Luminescent Functional Materials from Bio-anion Induced Co-assemblies of Chromophoric Amphiphiles

Biswas, Rakesh (2023) Luminescent Functional Materials from Bio-anion Induced Co-assemblies of Chromophoric Amphiphiles. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Rakesh Biswas (16RS049)) 16RS049.pdf - Submitted Version Restricted to Repository staff only Download (11MB)

Abstract

The research work depicted in this thesis is primarily focused on the development of luminescent functional materials using the self-assembly process of various types of chromophore-tagged amphiphiles. We have used anthracene, pyrene, and fumaronitrile as the different chromophores and mono/di positive charges as the polar part in those amphiphiles. By varying the length of the attached alkyl chains in the amphiphiles, their hydrophobicity was modulated and the change in their photo-physical properties in the self-assembled state was studied with the help of various techniques. Through the modulation of optical properties of the molecules in their self-assemblies, we have generated multi-color luminescence in aqueous media, detected important anionic bio-analytes and constructed artificial light-harvesting systems. The whole thesis is categorized into four chapters and their briefs are given below. Chapter-1, provides a brief overview of the self-assembly process of amphiphiles in aqueous media. The thermodynamic insights of the formation of self-assembled aggregates were explained in this chapter. Moreover, the chapter also included insights into the host-guest chemistry of macrocyclic host molecules and its effect on the photo-physical properties of guest molecules. The underlying reasons for the formation of host-guest complexes have been discussed with the help of literature reports. The latter part of the chapter mainly focused on the utilization of different bio-molecular scaffolds for the construction of artificial light-harvesting systems in aqueous media. Many different mechanisms for the energy transfer process have been discussed in detail. Chapter-2, described the use of self-assembled aggregates of imidazolium tagged-amphiphiles appended with anthracene and pyrene chromophores in aqueous media. The multivalency approach employing these self-assembled aggregates was utilized for the detection of different anionic bio-analytes (ATP, heparin, and DNA) in the aqueous and other competitive media through ratiometric fluorescence response. Anthracene-tagged amphiphiles efficiently detected ATP at sub-nanomolar concentration through a ‘turn-off’ fluorescence response while the pyrene-tagged imidazolium and bis-imidazolium amphiphiles exhibited a ‘turn-on’ response upon binding to ATP. A similar fluorescence response was also observed for the detection of heparin and DNA using the pyrene-tagged imidazolium and bis-imidazolium derivatives. Finally, the detection of heparin was demonstrated in extremely competitive media like 100% serum or plasma media using the multivalent aggregates of pyrene-tagged bis-imidazolium derivatives. With the help of heparin-based co-assemblies of these amphiphiles, protamine sulfate, an antidote of heparin, was also detected in 100% serum and plasma media. Chapter-3, was constructed based on the changes in photophysical properties of fumaronitrile derivatives in aqueous media. Fumaronitrile derivatives are known as intramolecularly twisted molecules which exhibited enhancement in their emission in the aggregated state as compared to their molecularly dissolved state. Interestingly, the self-assembled aggregates of the fumaronitrile derivatives also showed delayed emission properties. The multivalent aggregates were utilized to detect heparin through a dual luminescence mode of detection. Finally, fumaronitrile derivatives were employed for the formation of host-guest complexes with cucurbit[7]uril and cucurbit[8]uril in aqueous media. In addition, these host-guest complexes were further used for the modulation of photo-induced electron transfer process of the DNA base pairs. Chapter-4, demonstrated the fabrication of artificial light-harvesting systems in both solution and film state. In this chapter, we have depicted the use of different bio-molecular scaffolds as templates for energy transfer between organic donor and acceptor molecules. ATP, heparin, and DNA have been used as templates for this purpose. ATP-based co-assemblies of the pyrene-tagged imidazole derivatives exhibited excellent energy transfer efficiency of 95% at a very high donor-acceptor ratio. Moreover, these ATP-based co-assemblies also exhibited nice sensitivity to temperature, pH, and metal ions. The excellent stimuli-responsiveness of the co-assemblies was further used to modulate their energy transfer process and construction of encryption-decryption systems. Interestingly, heparin/DNA-based co-assemblies of pyrene-tagged imidazole derivatives displayed excellent single-step energy transfer and sequential energy transfer with different organic dyes as acceptors in both solution and film state. Nice stimuli-responsive energy transfer behavior was also observed for heparin/DNA-based co-assemblies of pyrene-tagged imidazolium derivatives. The heparin-based co-assemblies of fumaronitrile derivatives also manifested moderate energy transfer property with a variety of organic dyes.

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