2014 Published: March 31, 2014 Research Article www.acsami.org © 2014 American Chemical Society 5930 dx.doi.org/10.1021/am500903d | ACS Appl. Mater. Interfaces 2014, 6, 5930-5939