Small Organic Molecules as Chemosensors

Das, Tanmay (2018) Small Organic Molecules as Chemosensors. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The thesis entitled as “SMALL ORGANIC MOLECULES AS CHEMOSENSORS” is about synthesis, characterization of different stimuli responsive organic materials. These materials have been applied as chemosensors for various guest species. The results of this thesis have been investigated by the author under the supervision of Dr. Debasish Haldar at Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur Campus, Nadia, India during the period 2014-2018. This thesis is divided into six chapters. Chapter 1 describes the general introduction about chemosensor, design principles of different chemosensors and application of different chemosensors. Chapter 2 entitled “On-line Ammonia Sensor and Invisible Security Ink by Fluorescent Zwitterionic Spirocyclic Meisenheimer Complex” describes the synthesis of an ammonia sensor based on a zwitterionic spirocyclic Meisenheimer complex. The complex was highly fluorescent with a quantum yield of 67%. The fluorescence can be turned on-off by applying acid and base. Utilizing the fluorescence switching process, the same Meisenheimer complex was also utilized as a security ink. Chapter 3 titled as “Phenylalanine-urea hybrid gel as a broad-spectrum absorbent for rapid removal of oil and toxic organic pollutants from water” reports the gelation of a symmetric phenylalanine based urea in water and water miscible organic solvent. The xerogel can remove different types of oils as well as organic solvents from a biphasic system water-oil system. The methanol-water based gel of the same gelator can also mop up different toxic dyes from waste water. Along with that, the urea compound forms selective gel with picric acid in chlorobenzene and dichlorobenzene. This organogel can be applied as a sensor of different carbodiimide compounds and basic vapours like ammonia. Chapter 4 titled as “Isothiocyanate-modified phenylalanine metallogel for removing Hg(II) from waste water” reports the synthesis of a phenylalanine-based isothiocyanate derivative. The compound forms selective metallo-hydrogel only in presence of Hg²⁺ ion. No gelation takes place with other metal ions like Cd(II), Pb(II), Cu(II), Zn(II), Cr(III) and Fe(III). But below the critical gelation concentration the compound forms only precipitates in presence of Hg²⁺ ion. This property is utilized for removal of mercury from contaminated water and the mercury level can be dropped down below the WHO permissible limit within 10 minutes from a highly concentrated Hg(II) containing water. Chapter 5 titled as “Biphenyl amino acid methyl ester based sensor of HSO⁴⁻ and volatile organic compounds” reports the synthesis of a biphenyl amino acid methyl ester by Suzuki-Miyaura cross coupling and the compound was utilized for selective sensing of bisulphate ion. The sensor is a turn-on sensor which shows green emission under UV irradiation. Apart from that, the coating of the biphenyl amino acid methyl ester on silica surface such as TLC plate can be applied for the sensing of volatile organic compounds like acetone, DCM, chloroform, THF, diethyl ether, ethyl acetate, benzene, toluene and xylene. A device was fabricated for this detection purpose. Chapter 6 entitled “Mopping up the Oil, Metal and Fluoride Ions from Water” describes the recycling, cleaning and reuse of water for environmental remediation by a fluorescent zwitterionic spirocyclic Meisenheimer complex. The complex was utilized to mop up metal and fluoride ions from water. Apart from that, the compound was coated on polystyrene sponge to produce a hydrophobic sponge and this was utilized to soak oils from water surface as well as from the bottom of the water layer.

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