Rhodamine-azobenzene based single molecular probe for multiple ions sensing: Cu 2+ , Al 3+ , Cr 3+ and its imaging in human lymphocyte cells Subhabrata Mabhai a , Malay Dolai b , Surya Kanta Dey c , Anamika Dhara d , Sujata Maiti Choudhury c , Bhriguram Das e , Satyajit Dey e, ⁎, Atanu Jana f, ⁎ a Department of Chemistry, Mahishadal Raj College, East Midnapore, Mahishadal, West Bengal, Pin No. 721628, India b Department of Chemistry, Prabhat Kumar College, Contai, Purba Medinipur 721401, India c Department of Human Physiology with Community Health, Vidyasagar University, Rangamati, Medinipur, West Bengal, Pin No. 721102, India d Department of Chemistry, Jadavpur University, Raja S. C. Mallick Road, Kolkata 700032, India e Department of Chemistry, Tamralipta Mahavidyalaya, East Midnapore, West Bengal, Pin No. 721636, India f Center for Superfunctional Materials, Department of Chemistry, School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea abstract article info Article history: Received 4 March 2019 Received in revised form 18 April 2019 Accepted 19 April 2019 Available online 22 April 2019 A photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) regulated rhodamine- azobenzene chemosensor (L) was synthesized for chemoselective detection of Al 3+ , Cr 3+ , and Cu 2+ by UV– Visible absorption study whereas Al 3+ and Cr 3+ by fluorimetric study in EtOH-H 2 O solvent. L showed a clear fluo- rescence emission enhancement of 21 and 16 fold upon addition of Al 3+ and Cr 3+ due to the 1:1 host-guest com- plexation, respectively. This is first report on rhodamine-azobenzene based Cr 3+ chemosensor. The complex formation, restricted imine isomerization, inhibition of PET (photo-induced electron transfer) process with the concomitant opening of the spirolactam ring induced a turn-on fluorescence response. The higher binding con- stants 6.7 × 10 3 M -1 and 3.8 × 10 3 M -1 for Al 3+ and Cr 3+ , respectively and lower detection limits 1 × 10 -6 M and 2 × 10 -6 M for Al 3+ and Cr 3+ , respectively in a buffered solution with high reversible nature describes the poten- tial of L as an effective tool for detecting Al 3+ and Cr 3+ in a biological system with higher intracellular resolution. Finally, L was used to map the intracellular concentration of Al 3+ and Cr 3+ in human lymphocyte cells (HLCs) at physiological pH very effectively. Altogether, our findings will pave the way for designing new chemosensors for multiple analytes and those chemosensors will be effective for cell imaging study. © 2019 Elsevier B.V. All rights reserved. Keywords: Rhodamine Azobenzene Chemosensor PET CHEF 1. Introduction Environmental pollution caused by the high concentration of heavy metals in sewage remains a global challenging problem. Heavy metal ions like Cu 2+ , Al 3+ , and Cr 3+ provide essential indispensable nutrients for life when taken in regulated amount, but their uncontrolled or over- exposure generates acute biological and physiological disorder [1–3]. Cu 2+ , a cofactor of various enzymes like cytochrome co-oxidase, tyros- inase, and superoxide dismutase, plays a significant role in a physiolog- ical system such as iron regulation [4–6]. It turns as a toxic element when taken in excess of recommended amounts of 1.3 ppm (~20 μM) in drinking water and generated oxidative stress neurodegenerative diseases such as Alzheimer's disease, Wilson's disease, Menke's disease, gastrointestinal lipid metabolism disorders [7]. The toxic carcinogenic Cr 6+ is converted to Cr 3+ by bacterial reduction and bind nonspecifi- cally with DNA to damage the intracellular activity like DNA replication and transcription [8]. Although Cr 3+ is physiologically less harmful as compared to Cr 4+ and Cr 6+ , its deficiency increases the risk of diabetes, cardiovascular disease, and cancer [9]. Extensive use of other metalions such as aluminum in modern life increases the risk of aluminum toxicity which brings calcium metabolism disorder, interferes the concentration of iron in the blood causing Osteomalacia, microcytic hypochromic ane- mia. Unregulated intake of aluminum cause encephalopathy, myopathy, dementia, Guamanian amyotrophic lateral sclerosis, Parkinson's dis- ease, and Alzheimer's disease [10]. Therefore, a new challenging field is emerged for developing artificial chemosensor capable of recognizing the environmentally and physiologically important analytes in a rapid, inexpensive and sensitive way [11]. Due to high selectivity, sensitivity and easy operational use over other methods, colorimetric and fluo- rometric probes become the first choice for practical applications [12]. Meanwhile, the idea of designing a new cost-effective molecular probe which binds more than one analyte using a single detection method or an array of detection methods gain the importance over one-to-one normal sensors [13–15]. To date, in comparison to diamag- netic Al 3+ , there are very few ‘Switch-On’ sensors reported for para- magnetic Cu 2+ (d 9 ) and Cr 3+ (d 3 ) because of their fluorescence quenching property [16]. Higher photostability and longer absorption- Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 219 (2019) 319–332 ⁎ Corresponding author. E-mail addresses: satyajitdeyoc@gmail.com (S. Dey), atanujanaic@gmail.com (A. Jana). https://doi.org/10.1016/j.saa.2019.04.056 1386-1425/© 2019 Elsevier B.V. All rights reserved. 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