Sensors and Actuators B 208 (2015) 75–84 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo ur nal home page: www.elsevier.com/locate/snb Rhodamine-chloronicotinaldehyde-based “OFF–ON” chemosensor for the colorimetric and fluorescent determination of Al 3+ ions Jong Woo Jeong 1 , Boddu Ananda Rao 1 , Young-A Son ∗ Department of Advanced Organic Materials Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764, South Korea a r t i c l e i n f o Article history: Received 23 July 2014 Received in revised form 10 October 2014 Accepted 1 November 2014 Available online 8 November 2014 Keywords: Rhodamine B 2-Chloronicotinaldehyde Fluorescent chemosensor Aluminum Azide a b s t r a c t We have synthesized a novel 2-chloronicotinaldehyde-functionalized rhodamine B derivative (RBCN) that acts as an “OFF–ON” chemosensor. RBCN specifically binds Al 3+ in the presence of a large excess of competing metal ions (Li + , Na + , K + , Cs + , Mg 2+ , Ca 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Ag + , Cd 2+ , Hg 2+ and Pb 2+ ) and exhibits visible changes in its electronic and fluorescent spectral behavior. These spectral changes are significant in the visible region of the spectrum and thus enable detection with the naked eye. Upon coordination with Al 3+ , the promoted ring opening of the rhodamine spirolactam ring in the RBCN chemosensor evokes a fluorescence turn-on response via the chelation-enhanced fluorescence pro- cess. The probe exhibited good brightness and fluorescence enhancement in which the lower detection limit for Al 3+ was 2.86 × 10 -8 M. The ring-opening mechanism of the rhodamine spirolactam induced by Al 3+ binding and the 1:1 stoichiometric structure between RBCN and Al 3+ were supported by Job’s plot evaluation, UV–vis, fluorescence titrations, FT-IR and 1 H NMR spectroscopic studies. Finally, theo- retical calculations and modeling simulations were conducted using Material Studio 4.3 suite to simulate the formation of a 1:1 complex between RBCN and Al 3+ . However, the fluorescence and colorimetric response of the RBCN-Al 3+ complex was quenched by the addition of azide (N 3 - ) anion, which abstracts the Al 3+ ion from the complex and turns off the sensor, confirming that the recognition process is reversible. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The development of optical signaling systems based on organic scaffolds for sensing and recognition of specific ions has been a recent area of focus due to their potential applications in environmental detection, molecular catalysis and the monitoring of biological processes [1–3]. However, efficient techniques are required for the detection of specific metal ions or anions because analytes often tend to interfere with each other. Recently, fluoro- genic and chromogenic sensors have emerged as a valid alternative to conventional analytical methods [4–6] due to their simplic- ity, high efficiency in detecting low analyte concentrations and bioimaging applications [7–9]. Aluminum is well known to be the most abundant (8.3 wt%) metallic element and the third most abundant element (after oxygen and silicon). The widespread appli- cation of aluminum in modern society includes water treatment, food additives, medicines and the production of light alloys, which ∗ Corresponding author. Tel.: +82 42 821 6620; fax: +82 42 821 8870. E-mail address: yason@cnu.ac.kr (Y.-A. Son). 1 These authors contributed equally to this work. often exposes people to aluminum ions [10,11]. However, excess aluminum can cause damage to certain human tissues and cells, resulting in diseases such as Alzheimer’s disease [12] and Parkin- son’s disease [13]. Aluminum accumulation has been shown to cause cancer of the lung, breast, and bladder [14,15]. Aluminum may also directly affect iron metabolism by influencing the absorp- tion of iron via the intestine, hindering iron transport in the serum, and displacing iron by binding to transferrin [16]. Furthermore, nearly 40% of acidic soils worldwide are thought to be polluted due to the effects of aluminum toxicity, which is the critical factor that hampers crop performance in acidic soils [17–19]. For these reasons, the detection of Al 3+ is crucial in controlling its levels in the environment and minimizing the direct impact of aluminum on human health. The search for efficient fluorescent chemosen- sors for aluminum ions has recently attracted increasing attention [20–23]. In comparison to other metal cations, the detection of Al 3+ has always been problematic due to its poor coordination ability, strong hydration ability and lack of spectroscopic character- istics [24,25]. Moreover, the design of multifunctional sensors with varying responses toward different analytes is cost effective and convenient for practical applications. However, chemosensors for the detection and evaluation of aluminum ion concentrations are http://dx.doi.org/10.1016/j.snb.2014.11.002 0925-4005/© 2014 Elsevier B.V. All rights reserved.