Development of Small Molecule and Responsive Polymer Based Colorimetric and Fluorometric Chemosensors

Abstract

In recent years, the design and development of optical molecular probes for detection of toxic metal ions, anions, reactive species and gases have great interest in the field of chemistry and biology because of their impact on health and the environment. For instance, the over doses of toxic metals and anions result dangerous effects to human as well as eco-environment systems due to their indispensable roles in viral (or physiological) processes. Especially, mercury, iron and copper most toxic elements consequences most of the horrible diseases. Similarly, low concentrations toxic anions like fluoride and cyanide ions causes severe effects to human including the symptoms of dental and skeletal fluorosis, osteosarcoma, convulsion, vomiting and loss of consciousness. Furthermore, the detection of so called greenhouse gas carbon dioxide has gain wide interest due to effects to environment such as global warming. Thus, it is very important to design small molecule/stimuli responsive polymers based probes for selective and efficient detection of cations, anions and gases. In this thesis, we have developed both small molecules and responsive polymers based molecular probes for the detection of toxic metal ions, anions, chemical warfare agents and picric acid by colorimetric /fluorometric detection approach. Furthermore, it was also investigated tunable sensitivity of responsive polymer probes towards metal ions, nerve gases and picric acid by operating the external stimuli. The literature reports on design strategies of small molecular and polymeric probes for the detection of the various analytes including toxic cations, anions, gases, chemical warfare agents etc. and their detection methods are widely explained in the introduction chapter 1|Chapter 2 demonstrated the development of azoaniline based small molecular probes for dual sensing of copper, chemical warfare agents and fluoride ions with two distinct modes of detection. Two new bifunctional probes were designed, which contain Cu2+-sensitive o- (phenylazo)aniline, F--sensitive silyl groups and free amine group to provide the reaction site for the detection of nerve agent mimics (DCP). Absorption and emission studies were conducted to examine the dual sensing abilities of these probes with the sequential addition of F- followed by Cu2+ or the sequential addition of DCP followed by Cu2+ and vice-versa. Moreover, it was investigated that the detection time towards DCP could also be controlled by the cyclization extent through a changing of the amount of Cu2+ ions that is added.|Chapter 3 emphasized the synthesis and development of pyrene based turn-on fluorescent polymeric probe for the tunable detection of nerve agent mimics. The newly synthesized polymeric probe P2 has shown selective turn-on fluorescence response towards detect diethyl cyanophosphate (DCNP), a nerve agent mimic in both the solution and vapor phase with a detection limit of 0.1 mM due to DCNP promoted intramolecular N-alkylation. Moreover, the detection of DCNP was successfully controlled by altering the purging of CO2/N2 gases or tuning the pH of the solution. P2 showed an efficient ON/OFF reversible fluorescence response towards CO2 and N2 gases, further helping tunable ON/OFF sensing of DCNP. The CO2-tunable detection of DCNP was further correlated to the pH-dependent control of detection sensitivity. Thus, these CO2/pH controllable detection properties can offer new insights into the design of new stimuliresponsive polymeric probes with fluorescence turn-on detection of nerve agent mimics|Chapter 4 included a pyrene based polymeric probe for detection of picric acid in film state as well as in 100% aqueous media. Interestingly, the polymeric film showed a turn-off fluorescence signal with the addition of picric acid. A drastic quenching was observed in the emission spectra of the probe towards increasing the concentration of picric acid due to PET process through strong electrostatic interaction between picrate anions and quaternary ammonium cations. It is also important to note that, the detection sensitivity of the film towards picric acid was found in attogram and also used film could be recycled just by washing out the analyte with water. The pH- dependent sensing studies revealed that the sensitivity of polymer towards picric acid could be tuned by changing the pH in both solution and film state.|Chapter 5 contained an azo aniline-based colorimetric polymeric probe for the detection of Fe (III) metal ions and cyanide ions. After the incremental addition of Fe (III) ions, the probe showed a blue shift by changing its color from brick red to yellow color, whereas, in presence of cyanide ions it underwent a bathochromic shift with the color change from brick red to purple.