Fluorescent organic nanoaggregates with aggregation induced emission for sensing and antibacterial applications

Abstract

In this thesis, various structural modification of ACQ organic small molecules with the incorporation of positive charge, conjugated hydrophobic moiety and anionic polysaccharides have been studied and their tunable physicochemical properties originated from their self assembly into nanoaggregates in the aqueous medium and condensed state has been taken advantage of for sensing, imaging and other biological applications. We studied the AIE phenomenon originated from the Schiff base complexes, where the restriction of the imine bond rotation led to the enhanced fluorescence in the aggregated state. The photoinduced inhibition of imine bond rotation and restriction of phenyl ring rotors contributed to the intermolecular π-π stacking of planar ACQ molecules. Further, the self-assembly of highly fluorescent organic nanoaggregates of ACQphore pyrene and tetraphenylethene as AIE/AIEE luminogens in the dispersed state on multiple platforms with specific charge carrying functionalities has been used for sensitive detection of explosives, bioimaging of cells and bacteria, antimicrobial studies, discriminative detection of environmentally toxic chemicals and biologically used foreign analytes. Overall, the thesis work focuses on the prime exploration of fluorescent organic nanoaggregates with AIE/AIEE properties for sensing and antimicrobial applications on multiple platforms. Objective In this thesis, we have developed various AIE and AIEE active molecules as their fluorescent organic nanoaggregates in aqueous medium from classical ACQ fluorophores e.g. pyrene and tetraphenylethene with the strategic modifications. ➢ Development of pyrene excimer nanoaggregates with aggregation induced emission (AIE) in a THF-water aqueous mixture for ‘Turn off’ fluorescence detection of phenolic nitroaromatics with the xiv quenching mechanism and controllable aggregates size with encapsulation of amphiphilic block copolymer Pluoronics P-123 with reduced cytotoxicity for imaging of cells. ➢ Design and synthesis of a C3 symmetric cationic system as fluorescent nanoaggregates in an aqueous mixture of DMSO-water with aggregation induced emission for sensitive bacteria detection through a facile photoinduced electron transfer (PET), wash-free bacteria imaging and antimicrobial activity with possible electrostatic interaction with positive charge of nanoaggregates and negative charged bacterial membrane subsequent reactive oxygen species (ROS) generation. ➢ Design and synthesis of conjugated polymers bearing an AIE active unit as fluorescent nanoaggregates in an aqueous medium and film with aggregation induced emission enhancement (AIEE) for sensitive discrimination of aliphatic, aromatic electron-rich and electron deficient volatile organic contaminants (VOCs) in with ‘turn-on’ emission with or without shifting emission peak and ‘turn-off’ emission through donor-acceptor electron transfer mechanism and non-covalent interactions. ➢ Development of fluorescent organic nanoaggregates with aggregation induced emission properties in an aqueous medium for sensitive detection of biologically important antibiotics detection through ‘turn off’ fluorescence of tetracycline with inner filter effect (IFE) and PET process.